Onychobathynella bifurcata, Camacho & Hancock, 2011

Camacho, A. I. & Hancock, P., 2011, Two new species of the genus Chilibathynella Noodt, 1963 and Onychobathynella bifurcata gen. et sp. nov (Crustacea: Syncarida: Parabathynellidae) from New South Wales, Australia, Journal of Natural History 46 (3 - 4), pp. 145-173 : 163-172

Onychobathynella bifurcata gen. nov. sp. nov.

( Figures 7–9 )

Material examined

Type locality. The specimens were collected from the hyporheic zone of the Hunter River at Aberdeen, NSW, Australia (32 ◦ 10 ′ 03 ′′ S, 150 ◦ 52 ′ 58 ′′ E) on 18 May 2001; three females, including one juvenile, were collected.

The details of the description are based on all adult specimens. The holotype is a female, the allotype is another female, and the type series contains one additional specimen (female juvenile) (Holotype MNCN 20.04 / 8564, Allotype MNCN 20.04 / 8565 and type series MNCN 20.04 / 8566) .

Description

Body. Total length of holotype (female) 2.54 mm and allotype 2.49 mm. Body elongate, segments slightly widening towards posterior end. Length of head similar to width. All drawings are of the holotype.

Antennule ( Figure 7A, H ). Eight-segmented; combined length of first three segments similar to other five segments; inner flagellum trapezoidal; fifth to eighth segments decrease progressively in length; setation as in Figure 7A ; the plumose setae are similar to those of other genera, but smaller, while the rest of the setae, which are fine and smooth in all known species of Bathynellacea , are short, strong, barbed and claw-like; fifth and sixth segments with two small, similar-sized terminal aesthetascs, and the last two segments with three small aesthetascs similar in size. The unique curved setae present in this genus can be seen in Figure 7H (fifth and sixth segments).

Antenna ( Figure 7B ). Five-segmented; less than half the length of the A.I; first three segments are half the length of the last two and the fifth is a little longer than the fourth; last segment with one plumose subterminal seta and three apical strong barbed setae, as claws, similar to the remaining setation of the other segments; setal formula: 0 / 0 / 1 + 0 / 1 + 1 / 4(1).

Labrum ( Figure 7C ). Almost flat with eight main teeth, the central two with two points, and six lateral teeth at each side. Ventral surface with rows of fine spinules.

Mandible ( Figure 7D,G ). Pars incisiva with seven teeth (allotype eight teeth) and a thin, long tooth on the ventral edge; pars molaris with eight claws, one distal group of three claws slightly separated from the rest, second group of three claws, both groups with subdistal small spines and two small joined proximal claws with a large number of fine hairs; the mandibular palp, one segmented, with a distal seta which does not exceed pars incisiva in length.

Maxillule ( Figure 7E ). Proximal endite, well-developed, with four long serrulate claws and fine lateral setules; distal endite with six claws, the two distal ones smooth and the others with denticles and fine long, almost basal, setules and three subterminal barbed claw-like setae on the outer distal margin. Several groups of fine setules are present just under the claws.

Maxilla ( Figure 7F ). Four-segmented, segment three and four small; smooth setae on all segments; setal formula 3, 3 + 1, 9, 5.

Thoracopods I–VII ( Figure 8A,G ). Well developed, length gradually increasing from Th I to III, last five similar in size; epipod absent on Th I, present on Th II to VII, measuring almost a third the length of the basipod; basipod with one small barbed claw-like seta at the distal inner corner in Th I to VII. Exopod one-segmented shorter than the two first segments of endopod on all thoracopods, with two strong, short and unequal barbed terminal claw-like setae; one additional barbed claw-like seta present on the dorsal side of Th I to VII. Endopod four-segmented, the first segment almost half as long as the second, which is slightly longer than the third. The fourth endopodal segment is small with two smooth (barbed on Th I) similar claws and one strong barbed, curved seta; all setae on segments one to three are smooth on Th I; first and third segments without setae in Th II to VII; no setae in any thoracopods, nor in any segment of the distal outer corners; with groups of ctenidia at lateral edge of segments two and three. Thoracopod endopod setal formula: Th I, 2+0 / 3+0 / 2+0 / 3(1); Th II, 0+0 / 2+0 / 0+0 / 3(1); Th III to VII, 0+0 / 1+0 / 0+0 / 3(1).

Female thoracopod VIII ( Figure 9B). Large, elongated and with rounded tip, with a small distal denticle.

First pleopod ( Figure 9A). One-segmented, six times as long as wide, with two barbed short apical setae of different length.

Uropod ( Figures 9C). Sympod almost five times as long as wide, more than twice as long as endopod; with 18 barbed spines, bifurcated at the tip, of similar size occupying almost the entire length of sympod; endopod with two spines at the distal end, two short and strong barbed lateral, claw-like setae of equal length, and two other barbed short and strong setae near the inner margin, one of these is subterminal and does not exceed the distal end of endopod; exopod six times longer than wide, with four short, robust lateral setae curved inwards, and two long terminal setae.

Pleotelson ( Figure 9D). With one small plumose ventral seta on either side near the base of the furca. Anal operculum flat, not protruded.

Furca ( Figure 9D, E). Elongate, three times as long as wide, with 10 barbed, bifurcated spines, the two terminal ones longer than the others and with a kind of hyaline membrane; two small equal dorsal barbed claw-like setae; with a very apparent lateral furcal organ with distal elongated projection (see Figure 9E).

Etymology

The generic name, Onychobathynella gen. nov. is because of the claws (Greek “onyx, onychos”) present on the appendages. The species name, bifurcata (adjective), is named for the bifurcated spines present on the uropodal sympod and the furcal rami.

Remarks and discussion

The most striking feature of this new genus is the dominance of claw-like setae on many parts of the body (A.I, A.II, Mx.I, thoracopods, pleopod, furca and uropods). In 1987, when Schminke redescribed the species Thermobathynella adami Capart, 1951 , from a hot spring of Upemba National Park ( Zaire), he called attention to a normal and particularly robust seta (“les soies normales sont particulièrement robustes,”, Schminke 1987: p.108) in A.I. These “claws” are smooth and are not as strong and thick as those found in Onychobathynella gen. nov. In addition Schminke did not mention that he found these structures in other parts of the body of the specimens studied, as in our case. The similarity of the new genus with Thermobathynella Capart, 1951 ends here. Therefore, we believe that this kind of seta that strongly resembles real claws, and appears in different parts of the body, is unique to Onychobathynella and does not occur in any known species of Bathynellacea .

So far, Onychobathynella gen. nov. is the second genus of Parabathynellidae known in Australia with eight segments on the A.I, a character shared only with three other parabathynellid genera in the world ( Camacho and Hancock 2010): Allobathynella Morimoto and Miura, 1957 , Sketynella Camacho, 2005 and Octobathynella Camacho and Hancock, 2010 . The most frequent character state among parabathynellid genera is six or seven segments in the A.I and only one genus, Sinobathynella Camacho et al., 2006 , has more segments (10 segments) ( Camacho et al. 2006). The new genus has five segments in A.II (the most frequent number in all the species of the family Parabathynellidae ) as do most Australian genera (see Table 3) and only Allobathynella has a similar combination (A.I, eight-segmented, A.II five-segmented) ( Camacho 2005), Skethynella has A.II six-segmented.

The combination of characters of Onychobathynella gen. nov. is unique in Parabathynellidae ( Table 3): antennule eight-segmented; antenna with five segments; labrum with 20 teeth (eight main and six lateral teeth at either end); mandible with pars incisiva of seven teeth and pars molaris of eight teeth; maxillule with distal endite with six claws and barbed lateral setae (claw-like); exopod of the thoracopods with only one segment, endopod with claw-like setae; pleopods very well developed with setae as claws; female Th VIII very well developed; 18 spines on the sympod, two spines on the endopod and six claw-like setae on the exopod of the uropod.

Unfortunately no males were present in the sample so the male Th VIII remains unknown and cannot be compared with that of the other known genera in Australia and the world.

Onychobathynella gen. nov. is the ninth genus known from Australia, and has affinities with Chilibathynella (see Table 3), which also has one-segmented thoracopodal exopods and spines on the uropodal endopod. The other two genera with one-segmented exopods are Atopobathynella Schminke, 1973 and Kimberleybathynella Cho et al., 2005 , but these lack spines on the endopod of the uropod (see Table 3). The new genus has a large Th VIII in the female, as does Chilibathynella digitus sp. nov.. The new genus shares some characteristics with the remaining Australian genera, but fewer common morphological features (see Table 3).

General discussion and conclusion

Chilibathynella clandestina Noodt, 1963 was found in Chile, and was the first of the Chilibathynella species to be described ( Noodt 1963). This was followed in 1973 when Schminke described C. australiensis , the first Australian species, and revised and

No. st. endp 2 1–2 2 2 3 2 2 Th.VIII female S / XL (1-seg.) S (1 / 2-seg.) S (1-seg.) M / S (1-seg) / A M (1-seg) L-1-seg. S (1-seg) Pleopod P A P P / A A A / P P Urp

Symp: spines 7–20 6–13 5–17 2–8 28 10–15 6–20

Type spines Hom. / Inhom. Hom. / Inhom. Hom. / Inhom. Hom. Hom. Hom. Inhom.

Exp: No. st 3–4 2–4 2–4 2–4 23 6–7 5

Endp: No. spines 0–4 0–5 0 0 7 5–6 0

No. st 4 4–5 1–3 2–3 5 5 4 Furca No. spines 6–14 7–11 3–9 3 23 7–11 4–6 Anal operculum Pr / N.Pr NPr / Pr(S) NPr / Pr(S-XL) Pr(S to XL) NPr NPr NPr / Pr(S) Length min.–max. 1.2–2.8 1.2–2.3 1.0–3.0 0.6–1.7 5.4–6.0 1.1–1.8 0.9–3.5 Habitat C / R C / W / R R C / W / R W W R

2 S(1-seg) A

10–12 Inhom. 5 3–4 4 10–13 Pr(S) 1.4–2.11 R

– XL(1-seg.) P

18

Hom.

6

2

4

10

NPr

2.5

R

Notes: 1. Chilibathynella Noodt, 1963 ; 2. Notobathynella Schminke, 1973 ; 3. Atopobathynella Schminke, 1973 ; 4. Hexabathynella Schminke, 1972 ; 5. Billibathynella Cho, 2005 ; 6. Brevisomabathynella Cho, Park and Reddy, 2006 ; 7. Kimberleybathynella Cho, Park and Humphreys, 2005 ; 8. Octobathynella Camacho and Hancock, 2010 and 9. Onychobathynella gen. nov.

A, absent; A.I, antennule; A.II, antenna; A, absent; C, cave; D.end, distal endite; End., endopod; Exp., exopod; Hemisph., hemispherical; Hom., homonomous; Inhom., inhomonomous; Length, min.–max., minimum and maximum length in mm; L, large; M, medium-sized; Mx.I, maxillule; NPr, not pronounced; P, present; Pr, pronounced; R, river bank; Rect., rectangular; S, small; seg, segmented; Semic., semicircular; sgt, segment; st, setae; Subgl., subglobular; Symp, sympod; Th, thoracopod; Urp, uropod; W, well; XL, extra large.

corrected the generic diagnosis while redescribing the type species. Ranga Reddy (2006) described a new species, C. kotumsarensis , from India and found two characters unique within the genus Chilibathynella : the six-segmented antenna and the inhomonomous row of spines on the uropodal sympod. To acommodate the new species in this genus, Ranga Reddy amended the generic diagnosis of Chilibathynella ( Ranga Reddy 2006) . The two new species described here certainly belong to the genus Chilibathynella , but again the generic diagnosis needs to be amended because C. joshuai sp. nov. has an outer marginal seta on the second segment of the endopod on Th I, as does C. australiensis . The Th II to VII lack this seta in both species, although Schminke (1973) did not state this in his diagnosis. Chilibathynella digitus sp. nov. has a unique character within the genus, six teeth on the pars incisiva of the Md, but this feature does not appear in Schminke’s generic diagnosis. The generic diagnosis should also incorporate the lack of sexual dimorphism on the second segment of male A.I in some species.

To accommodate the features to Chilibathynella noted above, the amended diagnosis must be: male Th VIII with globular basal segment of the protopod; basipod is inserted at the same height; small endopod with two setae; small exopod with small terminal teeth. Exopod of the Th I to VII one-segmented; rudimentary or absent seta of the outer edge of the second segment of the Th II to VII and present or absent on Th I. Antennule seven-segmented; second segment with or without antennal organ in the males and with three or four peg-shaped and two unchanged setae. Antenna with five or six segments. Typical mandible with prominent “Borstenlobus” (pars molaris). Maxilla four-segmented and heavily armed. Th VIII of females and first pleopods, one-segmented. Sympod of the uropod with homonomous or inhomonomous row of spines; endopod dagger-shaped with one terminal spine. Large dorsolateral furcal organ.

The new genus, Onychobathynella gen. nov. is the second Australian parabathynellid genus with eight segments on the A.I. The most frequent character state among parabathynellid genera is six or seven segments in the A.I and only one genus, Sinobathynella Camacho et al., 2006 , has more segments (10 segments). This new genus has a five-segmented A.II, whereas the other Australian genus with an eightsegmented A.I, Octobathynella Camacho and Hancock, 2010 , has seven segments on A.II (see Table 3). The new genus differs from all known Australian parabathynellids, although there are some apparent morphological affinities with the Australian species of Chilibathynella . However, the complete set of characters, in unique combination (see Table 3), and the new character (unusual setae like curved claws) for Bathynellacea warrants the establishment of a new species belonging to a new genus.

Figures

Figure 7. Onychobathynella bifurcata gen. nov. sp. nov. (A–H) female holotype. (A) Antennule (dorsal view); (B) antenna (dorsal view); (C) labrum; (D) mandible; (E) maxillule; (F) maxilla; (G) pars incisiva of mandible; (H) detail of the segments five and six of antennule with special setae like curved claws and aesthetascs. Scale bar in mm.

Figure 8. Onychobathynella bifurcata gen. nov. sp. nov. (A–G) Female holotype. (A) Thoracopod I; (B) thoracopod II; (C) thoracopod III; (D) thoracopod IV; (E) thoracopod V; (F) thoracopod VI; (G) thoracopod VII. Scale bar in mm.