Chilibathynella joshuai, 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 : 148-157

publication ID	https://doi.org/ 10.1080/00222933.2011.626129
DOI	https://doi.org/10.5281/zenodo.10537064
persistent identifier	https://treatment.plazi.org/id/03F387A1-C559-ED7E-CC8B-0F67FD1FFD8A
treatment provided by	Felipe
scientific name	Chilibathynella joshuai
status	sp. nov.

Treatment

Chilibathynella joshuai sp. nov.

( Figures 1–3 View Figure 1 View Figure 2 View Figure 3 )

Material examined

Type locality. Department of Environment, Climate Change and Water (DECCW) groundwater monitoring bore number 36442 (32 ◦ 18 ′ 53 ′′ S, 148 ◦ 37 ′ 34 ′′ E), 18–21.5 m deep, 14 January 2005, in the alluvial aquifer beneath the Maquarie River floodplain, near Dubbo, NSW, Australia; three males and one female.

Details of the descriptions are based on all adult specimens (four males and eight females), although 19 juveniles were also collected. The holotype is a male and the allotype is female. The type series contains 10 additional specimens (three males and seven females) (Holotype MNCN 20.04 About MNCN / 8558, Allotype MNCN 20.04 About MNCN / 8559 and type series MNCN 20.04 About MNCN / 8560) .

Description

Body. Total length of holotype 2.4 mm and allotype 2.1 mm. Total length of male 1.83–2.4 mm, of female 1.82–2.8 mm. Body elongated, segments slightly widening towards posterior end; approximately 10 times as long as wide. Head as long as wide. Pleotelson with one medium-size barbed ventral seta on each side. All drawings are of the holotype (male) except for Th VIII female, and the dorsal view of pleotelson and furcal rami that belong to the allotype.

Antennule ( Figure 1A, I View Figure 1 ). Seven-segmented; with sexual dimorphism, antennal organ on segment two ( Figure 1I View Figure 1 ) very well-developed, inserted in protuberances and represented by two barbed thick setae almost as long as third segment; length of first three segments similar to other four segments; seventh segment smaller than the sixth; inner flagellum almost triangular; setation as in Figure 1A View Figure 1 ; segment three with four setae, one of which is barbed; segment five with two terminal aesthetascs, similar in size; sixth and seventh segments with three aesthetascs, each of a different size.

Antenna ( Figure 1B View Figure 1 ). Five-segmented; half the length of the A.I; first three segments shortest; last two segments similar in size, and almost three times longer than the third; last segment with four setae, one of which is plumose; fourth segment with inner and outer seta; setal formula: 0 / 0 / 1+0 / 1+1 / 4(1).

Labrum ( Figure 1C View Figure 1 ). Almost flat with eight main teeth, the central two slightly different from the others, and four lateral teeth at each side. Ventral surface with several rows of fine spinules.

Female labrum of the allotype ( Figure 1D View Figure 1 ). Almost flat with eight main teeth, the central two slightly different from the others, and five lateral teeth at each side. Ventral surface with several rows of fine spinules.

Mandible ( Figure 1E View Figure 1 ). Pars incisiva with seven teeth and a triangular, well-developed tooth on the ventral edge; pars molaris with ten claws, one distal group of three claws slightly separated from the rest, second group of five 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, almost five times as long as wide, with a distal seta that does not exceed pars incisiva in length.

Female mandible of the allotype ( Figure 1H View Figure 1 ). Pars incisiva with seven teeth; pars molaris similar to the holotype.

Maxillule ( Figure 1F View Figure 1 ). Proximal endite with four long serrulate claws; distal endite with six claws: two smooth, one apical and one subapical, and the other four with denticles and fine long setules and three subterminal smooth setae on outer distal margin.

Maxilla ( Figure 1G View Figure 1 ). Four-segmented, two first segments with an elongate endite and smooth setae, third segment almost square with smooth setae and fourth segment small with two strong barbed claws and six smooth setae; setal formula 3, 4+1, 9, 8.

Thoracopod I–VII ( Figure 2A View Figure 2 to G). Well developed, length gradually increasing from I to V, last three similar in size; epipod absent on Th I, small on Th II to Th VII, measuring less than half length of basipod; basipod with one smooth seta at distal inner corner in Th I to VII. Exopod one-segmented shorter than the two first segments of endopod on all thoracopods, with two unequal barbed terminal setae, one of these is small; one additional barbed seta present on dorsal side of Th I, V and VII and two additional setae on Th II to IV and VI. Endopod four-segmented, the first segment is almost half as long as the following two that are similar in length, and the fourth segment is small (with two barbed, similar claws and one smooth seta); all setae on segments one to three are smooth except the setae on the distal outer corner of segment two of Th I that is plumose and absent from other thoracopods. Thoracopod endopod setal formula: Th I, 3+1 / 2+1 / 1+0 / 3(1); Th II, 1+1 / 3+0 / 2+0 / 3(1); Th III, 1+1 / 2+0 / 2+0 / 3(1); Th IV, 1+1 / 2+0 / 1+0 / 3(1); Th V–VI, 1+1 / 2+0 / 0+0 / 3(1); Th VII, 1+1 / 1+0 / 0+0 / 3(1).

Allotype (female): setal formula of the endopods of thoracopods: Th I, 2+1 / 2+1 / 1+0 / 3(1); Th II, 1+1 / 3+0 / 2+0 / 3(1); Th III, 1+1 / 3+0 / 2+0 / 3(1); Th IV – V, 1+0 / 2+0 / 2+0 / 3(1); Th VI, 0+1 / 1+0 / 0+0 / 3(1); Th VII, 0+0 / 1+0 / 0+0 / 3(1).

Thoracopod VIII male ( Figure 3F, G View Figure 3 ). Massive, subrectangular; basal region of the penial complex supports three lobes: inner lobe (I. Lb.), outer lobe (O. Lb.) and dentate lobe (D. Lb.); rectangular inner lobe completely independent of the basal region; outer lobe longer than inner lobe, almost three times as long as wide and covering end of dentate lobe; outer lobe extends beyond the end of the basipod (Bsp); dentate lobe is similar to inner lobe and has many denticles; endopod (Endp.) small, almost three times smaller than exopod with two unequal smooth terminal setae; exopod (Exp.) big, curved, sharply bending backward and with a row of apical denticles; basipod roughly trapezoidal, in the internal side with a seta above its outer distal corner and with a small crest-like protuberance.

Thoracopod VIII female ( Figure 3A View Figure 3 ). Very reduced and fused, appears in ventral view as two triangular “hubs”, each with two small distal denticles.

First pleopods ( Figure 3B View Figure 3 ). One-segmented, four times as long as wide, with one long apical seta and one short subapical seta, both smooth.

Uropod ( Figure 3E View Figure 3 ). Sympod length five times width, almost twice as long as endopod and exopod, which are both similar in size; 17 barbed spines of similar size occupying half of length of sympod; endopod with four spines in the distal third, two subterminal plumose setae near inner margin, not exceeding the distal end of endopod, and two small barbed lateral setae of equal length; exopod has four barbed setae.

Pleotelson female ( Figure 3D View Figure 3 ). With one small, plumose ventral seta on either side near the base of the furca. Anal operculum almost flat, not protruded.

Furca ( Figure 3C View Figure 3 ). Almost triangular and nearly twice as long as wide, with 12–14 barbed spines similar in size; two small equal dorsal plumose setae; with a lateral furcal organ as a blunt ventral projection.

Variability

The number of spines on the furca varies from 12 to 14, the sympod of the uropod has from 14 to 20 spines. There is also variation in the number of setae on different endopodal segments of some thoracopods of males and females. The setal formula is: Th I, 2,3+1 / 2,3+1 / 1,2+0 / 3(1); Th II, 1+1 / 3,4+0 / 2+0 / 3(1); Th III, 1+1 / 2,3+0 / 1,2+0 / 3(1); Th IV, 1+1 / 2,3+0 / 1,2+0 / 3(1); Th V, 1+1 / 1,2+ 0 / 0,1+0 / 3(1); Th VI, 1+1 / 1,2+0 / 0+0 / 3(1); Th VII, 0,1+1 / 1,2+0 / 0+0 / 3(1).

Etymology

The species, “ joshuai ” (male gender), is named after Joshua Hancock, born soon after the species was first collected.

Remarks and discussion

The antennal organ on the second segment of the antennule distinguishes C. joshuai sp. nov. from other members of the genus. This is the first species of the genus with this organ so well-developed. Chilibathynella joshuai sp. nov. is the biggest species of the genus (2.8 mm) and has many teeth, spines and setae on its extremities (see Table 2). Chilibathynella joshuai sp. nov. is the first species of the genus with 20 spines on the sympod of the uropod, four spines on the endopod of the uropod and 14 spines on the furca. The setal formula of some thoracopods is also unique (see Table 2). All these characters leave no doubt that the specimens described here represent a new species belonging to the genus Chilibathynella , but the new species differs in some characters that appear in the generic diagnosis ( Schminke 1973): the basal segment of protopod of the male Th VIII is not balloon-shaped and there are outer marginal seta on the second segment of endopod of Th I.

Chilibathynella australiensis Schminke, 1973 , the other Australian species of the genus, also has five segments on A.II and the same setal formula as the new species (see Table 2). Both Australian species have more teeth on the pars incisiva of the Md (seven)

view); (F) thoracopod VIII (latero-external view); (G) thoracopod VIII (latero-frontal view); (H) thoracopod VIII (latero-caudal view). Scale bar in mm. Abbreviations: D.Lb, dentate lobe: I.Lb, inner lobe; O.Lb, outer lobe; Bsp, basipod; Endp, endopod; Exp, exopod.

than any other species in the genus, and they both lack the epipod on the Th I; the setal formula of thoracopods differs in both species but both have outer marginal seta on the second segment of the endopod of Th I. Females of the new species have Th VIII reduced and fused, as in C. clandestina , but different from the other Australian species, C. australiensis and C. digitus sp. nov. (big and elongated) described below. Despite these differences, the species with the most characters in common with C. joshuai sp. nov. are C. australiensis (from Victoria) and C. digitus sp. nov. that we describe below.

Previous descriptions of the genus Chilibathynella Noodt, 1963 have not included detailed drawings of male and female Th VIII for all species. This is unfortunate, as a comparison with these would have allowed a more complete understanding of how the new species are related to previous species.