Seborgia kanaka, Jaume & Sket & Boxshall, 2009

Jaume, Damià, Sket, Boris & Boxshall, Geoff A., 2009, New subterranean Sebidae (Crustacea, Amphipoda, Gammaridea) from Vietnam and SW Pacific, Zoosystema 31 (2), pp. 249-277 : 268-274

Seborgia kanaka n. sp.

( Figs 12-17 )

TYPE MATERIAL. — Loyalty Islands. Lifou, Grotte de Luengoni (20°58’38.5”S, 167°22’59.1”E), G. A. Boxshall and D. Jaume coll., 22.X.2000, holotype 1.71 mm, sex unknown (lacking oostegites or penile papillae), completely dissected and mounted on two slides (MNHN- Am7546).

Paratypes same data as holotype: 3 specimens of 1.77, 1.79 and 1.87 mm, former completely dissected and mounted on single slide (MNHN-Am7547) ; latter 2 preserved in 70% ethanol vial (MNHN-Am7548).

DIAGNOSIS. — Basis of maxillipeds fused to each other and incorporated into common segment with fused coxae. Posterior margin of basis of pereiopods V-VII angled. Coxal gills bilobed.

ETYMOLOGY. — Species name derived from the Kanak, the original inhabitants of the Loyalty Islands.

DESCRIPTION OF HOLOTYPE

Body ( Fig. 12A ) unpigmented, micro-occulate, eyes faintly pigmented retaining about five facets ( Fig. 12B ). Differing from S. sanctensis n. sp. in conspicuously hispid condition (see Fig. 12E ; short setules covering uniformly most of body integument omitted from most of figures) and in hardly developed rostrum ( Fig. 12B ). Posterodorsal margin of pleonites smooth ( Fig. 12E ), only epimeral plate II with posterodistal angle produced posteriorly into pointed process; plates I and III with groove immediately above angle ( Fig. 13F ).

Antennule ( Figs 12A ; 13A ) peduncle segments length ratio 46: 29: 25. Peduncle-to-main flagellum length ratio 60: 40. Main flagellum 4-articulate, distal article longest, all articles with aesthetasc. Accessory flagellum ( Fig. 13B ) with three simple slender setae and one shorter robust seta; penicillate seta apparently absent.

Antenna ( Figs12A ; 13C ) differing from S. sanctensis n. sp. in length ratio of peduncle segments 4-5 (57: 43 vs. 47: 53) and in length of peduncle segment 5 relative to first peduncle segment of antennule (segment shorter vs. longer in S. sanctensis n. sp.). In addition, proximal article of flagellum lacking aesthetasc (aesthetasc present in S. sanctensis n. sp.).

Labrum ( Fig.13A, D ) virtually identical to S. sanctensis n. sp. Paragnaths ( Fig. 13E ) inner lobes fused proximally (lobes separated in S. sanctensis n. sp.).

Mandibles ( Fig. 14 A-E) differing from S. sanctensis n. sp. in presence of four elements in spine row instead of three, in smooth anterior margin of molar, and in simple condition of seta on latter process. Palp ( Fig. 14D) segments almost identical in relative proportions in both species (23: 52: 25 vs. 22: 52: 26 in S. sanctensis n. sp.), although distal segment of S. kanaka n. sp. devoid of D-setae and with three E-setae (vs. four in S. sanctensis n. sp.).

Maxillule ( Fig. 15A ) as in S. sanctensis n. sp. except for sparsely setulose coxal endite and relative proportions of endopod segments (47: 53 vs. 20: 80 in S. sanctensis n. sp.).

Maxilla ( Fig. 15B ) reduced to single lobe with four simple setae; lobe equivalent to outer lobe of S. sanctensis n. sp., based on presence of same number of armature elements.

Maxillipeds ( Fig. 14F) differing from S. sanctensis n. sp. in basis of each limb fused to opposite member of pair and incorporated into common compound segment with fused coxae. Relative proportions of carpus-to-unguis of palp 47: 33: 16: 4 (vs. 40: 31: 20: 9 in S. sanctensis n. sp.); transverse comb of long spinules on dactylus lacking.

Coxal plate IV ( Fig. 15D ) 2.2 times longer than broad (vs. 1.6 times in S. sanctensis n. sp.), with both anterior and posterior margins straight (vs. slightly convex in S. sanctensis n. sp.); excavation covering only proximal 13% of posterior margin (26% in S. sanctensis n. sp.). Coxa V ( Fig. 17A ) anterior lobe wanting. Coxal gills ( Figs 15C, D ; 16C ) each with small sacciform protuberance posterolaterally on proximal part.

D

C E

Gnathopod I ( Fig. 16A ) subchelate, propodus about 1.1 times broader than long (vs. 1.5 times longer than broad in S. sanctensis n. sp.), with palm angle acute, located at 63% of maximum length of segment (vs. at 47% in S. sanctensis n. sp.). Palm margin broadly convex, covered with stout triangular denticles and with submarginal row of about five flagellate robust setae; palm angle with one long and stout simple robust seta on medial side, plus short and slender flagellate robust seta on lateral side. Dactylus ( Fig. 16B ) with two short robust setae terminally on medial margin, plus hyaline sheath almost completely covering unguis; latter minute, about 5% length of dactylus. Gnathopod II ( Fig. 16C ) propodus about 1.2 times broader than long (vs. 1.3 times longer than broad in S. sanctensis n. sp.), with palm angle strongly protruded distomedially; palm angle armed with single short and stout simple robust seta; palm margin with row of stout triangular denticles and with submarginal row of about six flagellate robust setae. Dactylus with two tiny terminal robust setae on medial margin, plus hyaline sheath almost completely covering unguis; latter tiny, about 6% length of dactylus (vs. 15% in S. sanctensis n. sp.). Pereiopods III and IV ( Fig. 15C, D ) each with unguis incorporated into dactylus, latter with single simple seta subterminally on medial margin; hyaline sheath on distal margin of dactylus covering unguis anteriorly; medial margin of dactylus with row of densely set spinules. Pereiopods V-VII ( Fig. 17 B-D) each with basis about 1.5 times longer than broad; anterior margin with 2 or 3 robust setae; posterior margin produced into angle (margin evenly convex in other species), with 1-3 notches each provided with slender simple seta. Pleopods ( Fig. 12C, D ) with protopod setulose along lateral margin only; proximal swelling on protopod I smooth. Uropods I-II ( Fig. 12F, G ) differing from S. sanctensis n. sp. in possession of additional robust seta about midway along each ramus, and in relative length of rami of uropod I, with exopod clearly shorter than endopod (rami about equal in length in S. sanctensis n. sp.). Uropod III ( Fig.12E ) uniramous, ramus shorter than protopod.

REMARKS

Seborgia kanaka n. sp. is unique in possessing an angled posterior margin of the basis of pereiopods V-VII, all other Seborgia species have a bowed, variably convex posterior margin on this segment. The fusion of the basis of both maxillipeds into a common compound segment with the fused coxae is also a unique feature of the new species, although such a fusion apparently also occurs in at least some members of Seba (see Larsen 2007: fig. 8j). Another probable autapomorphic trait of the new species is the loss of the anterior lobe of the coxa of pereiopod V; however, the state of this character is not indicated in the descriptions of S. minima Bousfield, 1970 and S. schieckei Ruffo, 1983 . Additional diagnostic features of the new taxon are given in Table 1.

Seborgia kanaka n. sp. is, together with the female of S. relicta Holsinger & Longley, 1980 , the only member of the genus displaying a strongly concave posterior margin of the propodus of gnathopod II, a by-product of the strong protrusion of the palm angle. Since the male of S. relicta does not display this feature, the morphology of the second gnathopod of the new species may provide evidence that the four specimens currently known are females.

ECOLOGY

Grotte de Luengoni – the type locality of the new species – lies about 2 km to the NE of the small village of Luengoni and opens in an upraised coral reef terrace via a sinkhole about 40 m in diameter and 30 m deep. A detailed description and topography of the cave appears in Thomas et al. (1995). There are two lakes, one in direct sunlight, the other fully subterranean. The surface water in both lakes is brackish, although the deepest parts (– 31 m) of the cave lake may be fully marine. Three of the specimens of Seborgia kanaka n. sp. were captured with baited traps set at a depth of 4 m inside the cave, whereas the fourth was caught with a hand net in the dimly lit part of the outside lake, which is directly connected to the cave lake.The accompanying fauna in the cave lake consisted of Stygocyclopia sp. (Copepoda, Calanoida , Pseudocyclopiidae Sars, 1902 ), Josephosella microps Stock & Iliffe, 1995 ( Amphipoda , Melitidae Bousfield, 1973 ), Macrobrachium microps Holthuis, 1978 ( Decapoda , Palaemonidae Rafinesque, 1815 ), eels and other fishes. In the exterior lake were harpacticoid and cyclopoid copepods plus undetermined polychaete worms.

Figures

FIG. 12. — Seborgia kanaka n. sp., holotype: A, body, lateral; B, detail of rostrum, lateral lobe and eye; C, right pleopod I, anterior; D, detail of retinacles; E, urosome and telson,dorsal;F, left uropod I, posterior;G, right uropod II, posterior.Scale bars:A, B, 0.25 mm; C, E-G, 0.125 mm; D, 0.05 mm.

FIG. 13. — Seborgia kanaka n. sp., holotype:A, head,labrum, paragnaths and left antennule,lateral;B, detail of accessory flagellum of latter;C, left antenna,lateral;D, labrum,posterior;E, paragnaths,posterior; F, left epimeral plates,lateral.Scale bars:A-C,F,0.125 mm; D, E, 0.05 mm.

FIG. 15. — Seborgia kanaka n. sp., holotype: A, right maxillule, posterior;B, right maxilla,posterior; C, right pereiopod III, lateral; D, left pereiopod IV, lateral. Scale bar: A, B, 0.05 mm; C, D, 0.125 mm.

FIG. 17. — Seborgia kanaka n. sp., holotype: A, left coxal plates V-VII, lateral; B, left pereiopod V, lateral; C, proximal segments of left pereiopod VI, lateral; D, right pereiopod VII, lateral. Scale bar: 0.125 mm.

FIG. 16.— Seborgia kanaka n. sp., holotype:A, right gnathopod I, lateral (integumental microspinulation on surface of dactylus omitted; arrow indicating anteroproximal seta of dactylus); B, dorsomedial aspect of nail of left gnathopod I (arrow pointing to anteroproximal seta of dactylus); C, left gnathopod II, lateral. Scale bar: 0.125 mm.