Synalpheus iocasta de Man, 1909

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. 357-435 : 383-386

3.2.12 Synalpheus iocasta de Man, 1909 ( Figs 18–19 )

Synalpheus iocasta de Man, 1909 . Tijdschr. ned. dierk. Verecn., 11(2): 119; 1911, Siboga Exped. 39(2): 235, fig. 33; Banner & Banner, 1975. Records of the Australian Museum, 29(12): pl. 368, fig. 24i–n.

Material examined. (MBM 270422), 1♂, CL 4.1 mm, Tonkin Gulf (Beibu Gulf), Sta. 7802, depth 67 m, 10 April 1962, coll. Fu-Zeng Sun; (MBM 270587), 1♂, CL 4.2 mm, Tonkin Gulf (Beibu Gulf), Sta. 6266, depth 50.5 m, 13 July 1960, coll. Shou-Peng Shen; (MBM 270423), 1♂, CL 4.1 mm, TL 11.1 mm, Tonkin Gulf (Beibu Gulf), Sta. 7303, depth 34 m, 20 April 1960.

Description. Carapace smooth, glabrous; rostrum about 2.8 times as long as wide at base, acute tip not reaching end of first segment of antennular peduncle; orbital hoods slightly shorter than rostrum; pterygostomial corner produced into acute angle; cardiac notch well developed.

Telson about 1.2 times as long as wide at base; dorsal surface with two pairs of moderately large spines, inserted approximately at 1/2 and 5/7 length of telson; posterior margin slightly produced, fringed with long setae, posterolateral angle each with two pairs of spines, lateral about 1/4 length of mesial, posterolateral margins not produced into acute tooth.

Eyes concealed in lateral and dorsal view.

Antennular peduncle moderately slender, with distally acute stylocerite, latter hardly reaching middle of second segment of antennular peduncle; second segment about 1.25 times as long as wide at base; visible part of first segment longer than second and about twice as long as third. Basicerite with acute distodorsal tooth, about 1/3 length of distolateral tooth, distolateral tooth distinctly shorter than stylocerite, hardly reaching end of first segment of antennular peduncle; carpocerite far overreaching end of third segment of antennular peduncle; scaphocerite blade moderately narrow, reaching 3/4 length of third segment of antennular peduncle, lateral spine developed, overreaching end of antennular peduncle, much shorter than carpocerite.

Third maxilliped far beyond antennular peduncle and carpocerite when extended; antepenultimate segment longest; penultimate segment about 1.3 times as long as wide at base; tip of ultimate segment bearing crown of five long spine-like setae, with transverse rows of setae along ventral margin.

Major cheliped with short, stout ischium; merus about 2.5 times as long as wide at base, superodistal margin with one acute triangular tooth; carpus cup-shaped, with setae distodorsally; palm about 2.5 times as long as dactylus, distodorsal of palm with one acute projecting, straightly, not curved to dactylus; dactylus near as long as pollex, distally slightly curved.

Minor chela with merus about 3.6 times as long as wide at base, superodistal margin with one acute triangular tooth; carpus cup-shaped, proportionally longer that of major cheliped; palm about 1.7 times as long as fingers; dactylus and pollex tapering, distal single tooth.

Second pereiopod with ischium shorter than merus; carpus five-segmented, segment ratio subequal to 6: 1: 1: 1: 2.5, with first segment longer than sum of last four segment; dorsal margin of palm convex; fingers about 1.5 times as long as palm. Third pereiopod moderately slender; merus shorter than propodus, about 5 times as long as wide at base, ventral margin with 2 spines; carpus less 1/2 length of merus, with dorsal margin extended into an obtuse tooth, ventral margin with one distal spine; propodus with nine spines along ventral margin plus one distal pair of spines near dactylus; dactylus about 2/7 length of propodus, slightly curved to propodus, biunguiculate, extensor tooth near as long as flexor tooth, notch between extensor and flexor tooth V-shaped, flexor tooth much wider at base than extensor tooth. Fourth pereiopod generally similar to third; merus shorter than propodus, ventral margin with one moderately large spine; ventral margin of propodus with seven spines plus one distal pair of spines. Fifth pereiopod similar to third and fourth pereiopods, ventral margin of carpus without distal one spine; ventral margin of propodus with five transversal rows of spine-like setae and four spines.

Remarks. This species is generally similar to Synalpheus pococki Coutière, 1898 . The only valid difference between them is the number of spines on propodus of the third pereiopods ( de Man, 1911; Banner & Banner, 1975).

De Man (1909) originally described this species. The present specimens are generally agreed with the original description, except the following characters: the posterolateral margins of the telson were not produced into acute teeth rather than “the outer angles of the posterior margin are spiniform, half as long as the contiguous short spinules”; the posterior margin of the telson only slightly produced rather than “the posterior margin rather prominent in the middle, almost semicircular”. Because these characters are variable in Synalpheus , it is not wise to take our specimens as a new species.

Distribution. South China Sea; Indonesia; Australia; Philippines.

Figures

Fig. 18. Synalpheus iocasta de Man, 1909, female (cl 4.1mm) (MBM 270587). a–b. Frontal region. a. Dorsal. b. Lateral. c–d. Third maxilliped. c. Dorsal. d. Tip, ventral. e–g. Major cheliped (left). e. Mesial. f. Chela, lateral. g. Merus, lateral. h–i. Minor cheliped (right). h. Lateral. i. Chela, mesial. j. Second pereiopod, lateral. k–l. Third pereiopod. k. Lateral. l. Distal propodus and dactylus, lateral. m–n. Fourth pereiopod. m. Lateral. n. Distal propodus and dactylus, lateral. Scale bars: a–c, e–k, m=1 mm; d, l, n =0.5mm.

Fig. 19. Synalpheus iocasta de Man, 1909, female (cl 4.1mm) (MBM 270587). a. Fifth pereiopod, propodus and dactylus, lateral. b. Second pleopod. c. Telson and uropod, dorsal. d. Abdomen, lateral. Scale bars=1mm.