Octobathynella peelensis, Camacho & Hancock, 2010

Camacho, A. I. & Hancock, P., 2010, A new genus of Parabathynellidae (Crustacea: Bathynellacea) in New South Wales, Australia, Journal of Natural History 44 (17 - 18), pp. 1081-1094 : 1083-1090

publication ID	https://doi.org/ 10.1080/00222931003624796
persistent identifier	https://treatment.plazi.org/id/03F287EA-FFAD-9C66-6BAB-FB21FCEEFB9B
treatment provided by	Carolina
scientific name	Octobathynella peelensis
status	gen. nov.

Treatment

Octobathynella peelensis gen. nov. sp. nov.

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

Material examined

Type locality. Department of Water and Energy monitoring piezometer number 30168, 31.18083° S, 151.0664° E, near Tamworth, NSW, Australia, 7 December 2005 GoogleMaps ; one male and three females were collected. Second location: Department of Water and Energy monitoring piezometer number 93024, 31.30528° S, 151.1528° E, near Tamworth, NSW, Australia, 9 December 2005 GoogleMaps ; one female and four juveniles were collected.

The details of the description are based on all adult specimens. The holotype is a male and the allotype is a female and the type series contains three additional specimens (three females) (Holotype MNCN20.04 About MNCN /8226, Allotype MNCN20.04 About MNCN /8227 and type series MNCN20.04 About MNCN /8228) .

Description

Body. Total length of holotype (male) 1.50 mm and allotype (female) 2.11 mm. Largest female total length 2.11 mm, smallest 1.28 mm. Body elongated, segments slightly widening towards posterior end. Length of head greater than width. All drawings are of the holotype except for female Th VIII.

Antennule ( Figure 1A View Figure 1 ) eight-segmented; no sexual dimorphism; length of first three segments similar to other five segments; inner flagellum almost square; fourth and fifth segments similar in size; sixth to eighth segments similar in size; setation as in Figure 1A View Figure 1 ; segment three with three smooth setae and one plumose seta; three aesthetascs on fifth and eighth segments and four on sixth and seventh segments.

Antenna ( Figure 1B View Figure 1 ) small, similar in length to first two segments of A.I. Sevensegmented; last two segments similar in size, smaller than fourth segment. Fifth segment is small, similar in size to second and third, while seventh segment has two smooth and one plumose terminal setae; setal formula: 0/0/1+0/1+0/0/1+1/3(1).

Labrum ( Figure 1C,D View Figure 1 ) with 10 main teeth and four lateral teeth at each side.

Mandible ( Figure 1 View Figure 1 E–G) with pars incisiva with four well-developed teeth and triangular small proximal tooth as in Figure 1 View Figure 1 (E,G); pars molaris with eight claws, six being strong with subdistal small spines and two small joined proximal teeth with a large number of fine hairs; mandibular palp does not exceed pars incisiva in length.

Maxillule ( Figure 1H View Figure 1 ) proximal endite with four claws; distal endite with seven claws, three smooth, one apical and two subapical, other four with denticles and three subterminal smooth setae on outer distal margin.

Maxilla ( Figure 1I View Figure 1 ) four-segmented; setal formula 4, 5, 9, 9.

Thoracopods I–VII ( Figure 2 View Figure 2 A–G) well developed, length gradually increasing from I to V, last three similar in size. Th I without epipod; epipod on II to VII, measuring less than half length of basipod; basipod with one lateral, smooth terminal seta in all Ths. Exopod three-segmented on Th I and Th VII ( Figure 2A,G View Figure 2 ), shorter than endopod; four-segmented on Th II, III and V ( Figure 2B,C,E View Figure 2 ), similar in length to endopod; five-segmented Th IV and VI, similar in length to endopod; first segment of the Th III and V with four barbed setae, in rest of thoracopods this first segment has only three barbed setae; all remaining segments of exopods of Th I to VII with two barbed setae (with one group of ctenidia at base of inner setae); endopods of Th 1 to 7 four-segmented, first segment has half length of second and third segments, and fourth is small (with two smooth strong claws of different length and one smooth seta), all inner setae on segments smooth and outer seta of first and second segments of Th I to VII are plumose, setal formulae: Th I, 2+1/3+1/2+1/3(1); Th II, 1+1/1+1/ 0+1/3(1); Th III, 1+1/2+1/0+1/3(1); Th IV, 1+1/2+1/1+1/3(1); Th V, 1+1/2+1/0+1/ 3(1); Th VI, 1+1/2+1/0+1/3(1); Th VII, 1+1/2+1/0+1/3(1). Allotype (female) setal formula of the endopods of thoracopods: Th I, 2+1/3+1/2+1/4(2); Th II, 1+1/3+1/1+1/ 4(2); Th III, 1+1/3+1/1+1/4(2); Th IV, 1+1/3+1/1+1/4(2); Th V, 1+1/3+1/1+1/4(2); Th VI, 1+1/3+1/1+1/3(1); Th VII, 1+1/3+1/0+1/3(1).

Thoracopod VIII male ( Figure 1J,K View Figure 1 ; 3E,F View Figure 3 ) twice as long as wide; basal region of penial complex supports three lobes: inner lobe (I.Lb.), outer lobe (O.Lb.) and dentate lobe (D.Lb.); triangular rounded inner lobe completely integrated into basal region, shorter than outer lobe; outer lobe almost three times as long as wide and longer than inner lobe and covers end of dentate lobe and does not exceed end of external side of basipod; dentate lobe is smaller than outer lobe, with small teeth and flat at distal end; endopod (Endp.) long and rounded with two terminal setae; exopod (Exp.) smaller than endopod, almost square, with small setules at apex; basipod trapezoidal in external face, in internal side with seta above its outer distal corner and with crest-like protuberance with two lobules, the distal with two denticles.

Thoracopod female VIII ( Figure 3G View Figure 3 ) small, rounded with one segment with one small tooth.

First pleopods absent.

Uropod ( Figures 3A View Figure 3 ) sympod almost three times longer than endopod and five times longer than wide; with 11 barbed spines of different size, distal spine twice length and wider than others; endopod slightly shorter than exopod, with two small spines and one strong spine on distal part, two plumose setae near inner margin, one basal and one subterminal, that exceed distal end of endopod, and two barbed terminal setae of different length; exopod has five barbed setae.

Pleotelson ( Figure 3D View Figure 3 of the allotype) with one small, plumose ventral seta. Anal operculum slightly concave.

Furca ( Figure 3B View Figure 3 ) with 11 barbed spines (the two terminal ones longer and thicker); two unequal dorsal plumose setae, the shorter does not exceed distal end of terminal spines.

Variability

There is a variation in the number of spines on the furca (11 to 13, see Figure 3D View Figure 3 of the allotype), the sympod of the uropod (10 to 12), and the endopod of the uropod (3 to 4, see Figure 3C View Figure 3 of the allotype). There is also variation in the number of setae on different thoracopod segments of female endopods, differing from the allotype as follows: Th I, 2+1/3+1/2+1/3-4(1-2); Th II , 1-2+1/1-3+1/0-1+1/3-4(1-2); Th III , 1+1/ 2-3+1/0-1+1/3-4(1-2); Th IV , 1+1/2-3+1/0-1+1/3-4(1-2); Th V , 1+1/2-3+1/0-1+1/3- 4(1-2); Th VI , 1+1/2-3+1/0-1+1/3(1); Th VII, 1+1/1-3+1/0-1+1/3(1).

Etymology

The generic name refers to the number of segments of the antennule: eight (Octo). The species name, peelensis , is named for the Peel River, which formed part of the aquifer containing this new species.

Remarks and discussion

So far, Octobathynella gen. nov. sp. nov. is the only species of Parabathynellidae known in Australia with eight segments on the A.I.; a character shared only with two other parabathynellid genera in the world: ( Camacho, 2005) Allobathynella Morimoto and Miura, 1957 and Sketynella Camacho, 2005. Both of these genera are Asiatic but do not have four aesthetascs in segments six and seven of A.I., as happens in O. peelensis gen. nov. sp. nov. The most frequent character state among parabathynellid genera is six or seven segments in the A.I. and only one genus, Sinobathynella Camacho et al., 2006 , has more segments (10 segments). These genera all have five or six segments in A.II (the most frequent number in all the species of the family Parabathynellidae ), whereas the new genus has seven segments, a characteristic appearing elsewhere only in Billibathynella Cho, 2005 , from Western Australia. The combination of eight segments in A.I and seven segments in A.II is only known in Octobathynella gen. nov. (see Table 2).

The new genus is the only genus of the Parabathynellidae family in the world displaying a crest with two lobules on the male Th VIII basipod.

The combination of characters of Octobathynella gen. nov. is unique in Parabathynellidae : antennule eight-segmented; antenna with seven segments; labrum with 18–20 teeth (10 main and four or five lateral teeth at either end); mandible with pars incisiva of four teeth and pars molaris of eight teeth; maxillule with distal endite with seven claws; exopod of the thoracopods with three to five segments, endopod with one dorsal plumose seta on the first and second segments and epipod absent only on Th I; pleopods absent; endopod of the Th VIII of male with two setae and exopod with setules and three lobes in the basal penial region; 10–12 spines on the sympod, three or four spines on the endopod and five setae on the exopod of the uropod.

Octobathynella gen. nov. is unlike any of the seven genera known to date in Australia, but it has affinities with Notobathynella (see Table 2), another uniquely Australian genus with seven claws on the distal endite of Mx.I. The new species is also similar to Notobathynella in the general structure of the male Th VIII, which is large in both. The endopod is smaller than the exopod in Notobathynella , but this is not the case in Octobathynella gen. nov.; both genera have a very different basipod, but Notobathynella lacks the crest-like projection with two lobules on the basipod. The new species has a plumose seta in segment three of the A.I, a character that appears in the genera Billibathynella and Brevisomabathynella , and in four species of Notobathynella , ( N. lemurum , N. williamsi , N. chiltoni and N. hineoneae ). Octobathynella gen. nov. is the only Australian genus with three or four segments on the exopod of Th I and four on the exopod of Th II. Brevisomabathynella has four or five segments in the exopod of the Th I, but always has six segments in Th II (see Table 2). The new genus shares some characteristics with the remaining Australian genera, but shares fewer common morphological features (see Table 2).

The new genus and species differ from all known Australian parabathynellids. Although there are some apparent morphological affinities with the Australian genus Notobathynella , the complete set of characters, in unique combination, warrants the establishment of a new species belonging to a new genus.