Halearcturus serrulatus ( Whitelegge, 1904 )

Poore, Gary C. B., 2015, Halearcturus, a new genus of Antarcturidae Poore, 2001 (Crustacea: Isopoda: Valvifera) with a key to genera of the family, Memoirs of Museum Victoria 73, pp. 13-18 : 15-17

Halearcturus serrulatus ( Whitelegge, 1904)

Fig. 1

Arcturus serrulatus Whitelegge, 1904: 414–416 , figs 118a–c.

Antarcturus serrulatus.— Stebbing, 1908: 53 .

Microarcturus serrulatus.— Nordenstam, 1933:128 .— Nierstrasz, 1941: 261.— Hale, 1946: 200–202, figs 23, 24.

Type locality. Australia, NSW, off Wattamolla [as Wata Mooli], 99– 108 m (HMCS Thetis stn 57) (type material lost) .

Figured specimens. Bass Strait, 70 km SW of Cape Otway, 39°26.60'S, 143°6.8'E, 115 m, NMV J8593 (male, 6.7 mm). 8 km S of South East Point, Wilsons Promontory, 39°13.80'S, 146°27.3'E, 65 m, NMV J62821 (ovigerous female, 10.0 mm).

Other material examined. NSW, off mouth of Manning River, 31°55'S, 152°52' E, AM P.11752. 25–28 km NE of South Head, Port Jackson, 33°44' S, 151°38'E, AM P.11671. Jervis Bay, 35°3'S, 150°44' E, AM G.940. 22.4 km off Batemans Bay, 35°45'S, 150°30' E, AM P.10715.

Bass Strait, Western Port and E of Tasmania: 43 specimens from Museum Victoria collections (see http://museumvictoria.com.au/ collections-research/our-collections/) .

Redescription. Ovigerous female, 10.0 mm. Head front, concave; with pair of anteriorly-directed curved blade-like projection between eyes; pair of tuberculate submedian bosses and pairs of small dorsolateral and lateral lobes on maxillipedal segment. Pereonites 1–4 each with pair of prominent submedian anteriorly-curved, hook-like projections, pair of smaller conical projections near posterior margin, pair of lateral anteriorly-directed projections each with small conical boss on anterior margin (lateral projection small on pereonite 1). Pereonites 5–7 each with pair of lateral flat-topped projections and much smaller cone near posterior margin. Pleonite 1 with pair of lateral posteriorly-directed. Pleonite 2 with pair of strong dorsolateral conical projections and smaller lateral posteriorly-directed cones. Pleonite 3 with low median boss, pair of smaller dorsolateral cones, pair of lateral wings directed posteriorly. Pleonites 4–6 and telson with 4 pairs of submedian conical tubercles, fourth largest, 3 sublateral conical tubercles, second largest, 3 pairs of lateral triangular tubercles, 1 median tubercles in front of apex, and apex with 1 dorsal median tubercle.

Coxa 1 fused to pereonite, with 3 triangular flat lobes. Coxae 2–4 free, each with 2 anterior and 2 posterior triangular flat lobes, the most posterior on pereopod 4 elongated as oostegite support. Coxae 5–7 fused, with lateral flat-topped tubercles and anterior and posterior triangular lobes.

Antennule flagellum blade-like, toothed; flagellum with 8 pairs of aesthetascs + 3 single subdistal aesthetascs. Antennal peduncle articles 2–4 laterally flattened, with teeth on upper margin.

Pereopod 2 basis with 2 teeth each on extensor and flexor margins; merus with small tooth at midpoint and large distal blade-like tooth on extensor margin; carpus with blade-like tooth at midpoint of extensor margin; propodus with 4 small teeth on extensor margin; dactylus with 2 small teeth on extensor margin, with short unguis. Pereopod 3 basis with 3 teeth on extensor and 6 on flexor margins; merus with distal blade-like tooth on extensor margin and small tooth on flexor margin; carpus with 2 blade-like teeth on extensor margin, small spine on flexor margin; propodus and dactylus as in pereopod 2. Pereopod 4 basis with 4 spines on extensor and 10 spines on flexor margin, irregularly arranged; ischium with spines on flexor margin; merus with distal blade-like tooth on extensor margin and small tooth on flexor margin; carpus with 2 blade-like teeth on extensor margin, small spine on flexor margin; propodus and dactylus as in pereopod 2.

Pereopod 5 with 4 tubercles on extensor margin, 3 on flexor margin; ischium irregularly tuberculate; merus and carpus each with 2 robust setae on conical projection on margin; propodus with 5 robust setae on conical projection on margin; dactylus curved. Pereopods 6 and 7 similar, less ornate, bases shorter.

Uropodal peduncle with 2 longitudinal-oblique rows of tubercles, 3 in row next to suture, 5 larger in midline; endopod triangular; exopod absent.

Sternite 8 simple flat, without oostegite.

Male, 6.7 mm. Body more slender than ovigerous female, as typical of Antarcturidae . Head with pair of blade-like horns between eyes, each with acute tip and small acute point on anterior margin; pair of large submedian hemispherical bosses. Pereonites 2–4 each with pair of sublateral hook-like anteriorly-directed tubercles, pair of small tubercles near posterior lateral margin, pair of lateral marginal flat triangular lobes, directed anteriorly. Pereonites 5–7 each with pair of lateral conical tubercles. Pleonite 1 with pair of small lateral tubercles, with pair of sharp conical tubercles on sternum anterior to pleopods 1. Pleonite 2 with pair of large sublateral tubercles. Pleonite 3 with median boss. Remaining pleotelson with 2 pairs of obsolete submedian tubercles, 3 pairs of sublateral tubercles, second largest, 3 pairs of lateral wings, first largest, 1 median tubercles in front of apex, and apex with 1 dorsal median tubercle.

Coxae 1–4 unarmed. Coxae 5–7 each with obsolete anterior and posterior lateral tubercles.

Pereopod 2 merus with blade-like tooth on extensor margin; carpus with 2 blade-like teeth on extensor margin; propodus with 3 teeth on extensor margin; dactylus with 2 teeth on extensor margin. Pereopods 3 and 4 similar: basis with small marginal teeth; ischium with small tooth on flexor margin; merus with 1 blade-like tooth on extensor margin; carpus with 2 blade-like teeth on extensor margin, small spine on flexor margin; propodus and dactylus as in pereopod 2. Pereopods 5–7 similar: basis with irregular teeth; merus and carpus each with 2 robust setae on conical projection on margin; propodus with 4 robust setae on conical projection on margin; dactylus curved.

Pleopod 1 exopod with oblique groove opening laterally at about 90% of length, opening surrounded by dense setation, most distal part lamellar. Pleopod 2 endopod with tapering simple appendix masculina curving anteriorly, 1.6 times length of endopod.

Uropodal peduncle with 2 longitudinal-oblique rows of tubercles, 3 in row next to suture, 3 larger in midline.

Colour. Pale with small brown lateral spot on each segment of pereon and pleon and pereopodal coxa, 1 or 2 on each pereopodal basis, ischium, merus and carpus, 2 on uropod.

Size (total length). Largest male, 6.7 mm; largest ovigerous female, 10.0 mm.

Distribution. Southeastern coast of Australia and eastern Bass Strait, 32°S – 43°S.

Remarks. The two syntypes are lost ( Springthorpe and Lowry, 1994). Nevertheless, Whitelegge’s (1904) description and his few drawings can be interpreted and reconciled with the abundant available material – the species is unmistakable and common in collections on the shelf of southeastern Australia. Sampling on the NSW shelf has been intensive, especially in the 1970s–1980s and no other antarcturid matches his description. Hale’s (1946) description and more complete illustrations of material from Bass Strait are similarly unmistakable. His habitus drawing is reproduced here. The redescription above is limited to the body armature and to those features important in differentiation of antarcturid genera: antenna, pereopodal dactyli, male pleopods 1 and 2, female sternite 8 and the uropod. Both Whitelegge and Hale illustrated and described ovigerous females. The diagnostic ornamentation can be discerned in a reduced form in specimens of all sizes.

Figures

Figure 1. Halearcturus serrulatus (Whitelegge, 1904). a, female habitus; b, dorsal view of pleotelson. c, d, left male pleopod 1 in anterior and posterior views. e, left male pleopod 2 in posterior view. f, ventral view of coxae and oostegites of pereopods 4, sternum of pereonite 5 [a, b, reproduced from Hale (1946); c–e, NMV J8593; f, NMV J62821].