Galeomma, TURTON, 1825

Lützen, Jørgen & Nielsen, Claus, 2005, Galeommatid bivalves from Phuket, Thailand, Zoological Journal of the Linnean Society 144 (3), pp. 261-308 : 297-302

GALEOMMA (GALEOMMA) AMBIGUA (DESHAYES, 1856)

( FIGS 6B , 41B, C , 45-47 )

Galeomma ambigua Deshayes, 1856a: 168 . – Mitchell, 1867: 63.

Galeomma layardi Deshayes, 1856a: 169 (in part). – Melvill & Standen, 1906: 818.

Scintilla pallidula Deshayes, 1856b: 178 (syn. nov.). – Sowerby, 1874: species 10, pl. II, fig. 10.

Scintilla forbesii Deshayes, 1856b: 179 (syn. nov.). – Sowerby, 1874: species 18, pl. II, fig. 18a, b.

Scintilla aurantiaca Deshayes, 1856b: 179 (syn. nov.). Scintilla adamsi Deshayes, 1856b: 179 (syn. nov.). – Sowerby, 1874: species 25, pl. III, fig. 25.

Scintilla faba Deshayes, 1856b: 180 (syn. nov.). – Shopland, 1902: 178. Pelseneer, 1911: 43, pl. XVI, fig. 7. Prashad, 1932: 169.

Scintilla ambigua Reeve, 1860: 127 (syn. nov.). – Sowerby, 1862: 176. Sowerby, 1874: species 19, pl. III, fig. 19A–D. Prashad, 1932: 169. Habe, 1977: 151. Morris & Purchon, 1981: 324.

Scintilla borneensis Sowerby, 1874 : species 22, pl. III, fig. 22 (syn. nov.). – Lamprell & Healy, 1998: 152, fig. 390.

Scintilla durbanensis Sowerby, 1897: 26 (syn. nov.). – Turton, 1932: 237. Kilburn, 1973: 703.

Scintilla elongata Preston, 1908: 206 , pl. XVII, fig. 71 (non Sowerby, 1897).

Galeomma peilei Le Tomlin, 1921a: 964 (syn. nov.). – Le Tomlin, 1921b: 156.

Solecardia durbanensis Barnard, 1964: 483 (syn. nov.).

Scintilla aurantia Lamprell & Healy, 1998: 152 , fig. 391 (syn. nov.).

Material examined

Syntypes: BMNH 196748 /1–4, Island of Ticoa , Philippines and Port Essington , Northern Territory, Australia .

Museum material: The larger ( SL = 10.2 mm) of two syntypes of Galeomma layardi, BMNH 196751/2, Sri Lanka; syntypes of Scintilla adamsi, BMNH 196787, Island of Bohol, Philippines, several shells, SL to 16 mm; holotype of S. aurantiaca, BMNH 196786, North Australia; holotype of S. borneensis, BMNH 196101, Borneo; syntypes of S. faba, BMNH 196792/ 1–4,4 Borneo; syntypes of S. forbesi, BMNH 196785/ 1–2, Borneo, SL to 14 mm; holotype of S. pallidula, BMNH 196784, San Nicola, Island of Cebu, Philippines; syntypes of S. durbanensis, BMNH 1899.4.14, 3502–3, Durban, South Africa, two specimens; syntypes of Galeomma peilei, BMNH , unregistered, Sri Lanka, two specimens; many specimens in BMNH (unregistered and undetermined or determined as Galeomma , G. ambigua , G. peilei , Scintilla aurantiaca or S. faba ) from the following localities: Karachi and Manora, Pakistan; Mumbai; Krusadei, Gulf of Mannar; Trincomalee, Sri Lanka; N and S Andaman Islands; Pulau Bidang, N of Penang, Malaysia; Borneo; Port Molle, Queensland, Australia; Fiji Islands; one specimen determined as S. borneensis, ZMUC , unregistered, Pulau Milu, Little Nicobar.

New material: Reef off PMBC: March 1975, four specimens; February–March 1982, several specimens; 5 and 9 February 2003, c. 20 specimens (one of them PMBC 20114 ) .

Description of material from Phuket

Shell: Oblong ovate, moderately inflated, colourless and vitreous, relatively thin, surface smooth, with very many close-set growth striae. The shell is dotted with numerous minute and mostly round or oblong pits in the surface ( Fig. 46 ). The pits apparently begin as small, irregular rifts that are elongate perpendicular to the growing edge of the shell ( Fig. 46E, F ). As the rifts grow deeper, and regular, coffee-bean-shaped images emerge ( Fig. 46C, D ). In the older parts of the shell, the pits sometimes fuse to form short sinuous figures, which may penetrate more deeply into the shell ( Fig. 46A, B ). In reflected light the pits appear as small whitish dots.

Shell about twice as long as high, all margins gently rounded, dorsal and ventral margin only slightly so. Size up to 17.2 ¥ 8.3 mm, the prodissoconch II 295– 305 Mm in diameter. The beaks are anterior to the middle. Hinge plate moderately stout. In small or moderate-sized bivalves the right valve has a large oblique cardinal basally flanked by two small tubercles plus a low posterior lateral well behind the resilifer. The left valve bears a longitudinal and a somewhat smaller oblique cardinal and has a posterior lateral. Larger specimens often develop a hooked shell margin anterior to the cardinals, protruding laterals and hooked dorsal extensions of the cardinals, which, on the right side, may split into two ( Fig. 45F ).

Soft parts: There are two fairly prominent tapering siphonal tentacles. The exterior mantle fold may cover the shell completely and bears numerous conical and pointed papillae of various size (poorly illustrated by Pelseneer, 1911). The surface of both tentacles and papillae is rough due to the presence of numerous minute hair-like protuberances. Spherical papillae borne on a short stalk, such as those found in G. layardi , were never seen.

Habitat

At Phuket, the species is relatively common on the underside of shale blocks resting on sand in the upper part of the tidal zone on the reef off PMBC. When at all noted by other authors, animals were always found under stones at low water. Two or three often occur together or in company with G. layardi . Juveniles up to SL 2.0 mm may attach to the exterior mantle of larger ones.

Distribution

Island of Ticoa, Philippines; Port Essington, Northern Territory, Australia; Sri Lanka ( Deshayes, 1856a); Mumbai, India ( Mitchell, 1867; Le Tomlin, 1921a, b); Chah Bahar, Gulf of Oman and Ras Ormara, Pakistan ( Melvill & Standen, 1906); San Nicola, Island of Cebu, Philippines; Borneo; North Australia; Baclayon, Island of Bohol, Philippines ( Deshayes, 1856b; Sowerby, 1874); Aden, South Yemen ( Shopland, 1902); Kuandang, Sulawesi; Ambon, Moluccas; Roti Island, W of Timor ( Prashad, 1932); S of Okinawa, Japan ( Habe, 1977); W coast of Malaysia ( Morris & Purchon, 1981); Central Queensland, Australia ( Lamprell & Healy, 1998); Durban, South Africa ( Sowerby, 1897); Port Alfred, South Africa ( Kilburn, 1973); Andaman Island ( Preston, 1908); Baia de Lourenco Marques (Delagoa Bay) ( Barnard, 1964); Sri Lanka ( BMNH); Karachi and Manora, Pakistan ( BMNH); Krusadei, Gulf of Manaar ( BMNH); Trincomalee, Sri Lanka ( BMNH); N and S Andaman Islands ( BMNH); Pulau Bidang, N of Penang, Malaysia ( BMNH); Port Molle, Queensland, Australia ( BMNH); Fiji Islands ( BMNH); Pulau Milu, Little Nicobar ( ZMUC); Phuket Island, Thailand (present study).

Remarks

The species has been described under at least 12 different species names. We have compared the type specimens of Galeomma ambigua with the larger (10.0 mm) of the two syntypes of G. layardi and the type specimens of G. peilei , Scintilla adamsi , S. aurantiaca , S. borneensis , S. faba , S. forbesi , S. pallidula , and S. durbanensis and found no noticeable differences. The hinge of Hong Kong specimens identified as G. polita Deshayes by Morton & Scott (1989) and Valentich-Scott (2003) differs considerably from that of the present species, although pits are numerous and scattered all over the shell.

The shape and dimensions of the shells of G. ambigua may vary, which was the only difference noted by Prashad (1932) between Sibogan specimens of G. ambigua and S. faba . A study of many specimens from a restricted area (the reef off PMBC) showed that the dentition in smaller specimens ( Fig. 45C, D ) is basically the same as in species of Scintilla , which explains why most of the records have been referred to that genus, while in larger specimens ( Fig. 45E, F ) it may vaguely resemble that of G. layardi . The hinge of all the specimens we have seen falls within this range of variation. The species’ most characteristic feature is that numerous minute pits are scattered more or less evenly over the shell. This was also noted by Sowerby (1874), who found the shell of G. ambigua ‘very minutely punctured’. SEMs demonstrate that they are true indentations in the surface of the shell ( Fig. 46 ), while the term ‘pustules’, used by some authors, is an inadequate description.

Tiny bivalves were occasionally seen attached to, or moving around upon, the reflected part of the mantle. The only one sectioned turned out to be a male ( SL

0.7 mm), provided with an ovoid testes filled with mature sperm cells.

Because they are so similar in external appearance, in the field Galeomma ambigua may be mistaken for G. layardi , with which it also shares the same habitat. However, the shells of the two species clearly differ in outline, dentition and in the size, shape and arrangement of the small pits and absence/presence of radial ribs (compare Fig. 41A and 41B, C ). The ventral gape of the closed shell of G. ambigua is also small compared to that in G. layardi .

The largest specimen (collected 9 February 2003) was ovigerous.

GALEOMMA PHUKETI SP. NOV.

( FIGS 6D , 48 , 49 )

Material examined

Holotype: PMBC 20115 , reef off PMBC, Thailand, 21 March 1975, SL = 6.0 mm.

Paratypes: Reef off PMBC: 21 March 1975, one specimen (section series of entire animal) ; 26 February 2002, one specimen .

Description of material from Phuket

Shell: Oblong ovate, rather inflated, colourless, quite thin, rather opaque, surface dull with many fine com-

clearly comparable to the pits of G. ambigua and G. layardi .

Etymology

The species is named after its locality.

GENUS PSEUDOGALEOMMA HABE, 1964

Shell thin, but rather solid, oblong ovate, narrowing towards the anterior end, with a narrow ventral gape. Each valve with a small tuberculous cardinal and with one or two minute denticles arising from the shell margins (emended from Habe, 1964). Reflected mantle with short finger-shaped siphonal tentacles, small scattered papillae and a number of spherical warts.

marginal striae. The shell displays a very characteristic pattern of radiating close-set slightly wavy grooves on its surface, which occasionally break up into shorter sections or merge with one another ( Fig. 49 ). Dorsal margin almost straight, both antero- and posterodorsal margins sloping, otherwise rounded at both ends, slightly gaping posteriorly. Size of the three specimens 4.6 ¥ 2.3, 4.6 ¥ 2.4, and 6.0 ¥ 3.2 ¥ 2.5 mm. The prodissoconch II is 300 Mm in diameter. Beaks prominent, slightly anterior to the middle. Hinge plate rather narrow. Right valve with a single rounded cardinal immediately in front of umbo, left valve with a large and a small cardinal below umbo. Short laterals are present behind the resilifer.

Soft parts: Live specimens were not studied, but the preserved ones displayed finger-shaped unpaired anterior and posterior siphonal tentacles.

Habitat

All three specimens were collected intertidally under pieces of shale.

Distribution

Phuket Island, Thailand (present study).

Remarks

The dentition places the species in the genus Scintilla , but is also similar to that of young specimens of Galeomma ambigua . We have referred the species to Galeomma because the grooves of the shell surface are

Type species (monotypy): Galeomma japonica A. Adams, 1862 .

PSEUDOGALEOMMA JAPONICA (A. ADAMS, 1862)

( FIGS 6E , 50 )

Galeomnia japonica A. Adams, 1862: 228 .

Solecardia vitrea japonica: Pilsbry, 1904: 558 , pl. 41, fig. 6.

Pseudogaleomma japonica: Habe, 1964: 185 , pl. 57, fig. 13. Kuroda et al., 1971: 410, pl. 120, figs 11, 12. Habe, 1981: 104. Higo et al., 1999: 460, B662., Tsi & Ma, 1982: 449. Okutani, 2000: 937, pl. 466, fig. 4. Valentich-Scott, 2003: 279.

Material examined

New material: Reef off PMBC: 3 March 2002, one specimen ( PMBC 20116 ) ; 3 March 2002, one specimen (section series of entire animal); 7 and 9 February 2003, two specimens.

Description of material from Phuket

Shell: Elongate-oval, rather compressed, semitransparent, rather thin, glassy, surface smooth. Anterior and posterior sides evenly rounded, maximum height between umbo and posterior margin. Ventral margins straight in the middle and slightly gaping. Two specimens measured 10.2 ¥ 4.9 mm (width 2.9 mm) and 10.2 ¥ 5.0 mm. The prodissoconch II is 240 Mm in diameter. Beaks small, distinctly anterior to the middle. Hinge plate narrow, each valve with a small tuberculous cardinal and with one (left) or two (right) minute denticles arising from the shell margins.

Soft parts: The dorsal part of the anterior inhalant region protrudes as a relatively small forwardly the species occurs under stones from the shore to a depth of> 100 m.

Distribution

Minoshima, Sea of Japan ( A. Adams, 1862); Hiradoshima, W Kyûshû, Japan ( Pilsbry, 1904); from Sagami Bay, Honshû to Kyûshû, Japan ( Habe, 1964); coast of Guangdong to Hainan Island, S China ( Tsi & Ma, 1982); Hong Kong ( Valentich-Scott, 2003); Phuket Island, Thailand (present study).

Remarks

The shell corresponds exactly in size and dimensions to Pilsbry’s Solecardia vitrea japonica . Morton & Scott (1989) considered Pilsbry’s specimen synonymous with Galeomma polita Deshayes , but the shell they illustrate of this species is higher, has two, not a single pointed and oblong cardinal in each valve, and a larger (300 Mm) prodissoconch II. The mantle of G. polita (as illustrated by Morton & Scott, 1989: fig. 23) bears numerous smaller or larger papillae, which differ markedly in number and size from those of the present species, the soft parts of which were unknown to Morton & Scott. In G. polita there is a large pedal gape ( Morton, 1975), while in P. japonica , this is small, even in the live animal.

directed siphon above which arises a finger-shaped short tentacle. The posterodorsally directed exhalant siphon is small and short, with another tentacle close to it. Ventrally on the reflected mantle there are a few serially placed pointed papillae and a small number of spherical warts ending in a minute whip. Numerous, very small papillae are spread nearly all over the mantle’s surface. Habe (1964) described the shell as covered by a ‘mammillated mantle’.

Habitat

All four specimens were found under rocks resting on coarse sand, in the upper part of the tidal zone, two of them together with specimens of G. layardi . In Japan

Figures

Figure 6. A, Galeomma (Amphilepida) obockensis, reef off Nai Yang, 7 July 1976, PMBC ref. coll. 916, M102. B, G. (Galeomma) ambigua, reef off PMBC, 9 February 2003, PMBC ref. coll. 20114. C, G. layardi, reef off PMBC, 3 February 2003, PMBC ref. coll. 20113. D, holotype of G. phuketi sp. nov., reef off PMBC, 21 March 1975, PMBC ref. coll. 20115. E, Pseudogaleomma japonica, reef off PMBC, 3 March 2002, PMBC ref. coll. 20116. F, holotype of Nudiscintilla glabra gen. et sp. nov., reef off PMBC, 8 February 1975, PMBC ref. coll. 20111. G, holotype of S. ovalis sp. nov., reef off PMBC, 3 March 2002, PMBC ref. coll. 20112. H, Ephippodonta gigas, Koh Rok, Phuket Island, 7 March 1982, PMBC ref. coll. 20117. I, holotype of Aclistothyra orientalis sp. nov., shells photographed with soft parts inside; reef off PMBC, PMBC ref. coll. 20118. Top: right valve; bottom: left valve, except G (left valve). Scale bar = 5 mm.

Figure 41. Shell structure (in transparency) of Galeomma layardi (A) and G. ambigua (B, C). Scale bars = 50 Mm.

Figure 45. Galeomma ambigua. A, living animal in left side view, dotted line indicating outline of shell. B, left valve in internal view. Hinges of small (C, D) and large (E, F) specimens. C, E, left and D, F, right valve hinge showing prodissoconch II and resilifer of internal ligament (black). Scale bars: A, B = 5 mm, C-F = 1000 Mm.

Figure 46. SEM of shell of Galeomma ambigua. A & B, older part of the shell with deep pits, some of which are confluent. C & D, younger part of the shell with coffee-bean-shaped pits. E & F, growing edge of the shell with narrow rifts and early pits of the coffee-bean shape. Scale bars: A, C, E = 200 Mm; B, D, F = 50 Mm.

Figure 47. Galeomma ambigua. Live specimen seen from the dorsal (A) and the left side. Scale bars = 5 mm.

Figure 48. Galeomma phuketi sp. nov. A, left valve in internal view. Left (B) and right valve hinge (C) showing prodissoconch II and resilifer of internal ligament (black). Scale bars: A = 3 mm, B, C = 1000 Mm.

Figure 49. Galeomma phuketi sp. nov. Shell structure seen in transmitted light. Scale bar = 50 Mm.

Figure 50. Pseudogaleomma japonica. A, living animal in left side view, dotted line indicating outline of shell. B, left valve in internal view. Left (C) and right valve hinge (D) showing prodissoconch II and resilifer of internal ligament (black). Scale bars: A = 5 mm, B = 3 mm, C, D = 500 Mm.