Synalpheus mortenseni Banner & Banner, 1985

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 : 401-404

3.2.18 Synalpheus mortenseni Banner & Banner, 1985 * ( Figs 31–32 )

Synalpheus mortenseni Banner & Banner, 1985 . Marine Research in Indonesia: 47, fig. 5.

Material examined. (MBM 270604), 1♀, CL 5.4 mm, TL 14.3 mm, Tonkin Gulf (Beibu Gulf), Sta. 6229, depth 41 m, 8 July 1960.

Description. Carapace smooth, glabrous; rostrum twice as long as wide at base, with lateral margins slightly convex, rounded tip bearing two short setae, overreaching 1/2 length of visible part of first segment of antennular peduncle; orbital hoods about 2.6 times as wide at base as rostrum, equal to rostrum, with rounded tip bearing two short setae; both rostrum and orbital hoods tips upturned; notches between orbital hoods and rostrum deep, narrow, V-shaped; pterygostomial corner produced into blunt acute angle; cardiac notch well developed.

Abdominal somites smooth, glabrous, posterolateral margin of sixth pleura each with one triangular tooth, margin between two teeth bearing eight subacute teeth; first-fifth pleura of male with posterior corner rounded. Telson as long as wide at base; lateral margin slightly concave posteriorly; dorsal surface without median groove, with two pairs of large spines, inserted approximately at 1/3 and 3/5 length of telson; posterior margin strongly produced, fringed with long setae, posterolateral angle each with two pairs of spines, lateral 2/3 length of mesial, posterolateral margins each produced into acute tooth, but shorter than lateral spines.

Eyes concealed in lateral and dorsal view.

Antennular peduncle slender, with distally acute stylocerite, latter hardly reaching middle of second segment of antennular peduncle; second segment 1.25 times as long as wide; visible part of first segment slightly longer than second and about twice as long as third. Antenna with basicerite with acute distodorsal tooth, about 1/2 length of distolateral tooth, latter overreaching end of first segment, slightly shorter than stylocerite; carpocerite beyond end of antennular peduncle by 1/4 length of third segment; scaphocerite blade narrow, hardly reaching end of third segment of antennular peduncle, lateral spine developed, with lateral margin slightly concave posteriorly, overreaching end of antennular peduncle, slightly shorter than carpocerite.

Mouthpart not dissected. Third maxilliped far beyond antennular peduncle and carpocerite when extended; antepenultimate segment longest, about five times as long as wide; penultimate segment as long as wide at base; tip of ultimate segment bearing crown of five spine-like long setae, with several brush consisting of 6–8 transverse rows of setae along ventral margin.

Major cheliped with short, stout ischium; merus 1.6 times as long as wide at base, with ventral margin convex medially, superodistal margin ending in subacute triangular tooth; carpus cup-shaped, with long setae distodorsally; chela cylindrical, not a bit compressed or twisted, with palm about 2.8 times as long as dactylus, distodorsal of palm with swollen tubercle, bearing in turn a smaller distinct and acute tooth; dactylus slightly longer than pollex.

Minor chela with merus about twice as long as wide, longer than that of major cheliped, superodistal margin with subacute triangular tooth, ventral margin bearing short setae; carpus cup-shaped, proportionally longer that of major cheliped; palm about 1.5 times as long as fingers; dactylus tapering, with flexor margin concave, distal single tooth; pollex tapering, distal single tooth.

Second pereiopod with ischium shorter than merus; carpus five-segmented, segment ratio subequal to 5: 1: 1: 1: 2, with first segment equal to sum of last four segment; dorsal margin of palm convex; fingers 1.5 times as long as palm. Third pereiopod stout; merus longer than propodus, about 3.8 times as long as wide at base, without spines on ventral margin; carpus about 1/3 merus length, with dorsal margin extended into an obtuse tooth, ventral margin with one distal spine; propodus with usual seven spines along ventral margin plus one distal pair of spines near dactylus; dactylus around 1/5 propodus length, triunguiculate, extensor tooth smallest, about 1/3 length of medial tooth, medial tooth five times as wide at base as extensor tooth, notch between extensor and medial tooth V-shaped; flexor tooth slightly shorter than medial tooth, 6/7 width at base of medial tooth, notch between medial and flexor tooth U-shaped. Fourth pereiopod generally similar to third; ventral margin of carpus with one distal spine. Fifth pereiopod similar to third and fourth pereiopods, but ventral margin of carpus without distal spine, with merus about 2.7 times as long as wide; carpus about 3/4 merus length, ventral margin without distal spine; propodus as long as merus, with six transversal rows of setae and five spines along ventral margin.

Remarks. The species is original described by Banner & Banner (1985), based on 13 specimens. The holotype, a ovigerous female, was collected from Kei Islands, Ambon, in a depth 13– 18 m. The description is intact, and the variations between the specimens were also well discussed. They also discussed the differences between S. mortenseni and other six species ( S. triunguiculatus , S. demani , S. trionyx , S. nilandensis , S. fossor , S. heroni ).

Another species, S. septemspinosus de Man, 1910 , also bears 7 spines on the posterior margin of the sixth abdominal somite, but it can be well distinguished from S. mortenseni by the merus of third pereiopod, which bears several spines along the ventral margin of the third pereiopods.

The present specimen is an ovigerous female collected from Tonkin Gulf (Beibu Gulf), in a depth 41 meters. The specimen is agreed well with the description of the holotype, except the number of the spines of the posterior margin of sixth abdominal somite, but this character was variable in S. mortenseni , as discussed in the original description (Banner & Banner, 1985).

Distribution. Tonkin Gulf (Beibu Gulf), South China Sea; Ambon, Indonesia.

Figures

Fig. 31. Synalpheus mortenseni Banner & Banner, 1985, male (cl 5.4mm) (MBM 270604). a–b. Frontal region. a. Dorsal. b. Lateral. c–d. Major cheliped. c. Chela, mesial. d. Lateral. e–g. Minor cheliped. e. Mesial. f. Merus. g. Chela. h. Second pereiopod, lateral. Scale bars =0.5mm.

Fig. 32. Synalpheus mortenseni Banner & Banner, 1985. a–b. Third pereiopod. a. Lateral. b. Distal propodus and dactylus, lateral. c–d. Fourth pereiopod. c. Lateral. d. Distal propodus and dactylus, lateral. e–f. Fifth pereiopod. e. Lateral. f. Propodus and dactylus, ventral. g–h. Third maxilliped. g. Dorsal. h. Tip, dorsal. i. Abdomen, lateral. j. Second pleopod. k. Telson and uropod, dorsal. l. Posterior margin of sixth abdominal somite. Scale bars =0.5 mm.