Hexabathynella miralgaensis 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 : 60-63

Hexabathynella miralgaensis Perina and Camacho , sp. nov.

urn:lsid:zoobank.org:act:F6DAB602-502C-4405-943A-241FAA5BBB72

( Figs. 25 to 26)

Material examined: Holotype female. AUSTRALIA: Western Australia: Miralga Creek, Pilbara Bore ALB0004 (stygofauna net haul) 20°45'05.8217"S, 119°19'20.2570"E, 7 November 2019, F. Rudin, M. Lythe. ( WAMC 78876 — BES8281 , permanent slide).

Paratypes: 1 female ( WAMC 78877 — BES7328 , uropods and furcal rami on permanent slide, rest of the body used for DNA), same details as holotype. This specimen was missing the head when collected .

Diagnosis: H. miralgaensis sp. nov. belongs to a group of Hexabathynella species small (0.75–0.9 mm); with three teeth on pars incisiva and five on pars molaris of mandible; epipod present on thoracopods III to VI; sympod with five inhomonomous spines, with distal spine much longer than the others; exopod and endopod of uropod with two setae, with exopod longer than the endopod. Similarities and differences with other Hexabathynella species are listed in Appendix 7. Unfortunately, males of this species were not collected. The sequenced specimens differ from all the other Hexabathynella species sequenced by COI = 17.7–21.9% and 12S = 21.9–23% ( Tables 4, 5).

Description: body length of females 0.75–0.9 mm (holotype 0.75 mm). Body elongated, eight and a half times as long as maximum width, almost cylindrical, segments slightly widening towards the posterior end of the body.

Antennula ( Figure 25A ): six-segmented. First and second articles similar in width, combined length similar to the length of the third, fourth and fifth articles together, with second article the longest, followed by first, third, and sixth, fifth article is the shortest followed by the fourth. Inner flagellum small, almost square. Article five and six with three terminal and three subterminal aesthetascs respectively. Setation as Fig. 25A .

Antenna ( Figure 25B ): five-segmented, distal article longest, fourth article slightly shorter and equal to the other three combined. Articles one to three with no setae. Article three with two setae and article five with three setae, with the shortest plumose.

Labrum ( Fig. 25C ): broken, with at least 10 teeth.

Mandible ( Fig. 25D ): 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 of the pars incisiva.

Paragnaths ( Fig. 25G ): presence of a rounded structure, with small spines on the distal end that could possibly support paragnaths, in this case absent.

Maxillula ( Fig. 25F ): proximal endite with four distal claws of different size, two longer and two shorter; distal endite with six claws, the four proximal with denticles; three smooth subterminal setae on the outer distal margin.

Maxilla ( Fig. 25F ): four-segmented, with short setae, setal formula 2, 4, 9, 1.

Thoracopods I to VI ( Figs. 25H, I and 26A–D ): length gradually increasing from thoracopod one to four, last two similar in size. Epipod present from Th III to VI, about one-half of the length of the corresponding basipod. Basipod of Th I and II ( Fig. 25H, I ) with one short, smooth, distolateral seta, absent in ThIII to VI ( Fig. 26A–D ). Exopod one-segmented and shorter than the first two articles of endopod in thoracopod I; two-segmented in ThII to VI with the first article similar in in length or longer than the first two articles of the endopod; exopod of ThII to VI similar or slightly shorter than endopod. First exopodal article of ThII to VI with two setae, one of which barbed. Endopod four-segmented, first article short, second and third articles similar in length and slightly longer than the first one; fourth segment reduced with two long claws on ThI , and one smooth long claw on thoracopods II to VI; outer plumose seta on second article of ThI –VI. Setal formula of endopods:

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

ThII to VI 0+0/0+1/0+0/1

Thoracopod VIII female: absent

Pleopod ( Fig. 26E ): one smooth seta.

Uropod ( Figure 26F ): sympod short, about twice as long as wide, with five inhomonomous spines occupying the distal third of the sympod, distal spine two times longer than others and longer than the exopod; exopod almost a third longer than endopod, with two terminal setae of different length; distolateral angle of the endopod bearing two similar setae slightly longer that the tip of the article.

Pleotelson ( Figure 26G, H ): with two lateral setae of different length on each side; anal operculum protruded.

Furca ( Figure 26G, H ): each ramus almost square, with three barbed spines of different sizes, basal spine shortest. Two dorsal setae similar in size exceeding the distal spine.

Variability: was observed in body size (0.75–0.9 mm).

Distribution and remarks: H. miralgaensis sp. nov. was collected from one bore near Miralga creek, in the De Grey River catchment ( Fig. 3 ). It appears genetically distant from all the other Hexabathynella species from Australia, although it occurs about 60 km south of the collection site of H. sp. 24 (Pardoo), in the same river catchment.

Etymology: the name of the species refers to the Miralga creek, where it was collected.

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 25. Hexabathynella miralgaensis sp. nov. Female holotype (WAMC 78876) unless specified: A, Antennula; B, Antenna; C, Labrum; D, Mandible; E, Maxillula; F, Maxilla; G, Paragnaths support; H, Thoracopod I; I, Thoracopod II; J, Thoracopod VIII. Scale bar in mm.

FIGURE 26. Hexabathynella miralgaensis sp. nov. Female holotype (WAMC 78876) unless specified: A, Thoracopod III; B, Thoracopod IV; C, Thoracopod V; D, Thoracopod VI; E, Pleopod; F, Uropod (latero external view); G, Furcal rami (latero external view, female paratype WAMC 78877); H, Pleotelson (dorsal view). Scale bar in mm.