Synalpheus gracilirostris de Man, 1910

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 : 379-381

3.2.10 Synalpheus gracilirostris de Man, 1910 * ( Fig. 16 )

Synalpheus gracilirostris de Man, 1910 . Tijdschr. ned. dierk. Vereen, 11(4): 291; 1911. Siboga Exped. , 39(2): 269, fig. 49; Banner & Banner, 1975. Records of the Australian Museum, 29(12): pl. 372, fig. 26.

Material examined. ( MBM 107784), 1♂, CL 3.6 mm, Slalao. 4 April 1992. ( MBM 159244), 1♂, CL 3.4 mm, Sanya, Dadonghai, South China Sea, 21 November 1997; ( MBM 158033), 1 ovigerous ♀, CL 4.2 mm, Nansha Islands, 2 August 1944; 1♂, CL 3.5 mm, ( MBM 157909), Nansha Islands, 29 May 1990.

Description. Carapace smooth, glabrous; rostrum about 4.5 times as long as wide at base, 7 times as long as wide at middle, acute tip reaching about 2/3 length of second segment of antennular peduncle; orbital hoods shorter than rostrum, not reaching end of first segment of antennular peduncle; pterygostomial corner produced into acute angle; cardiac notch well developed.

Telson about 1.3 times as long as wide at base; dorsal surface with two pairs of moderately large spines, inserted approximately at 3/7 and 5/7 length of telson; posterior margin strongly produced, fringed with long setae, posterolateral angle each with two pairs of spines, lateral about 1/3 length of mesial, posterolateral margins each produced into small acute tooth, distinctly shorter than contiguous short spines.

Eyes concealed in dorsal and lateral view.

Antennular peduncle moderately slender, with distally acute stylocerite, latter reaching middle of second segment of antennular peduncle; second segment near as long as wide at base; visible part of first segment longer than second and

about twice as long as third. Basicerite without distodorsal tooth, distolateral tooth distinctly shorter than stylocerite, not reaching end of first segment of antennular peduncle; carpocerite overreaching end of third segment of antennular peduncle; scaphocerite blade moderately narrow, hardly reaching end of third segment of antennular peduncle, lateral spine developed, overreaching end of antennular peduncle, longer than carpocerite.

Third maxilliped far beyond antennular peduncle and carpocerite when extended; antepenultimate segment longest; penultimate segment about 1.4 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 3.5 times as long as wide at base, superodistal margin with one acute triangular tooth; carpus cup-shaped, with setae distodorsally; palm about 2.8 times as long as dactylus, distodorsal of palm only slightly projecting; dactylus as long as pollex, distally slightly curved.

Minor chela with merus about 3.8 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 1.9 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 5.6: 1: 1: 1: 2.6, with first segment near as long as sum of last four segments; dorsal margin of palm convex; fingers slightly longer than palm. Third pereiopod moderately slender; merus longer than propodus, about 5.7 times as long as wide at base; carpus less 1/2 length of merus, with dorsal margin extended into an obtuse tooth, ventral margin with one distal spine; propodus with 6 spines along ventral margin plus one distal pair of spines near dactylus; dactylus about 1/4 length of propodus, slightly curved to propodus, biunguiculate, extensor tooth about twice as long as flexor tooth, notch between extensor and flexor tooth V-shaped, flexor tooth near as wide at base as extensor tooth. Fourth pereiopod generally similar to third; merus near as long as propodus; ventral margin of propodus with 5 spines plus one distal pair of spines.

Remarks. De Man (1910) originally described this species. The present specimens generally agree with that description. Banner & Banner (1975) redescribed this species based on Australian specimens. The redescription differs from the original decription in the following characters: basicerite with distolateral tooth subequal to stylocerite; basicerite present the distodorsal tooth; the distal superior margin of the palm in major chela bearing one acute projecting; posterolateral margins of the telson each produced in one acute tooth. Banner & Banner (1975) ever considered to give a new specific name to those varieties. But they took it as intraspecific variation at last because of the few specimens. Then, they (1985) recorded five specimens, three of which are agreed with Banner & Banner (1975), another two are agreed with the original description. All of our collection is generally agreed with the original description. The variety of Banner & Banner (1975) is not found here.

Distribution. South China Sea; Timor in Indonesia; southern Philippines; Red Sea; eastern Africa; Réunion; Mauritius; Australia.

Figures

Fig. 16. Synalpheus gracilirostris de Man, 1910, male (cl 2.5 mm) (MBM 157909). 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, lateral. 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. o. Second pleopod. p. Abdomen, lateral. q. Telson and uropod, dorsal. Scale bars: a–k, m, o–q=0.5mm; l, n=0.25 mm.