Atopobathynella lythei, Perina & Camacho & White & Callan & Abello & Morgan & Guzik, 2024

Atopobathynella lythei sp. nov. (figs. 6–9)

LSID: urn:lsid:zoobank.org:act:A10E63D3-F52B-45B0-BD3C-3DD3AE15C44D

Type locality: Bore WB12 K21W001 (22° 34’ 6.495“S, 119° 6’ 33.0588”E), Gudai Darri , Pilbara , Western Australia GoogleMaps .

Material examined: Holotype: WAM C76670 About WAM male, permanent slide, bore WB12 K21W001 (22° 34’ 6.495“S, 119° 6’ 33.0588”E), Gudai Darri, Pilbara , Western Australia. Lythe M, Paget S. 14 March 2021 (stygo net haul). GoogleMaps

Paratypes: WAM C76663 About WAM male , WAM C About WAM 76671 male, permanent slides, bore WB12 K21W001 (22° 34’ 6.495“S, 119° 6’ 33.0588”E), Gudai Darri, Pilbara , Western Australia. Curran, M., Paget S. 2 November 2020 (stygo net haul). Females of this species were not collected GoogleMaps .

Description male holotype ( WAMC 76670): Body length of 1.5 mm. Body seven and a half times as long as maximum width elongated, almost cylindrical, segments slightly widening and lengthening towards posterior end of body (fig. 6).

Antennula (fig. 7A): six-segmented. First three articles thicker than last three, first two articles longer than all the others, with the first one slightly longer than the second one, last four articles about the same length. Antennal organ not protruded and bearing two ventral setae. Very small inner flagellum almost square. Article five and six with three terminal aesthetascs. Antennula setation as in fig. 7A.

Antenna (fig. 7B): one-segmented; article rectangular with three terminal smooth setae and one terminal plumose seta.

Labrum (figs. 7C): slightly convex, free edge with 19 teeth: 18 main teeth, nine on each side and one central.

Paragnaths: absent.

Mandible (fig. 7D): pars incisiva with three teeth; pars molaris with five strong denticulate claws, with the two proximal ones joined together; tooth of ventral edge small and triangular. Mandibular palp with one long distal seta reaching beyond pars molaris, but not exceeding pars incisiva.

Maxillula (fig. 7E): proximal endite with four unequal claws; distal endite with five claws: all denticulated; three smooth subterminal setae on the outer distal margin, one of which is just over half length of the others.

Maxilla (fig. 7F): three-segmented (segment three and four fused), setal formula 2, 4, 15.

Thoracopods I to VII (figs. 8A–D, 9A–C): length gradually increasing from ThI to III, last four similar in size. Epipod present in all thoracopods, about half length of the corresponding basipod. All basipods with one smooth, distolateral seta slightly longer than the first article of the endopod. Exopod one-segmented in all thoracopods; exopod of ThI shorter than corresponding two first articles of the endopod, exopod similar in length to the first two articles of the endopod in ThII to IV and slightly longer in ThV to VII; provided with three barbed setae, two terminal, with the internal one very long, and one subterminal slightly longer than the outer terminal seta in ThI, and similar in length on the rest of thoracopods. Endopod four-segmented, first segment short with one barbed seta on ThI and no seta on the rest of thoracopods, second and third articles long and similar in length; second article with one plumose external seta in all thoracopods and two outer smooth setae only on ThI; third article of ThI with one internal and one small external seta, third article of ThII to VII with only one external seta; fourth article very reduced with two strong claws of different length on all thoracopods, ThI with one additional seta. Setal formula of endopods:

ThI1 + 0/2 + 1/1 + 1/3(1)

ThII to VII0 + 0/0 + 1/0 + 1/2

Thoracopod VIII (fig. 8E, F): compact, balloon-shape. Penial region with massive protopod, outer lobe triangular and defined at base in latero-external view and lobe dentate with four/five distal teeth; inner lobe longer than outer lobe and drawn out into a projection. Basipod with inner distal end pointy and over-reaching the outer lobe, and with one spine-seta of uncertain interpretation.

Pleopod I (fig. 9F): one smooth seta on each side.

Uropod (fig. 9D): sympod over three and half times the length of the endopod (excluding the dagger- shaped structure) and almost four times as long as wide, with eleven subequal spines. Endopod almost as long as exopod, with internal row of setulae in the middle, and drawn out distally into a dagger-shaped structure with terminal setulae, and with distolateral angle bearing two barbed setae of different length. Exopod with two terminal barbed setae (outer one shorter), and one short basal seta.

Pleotelson (fig. 9E): with two very small plumose lateral setae (one on each side); anal operculum not pronounced.

Furca (fig. 9E): each ramus almost rectangular, with seven barbed spines, the two distal spines one and a half time longer than the others. Two dorsal plumose setae on each ramus, the inner one very short and the outer one exceeds the tip of the most distal spine.

Variability: Variability was observed in body size (1.25 to 1.5 mm), number of teeth on labrum (20–22), number of setae on the last article of MxII (14/15), number of inner and outer setae on the third article of ThI (respectively zero to two, and one or two) number of spines on sympod (ten or 11), and number of setae on exopod of uropod (three or four).

Etymology: The name of the species is dedicated to Morgan Lythe, one of the collectors of the species.