Billibathynella cassidis, 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 : 2378-2384

Billibathynella cassidis sp. nov.

( Figures 10–13 )

Etymology

The specific epithet is derived from the large helmet-like head of the new species (Latin cassidis ).

Type material

Holotype. Male, dissected on six slides. Australia, Western Australia, Pilbara, Ethel Creek , Bore W 6 (23°20′ S, 119°50′ E), BES 3581. November 1998, (S.M. Eberhard ( WAM C 40068).

Allotype. Female, dissected on five slides, same data as for holotype ( WAM C 40069).

Paratypes. One male and one female each kept as a whole specimen in a slide, same data as for holotype ( WAM C 40070 – C 40071) .

Description of adult male (holotype)

Body ( Figure 10 ). Elongated and cylindrical, length 2.15 mm (other males: 2.11 mm), approximately 10 times as long as wide. Head helmet-like, as long as anterior four thoracic segments combined, 1.5 times thicker than segment 1.

Antennule ( Figure 11A ). Seven-segmented. First segment with one seta on inner distal margin, three groups of spikes inner ventrally and two simple dorsal setae, as well as each one dorsal, one ventromedial and one lateral plumose setae. Second segment with one group of four plumose setae and three simple setae on inner margin. Third segment with two lateral setae including one plumose seta and two 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 plumose setae on outer distal apophysis. Fifth segment with one simple seta and two aesthetascs dorsally, and three setae including one plumose seta on inner margin. Sixth segment with one aesthetasc, one seta, and two aesthetascs dorsally, and three setae on inner margin. Seventh segment with three aesthetascs and four simple setae.

Antenna ( Figure 11B ). 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+1/3(1).

Labrum ( Figure 11C ). Flat with 12 teeth of more or less similar size flanked by five (right) or six (left) teeth decreasing in size laterally on both lateral sides. Inner surface with numerous rows of ctenidia and a few nipple-like protrusions.

Mandible ( Figure 11D ). With incisor process of five teeth. Tooth of ventral edge prominent and triangular with bifurcated end ( Figure 11E ). Spine row consisting of nine spines. Palp of one segment, with one apical seta.

Maxillule ( Figure 11F ). Two-segmented. Proximal segment with four setae on inner distal margin. Distal segment with two terminal spines, one large most distal spine and six 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 11G ). Four-segmented, setal formula 3-4-10-6.

Thoracopods. Thoracopods I–IV ( Figures 12A–C , 13A ) increasing in size posteriorly. Thoracopods IV–VII ( Figures 13A–D ) similar in size. Thoracopods I–VII each bearing one epipod measuring half length of basipod on protopod and one seta on basipod. The number of segments of exopod of thoracopods I–VII: 4-5-5-5-6-5-4. All segments of exopod of thoracopods I to VII with two setae. Endopod of thoracopods I–VII four-segmented, setal formulae are given in Table 2. Thoracopod VIII ( Figure 11H,I ) more or less rectangular in frontal view, 1.5 times longer than 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-third size of the basipod, triangular with dentate end, bearing two subterminal setae. Endopod half as large as exopod, with two distal setae.

First pleopod ( Figure 11K ). In form of two stubs being distanced from each other basally. Each stub bearing one distal seta.

Uropod ( Figure 12F,G ). Sympod five times longer than wide, bearing 13 spines of similar size on inner margin that occupy one-half of its length. Endopod 37% as long as sympod, dorsally with one long plumose seta near the base and one subterminal plumose seta, two terminal setae on outer distal margin, and one distal spine, one subterminal spine and one spine on inner margin. The distal and subterminal spines similar in size, one inner marginal spine one-third as long as terminal one. Exopod 50% as long as sympod, with seven setae, two terminal and five along the outer margin, and one basi-ventral seta.

Pleotelson ( Figure 12D,F ). With one seta near the base of furcal rami on both sides. Anal operculum concave.

Furcal rami ( Figure 12D,F ). Twice as long as wide, with two large distal spines and eight smaller spines on inner margin, and two dorsal plumose setae of different length.

Description of female (allotype)

The female differs from the male as follows. Body length 2.15 mm (other females: 2.14 mm). Number of exopodal segments of thoracopods I–VII: 4-5-5-6-5-5-4. Setal formulae of thoracopodal endopods are given in Table 2. Both right and left thoracopods VIII ( Figure 11J ) cone-shaped, half as large as endopod of male thoracopod VIII, and distal end with tiny teeth. Uropodal sympod with 14 spines; endopod with three spines on inner margin; exopod with six setae on outer and terminal margin.

Figures

Figure 10. Billibathynella cassidis sp. nov. (male: holotype). General habitus (lateral).

Figure 11. Billibathynella cassidis sp. nov. (male: holotype, female: allotype): (A) Right antennule, male (lateral); (B) right antenna, male (dorsal); (C) labrum, male (ventral); (D) right mandible, male (dorsal); (E) proximal tooth of right mandible, male; (F) right maxillule, male (dorsal); (G) left maxilla, male (dorsal). (H) left thoracopod VIII, male (inner lateral); (I) right thoracopod VIII, male (outer lateral); (J) thoracopod VIII female (ventral); (K) pleopod I, male (ventral). Scale bars 0.1 mm.

Figure 12. Billibathynella cassidis sp. nov. (male: holotype). (A) Left thoracopod I (frontal); (B) left thoracopod II (frontal); (C) left thoracopod III (frontal); (D) pleotelson and furcal rami (dorsal); (E) distal part of left furcal ramus with furcal organ; (F) uropod, pleotelson and furcal rami (lateral); (G) right uropod (dorsal). Scale bars 0.1 mm.

Figure 13. Billibathynella cassidis sp. nov. (male: holotype). (A) Left thoracopod IV (frontal); (B) left thoracopod V (frontal); (C) right thoracopod VI (frontal); (D) left thoracopod VII (frontal). Scale bar 0.1 mm.