New and uncommon Bivalvia Mollusca of Thermaikos Gulf (NW Aegean Sea)

Headnote

The molluscan bivalve fauna of Thermaikos Gulf was investigated and collected with emphasis on the minor in size species during the period from october 2008 to June 2013. Forty six species belonging to 23 families were identified and their biodiversity was compared with the current checklists of marine bivalve molluscs for the Hellenic seas based on previous surveys. in this col- lection of bivalves, nine are new for the Eastern Mediterranean sea, 15 are new for the Hellenic fauna (three of which are alien) and 39 are new for Thermaikos Gulf (five of which are alien). These records raise the Hellenic and Thermaikos Gulf bivalve fauna by approximately 5.5% and 21%, respectively. The main identification characteristics and ecological information such as ha- bitat, distribution and origin are given and discussed.

Key words: alien species, Greece, Mediterranean sea, molluscs, n aegean sea, Thermaikos Gulf, uncommon marine bivalves.

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inTRoduCTion

The Thermaikos Gulf (nW aegean sea) comprises one of the most complicated and multi-used ecosys- tems of the Eastern Mediterranean sea. For such an ecosystem, although there are numerous environmen- tal investigations, only a few are referred exclusively to its fauna and even to its bivalve molluscs (e.g. sa- kellariou, 1957; Zenetos, 1996; Zenetos et al., 2005; Manousis et al., 2010). as alien species are rapidly changing the marine ecosystems (Por, 1978, 1990; Ga- lil & Zenetos, 2002; Zenetos et al., 2003; Pancucci-Pa- padopoulou et al., 2005; streftaris et al., 2005; stref- taris & Zenetos, 2006; Zenetos et al., 2007) and as the Thermaikos Gulf has not been intensively searched, a more thorough investigation of its malacofauna could lead to new findings. apparently, Thermaikos Gulf is a marine basin on the navigation line to the second largest port of Greece with recorded traffic of more than 3000 ships per year; therefore, it is expected that alien species occur continuously. a dynamic evidence of this fact is the recent record of six alien bivalve spe- cies from the same area (Manousis et al., 2010). Thus, the main purpose of this study is: a) to further con- tribute to the knowledge of (mainly small in size) bi- valve biodiversity of Thermaikos Gulf and re-describ- ing and comparing its significant systematic charac- teristics, b) to compare the present biological diversi- ty of the area with that recorded in publications of the past, and c) to improve the knowledge on the distri- bution and expansion of alien bivalve species.

MaTERials and METHods

The sampling of specimens was conducted from oc- tober 2008 to June 2013 in E Thermaikos and Thes- saloniki Gulfs (Fig. 1) by methods describe in Ma- nousis et al. (2012) with the addition of a fourth sam- pling approach, i.e. the searching of only fresh trawled and discarded material from small scale fishing nets taken from the vessels. Wood-eaters were dissected out of submerged infested wood by means of fine scalpels and a pair of tweezers. after cleaning with fresh water, shells were treated with 25% glycerin in ethanol and examined under a stereoscope with a ma- gnification of up to × 80. For each species collected, the following data have been recorded: location, depth, type of habitat and size (length, unless otherwise stat- ed). The species recognition was based on literature provided in Manousis et al. (2012). For the species nomenclature update (30 June 2013), the Marine Bi- odiversity and Ecosystem Functioning Eu network of Excellence - The European Register of Marine species (MarBEF - ERMs) (www.marbef.org) and the ClEMaM (www.somali.asso.fr) were used. The taxono- mic order followed the guides provided in ClEMaM. in addition, the Ellenic network on aquatic invasive species (Elnais, https://services.ath.hcmr.gr/) was used for the alien species status in the Hellenic seas.

The specimens are deposited in the premises of the alexander Technological Educational institute of Thessaloniki and those of dr. T. Manousis. scientists are welcome to have access to the biological material at will.

REsulTs

as a result of this investigation, approximately 700 specimens were collected and 46 species belonging to 23 families were identified. They are listed in phylo- genetic order within families in Table 1, with their last recorded distribution and mode of life. among the identified species, nine are new for the Eastern Mediterranean sea, 15 are referred for the first time for the Hellenic fauna (Table 2), three of which are alien and 39 species are new for Thermaikos Gulf (fi- ve of which are alien). in the study area, three known alien species (Fulvia australis, Fulvia fragilis and Pinc- tada imbricata radiate) and six of West Mediterranean or atlantic origin are recognized. Brief text with in- formation and discussion for each species within fam- ilies follows:

nuCulidaE

Nucula sp. (Fig. 2a). one right valve (0.7 mm) and one left valve (1.0 mm) were found in discarded material brought to the surface from about 25 m depth at sta- tion 3. The almost ovate right valve has a prominent and flat umbo (as if cut), smooth margin, weak growth lines and microscopic radial striae. internally it is glossy, with a trigonal chondrophore under the pro- dissoconch. The hinge of the right valve bears four large trapezoidal anterior teeth as well as one poste- rior, while that of the left valve four anterior and two posterior teeth. Externally, the valves resemble those of Austronucula perminima (Monterosato, 1875) in their overall shape, the flat prodissoconch and the ax- ial striation but internally they lack the characteristic for A. perminima two types of hinge teeth (Gofas et al., 2011). Moreover, comparing the samples with sa- me size juveniles of the sympatric species N. nitidosa Winckworth, 1930, N. nucleus (linnaeus, 1758) and N. sulcata Bronn, 1831 it was found out that none of them shares the same type of prodissoconch and shell's shape with our specimens.

Ennucula aegeensis (Forbes, 1844) (Fig. 2B). one left valve (1.2 mm) was found in rocky material trawl- ed from silty bottom at a depth of 70 m of station 7 (central Thermaikos Gulf). The fragile, grey-white and transparent shell is equivalve, inequilateral and tumid with a trapezoidal oval outline. its anterior dor- sal margin is slightly rounded and slopes gently, while its posterior dorsal margin is slightly rounded and slo- pes steeply. The anterior margin is widely rounded, while the ventral margin is deeply rounded. The es- cutcheon is broad, raised, elliptical and long, and the lunule is elliptical, long and raised. The umbos are broad and prominent as they project above the dorsal margin. The outer surface is smooth with fine concen- tric growth lines. The prodissoconch is also smooth, prominent and well defined. The shell's inner margin is smooth. The ligament is internal, opisthodetic and inserted in a deep and wide resilifer. The taxodont hinge is formed on a wide and continuous hinge plate bearing 3 anterior and 2 posterior short and blunt teeth. a deep water species recorded from all the Hel- lenic seas and now from Thermaikos Gulf. Ennucula aegeensis is similar in its outlook to E. corbuloides. When comparing E. aegeensis with E. corbuloides, the late exhibits a different in size and orientation chon- drophore, has narrower crenulation and lacks the wi- de space next to it on the hinge plate.

nuCulanidaE

Nuculana cf. pella (linnaeus 1767) (Fig. 2C). one shell (4.7 mm) was collected at 8 m in mixed bottom at sta- tion 3. The specimen is slightly more rounded but ve- ry similar to the elliptic Nuculana pella. its main diffe- rence is in the posterior area which is demarcated by two ribs at the junction with the middle area of the shell. according to Cachia et al. (2004), some varia- tion in the radial ribs has been noted for N. pella with- out any additional information.

Saccella commutata (Philippi, 1844) (Fig. 2d). one live specimen (4.8 mm) was found in discarded mate- rial brought to the surface from about 10 m depth at station 5, and several juvenile shells (1.0-1.2 mm) in rocky material trawled from silty bottom from a depth of 70 m at station 7 (central Thermaikos Gulf). The species is common in the Mediterranean sea (Zene- tos, 1996; Cachia et al., 2004; Repetto et al., 2005; Ze- netos et al., 2005) and this is the first record from Ther- maikos Gulf.

aRCidaE

Asperarca secreta la Perna, 1998 (Fig. 2E). Two live specimens (2.4 mm and 2.9 mm) and a shell (2.3 mm) was collected from discarded material of a small scale fishing boat fishing at 15-20 m depth of mixed bottom at station 3. The shell is sub rectangular, equivalve and inequilateral. The umbos are situated at the ante- rior area of the shell. The light brown scaly periostra- cum becomes more wide and extended at the posterior- ventral area. The hinge bears large teeth, 4 anterior and 6 posterior. The species is found for the first time in Greece and it is already known from the Central Mediterranean sea (Cachia et al., 2004; Repetto et al., 2005; Cossignani & ardovini, 2011).

Bathyarca pectunculoides (scacchi, 1834) (Fig. 3a). one shell (2.0 mm) and several valves (2.0-3.0 mm) were found in rocky material trawled from 70 m at station 7. The species is common in the Mediterra- nean sea (Cachia et al., 2004) and this is the first re- cord from Thermaikos Gulf. The species has been re- ferred from all the Hellenic seas by Tenekidis (1989), Zenetos (1996) and Zenetos et al. (2005) as B. greno- phia (Risso, 1826).

Bathyarca philippiana (nyst, 1848) (Fig. 2E). one live individual (5.0 mm) and one left valve (4.5 mm) were found in two different instances in rocky mate- rial trawled from 70 m depth at station 7. The species has a similar outline with that of B. pencunculoides but is more oblique rectangular, the margin is finely crenulated and the sculpture is reticulated with fine radiating and concentric ribs that are slightly stronger in the posterior area. The taxodont hinge line is wide bearing 6 anterior strong teeth and 10 also strong po- sterior plus one vestigial tooth at the posterior end of the hinge. The species which is referred as rare (do- gan et al., 2009) or rather uncommon (Repetto et al., 2005) is also known from the aegean and Mediterra- nean seas (Zenetos et al., 2005; dogan et al., 2009; Cossignani & ardovini, 2011).

MYTilidaE

Crenella arenaria Monterosato, 1875 (Fig. 3B). several live specimens, shells and valves (1.0-2.5 mm) were found in detritus material trapped in small scale fish- ing nets at 20 m depth from mixed bottom at station 3 and in trawled material from the muddy bottom of station 7 at 70 m depth. The convex shells with smooth margins are oval, glossy, semi-transparent, white to cream in color and with fine growth lines. The hinge is finely crenulated. The species has been recorded from the s aegean sea (Zenetos et al., 2005) while it is also known from the Central and W Mediterranean sea (Cachia et al., 2004; Repetto et al., 2005; Cossig- nani & ardovini, 2011).

Dacrydium hyalinum (Monterosato, 1875) (Fig. 3C). one live specimen (1.7 mm) and several valves (1.8- 2.5 mm) were found in trapped detritus material from 20 m depth in small scale fishing nets from mixed bot- tom at station 3 and also several valves of the same lengths in trawled material from muddy bottom and 70 m depth at station 7. The rather large umbos are situated almost at the middle area of the hinge. The external surface is smooth or with conspicuous growth lines. Hinge with a narrow ligament beneath the um- bos. small teeth are situated on both sides of the liga- ment followed after a toothless interval by a series of 12-13 larger teeth on the two thirds of the dorsal but- tress. a species is referred as a) D. vitreum (Hollboll, 1842), with D. hyalinum Monterosato, 1875 as a syno- nym, from the seas of s Greece (Zenetos, 1996) and n aegean sea (Zenetos et al., 2005). according to salas & Gofas (1997), D. vitreum (Holbøll in Møller, 1842) or (Møller, 1842) (ClEMaM, www.somali.asso.fr) is an atlantic species while in the literature on Medi- terranean shells (i.e. Giannuzzi-savelli et al., 2001; Cachia et al., 2004; Cossignani & ardovini, 2011) the species D. hyalinum (Monterosato, 1875) is the only Dacrydium species referred. Dacrydium hyalinum (Monterosato, 1875) has been also recorded from the Turkish E aegean sea by Önen & dogan (2007).

Idas sp. (Fig. 3d). one small live specimen (2.3 mm) was collected from the surface of a live Pinctada im- bricata radiata (leach, 1814) beached after a storm at station 4. The shell is modioliform of yellowish-white color and tumid. The beaks are situated close to and behind the anterior end. The hinge has 5-6 teeth under the umbo area as well as 13-14 teeth behind the liga- ment. The mantle is quite wide mainly at the posterior- ventral area. The byssus muscle is undivided as it is referred for the genus Idas according to Gustafson et al. (1998).

Septifer cumingii Récluz, 1849 (Fig. 4a). a left val- ve (2.1 mm) was collected from a shallow Zostera bed at station 5. The mytiliform shell with red and green blots over a whitish background is solid with subter- minal umbos - a distinguishing characteristic of the species from S. bilocularis (albayrak & Çaglar, 2006). internally, it is shinny and bears a septum across the umbonal cavity. The sculpture consists of many strong radial ribs, occasionally bifurcating and crossed by fi- ner concentric lines showing a nodulous appearance. Hinge with 3 large teeth under the umbo and 8 large teeth behind the ligament. inner margin crenulate. The light brown periostracum bears scattered simple long fine hairs. The species is known from s Greece since 2010 (Elnais, https://services.ath.hcmr.gr/; Zene- tos et al., 2011) and this is the first record from the n aegean sea.

PTERiidaE

Pinctada imbricata radiata (leach, 1814) (Fig. 4B). since the last recorded reference of the species in Ther- maikos Gulf (Manousis et al., 2010), the species is now recorded further north in E Thessaloniki Gulf and its abundance seems to rise rapidly as 20 live specimens of different sizes (0.5-7 cm in length) were collected in december 2011. The majority (15 individuals) of small size shells (< 3 cm) were attached to fished Fle- xopecten glaber shells and the rest five were bigger (3- 7 cm). dead animals of a length ranging from 2 to 5 cm were found in a long beach of E Thessaloniki Gulf after a medium storm in January 2012, some of which with remnants of the soft parts of their body.

PRoPEaMussiidaE

Cyclopecten brundisiensis smriglio & Mariottini, 1990 (Fig. 4C). Three left valves (1.7-2.1 mm) were collect- ed from trapped detritus material in small scale fish- ing nets at 25 m depth from mixed bottom of station 3. The external surface of the valves bear a number of 17 primary, secondary and tertiary radial ribs densely covered with convex scales. The bases of the scales extend on both sides in a form of down curved lirae, which in combination with the radial ribs give the shell's surface an imbricate appearance. The large and al- most equal ears bear ribs, with a similar sculpture as of the rest of the shell. The species is referred from the Gulf of lion as well as from the Central Mediter- ranean sea (ligurian, n adriatic sea and sicily) (Ca- chia et al., 2004; Repetto et al., 2005; Cossignani & ardovini, 2011), while the current reference is the first from the E Mediterranean sea.

Cyclopecten hoskynsi (Forbes, 1844) (Fig. 4d). one right valve (2.45 mm) was collected from trapped de- tritus material in small scale fishing nets at 25 m depth from mixed bottom of station 3. The sub circular val- ve is fragile and transparent. The valve in-between the com-marginal granulated lines is decorated by ve- ry fine radial lines. The anterior ear is wider and lon- ger than the posterior decorated with evenly spaced co-marginal lirae which turn into weak co-marginal ridges of a very fine granular aspect. The species has been referred from s and W Greece (Zenetos et al., 2005) as well as, as a rare species, from the Mediter- ranean sea (Reppeto et al., 2005; Gofas et al., 2011) while it is known from n atlantic (dijkstra et al., 2009), n and W Europe (MarBEF, www.marbef.org).

sPondYlidaE

Spondylus cf. multisetosus Reeve, 1856 (Fig. 4E). one live specimen (58.0 mm length, 88.0 mm height) was found on a rock at 5 m depth in the sublittoral zone of station 5. The specimen was cemented to the sub- strate by a small area of its right (lower) valve. The sculpture of the left (upper) valve consists of numer- ous dominant radial ribs with regularly spatulate dark orange upstanding spines that are hollow underneath. in between these ribs, there are finer ribs with smaller sharp spines. The external color of the shell is burgun- dy red and the internal is dull cream-yellow with vivid burgundy-red crenulated margin. as the shell grows, the umbo of the right (lower) valve distances away from the umbo of the left one leaving behind a large, ivory white and triangular cardinal area. The current reference is the first from Greece. The species was re- ferred from israel and Turkey by Zenetos et al. (2003), Repetto et al. (2005) and Cossignani & ardovini (2011), while its presence in the Mediterranean sea is disput- ed as its shell's characteristics are similar to those of Spondylus spinosus (Zenetos et al., 2003).

anoMiidaE

Monia squama (Gmelin, 1791) (Fig. 4F). Two live spe- cimens (14.0 mm and 7.0 mm) attached to bivalve shells were collected from 6 m depth at station 3. The main distinguishing characteristic among anomiidae species is the position to each-other of the adductor muscle scars of their left (upper) valve (Poppe & Go- to, 2000). The two unequal adductor muscle scars of M. squama left (upper) valve are completely coalescent to form one large impression. The species is referred from the Central and the Western Mediterranean sea (Repetto et al., 2005; Cossignani & ardovini, 2011) and this is a confirmed reference from Greece.

liMidaE

Limatula gwyni (sykes, 1903) (Fig. 5a). one right val- ve (2.2 mm) was found in trapped detritus material in small scale fishing nets at 20 m depth from mixed bot- tom of station 3. The valve bears 30 radial riblets the two central of which are thicker. The hinge plate on either side of the triangular wide resilifer is smooth with a narrow but distinct sinus behind the ears. The species is similar to L. subovata but the late has much more radial riblets (about 50) (Marine Bivalve shells of the British isles, www.naturalhistory.museumwales.ac. uk) in contrast to L. gwyni which has 30 (Gofas et al., 2011). Limatula gwyni is referred from all over the Mediter- ranean sea (Repetto et al., 2005; Zenetos et al., 2005) and now, for the first time, from Thermaikos Gulf.

Limatula subauriculata (Montagu, 1808) (Fig. 5B). one right valve (2.9 mm) was found in trapped detri- tus material in small scale fishing nets at 20 m depth from mixed bottom of station 3. The valve is ovate, translucent, with one central thicker rib and 30 radial riblets. The hinge plate is smooth with a triangular less wide than L. gwyni resilifer on the cardinal area. The species is known from allover the Mediterranean sea (Repetto et al., 2005; Zenetos et al., 2005) and now from Thermaikos Gulf.

Limatula subovata (Monterosato, 1875) (Fig. 5C). a right valve (2.0 mm) was found in rocky material trawled at 70 m from station 7. The valve bears 40 fi- ne radial riblets and a thicker one at the center. some of these riblets do not start from the umbones. The hinge plate is situated over an arc and bears a trian- gular smooth resilifer for the ligament on its cardinal area. The species is similar to L. gwyni but the late has 30 radial riblets (Gofas et al., 2011) and wider resilifer in contrast to L. subovata which has about 50 radial riblets (Marine Bivalve shells of the British isles, nat- uralhistory.museumwales.ac.uk) and smaller resilifer. The species is distributed all over the Mediterranean sea (Repetto et al., 2005; Zenetos et al., 2005) while this is the first record from Thermaikos Gulf. allen (2004) redescribing the species refers that the distribution depths of the species in the Mediterranean sea is un- known.

Notolimea crassa (Forbes, 1844) (Fig. 5d). a live specimen (2.2 mm) and two valves, one right (2.0 mm) and one left (1.5 mm), were found in rocky material trawled at 70 m from station 7. The shell is tumid, ovate, with rather small ears. The ribs are thicker at the middle area and with laminate ridges. The hinge bears eight teeth on both sites of a triangular pit. The species is considered as common in Malta (Cachia et al., 2004) and rare in the Mediterranean sea (Repet- to et al., 2005), while it is also distributed in the Hel- lenic seas (Zenetos et al., 2005).

osTREidaE

Crassostrea gigas (Thunberg, 1793) (Fig. 5E). a live specimen (39 mm) was collected from an anchor rope at station 1 at 2 m depth. according to Minchin & Gollasch (2008), this alien species has expanded in the s aegean and the ionian sea. according to Zene- tos et al. (2003) and Elnais database (https://services. ath.hcmr.gr/), the species is established in the ionian sea and particularly in Patraikos and Korinthiakos Gulfs. This is the first documented record from the n aegean sea. There is unconfirmed information that the species was imported for aquaculture into Ther- maikos Gulf in 2007 (Katsanevakis et al., 2008).

THYasiRidaE

Thyasira alleni Carrozza, 1981 (Fig. 5F). one live spe- cimen (1.2 mm) was collected at 5 m from mixed bot- tom of station 5. The shell outline is subequilateral- rhomboidal and weakly sinuate posteriorly. The ex- ternal surface is rough with visible growth lines. The lunule is well demarcated, sung below the umbones and with two creases. The lanceolate escutcheon and the auricle are distinct with a shallow sub-marginal sulcus and a weak posterior sulcus. it is a rare species (Repetto et al., 2005) known from the Mediterranean sea and the n aegean sea, Evoikos Gulf (Zenetos, 1996), strymonikos Gulf (simboura & Zenetos, 2002) and now from Thermaikos Gulf.

Thyasira biplicata (Philippi, 1836) (Fig. 5G). Two right and four left valves (1.5-4.0 mm) were collected from trapped detritus material in small scale fishing nets at 20 m depth from mixed bottom of station 3 and from Maerl material trawled at 70 m from station 7. The external surface of the right valve is rough, cha- racteristically granulate and translucent. The valve is subequilateral-rhomboidal, trisinuate, posterior pro- file distinctly biangulate, tumid and higher than long. The umbo and auricle are projecting. The auricle is a prominent crest while the posterior sulcus is well de- veloped and the submarginal sulcus strongly demar- cated. The broad cordiform lunule is weakly excavated. The escutcheon is lanceolate and well marked. The hinge bears one obsolete cardinal tooth. The anterior shell margin runs all along the prodissoconch length - a characteristic that differs from T. flexuosa while is similar to T. granulosa (oliver & Killeen, 2002). The species resembles T. granulosa in its general outlook and particularly in the granulate sculpture but T. gra- nulosa lacks the auricle. according to scaperrotta et al. (2010), T. biplicata has been referred for long in the literature as T. flexuosa or T. polygona, while MarBEF (www.marbef.org) and ClEMaM (www.somali.asso.fr) accept T. polygona as a junior synonym of T. biplicata. The species is uncommon in the Mediterranean sea (scaperrotta et al., 2010), has been referred from al- bania (dhora, 2012) and this is the first record from Greece.

Thyasira flexuosa (Montagu, 1803) (Fig. 6a). Three live individuals (1.2-3.1 mm), several shells (1.4-3.5 mm) and two left valves (1.5 mm and 1.8 mm) were found in trapped detritus material in small scale fish- ing nets at 20 m depth from mixed bottom of the sta- tions 3 and 4. its right valve is equilateral ovate, tumid and higher than long. The external surface is rough with visible growth lines. The umbo and auricle are projecting, the posterior profile is distinctly biangula- te, the posterior sulcus is well developed and the sub- marginal sulcus strongly demarcated. The first poste- rior fold is prominent and the posterior sulcus well developed. The broad lunule is weakly excavated. The escutcheon is lanceolate with shallow sub-marginal sulcus and weak posterior sulcus. The ligament is sun- ken. The species is common in the Mediterranean sea (Cachia et al., 2004) and the aegean sea (Zenetos, 1996) and is already recorded from Thermaikos by Zarkanellas (1980) and Zenetos et al. (1993 cited in Zenetos, 1996).

GalEoMMaTidaE

Vasconiella cf. jeffreysiana (Fischer P in de Folin & Périer, 1873) (Fig. 6B). one live juvenile specimen (2.4 mm) was collected from 0.2 m at station 4. This small sub ovate shell bears a light orange periostracum. The hinge plate of the right valve bears a single cardinal tooth and a single thin lateral just over the ligament, while the left one bears two cardinals: the tuberculous anterior and the sphenoid posterior. The overall ap- pearance of the hinge is very similar to that of Vasco- niella jeffreysiana shown clearly by Coney (1990), but the right valve does not show the typical notch known for the species. Vasconiella jeffreysiana is a rare spe- cies known from the northern part of the Gibraltar straight (Coney, 1990; Repeto et al., 2005; Cossignani & ardovini, 2011) and from the sW Mediterranean sea according to Repetto et al. (2005). in case that the characteristic notch of the RV is not present in ju- veniles of V. jeffreysiana, the specimen presented here is the first collected V. jeffreysiana from the rest (Cen- tral and East) of the Mediterranean sea.

lEPTonidaE

Litigiella glabra (Fischer P in de Folin & Périer, 1873) (Fig. 6C). Three live specimens (1.0-6.8 mm) and se- veral individual valves (0.9-5 mm) were collected at stations 5 and 6 from 0.2 m and 8.0 m depth, respec- tively. The species is common in the Mediterranean sea and these must be the first records from the n aegean as Zenetos et al. (2005) only refer the species in detail from the ionian and s aegean seas.

lasaEidaE

Lepton squamosum (Montagu, 1803) (Fig. 7a). one right valve (1.2 mm) was collected from material trap- ped in nets at approximately 35 m and brought to the surface from the mixed bottom of station 4 and one left valve (4.5 mm) was trawled from 70 m at station 7. The right valve is white, transparent, thin and fragi- le, sub equilateral and with the beak just in front of the midline. it is compressed, rhomboidal in its outli- ne, with its dorsal and ventral margins parallel. The anterior and posterior margins slope obliquely with the anterior slightly more narrow. The outer surface is densely punctuate and bears prominent growth li- nes and fine co-marginal lines. The inner margin is smooth. The hinge has a paired anterior and posteri- or lateral teeth and a very small cardinal. The left val- ve, which is partially damaged, is also thin and fragile with small umbo just anterior to the midline. The sculpture of its outer surface consists of fine concen- tric lines, most conspicuous close to the distinct growth lines, and dense punctulations showing through from the inside. The hinge bears two small cardinal teeth and single anterior and posterior laterals. an atlantic and Mediterranean rare species (Repeto et al., 2005; Ma- rine Bivalve shells of the British isles, http://naturalhis- tory.museumwales.ac.uk), already known from the ionian and the n aegean sea (Zenetos et al., 2005) and now reported for the first time from Thermaikos Gulf.

MonTaCuTidaE

Coracuta obliquata (Chaster, 1897) (Fig. 7B). six val- ves (1.2 mm to 2.2 mm) were collected from material brought to the surface trapped in nets at approxima- tely 35 m from mixed bottom at station 4. The inequi- lateral valve (left) bears beaks situated at approxima- tely the 2/3 of the shell, is obliquely subovate, with an- terior margin prominent sloping gently and slightly angled at the junction with the anterior margin which is rounded. The ventral margin is gently curved and the posterior one is subtruncate. The posterior dorsal margin is short, steeply angled and slightly convex. The outer surface bears fine, concentric and occassio- naly dichotomous ridges. The valve bears no laterals but dorsal margins extended as marginal flanges in contrast to those of the right valve which are narrow, elongate and separated from the shell margin. The co- lor is creamy, the inner surface glossy and the prodis- soconch smooth. This rare species (Repeto et al., 2005) is referred from Greece as Neolepton obliquatum (Mon- terosato in Chester, 1897) (Zenetos et al., 2005).

Devonia perrieri (Malard, 1904) (Fig. 7C). one live specimen (1.9 mm) was found in sandy-muddy bot- tom of station 5 at 0.2 m depth. The shell is sub qua- drate, compressed, with the beaks close to the poste- rior end. There are distinct co-marginal and indistinct radial lines. The ligament is small, internal, on a shal- low resilifer in the proximity of a faint tubercle. The thin and transparent reriostracum covers the ivory white shell, while the umbos are tinted light brown. The species is referred from the nE atlantic, the W Mediterranean (www.marbef.org) and now from the E Mediterranean sea.

Kelliopsis jozinae (van aartsen & Carrozza, 1997) (Fig. 7d). one live specimen (1.7 mm) partially filled with a mass of larvae in the ontogenetic stage of d sha- pe was collected from material trawled from sandy- muddy bottom at station 7. in addition, two live juve- niles (both 0.9 mm), one shell (1.9 mm) and one left valve (1.0 mm) were found in rocky material trawled from 70 m at station 7. The prosogyrate, thin and tran- slucent shell is equivalve, subequilateral, with promi- nent beaks situated just behind the midline. The shell is tumid, sub circular, posteriorly narrow, with dorsal margin slightly depressed and bears thin pale brown periostracum. Externally the shell's surface is deco- rated with fine co-marginal lines. The ligament is in- ternal on a shallow resilifer. The hinge is weak, with a small cardinal tooth, a short anterior lateral flange and a longer posterior lateral tooth behind the resili- fer of the right valve. The left valve bears a posterior long groove, a poorly differentiated cardinal tooth and an anterior distinctive lateral tooth. The species has been referred from the nE atlantic (van aartsen & Carrozza, 1997; Marine Bivalve shells of the Bri- tish isles, http://naturalhistory.museumwales.ac.uk) and the West and Central Mediterranean sea (Cachia et al., 2004; Repeto et al., 2005; Cossignani & ardovini, 2011). This record seems to be the first for the E Mediterra- nean sea.

Kurtiella tumidula (Jeffreys, 1866) (Fig. 8a). one live specimen (1.5 mm) as well as two left valves were collected from material brought to the surface trap- ped in nets at approximately 35 m from mixed bottom at station 4. The thin and fragile shell, is equivalve and inequilateral with light brown prodissoconch in its posterior 1/4. it is sub-ovate in its outline and ex- panded anteriorly with the anterior dorsal margin long and straight while the anterior area is widely rounded. The posterior dorsal margin is straight sloping steeply to the rounded posterior. it bears fine, co-marginal li- nes on its surface and its inner margin is smooth. The ligament is internal in a wide pit beneath the beaks and inserted deep inside the umbos. The hinge con- sists of two diverging lateral teeth in each valve; those in the right valve are narrow, elongate, separated from the shell margin and with an angle of divergence of approximately 110° while those of the left valve ap- pear as extensions of the shell margin, with an angle of divergence of approximately 130°. The pallial line is entire, the periostracum is light yellow and the color is whitish. The inner surface of the valves is highly shi- ny. The species, already referred from Greece (Kouk- ouras, 2010) and known from the aegean sea as My- sella tumidula (Jeffreys 1866) (Zenetos et al., 2005), is now reported from Thermaikos Gulf.

Montacuta goudi (van aartsen, 1997) (Fig. 8B). o- ne live specimen (1.3 mm) as well as two right valves (both 1.2 mm) were collected from a shallow Zostera bed at station 5. The transparent, convex and smooth shell is trapezoidal in shape, fragile and has large beaks situated close to its anterior end. The promi- nent prodissoconches are of light chestnut brown color. The hinge plate is very narrow with tooth-like tuber- culate projections. This rather recently described spe- cies is known only from the Central Mediterranean sea (Cachia et al., 2004; associazione naturalistica Malachia, www.malachia.it).

Montacuta phascolionis dautzenberg & H. Fischer, 1925 (Fig. 8C). Two live specimens (1.9 mm and 2.4 mm) were collected from fine sand and mud bottom at station 5 and seven individual valves (1.5-3.0 mm) were found in shallow (0.2 m) Zostera beds at the sa- me station. The white, thin and rather fragile shell is almost equivalve and equilateral (with shorter the po- sterior part) with the left valve slightly smaller and fit- ting within the right valve. The posterior and anterior sides are rounded and the ventral edge straight or even concave. Each valve bears a single anterior car- dinal tooth with that of the right one obliquely elon- gated. shell surface smooth with fine concentric growth lines and faint radials. Known from the E atlantic ocean and the W and Central Mediterranean sea (Cachia et al., 2004; Repeto et al., 2005; Cossignani & ardovini, 2011) it is now reported from the E Medi- terranean sea.

CaRdiidaE

Acanthocardia deshayesii (Payraudeau, 1826) (Fig. 8d). one live specimen (30.8 mm) was collected from ma- terial brought to the surface trapped in nets at appro- ximately 10 m from mixed bottom at station 3. The shell bears 22-23 radial ribs with spatulate tubercules, mainly by the margin area, and the interspaces in be- tween the radial ribs with wavy concentric striae. The species which is considered as rare according to Pop- pe & Goto (2000), Cachia et al. (2004) and la Perna & d'abramo (2009), is distributed all over the Medi- terranean sea and has been generally referred from the n aegean sea (Zenetos et al., 2005) and Evoikos Gulf (W Central aegean sea) (Tenekidis, 1989; Ze- netos, 1996).

Fulvia australis (sowerby ii, 1834) (Fig. 9a). Five right valves (10.5-11.2 mm) were found at 8.0-12.5 m depth at stations 3, 3a and 5 of the E Thermaikos Gulf. The valve is rather thin but not fragile, ovate, slightly higher than long with truncated posterior. on its outer surface it bears 40 weakly marked flat ribs, more prominent at the posterior area. The color is cream white with light pinkish purple blotches. The hinge is strongly arched, in comparison with the an- gulated hinge of the species F. fragilis, and bears two rounded cardinal teeth, a single posterior lateral and two long anterior laterals. The lateral teeth are at equal distances from the umbo (equilateral) while the pos- terior lateral tooth of F. fragilis is more distant from the umbo than the anteriors (inequilateral). The inner periphery of the shell is crenulated. This lessepsian migrant, though rare, is established in the coasts of is- rael (Zenetos et al., 2003; www.ciesm.org) and now is reported for the fist time from the Greek waters.

Fulvia fragilis (Forsskål in niebuhr, 1775) (Fig. 9B). one live individual (30.6 mm), one shell (17.0 mm) as well as one broken right valve with intact hinge were collected from a depth of 5 m at station 2 (nE Ther- maikos Gulf) in december 2010 after a severe nW wind of 10 Bf during 10 and 11 december 2010 (na- tional observatory of athens, www.meteo.gr) and in the same area where the species was also recorded by angelidis (2013) on February 2012. Moreover, a left valve was collected at the beach of Palioura (station 3) (E Thermaikos Gulf). The beige fragile shells are slightly longer than high with 35-39 smooth ribs bear- ing small calcareous spines in the posterior part, are in morphological accordance with the described form of the specimens from izmir Gulf by Öztürk & Pou- tiers (2005). Radial periostracum lamellae arise from the mid-line of the ribs, becoming more prominent towards the anterior part of the valves. internally, the margin is evidently crenulated and the color is creamy white at the anterior part, yellowish pink with a longi- tudinal blotch under the umbo and violet across the posterior part. Fulvia fragilis is an already established alien species in saronikos and Evoikos Gulfs (Zene- tos et al., 2003; Elnais, https://services.ath.hcmr.gr/; an- gelidis, 2013).

Parvicardium hauniense (Peterson & Russel, 1971) (Fig. 9C). one live juvenile specimen (1.5 mm) was collected from shallow (0.2 m) Zostera beds at station 5. The reddish brown shell is thin, equivalve, inequila- teral, slightly inflated, with prosogyrate beaks in front of the midline. it is oval in its outline and a little ex- panded posteriorly. its sculpture consists of 23 radial low ribs of the same width as that of the interspaces. a few blunt spines decorate the posterior dorsal ribs. The margin is crenulate and the parivincular short li- gament sits on a prominent nymph. The hinge is rather weak and bears on the right valve one anterior and a pair of posterior laterals as well as two small cardinals and on the left valve single almost marginal laterals and two small cardinal teeth. a north atlantic species restricted to the Baltic sea (Marine Bivalve shells of the British isles, http://naturalhistory. museumwales.ac.uk) but was recorded for the first time from the W Medi- terranean sea (The Conchological society of Great Britain and ireland, www.conchsoc.org) and now is re- ferred for the first time from the Greek waters.

TRaPEZidaE

Coralliophaga lithophagella (lamarck, 1819) (Fig. 9d). one live specimen (11 mm) and a shell (7 mm) were dissected out of a calcareous block trawled at 20 m from mixed bottom at station 3. The equivalve and strongly inequilateral prosogyrate shell is solid and modioliform with anterior end reduced and rounded and posterior end expanded and slightly truncated. The ventral line is rather straight while the dorsal one is almost straight. The sculpture consists of concentric lines, growth stops and ridges. The inner margin is smooth and the ligament is external, behind the beaks and set on a shallow nymph. a pale yellow periostra- cum covers a white shell. already known from the Greek seas, it is now referred for the first time from Thermaikos Gulf.

MYidaE

Sphenia binghami Turton, 1822 (Fig. 10a). Three live specimens (1.5 mm, 2.0 mm and 2.1 mm, respectively) were collected from sandy muddy bottom of station 4 at 0.2 m and several individual valves (0.9-3.2 mm) were found in shallow Zostera beds at station 4. Mo- reover a valve (3.0 mm) was collected from trawled bottom material from 70 m at station 7. The rather thin and brittle shells are equivalve, inequilateral with prosogyrate beaks situated at the middle of the ante- rior part. Their outline varies; they are irregular, rough- ly rectangular and longer than high. The anterior part slopes steeply towards a rounded anterior ventral margin. The posterior dorsal line is long and sub pa- rallel to the ventral sloping to a broad or narrow sub- truncate posterior. The posterior area is defined by an angular ridge running from the umbo to the poste- rior ventral junction. The sculpture consists of irregu- lar undulations and co-marginal lines. The inner mar- gin is smooth and the ligament is internal lying on a shallow and small chondrophore. Hinge without teeth. The periostracoum is persistent, of straw yellow color and the shell itself is white. it is an uncommon inhabi- tant of the Mediterranean sea (Gofas et al., 2011) and the Greek waters (Zenetos et al., 2005).

TEREdinidaE

Bankia carinata (J.E. Gray, 1827) (Fig. 10B). several live specimens (2.2-3.5 mm) were dissected out of sub- merged wood from 7 m depth at station 5. The main characteristic of the species are its pallets which con- sist of a long white cylindrical stylet with a series of cones covered with a brown unserrated periostracal sheath. The species is cosmopolitan (Gofas et al., 2011), it has been recently collected in Thermaikos Gulf (www.shellauction.net, but with no figure available) and now its occurrence is documented from E Thermai- kos Gulf for the first time for Greece.

Lyrodus pedicellatus (de Quatrefages, 1849) (Fig. 10C). several live specimens (3.2-6.4 mm) were disse- cted out of submerged woods beached at the stations 3, 4 and 6. The pallets consist of a white cylindrical stylet connected with a suture to a blade of equal length which is elongate, oval and with a brown periostracal sheath on its tip. This cosmopolitan species (Gofas et al., 2011) is distributed all over the Mediterranean sea (Reppeto et al., 2005). Recently it was collected in Korinthiakos Gulf, s Greece (www.shellauction.net, but with no figure available) and now its occurrence is documented from E Thermaikos Gulf for the first time.

Nototeredo norvagica (spengler, 1792) (Fig. 10d). several live specimens (4.0-12.2 mm) were dissected out of submerged wooden poles of fish traps from 7 m depth at station 3. The shell outline and sculpture are very variable. nevertheless, the pallets are quite distinct with a more or less oval blade, obscurely seg- mented, having a ribbed or striated appearance and a short stylet (1/3-1/4 the length of the blade). The spe- cies is known from the atlantic ocean and Mediter- ranean sea (shipway et al., 2011; Borges et al., 2012) and has also been referred for Greece from the ae- gean sea (natuurhistorich Museum Rotterdam, http:// nlbif.eti.uva.nl/nmr).

XYloPHaGidaE

Xylophaga dorsalis (Turton, 1819) (Fig. 11a). several live specimens (7.5-9.2 mm) were dissected out of a submerged old wooden door found at station 5. The species has been referred from s and W Greece (Ze- netos et al., 2005) and this is the first record from the n aegean sea.

THRaCiidaE

Thracia sp. (Fig. 11B). Two live specimens (1.94 mm and 1.50 mm) and 8 valves (1.55-2.10 mm) were colle- cted at 0.2 m from a Zostera bed at station 5. The shell is equilateral, slightly inequivalve, with the dor- sal margins of the left valve fitting inside those of the right valve, and compressed. it is subtrigonal in its out- line and truncated posteriorly. The beaks are promi- nent and the anterior dorsal margin is straight sloping steeply towards the narrowly rounded anterior mar- gin. The ventral margin is straight, the posterior mar- gin is broadly truncate while the posterior dorsal mar- gin is straight with a slope less steeply than the ante- rior dorsal margin. its posterior dorsal area is devel- oped as a flat escutcheon and its anterior dorsal area is slightly cleft. The hinge is weak with the right valve bearing a well-developed anterior tooth which contin- uous with a weak ridge more prominent at the ante- rior end of the dorsal slope, and a weaker posterior tooth. The left valve bears no teeth. The ligament is internal and attached to a poorly developed sub-um- bonal plate. The prodissoconch, of 190 μm in diame- ter, is simple with a well-demarcated rim. seen from the inner surface it gives the impression of sugar grains stack together to form the valves, while the outer sur- face under high magnification seems to consist of un- even series of fine papillae (8-10 μm in diameter) to form ridges interrupted usually every three or two pa- pillae. When compared with the relevant photographs of oliver & Holmes (2004), the shell strongly resem- bles in its outlook and the umbo type and size that of Thracia arianatoma oliver & Holmes, 2004 and T. myopsis Møller, 1842 with photographs shown in Coan (1990) and World Register of Marine species (WoRMs) (www.marinespecies.org), while in its outer surface mi- crosculpture it is closer to that of T. myopsis Møller, 1842 (Coan, 1990) or T. kowiensis Turton, 1932 (oliver & Holmes, 2004).

CusPidaRiidaE

Cardiomya costellata (deshayes, 1833) (Fig. 11C). Three shells (1.5-5.5 mm) and two broken left valves were found in rocky material trawled from 70 m at station 7. The very thin, fragile and rather inflated shell is slightly inequivalve with the left valve overlapping the right valve. The beaks are situated slightly behind the midline. The body of the shell is ovate, oblique, with its ventral extremity well in front of the line through the beaks and with the anterior dorsal margin sloping steeply. The rostrum is short, slightly turned upwards, triangular and with its dorsal margin concave. The ventral margin is weakly concave corresponding to a weak sulcus at the junction between the rostrum and the body. The shell body bears several radial riblets increasing in size posteriorly. already known from the Greek seas (Zenetos et al., 2005) it is now referred for the first time from Thermaikos Gulf.

disCussion

The new records

The last list of the known species of bivalves from Thermaikos Gulf (Manousis et al., 2010) included 188 species. This survey increases that number by > 20%, as it adds 39 new species, brings the total number to 227 and presents new data on the biodiversity of the area. at the same time, it reveals the presence of 15 new species from the Hellenic seas. The current ad- dition of those new records (Table 2) increases the bi- valve biodiversity of the Hellenic fauna from 319 (Ze- netos et al., 2005, 2007; Manousis et al., 2010) to the total number of 334 species, or by approximately 5.5%. as the majority of all those new species are of small size (<5 mm), their finding is attributed to the inten- sive, frequent and thorough sampling effort as well as to the careful sorting under magnification and the ap- propriate and delicate handling of the material.

out of the two nuculanid species recorded, Nucu- lana cf. pella (linnaeus 1767) comprises a temptation to be considered as a variant of the known in the area Nuculana pella (linnaeus 1767) but as the members of this family separate from each other often on the basis of minor morphologic differences, such a "vari- ant" should be kept separate from its close relative.

The finding of a number of minute and rare mon- tacutids reported in this work for the first time from Greece, namely, Devonia perrieri (Malard, 1904), Kel- liopsis jozinae (van aartsen & Carrozza, 1997), Mon- tacuta goudi (van aartsen, 1997) and M. phascolionis dautzenberg & Fischer H., 1925, as well as the small and fragile species Cyclopecten brundisiensis smriglio & Mariottini, 1990, Monia squama (Gmelin, 1791) and Thyasira biplicata (Philippi, 1836), known inhabi- tants of the West and/or Central Mediterranean sea, indicates that the sorting of delicate bivalve fauna ne- cessitates the appropriate handling in order to survive treatment.

it should be pointed out that a considerable num- ber of the presented miniature bivalve species are col- lected from the station 5 and particularly from 10 m2 of a Zostera bed (protected from the waves, not excid- ing the 20 m2 in its total surface). This is reminiscent of another great biodiversity "hot spot" harboring a remarkable association of, similar to those of this pu- blication, miniature bivalves of the lower Pliocene in Peloponnesus, Greece (schneider & Hochleitner, 2006).

among the wood eating members of the family TEREdinidaE, the presence of Bankia carinata (Je Gray, 1827) and Lyrodus pedicellatus (de Quatrefages, 1849) in the Greek waters is now documented. Their identification is mainly based on the morphological characteristics of their pallets which are only present in live and intact biological material. after the death of the wood inhabiting organisms, their pallets are lost (either due to drifting or they are cemented in the wooden substrate) and thus complicate the systema- tic study these xylophages organisms.

The alien species status

From the three new alien species for Greece, Fulvia australis seems to have started expanding from the coasts of israel towards the nW aegean (Thermaikos Gulf) or it has been introduced by shipping as there is no reference from the rest of the aegean sea yet, while the congeneric and very similar species F. fragi- lis is well established in Thessaloniki and Thermaikos Gulfs according to the existing information by Zene- tos et al. (2003), angelidis (2013) and the current study.

Pinctada imbricata radiata is now successfully esta- blished in the s aegean (Elnais, https://services.ath. hcmr.gr). The specimens of this study, with age up to three years, all with a rather high growth rate which is very similar to that of individuals from israel and the Red sea (Fig. 12) show establishment and a quick ex- pansion in the E Thessaloniki Gulf (n aegean, E Me- diterranean sea) perhaps due to appropriate ambient conditions of the area.

Beside Pinctada imbricata radiata, Crassostrea gigas is another commercial alien that is recorded in the E Thessaloniki Gulf where the alien gastropod Bur- satella leachii was also found (Manousis et al., 2012) in coincidence with a massive expansion of the alien alga Caulerpa racemosa which is recorded in quanti- ties along almost all the eastern littoral zone of Thes- saloniki and Thermaikos Gulfs during the current study.

apart from the different collection stations of the recorded alien species in Thermaikos Gulf (nW part of the aegean sea), their successful establishment is also indicated by the collection of live juveniles, live individuals filled with d shape larvae, intact shells and individual valves. This success could be attributed to an adaptability of their populations to the Hellenic marine environment as it was also referred for Parvi- cardium hauniense (Peterson & Russel, 1971) (The Conchological society of Great Britain and ireland, www.conchsoc.org) or/and to the fact that the environ- ment in the E Mediterranean sea has changed during the last decade and became warmer (saaroni et al., 2003; Hansen et al., 2010) with the n aegean sea be- ing more rapidly warmed than the rest of the Medi- terranean sea basin (skliris et al., 2011)

The goal set in a previous publication (Manousis et al., 2010) to "further research emphasizing on small in size species, symbionts, epibionts and rare species needs to be contacted in order to further explore the present biodiversity of bivalves in the area" seems to be accomplished. The present and the previous find- ings consist a reference base for any future study of the bivalve malacofauna of Thermaikos and Thessa- loniki Gulfs.

aCKnoWlEdGEMEnTs

The authors are grateful to dr. C. salas and dr. s. Go- fas for their support and help on identification issues and to Evangelos Tsourmas for his kind help in find- ing trawled material.

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