Nudiscintilla, Lützen & Nielsen, 2005

Lützen, Jørgen & Nielsen, Claus, 2005, Galeommatid bivalves from Phuket, Thailand, Zoological Journal of the Linnean Society 144 (3), pp. 261-308 : 291-297

NUDISCINTILLA GEN. NOV.

Diagnosis

Shell subovate, rather thin, surface smooth. Umbones small, submedian. Each valve with a single small low cardinal. Lateral teeth absent. Mantle smooth, partly reflected over the shell. Without papillae nor tentacles, except for a minute posterior siphonal tentacle.

Soft parts: A very small anterior siphonal tentacle occurs dorsal to the large inhalant region and an equally small posterior tentacle is placed above the exhalant siphon. Numerous small pointed papillae are scattered all over the reflected mantle lobes, less commonly near the two mantle openings. When maximally extended, the papillae may be longer than illustrated.

Habitat

All specimens were attached to grooves or crevices on the underside of Porites , in the lower part of the tidal zone.

Distribution

Phuket Island, Thailand (present study).

Remarks

The inclusion of the species in Scintilla is provisional, as the rudimentary state of the cardinals and the total absence of laterals do not fit the definition of the genus. The poorly developed hinge resembles that of S. stevensoni Powell, 1932 , except that in this species there is only one, not two obsolete cardinals in the left valve. The mantle of S. stevensoni , described by Pon- der (1967) is also covered all over with numerous papillae, although they are much longer than in S. papillosa .

Etymology

From Latin papilla (wart), referring to the warty appearance of the mantle surface.

Type species: Nudiscintilla glabra sp. nov.

Remarks

The combination of a single cardinal in both valves and the total absence of papillae or paired tentacles distinguish the genus from all other galeommatid genera in which the soft parts are known.

Etymology

Prefix Latin nudus (naked), in allusion to the absence of papillae and tentacles on the mantle folds.

NUDISCINTILLA GLABRA SP. NOV.

( FIGS 6F , 38 , 39 )

Material examined

Holotype: PMBC 20111 , reef off PMBC, Thailand, February 1975, SL = 6.8 mm.

Description of material from Phuket

Shell: Subovate, rather compressed, whitish, opaque, relatively thin, irregularly commarginally striate, surface smooth. Anterior and posterior sides evenly rounded, dorsal and ventral margin slightly curved. Size 6.8 ¥ 4.25 mm, prodissoconch II 260 Mm in diameter. Umbones small, submedian, posterior region only a little longer than the anterior. Maximum height occurring in posterior part. Hinge plate narrow, with a small opisthodetic resilifer and a single small low cardinal in each valve. No lateral teeth.

Soft parts: The anterior part of the reflected mantle folds forms a wide inhalant region in front of the shell. An anterior siphonal tentacle is apparently absent, but a small pointed tentacle rises above the exhalant opening, which is without a true siphon. The mantle may be reflected over at least the marginal parts of the shell. It is unusual in being completely smooth, without traces of papillae or tentacles. The foot is tongueshaped.

Habitat

The only specimen was found intertidally and brooded 120–125 Mm long D-larvae in the gills. The number of larvae was estimated at 6000. Three

GENUS GALEOMMA TURTON, 1825

Shell irregularly quadrangular-transverse, more or less gaping ventrally. Sculpture of weak radial riblets and/or pits into the surface. Hinge margin straight, umbones low. True cardinals and laterals absent, replaced by low tubercles. Live animal with mid-mantle folds reflected over the shell. The mantle folds are unfused anteriorly and form a wide inhalent-pedal aperture. The small posterior exhalent siphon is low and conical. Mantle with anterior and posterior short siphonal tentacles guarding the two openings and numerous relatively large pointed papillae scattered evenly all over the surface.

small juveniles had settled close to each other on the left mantle lobe.

Distribution

Phuket Island, Thailand (present study).

Etymology

From Latin glaber (bald), in allusion to the smooth surface of the mantle.

Type species (monotypy): Galeomma turtoni Turton, 1825 .

GALEOMMA (AMPHILEPIDA) OBOCKENSIS ( JOUSSEAUME, 1888)

( FIG. 6A )

Scintilla obockensis Jousseaume, 1888: 202 . – Shopland, 1902: 178.

Galeomma (Amphilepida) obockensis Chavan, 1953: 136 , figs 8–10.

Galeomma obockense Tantanasiriwong, 1979: 9 .

Material examined

Museum material: PMBC 916, M102, reef off Nai Yang, 7 July 1976, a cleaned and dried shell.

Description

The shell is described and illustrated by Jousseaume (1888) and Chavan (1953). Size ranges from 10.0 ¥ 5.0 mm ( Jousseaume, 1888) to 13.1 ¥ 7.6 mm

(present material). The live animal has never been described.

Habitat

The Phuket specimen was taken from the underside of corals.

Distribution

Red Sea ( Jousseaume, 1888); Gulf of Aden ( Shopland, 1902); Phuket Island, Thailand ( Tantanasiriwong 1979).

GALEOMMA ( GALEOMMA ) LAYARDI DESHAYES, 1856

( FIGS 6C , 40–44 )

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

Scintilla layardi: Sowerby, 1874 : species 31, pl. IV, fig. 31a, b.

Galeomma indecora Deshayes, 1856a: 169 (syn. nov.). – Sowerby, 1874: species 8, pl. I, fig. 8.

Galeomma paucistriata Deshayes, 1856a: 170 (syn. nov.). – Sowerby, 1874: species 2, pl. I, fig. 2.

Galeomma chloroleuca Deshayes, 1856a: 170 (syn. nov.). – Sowerby, 1874: species 5, pl. I, fig. 5.

Galeomma angusta Lynge, 1909: 184 (syn. nov.).

Galeomma (Paralepida) takii Kuroda, 1945: 39 , pl. 2, figs 9–12 (syn. nov.). – Morton, 1973: 133–150, pl. 1, text-figs 1–9.

Paralepida takii: Habe, 1964: 185 , pl. 57, fig. 12. Kuroda et al., 1971: 411, pl. 120, figs 3, 4. Higo et al., 1999: 460, B658.

Galeomma argentea: Tantanasiriwong, 1979: 9 .

Lepirodes takii: Habe, 1981: 104 ; Okutani, 2000: 937, pl. 465, fig. 2.

Galeomma takii: Morton & Scott, 1989: 150 , pl. I, q, text-figs 21, 22A.

Galeomma (Pseudogaleomma) sp. Fukuda et al., 1999: 54, figs 11–15.

Material examined

Lectotype (here designated): BMNH 196751 /1, Sri Lanka, SL = 8.2 mm.

Museum material: Syntypes of Galeomma chloroleuca, BMNH 196757, Basay, Island of Samar, Philippines; holotype of G. indecora, BMNH 196752, Island of Masbate, Philippines; syntypes of G. paucistriata, BMNH 196755/1–3, Basay, Island of Samar, Philippines. Phuket Island: PMBC Ref.Coll. 918, M104, one specimen (as G. argentea ); Koh Chang and coast of Lem Ngop, Gulf of Thailand: ZMUC, unregistered, 150 specimens (as G. angusta, Lynge ). BMNH, unregistered: specimens from Pulau Sakra, off Singapore (as G. angusta ); Port Galera, Island of Mindoro, Philippines (as G. argentea ); 20 miles from Dar es Salaam, Tanzania (as G. (Paralepida) formosa ); Bai Chai, Ha Long City, Vietnam and from Ibrahim Maidari (both undetermined).

New material: Reef off PMBC: February 1975, five specimens ; 23 February to 4 March 2002, 32 specimens ; 3 February 2003, c. 20 specimens (one of them PMBC 20113 ) . Tai Tam Bay , Hong Kong: March 2002, several specimens .

Description of material from Phuket

Shell: Elongate-ovate, whitish to pale yellow, translucent, rather thin and brittle, surface smooth and polished. With many large, irregularly shaped pits in the surface, framed in between numerous radiating riblets that tend to branch towards the margins ( Figs 41A , 42 ). Morton & Scott (1989) construed the surface pits as ‘pustules’, which they resemble under LM, but SEM of our material leaves no doubt that they are pits. They are basically circular in outline, but in the older parts of the shell may unite to form irregularly shaped figures and penetrate more deeply into the shell. Outline variable, with a straight dorsal margin and sloping antero- and posterodorsal margins, otherwise regularly rounded in front and behind, but most often sometimes angular at both ends. The ventral margins of both valves are gently rounded, producing a characteristic wide gape, which cannot be closed. SL and SH of three specimens 6.4 ¥ 3.0 mm, 8.4 ¥ 4.2 mm, and 10.5 ¥ 5.2 mm. The ratio SL: SH varies considerably. Maximum SL 19.2 mm. The prodissoconch II is 285 Mm in diameter. Umbones slightly posterior to centre of shell, shell highest behind the umbones. Right valve with a pair of unequally large subtriangular teeth both anterior and posterior to the internal ligament. Left valve with two similar anterior teeth and a single larger posterior tooth.

Soft parts: The reflected middle fold of the mantle is whitish or greyish yellow, transparent and almost entirely covers the shell. It bears numerous conical, pointed papillae and fewer spherical stalked excrescences believed to have arisen from the papillae and to be capable of autotomy, releasing a noxious secretion to deter would-be predators ( Morton, 1973). Two short siphonal tentacles arise dorsal to the large anterior inhalant and much smaller posterodorsal exhalant apertures. Papillae and tentacles are adorned by numerous minute hair-like processes. The soft parts are illustrated in colour by Fukuda, Yamashita & Fujii (1999).

Habitat

At Phuket, the species is common in middle and inner intertidal zones under rocks; it is often found in groups ( Fig. 44), occasionally with G. ambigua ,

G. phuketi sp. nov., Scintilla imperatoris , and Pseudogaleomma japonica .

Distribution

Sri Lanka; Islands of Masbate and Samar, Philippines ( Deshayes, 1856a); Arabian Sea ( Melvill & Standen, 1906); Koh Chang and Lem Ngop, Gulf of Thailand ( Lynge, 1909); Kii Peninsula; Honshû to Kyûshû, Japan ( Kuroda, 1945; Habe, 1964); Hong Kong ( Morton, 1973); Phuket Island, Thailand ( Tantanasiriwong, 1979 and present study); Saga Prefecture, Japan ( Fukuda et al., 1999); Pulau Sakra, off Singapore ( BMNH); Port Galera, Island of Mindoro, Philippines ( BMNH); Dar es Salaam, Tanzania ( BMNH); Bai Chai, Halong City, Vietnam ( BMNH); Ibrahim Maidari ( BMNH).

Remarks

The radial riblets, irregularly shaped pits, details of the hinge and large ventral gape are always present in our specimens. The combination of these characters is perfectly matched by the smaller of the two syntypes of G. layardi , here selected as lectotype. The same characteristics also occur in the holotype of G. indecora , and in the syntypes of G. paucistriata , and G. chloroleuca . The second syntype of G. layardi ( BMNH 196751/2) belongs to G. ambigua (Deshayes) (see below). All the specimens identified by Lynge (1909) as G. angusta Deshayes are also identical with G. layardi .

The type specimen of G. angusta ( BMNH 196754) has a prominent concentric sculpture unlike that of G. layardi , and we therefore disagree with both Lynge (1909) and Prashad (1932) in synonymizing G. angusta with G. chloroleuca (= G. layardi ). Hong Kong specimens identified as G. takii by Morton (1973) and Morton & Scott (1989) and those seen by us share the shell outline, hinge, large ventral gape and shell sculpture with G. layardi and with our Thai material. Another Hong Kong specimen ( SBMNH 35065, identified as G. takii ; Scott, 1994; Valentich- Scott, 2003) does not appear to be identical to G. layardi as the pits are absent, but is otherwise indeterminable. The Japanese records of G. takii are probably identical with G. layardi , but the type specimen could not be located. The outline of the shell of Galeomma (Pseudogaleomma) sp. from western Japan illustrated by Fukuda et al. (1999) matches that of G. layardi .

The holotype of Scintilla porulosa Deshayes, 1856 ( BMNH 196790) has pits of the same size and shape as those in G. layardi , but there are no radial riblets.

Several specimens (SL = 9.2–19.2 mm) had 1–3 very small bivalves (SL = <1.75 mm) attached to the reflected mantle fold, usually near the edge of the valves. Two were sectioned and proven to be juveniles. Morton (1973) also observed postlarvae attached between the papillae of the adult of the same species.

Only three (SL = 12.5–14.5 mm) of c. 57 specimens collected during February- March (1975, 2002 and 2003) brooded larvae in the gills. SL of the prodissoconch I (D-larva) is 150 Mm.

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 38. Nudiscintilla glabra gen. et sp. nov. holotype: 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, B = 3 mm, C, D = 500 Mm.

Figure 39. Nudiscintilla glabra gen. et sp. nov. Live holotype in dorsal view. Scale bar = 5 mm.

Figure 40. Galeomma layardi. A, living animal in left side view, dotted line indicating out line 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 = 1000 Mm.

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

Figure 42. SEM of shell of Galeomma layardi on the middle of the shell (A, B) and at the shell margin seen (C, D). Scale bars: A, C = 200 Mm; B, D = 50 Mm.

Figure 43. Live specimen of Galeomma layardi seen from the dorsal side. Scale bar = 5 mm.