Paraeobathynella vietnamensis, 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 : 2863-2873

Paraeobathynella vietnamensis n. g. n. sp.

( Figures 1–7 )

Material examined

Type locality. Cave Hang Trinh Nu , Bo Hon Island, Vinh Ha Long, SW part (11 June 2003), (abundant males and females collected—very dense colony on the bottom covered by a layer of pebbles). The details of the new description are based on adult specimens (15 males and 13 females). The holotype is a male and the type series contains 27 specimens (paratypes) ( MNCN 20.04 /5911) .

There are two other populations: one in the Trung Trang Cave , Cat Ba Island , W of Vinh Ha Long (14 June 2003, five males and five females collected) and the other in the Ang Vem Cave, Cat Ba Island, W of Vinh Ha Long (one female, 15 June 2003) .

Description

Body. Total length of holotype male 1.56 mm (species range type locality: males n 515: 0.90–1.56 mm; females n 513: 0.96–1.33 mm; population 1: males 1.16–1.71 mm and females 1.28–1.55 mm; population 2: female 1.38 mm). Body elongated, segments progressively widening towards posterior end of body ( Figures 1 , 2 —female paratype and male holotype, respectively). Length of head greater than width. All drawings are of the holotype (male) and the Th 8 female is of one paratype (female selected).

Antennule ( Figure 3A ). Antennule has seven segments; no sexual dimorphism; length of first four segments greater than that of last three; setation as in Figure 3A (segment 5 with two aesthetascs; segments 6 and 7 with three aesthetascs, on the last segment aesthetascs are subterminal).

Antenna ( Figure 3B ). Antenna six-segmented, last four segments similar in size, longer than the two first segments; last segment with three smooth and one plumose terminal setae; segments 1 and 4 without setae; setation in the other segments as in Figure 3B .

Labrum ( Figure 3C ). Labrum concave, with eight main teeth, and three lateral teeth at either end.

Mandible ( Figure 3D ). Pars incisiva with five well-developed teeth and small proximal tooth as in Figure 3D ; pars molaris with 10 teeth, eight being strong and distal with small spines and two small joined proximal teeth with a large number of fine setae; mandibular palp does not exceed pars incisiva in length.

Maxillule ( Figure 3E ). Proximal endite with four claws (spines of different sizes); distal endite with seven claws, two smooth and apical, the other five with strong spines and three subterminal smooth setae on outer distal margin.

Maxilla ( Figure 3F ). Four-segmented, with two setae on basal segment; segment 2 with two long setae and one shorter one at distal end; segment 3 elongated with 12 setae and last segment with a strong terminal seta and two lateral setae.

Thoracopods 1–7 ( Figures 4A–C , 5 , 6 ). Well developed, length gradually increasing from 1 to 5, last three similar in size; well-developed epipodite on 3–7, measuring more than half length of basipod; basipod with one lateral, barbed terminal seta in Th 2–7; exopods of the Th 1 and 2 shorter than endopods; exopods of the Th 3–7 longer than endopods. Thoracopod 1 ( Figure 4A ): has two lateral smooth terminal setae on basipod; exopod three-segmented, with two barbed setae on each segment and one group of ctenidia at the base of setae; endopod four-segmented: first segment has three barbed dorsal setae and one plumose seta, second has three barbed dorsal setae and one plumose seta, third has three barbed dorsal setae and one small, smooth, terminal seta, terminal segment has two slightly barbed claws of similar length and one smooth seta. Thoracopod 2 ( Figure 4B ): exopod four-segmented, with two barbed setae on each segment and with one group of ctenidia at the base of setae; endopod four-segmented, first segment short and with one barbed and one plumose seta; second with two 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 slightly barbed claws of different length. Thoracopod 3 ( Figure 4C ): exopod five-segmented, with two barbed setae on each segment and one group of ctenidia at the base of setae; endopod four-segmented, first segment short with one barbed and one plumose seta; second with two 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 slightly barbed claws of different length. Thoracopods 4–7 ( Figure 5A, B , 6A, B ): exopod five-segmented, 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 four groups of lateral ctenidia and two 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 slightly barbed claws of different length. Thoracopod 8 male ( Figure 4D, E, F ): large, massive, almost square; basal region massive; inner lobe completely integrated into the basal region, barely exceeds distal end of dentate lobe; basipod with one distal protuberance on the internal lateral edge which exceeds the end of internal lobe; endopod almost square, with two long setae; large exopod, longer than wide and overhanging the basipod and the outer lobe; rounded outer lobe is not fused with basipod and exceeds the end of the external side of the basipod; dentate lobe with small teeth and rounded distal end. Thoracopod 8, female paratype ( Figure 4G ): large with smooth cuticle, almost square, has one long terminal seta and two small teeth. Dorsal margin of pleotelson ( Figure 7A, B ): pronounced anal operculum; one barbed ventral seta.

Uropod ( Figure 7C ). Sympod slightly longer than the endopod and four times longer than wide; with seven barbed spines of different size; endopod slightly shorter than exopod with two strong, barbed spines and one claw ( Figure 7D ) on the distal end and two plumose setae on the external part which exceed the distal end of the endopod, and two barbed terminal setae, four groups of ctenidia on dorsal face; exopod has two barbed terminal setae, the outer longer than the inner, and four barbed setae on external face.

Furca ( Figure 7A, B ). Furca has five barbed spines (the two terminal ones being a little longer and thicker); two dorsal plumose setae similar in size.

Etymology

The generic name is to be nearest to Eobathynella genus. The species name is dedicated to Vietnam.

Remarks

The combination of characters of Paraeobathynella n. g. (number 7 in Table I) is similar to some of the possible combinations present in the genus Allobathynella (number 1 in Table I) due to its great variability. According to Schminke (1973) and Serban (1994) it is possible that this last genus includes species that belong to two or three different genera. The different combinations of the characters of the species of the possible different genera (numbers 6–8 in Table II) do not coincide with Paraeobathynella n. g. (number 19) (see Table II). Paraeobathynella vietnamensis n. g. n. sp. is different to the five first species in Table II which are possibly true ‘‘allobathynels’’. The most similar species is A. coreana (number 5) but this species has one pair of pleopods with one segment and two setae, whereas the new species do not have pleopods. In both species the Th 8 female and the uropod are very different and there are also other differences in almost all structures of the body. In Allobathynella the exopod of the Th 8 male is on the external face of the basipod, whereas in Paraeobathynella n. g. this structure is on the distal face of the basipod, as in the genus Issykkulibathynella (number 5 in Table I) and the other new genus, Sketinella n. g. (number 8 in Table I).

Only E. mesasiatica (number 9 in Table II) is definitely a species of the genus Eobathynella and the new species (number 19 in Table II) is very different from E. mesasiatica to belong to this genus. In E. mesasiatica the exopods of Th 1–7 have more than two segments and the A.I has seven segments, like Paraeobathynella n. g. (number 18 in Table II), whereas in the other four species assigned to Eobathynella (numbers 10 to 13 in Table II) the A.I has six segments and the exopods of all the thoracopods are always bisegmented. Paraeobathynella n. g. (number 19 in Table II) is a medium-sized species, but E. mesasiatica is a large species and both species have a lot of different characters (see Table II): number of teeth on pars molaris; number of teeth on distal endite of the Mx.I; epipodite of Th 3 present in Paraeobathynella n. g., absent in Eobathynella; number of setae in Th 1–7; ratio of exopod to endopod of the thoracopods; number of setae on the endopod of Th 8 male and size and shape of all the lobes; size and number of spines on the sympod and endopod of the uropod and number of setae on the exopod of the uropod and presence or absence of anal operculum.

In the new species the pars molaris of the Md is very well developed (with 11 teeth) as in Allobathynella gigantea pluto (number 7 in Table II), which is a very large species and very different from P. vietnamensis n. g. n. sp. in the rest of its characters.

Paraeobathynella vietnamensis n. g. n.sp has a unique combination of characters and the Th 8 female is completly different from the other asiatic species.

Figures

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

Figure 2. Photograph of Paraeobathynella vietnamensis n. g. n. sp., male holotype (optical microscope 10×).

Figure 3. Paraeobathynella vietnamensis n. g. n. sp., male holotype. (A) Antennule (ventral view); (B) antenna (dorsal view); (C) labrum; (D) mandible (ventral view); (E) maxillule; (F) maxilla. Scale bar in mm.

Figure 4. Paraeobathynella vietnamensis n. g. n. sp. (A–F) Male holotype: (A) thoracopod 1; (B) thoracopod 2; (C) thoracopod 3; (D) thoracopod 8 (lateral internal view); (E) thoracopod 8 (latero-external view); (F) thoracopod 8 (latero-frontal view); (G) Female paratype (frontal view). Scale bars in mm.

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

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

Figure 7. Paraeobathynella vietnamensis n. g. n. sp., male holotype. (A) Pleotelson and furca (lateral view); (B) pleotelson and furca (dorsal view); (C) uropod (latero-external view); (D) detail of terminal end of the endopod of the uropod (latero-external view). Scale bars in mm.