Synalpheus biunguiculatus (Stimpson, 1860)

Wang, Yan-Rong & Sha, Zhong-Li, 2015, A review of the genus Synalpheus (Crustacea: Decapoda: Caridea: Alpheidae) from China seas, Zoological Systematics 40 (4), pp. 355-435 : 361-364

3.2.3 Synalpheus biunguiculatus (Stimpson, 1860) * ( Figs 2–3 )

Alpheus biunguiculatus Stimpson, 1860 . Acad. Nat. Sci. Phila., Proc., 1860: 31.

nec Alpheus biunguiculatus de Man, 1887 . Arch. f. Naturgesch., 53: 502, figs 6, 6a.

nec Alpheus biunguiculatus Spence Bate, 1888 . Challenger Rpt., 24: 562, pl. 51, figs 4, 4o, 4z.

nec Synalpheus biunguiculatus Coutiere, 1898 . Soc. Ent. de France, Bui., 11: 232, figs 1–4.

nec Synalpheus biunguiculatus Coutiere, 1905 . Fauna and Geog. Maid, and Laccad., 2(4): 873, pl. 71, fig. 8.

Material examined. 1♂, CL 3.1 mm, TL 8.2 mm, Dengqing island, 3 May 1958, coll. Zhen-Gang Fan, Jie-Shan Xu; 2♂, CL 4.2 mm, TL 10.1 mm, Subi Reef, Nansha Islands, Sta. 8, depth 2 m, 12 May 2004; ( MBM 157909), 1♀ (nonovigerous), CL 4.1 mm, TL 10.5 mm.

Description. Carapace smooth, glabrous; rostrum acute, twice as long as wide at base, with lateral margins slightly concave, acute tip bearing two short setae, slightly overreaching end of first segment of antennular peduncle; orbital hoods acute, much wider at base than rostrum, about 2/3 length of rostrum, notches between orbital hoods and rostrum V-shaped; pterygostomial corner produced into blunt acute angle; cardiac notch well developed.

Abdominal somites smooth, glabrous. Telson about 1.4 times as long as wide at base; lateral margin slightly concave posteriorly; dorsal surface with two pairs of spines, inserted approximately at 1/2 and 3/4 length of telson; posterior margin strongly convex, fringed with long setae, posterolateral angle each with two pairs of spines, lateral about 1/4 length of mesial, posterolateral corner right angle.

Eyes concealed in lateral and dorsal view.

Antennular peduncle stout, with distally acute stylocerite, latter hardly reaching end of second segment of antennular peduncle; second segment wider than long; visible part of first segment longer than second, later slightly longer than third. Antenna with basicerite without distodorsal tooth, distolateral tooth acute, distinctly shorter than stylocerite; carpocerite beyond end of antennular peduncle by 1/2 length of third segment; scaphocerite blade much wider, shorter than antennular peduncle, lateral spine with lateral margin slightly concave posteriorly, slightly overreaching end of third segment, shorter than carpocerite.

Third maxilliped far beyond antennular peduncle and carpocerite when extend; antepenultimate segment longest; penultimate segment about 1.8 times as long as wide at base; tip of ultimate segment bearing crown of five spine-like setae, with several brush transverse rows of setae along ventral margin.

Merus of major cheliped 3.1 times as long as wide at base, superodistal margin ending in acute triangular tooth; carpus cup-shaped, with long setae distodorsally; chela with palm about 2.8 times as long as dactylus, superior distal margin of palm at most with one obtuse tooth; dactylus distinctly longer than pollex.

Minor chela with merus about 3.5 times as long as wide, longer than that of major cheliped, superodistal margin ending in acute triangular tooth; carpus cup-shaped proportionally longer that of major cheliped; palm about 1.8 times as long as fingers; dactylus as long as pollex, distally slightly curved.

Second pereiopod slender, with ischium distinctly shorter than merus; carpus five-segmented, segment ratio subequal to 10: 2: 2: 1.7: 4.2, with first segment subequal to sum of last four segment; fingers slightly longer than palm. Third pereiopod slender, with merus slightly longer than propodus, about 5.4 times as long as wide at base, without spines on ventral margin; carpus about 1/2 merus length, with dorsal margin extended into an obtuse tooth, ventral margin with one distal spine; propodus with 4–6 spines along ventral margin plus one distal pair of spines near dactylus; dactylus slender, about1/5 propodus length, biunguiculate, flexor tooth distinctly smaller than extensor,1/3 length of extensor tooth and 2/3 width of extensor tooth; notch between extensor and flexor tooth V-shaped. Fourth pereiopod generally similar to third; but ventral margin of carpus without distal spine. Propodus of fifth generally similar to that of fourth and third pereiopod, but with 4–5 transversal rows of spine-like setae and two spines along ventral margin plus one pair of spines near dactylus.

Remarks. This species was originally reported by Stimpson (1860). But its original description was much simple and without figures to illustrate. Therefore, this species was controversial ( Banner, 1953).

The species is generally identified following the redescription of Banner (1953). But our collection has following different characters: the stylocerite not overreaching the end of the second segment of the antennular peduncle; the ventral margin of fifth pereiopod as usual with 4–5 transversal rows of spine-like setae rather than "with no trace of brush"; the anterior pair dorsal spines of the telson inserted about 1/2 length of the telson rather 0.3 length of that. Additionally, one specimen is much different with others in following characters: the merus of the major chela more slender, about 4.6 times as long as wide ( Fig. 3d ); the fingers of the major chela much longer, slender and a little compressed, with palm about 2.2 time as long as fingers ( Figs 3d–e ). As species of Synalpheus are always variable in these kinds of characters, those differences are taken as variation of the S. biunguiculatus .

Distribution. South China Sea; Hanauma Bay, Oahu; Oahu off Waikiki, off Nanakui, Maui off Kalama Park; off Hawaii at Halape.

Figures

Fig. 2. Synalpheus biunguiculatus (Stimpson, 1860), male (cl 2.7mm). a–b. Frontal region. a. Dorsal. b. Lateral. c. Third maxilliped, ventral. d–f. Major cheliped (left). d. Lateral. e. Merus, lateral. f. Chela, lateral. g. Minor cheliped (right), lateral. h. Second pereiopod, lateral. i–j. Third pereiopod. i. Lateral. j. Distal propodus and dactylus, lateral. k–l. Fourth pereiopod. k. Lateral. l. Distal propodus and dactylus, lateral. m. Fifth pereiopod, propodus and dactylus, ventral. n. Telson and right uropod, dorsal. Scale bars: a–i, k, m–n=0.5mm; j, l=0.25mm.

Fig. 3. Synalpheus biunguiculatus (Stimpson, 1860), female (cl 2.9mm) (MBM 157909). a–b. Frontal region. a. Dorsal. b. Lateral. c. Third maxilliped, tip, dorsal. d–e. Major cheliped. d. Mesial. e. Chela, lateral. f. Second pereiopod, lateral. g–h. Third pereiopod. g. Lateral. h. Distal propodus and dactylus, lateral. i. Fifth pereiopod, lateral. j. Second pleopod. k. Abdomen, lateral. Scale bars= 0.5 mm.