Tethygeneia sunda, Azman, B. A. R. & Othman, B. H. R., 2013

Azman, B. A. R. & Othman, B. H. R., 2013, Shallow water marine gammaridean amphipods of Pulau Tioman, Malaysia, with the description of a new species, ZooKeys 335, pp. 1-31 : 14-16

Tethygeneia sunda sp. n. Figures 12; 13; 14

Type material.

Holotype, male, body length 4.5 mm (from tip of rostrum to apex of telson) (Ref: UKMMZ-1252).

Type locality.

Marine Park, Pulau Tioman, (2°49'48"N, 104°9'48"E) Peninsular Malaysia; intertidal rocks; coll. Azman, B.A.R., Jusim, J.J., 23 August 2001, UKM I.D. 6687.

Additional material examined.

32 specimens, TIO 22, Marine Park, Pulau Tioman, 2°49'48"N, 104°9'48"E, intertidal rocks, Azman, B.A.R., Jusim, J.J., 23 August 2001.

Diagnosis.

Rostrum long and linguiform. Accessory flagellum absent. Maxilla 1, palp article 2 stout armed with several short teeth apically. Maxilla 2, outer plate broader than inner plate, both with plumose setae along margin. Lower lip lacking inner lobes. Mandible palp article 2 long. Gnathopod 2 lacking carpal lobe, more slender articles of carpus and propodus. Pereopods 3-4 with pair of stout locking spines. Telson cleft, lacking large spines on apices.

Description.

Male: 4.5 mm. Head, rostrum large, long, curved down, apically blunt, lateral cephalic lobe broad, shallow, quadriform, defined below by weak but sharp incision; antero-ventral margin bulbous, rounded. Eye large, occupying more than half of head area.

Antenna 1 only about 70 percent as long as antenna 2; flagellum with about 21-articulate, ornamented with aesthetascs ventrally; accessory flagellum absent. Antenna 2 about half as long as body; gland cone of peduncular article 2 broad, extending beyond of peduncle article 3; flagellum long and thin with about 28 articles.

Mandible, molar triturative, each with ragged seta; lacinia mobilis serrate and clearly distinct; palp with article 2 about twice as broad as article 3, latter slightly falcate. Lower lip lacking inner lobes, mandibular lobes subtruncate and apically fringed with small setae. Maxilliped inner plate with apicolateral spine separated from 2 medioapical spines by gap and hollow; outer plate with facial setules in 1 row and a few scattered; palp article 2 broad. Maxilla 1, palp article 2 stout armed with several short teeth apically. Maxilla 2, outer plate broader than inner plate, both with plumose setae along margin.

Gnathopod 1-2 small, subequal in size to each other, basis scarcely setose posteroventrally; propodus long, thin, sub-rectangular, palm evenly oblique.

Gnathopod 1 carpus sub-triangular, posterior margin short, lobe extended; dactylus not serrate on grasping margin. Gnathopod 2 similar to gnathopod 1. Pereopods 1-7 elongate. Pereopods 3-4 homopodous; merus slightly expanded posterodistally; carpus about ½ the length of propodus. Pereopods 5-7 homopodous; basis expanded roundly. Pereopod 7 similar but longer than pereopod 6; basis more elongate than pereopod 6.

Uropod 1 peduncle spinose on lateral margin, almost 2 times as long as outer ramus, one medium sized robust seta at distal part; outer ramus about 0.7 times as long as inner ramus, apex bifid, armed with several apical spines, one elongate. Uropod 2 extending beyond telson; peduncle subequal in length to inner ramus, spinose, and with one long robust seta at distal end; outer ramus almost 0.6 times as long as inner ramus with several apical robust setae; inner ramus apically bifid with several robust setae along margin. Uropod 3 peduncle short; rami foliaceous, subequal in length, marginally spinose and setose. Telsonflat, broad, cleft more than halfway, apices slightly rounded, broad, smooth, lateral margins of lobes with 2 pairs of partial sets of fine short setae.

Remarks.

J.L. Barnard (1972) proposed the genus Tethygeneia to group the existing eusiriid amphipods that are limited to a Tethyan distribution, referring to the warm temperate waters of both hemispheres. The key character that clearly differentiates the genus from the other known eusiriids is the long and linguiform rostrum. Although this linguiform nature of the rostrum is also observed in some genera within the family (e.g. Pontogenia , Gondogeneia ), Tethygeneia relatively exhibits a stronger form of prolonged rostrum. Since 1991, Barnard and Karaman listed 10 species of Tethygeneia that are mostly described from the warm-temperate waters of Australia. Tethygeneia sunda sp. n. falls undoubtedly into the genus according to J.L. Barnard’s eusiriid revisional framework (1972). It resembles Tethygeneia intermedia (Gurjanova) in lacking a carpal lobe on gnathopod 2, but is rather closely related to Tethygeneia rostrata (Gurjanova) and Tethygeneia longleyi (Shoemaker) in the other characters. Differing from Tethygeneia rostrata in the more slender articles of carpus and propodus of gnathopod 2, in the slightly more produced article 3 of antenna 1, and the more spinose rami of uropod 3. Tethygeneia longleyi shares the same form of head, gnathopods and uropods as in Tethygeneia sunda sp. n. However some noteworthy differences are observed in the mouthparts, especially the mandible. The length and structure of article 2 of the mandible palp clearly distinguish Tethygeneia longleyi from Tethygeneia sunda sp. n.

Etymology.

The specific designation is derived from the name of the Sunda shelf, which was part of the south-east Asian continent during the Pleistocene.