Billibathynella ilgarariensis, Hong & Cho, 2009

Hong, Sungwon J. & Cho, Joo-Lae, 2009, Three new species of Billibathynella from Western Australia (Crustacea, Syncarida, Parabathynellidae), Journal of Natural History 43 (37 - 38), pp. 2365-2390 : 2373-2378

Billibathynella ilgarariensis sp. nov.

( Figures 6–9 )

Etymology

The specific epithet is derived from Ilgarari Creek, where the material was collected.

Type material

Holotype. Male, dissected on six slides. Australia, Western Australia, Gascoyne, Bulloo Downs Station , Ilgarari Creek-Yanneri Well (24°26′22′′ S, 119°45′27′′ E), BES 8494 and 8498, 7 September 2000, (W.F. Humphreys and J.M. Waldock) ( WAM C 40061).

Allotype. Female, dissected on five slides, same data as for holotype ( WAM C 40062).

Paratypes. Two males and three females each kept as a whole specimen in a slide, same data as for holotype ( WAM C 40063 – C 40067) .

Description of adult male (holotype)

Body ( Figure 6A ). Elongated and cylindrical, length 3.17 mm (other males: 3.02, 3.00 mm), approximately 10 times as long as wide. Head as long as anterior three thoracic segments combined.

Antennule ( Figure 6B ). Seven-segmented. First segment with one seta on inner distal margin, four simple dorsal setae, and one dorsal, one ventromedial and two lateral plumose setae. Second segment with one group of four plumose setae and seven simple setae on inner margin. Third segment with two lateral setae including one plumose seta and six setae on inner margin. Inner flagellum of third segment with three simple setae. Fourth segment with one stub seta and one plumose seta on dorsal margin, and two stub setae and two plumose setae on outer distal apophysis. Fifth segment with one aesthetasc, one seta and two aesthetascs dorsally, and four setae on inner margin. Sixth segment with one aesthetasc, one seta and two aesthetascs dorsally, and with five setae on inner margin. Seventh segment with three aesthetascs and four simple setae.

Antenna ( Figure 6C ). Seven-segmented, as long as the length of antennular segments 1–5. Setal formula: 0+0/0+0/1+1/1+1/0+0/0+2/4(1). One outer seta of sixth segment is plumose.

Labrum ( Figure 6D ). Flat with 12 teeth of more or less similar size flanked by five teeth decreasing in size laterally on both lateral sides. Inner surface with numerous rows of ctenidia and a few nipple-like protrusions.

Mandible ( Figure 6E ). With incisor process of four teeth. Tooth of ventral edge triangular. Spine row consisting of 12 spines. Palp of one segment, with one apical seta.

Maxillule ( Figure 6F ). Two-segmented. Proximal segment with four setae on inner distal margin. Distal segment with two terminal spines, one large most distal spine

and seven spines on inner edge, and three simple setae on outer distal margin. The most distal spine of distal segment twice as long as the other spines.

Maxilla ( Figure 6G ). Four-segmented, setal formula 4-6-13-8.

Thoracopods. Thoracopods I–IV ( Figure 8A–D ) increasing in size posteriorly. Thoracopods IV–VII ( Figures 8D , 9A–C ) similar in size. Thoracopods I–VII each bearing one small epipod on protopod and one seta on basipod. The number of segments of exopod of thoracopods I–VII: 6-7-8-8-9-9-7. All the thoracopods with two setae in each segment of the exopod, except on the first segment that have three or four setae. Endopod of thoracopods I–VII four-segmented, setal formulae shown in Table 2. Thoracopod VIII ( Figure 6I,J ) more or less rectangular in frontal view, twice as long as wide. Protopod massive, with prominent penial region with a distal opening. Epipod large, triangular, its distal part reaching the penial region of the protopod. Basipod without setae, inner margin of basipod drawn out into projection. Exopod one-quarter the size of basipod, triangular, bearing four subterminal setae. Endopod half as large as exopod, with two distal setae of different length.

First pleopod ( Figure 7A ). In form of two stubs distanced from each other basally. Each stub bearing one distal seta.

Uropod ( Figure 7C,D ). Sympod four times longer than wide, bearing 13 spines of similar size on inner margin; those occupy 50% of its length. Endopod 50% as long as sym- pod, dorsally with two plumose setae of different length near the base and one subterminal plumose seta, two terminal setae on outer distal margin, and one distal spine, one subterminal spine and four spines on inner margin. The distal and subterminal spines similar in size, four inner marginal spines two-thirds as long as and one-half as thick as terminal spine. Exopod almost 66% as long as sympod, with 12 setae, three on the end and nine on the outer margin, on outer and terminal margin and one basi-ventral seta.

Pleotelson ( Figure 7B,C ). With one seta near the base of furcal rami on both sides. Anal operculum concave.

Furcal rami ( Figure 7B,C ). Three times as long as wide, with two large distal spines and 14 smaller spines on inner margin, and with two dorsal plumose setae.

Description of female (allotype)

The female differs from the male as follows. Body ( Figure 6A ) length 3.48 mm (other females: 3.25, 3.22, 3.10 mm). Number of exopodal segments of thoracopods I–VII: 6-7-8-9-9-8-7. Setal formula of thoracopodal endopods is shown in Table 2. Both right and left thoracopods VIII ( Figure 6H ) cone-shaped, half as large as the endopod of the male thoracopod VIII, distal with two or three teeth.

Variation

The following variations are observed in the five paratypes. Number of exopodal segments of thoracopods I–VII: 4-6-6-6-6-6-5, 6-7-8-9-9-8-7, 6-8-8-9-9-9-8, 5-7-8-8-8-7- 6, 5-6-7-7-8-6-6. Uropodal sympod with 10 to 13 spines; endopod with three to four spines on inner margin; exopod with nine to 12 setae on outer and terminal margin. Furcal rami with 11 to 15 spines on inner margin

Figures

Figure 6. Billibathynella ilgarariensis sp. nov. (male: holotype, female: allotype). (A) General habitus, female (lateral); (B) left antennule, male (dorsal); (C) left antenna, male (dorsal); (D) labrum male (ventral); (E) left mandible, male (ventrolateral); (F) left maxillule, male (ventral); (G) right maxilla, male (dorsal); (H) right and left thoracopod VIII, female; (I) left thoracopod VIII, male (inner lateral); (J) right thoracopod VIII, male (outer lateral). Scale bars 0.1 mm, unless specified.

Figure 7. Billibathynella ilgarariensis sp. nov. (male: holotype). (A) Pleopod I (ventral); (B) pleotelson and left furcal ramus (dorsal); (C) uropod, pleotelson and furcal rami (lateral); (D) right uropod (dorsal). Scale bars 0.1 mm.

Figure 8. Billibathynella ilgarariensis sp. nov. (male: holotype). (A) Left thoracopod I (frontal); (B) left thoracopod II (frontal); (C) left thoracopod III (frontal); (D) left thoracopod IV (frontal). Scale bar 0.1 mm.

Figure 9. Billibathynella ilgarariensis sp. nov. (male: holotype). (A) Left thoracopod V (frontal); (B) left thoracopod VI (frontal); (C) left thoracopod VII (frontal). Scale bar 0.1 mm.