Sketinella trontelji, Camacho, 2005

Camacho, Ana Isabel, 2005, Disentangling an Asian puzzle: Two new bathynellid (Crustacea, Syncarida, Parabathynellidae) genera from Vietnam, Journal of Natural History 39 (31), pp. 2861-2886 : 2876-2883

Sketinella trontelji n. sp.

( Figures 8–13 )

Material examined

Type locality. Cave with no name, Rom Island, Vinh Ha Long, E part (16 June 2003, three males and three juveniles collected). The details of the new description are based on adult specimens (three males). The holotype is a male and the type series contains two specimens (paratypes) ( MNCN 20.04 /5911) .

Description

Body. Total length of holotype male 1.70 mm (species range: n 52: 1.80–1.94 mm). Body elongated, segments progressively widening towards posterior end of body. Length of head greater than width ( Figure 8 ). All drawings are of the holotype (male).

Antennule ( Figure 9A ). Antennule has eight segments; no sexual dimorphism; length of first four segments slightly longer than that of last four; setation as in Figure 1A (segments 6–8 have three aesthetascs, on the last segment aesthetascs are subterminal).

Antenna ( Figure 9B ). Six-segmented, last three segments are longer than the three first segments; last segment has three smooth and one plumose terminal setae; segments 1 and 4 have no setae; setation in other segments as in Figure 6B .

Labrum ( Figure 9C ). Concave, with eight main teeth, and two lateral teeth at either end.

Mandible ( Figure 9D ). Pars incisiva has six well-developed teeth; pars molaris has eight teeth, five of which are strong and distal with small spines, the remaining three being small joined and proximal with a large number of fine setae; mandibular palp does not exceed pars incisiva in length.

Maxillule ( Figure 9E ). Proximal endite has four claws (with spines of different sizes); distal endite has seven claws, two smooth and apical, the other five with strong spines; and with three subterminal smooth setae on outer distal margin.

Maxilla ( Figure 9F ). Four-segmented, with three setae on basal segment, two of which are distal; segment 2 with two long setae and one shorter one at distal end; segment 3 elongated with 11 setae, the last segment having a strong terminal seta and four lateral setae.

Thoracopods 1–7 ( Figures 10A–C , 11 , 12 ). Well developed, length gradually increasing from 1 to 5, last three similar in size; well-developed epipodite on 3–7, measuring half length of basipod; basipod has one barbed lateral terminal seta on Th 1–7; exopods of Th 1 and 2 shorter than the endopods; exopod of Th 3 and 4 longer than the endopod, and exopods of Th 5–7 similar in length to the endopods. Thoracopod 1 ( Figure 10A ): two lateral smooth terminal setae on basipod; exopod three-segmented, with three barbed setae on the first segment and two barbed setae on the other two segments and one group of ctenidia at the base of the setae; endopod four-segmented: first segment with three barbed dorsal setae and one plumose seta, second with four barbed dorsal setae and one plumose seta, third with three barbed dorsal setae and one small, smooth, terminal seta, terminal segment with two claws of similar length and one smooth seta. Thoracopod 2 ( Figure 10B ): exopod foursegmented, with three barbed setae on first segment and two barbed setae on the rest of the segments, and with one group of ctenidia at the base of the setae; endopod four-segmented, first segment short and with two barbed setae and one plumose seta; second with four groups of lateral ctenidia and three barbed dorsal setae and one plumose seta; third with three barbed dorsal setae and one tiny terminal seta; and fourth with one smooth seta and two strong claws of similar length. Thoracopod 3 ( Figure 10C ): exopod five-segmented, with three barbed setae on the first segment and two barbed setae on each one of the other segments and with one group of ctenidia at the base of the setae; endopod four-segmented, first segment short with one barbed and one plumose seta; second with three groups of lateral ctenidia and three barbed dorsal setae and one plumose seta; third with two barbed dorsal setae and one tiny terminal seta; and fourth with one smooth seta and two strong claws of different length. Thoracopods 4–7 ( Figures 11A, B , 12A, B ): exopod fivesegmented, with two barbed setae on each segment and with one group of ctenidia at the base of setae; endopod four-segmented, first segment short with one barbed and one plumose seta; second with groups of lateral ctenidia and three (four in Th 5) barbed dorsal setae and one plumose seta; third with two (three in Th 6) barbed dorsal setae and one tiny terminal seta; and fourth with one smooth seta and two strong claws of different length. Thoracopod 8 male ( Figure 10D, E ): large, massive and square; basal region massive; inner lobe almost trapezoidal; basipod with protuded distal end on the internal lateral edge; endopod, well developed with two long plumose setae; very large exopod, terminal end sharply pointed and with one small ‘‘tooth’’; outer lobe is not fused with basipod and is tongue-like in shape and does not exceed the distal end of basipod; dentate lobe with strong teeth.

Pleopod ( Figure 13A ). Pleopod present, as a single long seta, on the first segment of the pleon.

Dorsal margin of pleotelson ( Figure 13B ). Dorsal margin of pleotelson pronounced, but not very pronounced, anal operculum; one ventral barbed seta.

Uropod ( Figure 13C ). Sympod longer than endopod and four times longer than wide; has 12 barbed spines, the three terminal ones longer than the rest; endopod shorter than exopod with two strong, barbed spines and one claw ( Figure 13C ) on the distal end and two plumose setae on the external face, of these the most distal exceeds the distal end of the endopod, the basal one being small, and two barbed terminal setae have five groups of ctenidia on dorsal face; exopod has two terminal barbed setae, the outer longer than the inner, and five barbed setae on external face.

Furca ( Figure 13B ). Furca has seven barbed spines (the two terminal ones being longer and thicker); and two dorsal barbed setae which are similar in size.

Etymology

The new genus is named after Prof. Boris Sket and consists of the surname Sket, plus ‘‘i’’, followed by the last five letters of the name of the first genus described, Bathynella , and the species is named after Peter Trontelj, with thanks for their providing me with the material.

Remarks

The combination of characters in Sketinella n. g. is unique (see Table I). Its exclusive characters are: the pleopods (it only has the first pair) are reduced to a single seta (in the asiatic species which have pleopods these consist of a segment and two long setae); the basipod, the outer lobe and the exopod of the Th 8 male are different to that found in the other known asiatic species.

Sketinella n. g. presents some characters which are similar to Allobathynella (see Table I). According to Schminke (1973) and Serban (1994), the generic diagnosis of Allobathynella is not sufficiently detailed to assign any species to it and it is possible that the genus may include species that belong to two or three different genera. The only five species (1–5 in Table II) that belong to Allobathynella (A.I with seven segments; four or five of teeth on pars incisiva, and four or nine teeth on pars molaris of the Md; exopod of the Th 8 male on latero-external face of the basipod; pleopods one-segmented and with two long setae; etc.) are very different from Sketinella trontelji n. sp. (number 20 in Table II).

Sketinella trontelji n. sp. has a unique combination of characters. This species is nearest to Allobathynella gigantea pluto in the number of segments that make up the A.I and A.II, the number of teeth on the Md and the type of uropod. But the new species (medium-sized and cave dwelling) is different from Allobathynella gigantea pluto (large and an inhabitant of wells) in that it has: seven teeth on the distal endite of the Mx.I; protruded anal operculum; epipod present on the Th 3; a simplified first pair of pleopods; different number of segments in the exopod of Th 1–3 and the exopod and endopod of different proportions; more spines on the furca in spite of it being smaller in size, and a male Th 8 which is square and in which the basipod, the outer lobe and the exopod (with a lateral ‘‘tooth’’) are exclusive in shape. The internal side of the basipod of the Th 8 male (which has protruded distal end) is similar in the two new genera, but the external side is different in both genera (bigger in Sketinella ); the exopod is similar in both new genera in shape, but is smaller and less curved in Sketinella than in Paraeobathynella , and the lateral tooth does not exist in Paraeobathynella .

Figures

Figure 1. Photograph of Paraeobathynella vietnamensis n. g. n. sp., female (optical microscope 10×).

Figure 6. Paraeobathynella vietnamensis n. g. n. sp., male holotype. (A) Thoracopod 6; (B) thoracopod 7. Scale bar in mm.

Figure 8. Photograph of Sketinella trontelji n. g. n. sp., male holotype (optical microscope 10×).

Figure 9. Sketinella trontelji n. g. n. sp., male holotype. (A) Antennule (dorsal view); (B) antenna (dorsal view); (C) labrum; (D) mandible; (E) maxillule; (F) maxilla. Scale bar in mm.

Figure 10. Sketinella trontelji n. g. n. sp., male holotype. (A) Thoracopod 1; (B) thoracopod 2; (C) thoracopod 3; (D) thoracopod 8 male (lateral internal view); (E) thoracopod 8 male (latero-caudal view). Scale bars in mm.

Figure 11. Sketinella trontelji n. g. n. sp., male holotype. (A) Thoracopod 4; (B) thoracopod 5. Scale bar in mm.

Figure 12. Sketinella trontelji n. g. n. sp., male holotype. (A) Thoracopod 6; (B) thoracopod 7. Scale bar in mm.

Figure 13. Sketinella trontelji n. g. n. sp., male holotype. (A) First pleopod (latero-ventral view); (B) pleotelson and furca (dorsal view); (C) uropod (latero-external view). Scale bar in mm.