Hexabathynella julianae Perina and Camacho, 2025

Perina, Giulia, Camacho, Ana I., Morgan, Liesel, Lawrie, Angus, Floeckner, Stephanie & Guzik, Michelle T., 2025, New species of Atopobathynella, Kimberleybathynella and Hexabathynella (Parabathynellidae, Bathynellacea) from the arid zones of Western Australia, Zootaxa 5655 (1), pp. 1-103 : 64-67

Hexabathynella julianae Perina and Camacho , sp. nov.

urn:lsid:zoobank.org:act:CA3DEAFA-1950-4BFC-8B1C-1EFE2B83FCAC

( Figs. 27 to 28, Appendix 8)

Material examined: Holotype male. AUSTRALIA: Western Australia: Robe Valley, Pilbara , Bore RC 18MEK0211 (stygo net haul) 21°43'42.1018"S, 116°15'36.5101"E, 21 September 2021, J. Pille Arnold, S. Rodman. ( WAMC 78876 — BES8281 , permanent slide).

Paratypes: 1 male, Robe Valley , Pilbara, Bore BC443 (stygo net haul) 21°57'40.4489"S, 116°29'13.1366"E, 11 April 2021, J. Pille Arnold, S. Rodman, ( WAMC 78963 — BES12528 — BMR05216 , permanent slide) ; 1 female, Robe Valley , Pilbara, Bore BUNWB13 (stygo net haul) 21°57'04.0981"S, 116°27'54.8935"E, 23 September 2021, J. Pille Arnold, S. Rodman ( WAMC 78964 — BES12690 — BMR05468 , permanent slide) ; 1 female, Robe Valley , Pilbara, Bore BUNWP0006 (stygo net haul) 21°54'54.1149"S, 116°24'29.9804"E, 24 September 2021, J. Pille Arnold, S. Rodman, ( WAMC 78965 — BES12462 — BMR05469 , permanent slide) ; 1 male, Robe Valley , Pilbara, Bore MB16 MEH0016 (stygo net haul) 21°42'48.4313"S, 116°12'55.7428"E, 16 August 2022, J. Pille Arnold, S. Rodman, ( WAMC 78966 — BES16291 — BMR07056 , permanent slide) ; 1 female, Robe Valley , Pilbara, Bore PZ10BUN037 (stygo net haul) 21°50'48.0297"S, 116°23'42.0475"E, 20 March 2022, J. Pille Arnold, S. Rodman, ( WAMC 78970 — BES14882 — BMR07007 , permanent slide) ; 1 male, Robe Valley , Pilbara, Bore YALLWP01 (stygo net haul) 21°41'29.1726"S, 116°19'33.6756"E, 13 August 2022, J. Pille Arnold, S. Rodman, ( WAMC 78972 — BES7934 — BMR07057 , permanent slide) ; 1 female ,, Robe Valley , Pilbara, Bore MB18 MEK0004 (stygo net haul) 21°43'40.2798"S, 116°15'34.8116"E, 23 March 2022, M. Curran, M. van Wees ( WAMC 78968 — BES17383 — BMR07032 , in alcohol) .

Additional material: 1 juvenile, 2 males, ( WAMC 78962 — BES13101 , in alcohol), same details as WAMC 78963 ; 2 females, Robe Valley , Pilbara, Bore MB18 MEK0004 (stygo net haul) 21°43'40.2798"S, 116°15'34.8116"E, 23 March 2022, M. Curran, M. van Wees ( WAMC 78967 — BES14372 , in alcohol) ; 1 specimen (sex not available) Robe Valley , Pilbara, Bore PZ 09BUN016 (stygo net haul) 21°49'58.4930"S, 116°20'42.3708"E, 19 March 2022, J. Pille Arnold, S. Rodman, ( WAMC 78969 — BES14470 — BMR07006 , in alcohol) .

Diagnosis: H. julianae sp. nov. belongs to a group of small (0.38–0.53 mm) Hexabathynella species; with male antennal organ formed by one modified seta without protuberance; three teeth on pars incisiva and five on pars molaris of mandible; presence of a rounded structure with small spines on the distal end that could represent the support of possible paragnaths, in this case absent; pleopods absent; sympod with inhomonomous spines, the distal one slightly longer than others; exopod of uropod slightly longer than endopod, with three setae, endopod of uropod with two setae and a spine-like structure; anal operculum not protruded. It differs from all the other Hexabathynella species (except H. robeensis ) by the presence of an epipod only on thoracopods III and IV. Similarities and differences with other Hexabathynella species are listed in (Appendix 7). The sequenced specimens differ from all the other Hexabathynella species sequenced by COI = 9–24.3% and 12S = 8.2–21.9%. This species shows mean intraspecific variation of COI=7% and 12S=3.6% ( Tables 4, 5).

Description male holotype (WAMC 78971): Body elongated, about six times as long as maximum width, almost cylindrical, segments slightly widening towards the posterior end of the body (Appendix 8).

Antennula ( Fig. 27A ): six-segmented. Length of first three articles about 1.3 times as long as the last three. First article is the longest followed by the sixth one. Fourth article is the shortest, followed by the fifth one. Antennal organ on the second article without protuberance, formed by one modified smooth seta that reaches the distal end of the third article. Inner flagellum almost square. Article five and six with three terminal and three subterminal aesthetascs respectively. Setation as Figure 27A .

Antenna ( Fig. 27B ): five-segmented, distal article is the longest, similar in length to the other four combined. Articles one and two with no setae. Articles three and four with one seta each, and article five with two smooth and one plumose setae.

Labrum ( Fig. 27C ): almost flat, with eleven main teeth.

Mandible ( Fig. 27D ): pars incisiva with three teeth, pars molaris with five teeth, with the two most proximal ones joined together and covered in fine setules; tooth of ventral edge triangular. Mandibular palp with one distal seta reaching beyond the distal end the pars incisiva.

Paragnaths ( Fig. 27E ): presence of a rounded structure, with small spines on the distal end,that could represent the support of possible paragnaths, in this case absent.

Maxillula ( Fig. 27F ): proximal endite with four distal claws of different size, two very long; distal endite with five claws, the three proximal with denticles and all very long, as long setae; three smooth subterminal setae on the outer distal margin.

Maxilla ( Fig. 27G ): four-segmented, with long setae, setal formula 2, 3, 9, 1.

Thoracopods I to VI ( Fig. 28A–G ): length gradually increasing from thoracopod one to three, ThIV and VI slightly longer than ThV. Epipod present in ThIII and IV, about one-third of the length of the corresponding basipod. Basipod of ThI and II ( Fig. 28A, B ) with one short, smooth, distolateral seta, absent in ThIII to VI ( Fig. 28C–G ). Exopod one-segmented and shorter than the first two articles of the endopod, with one barbed seta in ThI ; two-segmented in ThII to VI, shorter than the endopod, with the first article similar in in length to the first two articles of the endopod. First and second exopodal article of ThII to VI provided with one barbed seta. Endopod four-segmented, first article short, second and third long and similar in length; fourth segment reduced with two strong claws and one seta on ThI , one smooth long claw and one seta on ThII to IV, and one long claw on ThV to VI; outer seta on second segment of ThI –VI plumose. Setal formula of endopods:

ThI 1+0/0+1/1+0/2+1

ThII to IV 0+0/0+1/0+1/1+1

ThV to VI 0+0/0+1/0+0/1

Thoracopod VIII male ( Fig. 27H, I ): compact, almost rectangular. Penial region with massive protopod, frontal lobe trapezoidal, and middle lobe square with several teeth. Endopod as long as basipod, with two small terminal spines. Basipod with one seta and a rounded distal “crest” on inner edge. Exopod small, almost square, with two small teeth.

Pleopod: absent.

Uropod ( Fig. 28H ): sympod almost three times the length of the exopod and almost five times as long as wide, with eight inhomonomous spines, with the distal one slightly longer, occupying a little more than half of the sympod length. Exopod slightly longer than endopod, with two terminal barbed setae of different length and a short spine-like seta; distolateral angle of the endopod bearing a short spine-like structure, and two setae, one short and smooth, and one plumose that exceeds the tip of the dagger-shaped distal end of the endopod.

Pleotelson ( Fig. 28I ): with two smooth lateral setae on each side; anal operculum not protruded.

Furca ( Fig. 28I ): each ramus almost square, with three barbed, distally bifurcate spines; basal spine shorter. Two dorsal plumose setae, one small and one over twice the length of the distal spine.

Female paratype differs from male in the absence of AO on the second antennular segment ( Fig. 27K ) and in the thoracopod VIII, which is a small “bump-like” structure ( Fig. 27J ).

Variability: variability was observed in body size (males body length 0.38–0.48. mm, and females 0.42–0.53 mm), and number of spines on sympod (six to eight, one case (on one side) had five spines).

Distribution and remarks: H. julianae sp. nov. was collected from nine bores along the Robe River valley. Sampling is still occurring in the area,and it is possible that the distribution could extend beyond these nine bores (Biologic Environmental Survey unpublished data). This species was previously known by Biologic Environmental Survey as H. sp. PBAT037. The clade representing this species is not supported in our analyses, however the clade including H. julianae sp. nov., H. sp. 24 (Pardoo) and H. sp. GrPar is supported in both analyses ( Fig. 3 , Appendix 4). H. julianae sp. nov. has high COI intraspecific variation comprised between 0.2 and 10.2% (mean 7%, Table 4, Supplementary Material Table S3), similar to the COI p-distance between H. julianae sp. nov. and H. sp. 24 (Pardoo) (7–10.5%, mean 9%). COI p-distance between H. julianae sp. nov. and H. sp. GrPar is slightly higher (10.4–14.4%, mean 12.7%). Although H. sp. 24 (Pardoo) and H. sp. GrPar occur respectively over 300 km away and over 170 km from H. julianae sp. nov. ( Fig. 3 ), it is possible that they represent populations of the same species complex. H. sp. 24 (Pardoo) morphological analysis was not possible as the posterior half of the body was used for DNA extraction, however a preliminary study showed the presence of epipod only on thoracopods III and IV (Appendix 9). We did not conduct a thorough morphological study of H. sp. GrPar specimens, however, a preliminary analysis showed similarities with H. julianae sp. nov., like the peculiar presence of epipod on thoracopods III and IV only (Appendix 10).

Etymology: the species is dedicated to Juliana Pille-Arnold, one of the collectors of the species and a colleague.

Figures

FIGURE 3. Hexabathynella species distribution in the Pilbara (WA) at the top. Hexabathynella clade extracted from the threegenes ML tree (bottom right). Bottom left (yellow rectangle): clade from the two-genes ML tree.

FIGURE 27. Hexabathynella julianae sp. nov. Male holotype (WAMC 78971) unless specified: A, Antennula; B, Antenna; C, Labrum; D, Mandible; E, Paragnaths support; F, Maxillula; G, Maxilla; H\, Thoracopod VIII (latero external view); I, Thoracopod VIII (latero internal view); J, Female thoracopod VIII (female paratype WAMC 78968); K, Second article of antennula of female (paratype WAMC 78965). Scale bar in mm.

FIGURE 28. Hexabathynella julianae sp. nov. Male holotype (WAMC 78971) unless specified:A, Thoracopod I; B, Thoracopod II; C, Thoracopod III; D, Thoracopod IV; E, Thoracopod V; F, Female thoracopod V (paratype WAMC 78965); G, Thoracopod VI; H, Uropod (latero external view); I, Pleotelson and furcal rami (dorsal view). Scale bar in mm.