Hexabathynella robeensis, 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 : 68-71

H. robeensis Perina and Camacho sp. nov.

urn:lsid:zoobank.org:act:34C741B7-8DDA-41A3-9001-D15C600C8C3A

( Figs. 29 , 30 , Appendix 11)

Material examined: Holotype male. AUSTRALIA: Western Australia: Robe Valley, Pilbara , Bore BC 4341 (stygo net haul) 21°56'57.5344"S, 116°27'46.7950"E, 17 March 2022, J. Pille Arnold, S. Rodman, ( WAMC 79100 — BES14051 , permanent slide).

Paratypes: 1 specimen (sex not available) ( WAMC 78949 — BES17250 — BMR07033 ), same details as holotype ; 1 female ( WAMC 789101 — BES14051 ), same details as holotype ; 1 male, Robe Valley , Pilbara, Bore BC401 (stygo net haul) 21°56'10.5876"S, 116°27'12.5644"E, 24 May 2021, J. Pille Arnold, S. Rodman, ( WAMC 78947 — BES12997 — BMR01291 , permanent slide) ; 1 female, Robe Valley , Pilbara, Bore BUNWP0005 (stygo net haul) 21°55'47.0437"S, 116°26'06.1447"E, 17 March 2022, J. Pille Arnold, S. Rodman, ( WAMC 78952 — BES17554 — BMR07029 , permanent slide) ; 1 male ( WAMC 78953 — BES14471 , permanent slide), same details as WAMC 78952 ; 1 specimen (sex not available), Robe Valley , Pilbara, Bore PZ10BUN041 (stygo net haul) 21°48'53.3830"S, 116°19'46.2076"E, 25 September 2021, J. Pille Arnold, S. Rodman, ( WAMC 78955 — BES13433 — BMR05498 , permanent slide) ; 1 specimen (sex not available), Robe Valley , Pilbara, Bore PZ10BUN043 (stygo net haul) 21°51'18.4911"S, 116°23'03.3166"E, 25 September 2021, J. Pille Arnold, S. Rodman, ( WAMC 78959 — BES13555 — BMR05504 , permanent slide) ; 1 female, Robe Valley , Pilbara, Bore BC434 (stygo net haul) 21°56'57.5344"S, 116°27'46.7950"E, 11 August 2022, J. Pille Arnold, S. Rodman, ( WAMC 79012 , permanent slide) .

Additional material: 2 males, 1 female ( WAMC 78946 — BES13080 , in alcohol), same details as WAMC 78947 ; 13 specimens ( WAMC 78948 — BES12437 , in alcohol), same details as WAMC 78947 ; 13 specimens ( WAMC 78948 — BES12437 , in alcohol), same details as WAMC 78947 ; 4 males, 9 females ( WAMC 78950 — BES14051 , in alcohol), same details as holotype ; 1 female ( WAMC 78951 — BES15661 , in alcohol) same details as holotype ; 3 males Robe Valley , Pilbara, Bore BUNWP0005 (stygo net haul) 21°55'47.0437"S, 116°26'06.1447"E, 11 August 2022, J. Pille Arnold, S. Rodman ( WAMC 78954 — BES16815 , in alcohol) ; 1 male ( WAMC 78956 — BES13351 , in alcohol), same details as WAMC 78955 ; 1 male, 1 female ( WAMC 78957 — BES15599 , in alcohol), same details as WAMC 78955 ; 1 male ( WAMC 78958 — BES13359 , in alcohol), same details as WAMC 78959 ; 2 males, 1 female, Robe Valley , Pilbara, Bore PZ10BUN043 (stygo net haul) 21°51'18.4911"S, 116°23'03.3166"E, 14 August 2022, J. Pille Arnold, S. Rodman, ( WAMC78961 — BES15925 , in alcohol) .

Diagnosis: H. robeensis sp. nov. belongs to a group of Hexabathynella with small size (0.36–0.51 mm); 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; exopod of all thoracopods two-segmented; pleopods absent; sympod of the uropod inhomonomous; exopod and endopod of uropod with three setae, with exopod slightly longer than endopod; anal operculum not protruded. This species is characterized by the presence of epipod on thoracopods III and IV only. H. robeensis sp. nov. is very similar to H. julianae sp. nov. It differs from it by the number of setae on maxilla, the number of spines on the sympod of uropod, the length of setae on exopod and endopod of uropod, and the absence of female thoracopod VIII. Similarities and differences with other Hexabathynella species are listed in Table 10. The sequenced specimens differ from all the other Hexabathynella species sequenced by COI = 11.6– 22% and 12S = 11.3–22.2% This species shows intraspecific variation of COI=3% and 12S=2.6% ( Tables 4, 5).

Description male holotype (WAMC 79100): Body elongated, almost cylindrical, about five and a half times as long as maximum width, segments slightly widening towards the posterior end of the body (Appendix 11).

Antennula ( Fig. 29A ): first three articles as long as the last three. The first and last articles longest and similar in length, followed by the second article, a little shorter, third and fourth articles similar in length, and fifth one is the shortest. Antennal organ on the second article without protuberance, formed by one smooth modified seta that does not reach the distal end of the third article. Inner flagellum rectangular. Article five and six with three terminal and three subterminal aesthetascs respectively. Setation as Figure 29A .

Antenna ( Figure 29B ): five-segmented, distal article longest, about 1.5 times longer than third and fourth ones, which are similar in length, first and second articles shortest, about half of the length of the third one. Articles one, two and four with no setae. Article three with one seta, and article five with two smooth and one plumose seta.

Labrum ( Fig. 29C ): almost flat, with 12 similar teeth in the distal end.

Mandible ( Fig. 29D ): 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 the distal end the pars incisiva.

Paragnaths ( Fig. 29E ): presence of a rounded structure, with small spinnule on the distal end, that could represent the support of possible paragnaths, in this case absent.

Maxillula ( Fig. 29F ): proximal endite with four distal claws of different size, one very long and two short ones similar in length; distal endite with five claws, the three proximal ones with denticles, and the basal one short; three smooth subterminal setae on the outer distal margin.

Maxilla ( Fig. 29G ): four-segmented, with long setae, setal formula 2, 4, 13, 1.

Thoracopods I to VI ( Fig. 30A–F ): ThII slightly longer than ThI, ThIII to VI longer than ThII and similar in size. Epipod present on ThIII and IV only, small, about one-third of the length of the corresponding basipod. Basipod of thoracopods I and II with distolateral seta, basipod of ThIII to VI without. Exopod one-segmented and shorter than the first two articles of the endopod in ThI , with only one distal seta; exopod two-segmented and shorter than the first three segments of the endopod in ThII to VI, with two barbed setae, one terminal and one subterminal. Endopod four-segmented, first article short, second and third long and similar in length; fourth segment reduced with two smooth claws and one seta on ThI , one smooth claw and one seta on thoracopods II to IV, and one claw on ThV and 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+0/1+1

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

Thoracopod VIII male ( Fig. 29H, I ): compact, rectangular. Penial region with massive protopod, frontal lobe rectangular, and middle lobe nearly square. Endopod short, with one strong terminal seta. Basipod slightly longer than endopod, without seta and with a lobed distal “crest” on inner edge. Small subtriangular exopod without teeth.

Pleopod: absent.

Uropod ( Fig. 30G ): sympod almost 2.5 times the length of the exopod and over six times as long as wide, with five inhomonomous spines occupying 2/3 of its length, with distal spine longer. Exopod slightly longer than endopod, with one short subterminal barbed seta, and two terminal setae, one barbed and one long and smooth; distolateral angle of the endopod bearing one plumose seta, and two smooth short setae not reaching the end of the dagger-shaped structure of the endopod.

Pleotelson ( Fig. 30H ): with two plumose lateral setae on each side; anal operculum not protruded.

Furca ( Fig. 30H ): each ramus rectangular, with three barbed spines; basal spine shortest, other two similar in length. Two dorsal plumose setae, one short and one slightly longer than the distal spine.

Female paratype differs from male in the second antennular segment without AO ( Fig. 29J ), and the absence of thoracopod VIII.

Variability: variability was observed in body size (males 0.36–0.5 mm and females 0.37–0.47 mm), and number of inhomonomous spines on sympod (four to six). In some cases, left and right exopods of thoracopods are different, with one side presenting one-segmented exopod.

Distribution and remarks: H. robeensis sp. nov. was collected in five bores in the Robe River valley and its distribution overlaps with H. julianae sp. nov. one ( Fig.3 ). Sampling is still occurring in the area, and 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. PBAT033/PBAT047/Helix-SPA051. The clade representing this species is well supported and is sister to the clade formed by H. julianae sp. nov., H. sp. GrPar and H. sp. 24 (Pardoo), with COI p-distances comprised between 11.6 and 14.7% ( Table 4).

Etymology: the name of the species refers to the Robe Valley where it occurs.

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 29. Hexabathynella robeensis sp. nov. Male holotype (WAMC 79100) 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, AI second segment female (paratype WAMC 79012). Scale bar in mm.

FIGURE 30. Hexabathynella robeensis sp. nov. Male holotype (WAMC 79100): A, Thoracopod I; B, Thoracopod II; C, Thoracopod III; D, Thoracopod IV; E, Thoracopod V; F, Thoracopod VI; G, Uropod latero external view; H, Furcal rami (dorsal view). Scale bar in mm.