Mallacoota sirius, Hughes, 2011

HUGHES, L. E., 2011, New species of Hoho, Mallacoota and Parelasmopus (Maeridae: Amphipoda) from Australian waters, Zootaxa 2955 (1), pp. 1-79 : 62-65

Mallacoota sirius sp. nov.

(Figs 40, 41)

Type material. Holotype: male, 6.2 mm, dissected, 4 slides, AM P.85250, Swiss Cheese Reef, near Kingston wharf (29°00'22"S 167°56'50"E), 14 m, overhang, sponges, encrusting algae, 15 May 2008, coll. J.K. Lowry, MV Jenny (MI NFK 38 ).

Type locality. ‘ Swiss Cheese Reef’ dive site, near Kingston wharf, Norfolk Island, Tasman Sea (29°00'22"S 167°56'50"E) .

Etymology. Named from the HMAS Sirius which was wrecked on the reef from which this species is described.

Description. Based on holotype, male, 6.2 mm, AM P.85250.

Head. Eyes ovate; lateral cephalic lobe broad, rounded, anteroventral margin with notch/slit. Antenna 1 longer than antenna 2; peduncular article 1 subequal in length to article 2, with 3 robust setae along posterior margin; article 2 longer than article 3; flagellum articles longer than broad, with 19+ articles; accessory flagellum minute, with 3 articles. Antenna 2 peduncular article 2 cone gland reaching at least to end of peduncular article 3; article 4 length than article 5; flagellum with 8 articles. Maxilla 1 inner plate subtriangular, with 2 apical plumose setae. Lower lip outer lobes with two pair of ducts, mandibular lobes apically rounded. Mandible accessory setal row well developed with 3 setae; molar well developed, triturative; mandibular palp well developed, 3-articulate; article 1 three times as long as broad, longer than article 2; article 2 subequal to article 3, without setae; article 3 rectolinear, long (4 times as long as broad), shorter than article 1, with 2 apical setae.

Pereon. Gnathopod 1 coxa anterior margin concave, anteroventral corner slightly produced, rounded; carpus about twice as long as broad, subequal in length to propodus; propodus medial surface with comb, palm acute, straight, entire, defined by posterodistal corner, with 1 robust setae. Gnathopod 2 subchelate; basis slender, antero- and propodus; propodus expanded, with sparse slender long seta along medial surface, palm straight, smooth, about half length of propodus, subrectangular distomedial shelf, with 7 robust setae on shelf, palm with 1 subacute tooth, defined by posteroventral tooth, without posterodistal robust setae, subpalmar surface smooth; dactylus without posteroproximal shelf, apically subacute, closing along palm. Pereopod 4 coxa posteroventral lobe well developed, with subrectangular posteromedial corner. Pereopods 5–7 slender distally; basis posterior margin minutely castelloserrate, without long slender setae; merus and carpus not broadened; propodus with few long, slender setae along posterior margin, not expanded posterodistally; dactylar ungues simple. Pereopod 5 unknown. Pereopod 6 basis posterior margin straight, posteroventral corner broadly rounded. Pereopod 7 basis posterior margin convex, posteroventral corner broadly rounded. Pereonite 7 without carina.

Pleon. Pleonites 1–3 without carina. Epimera 1–2 posteroventral corner with small acute tooth. Epimeron 3 ventral margin smooth, posteroventral margin smooth, posteroventral corner subquadrate. Urosomite 1 bicarinate, subtriangular. Urosomites 2–3 without carina. Uropod 1 peduncle with 1 basofacial seta; outer ramus slightly shorter than inner ramus. Uropod 2 outer ramus slightly shorter than inner ramus. Uropod 3 rami distally truncated; inner ramus short (length 2.1 times breadth), shorter than outer ramus; outer ramus longer than peduncle. Telson deeply cleft, broader than long, tapering distally, apical margins concave, with 3 long and 1 short apical robust setae.

Remarks. Mallacoota sirius sp. nov. is most similar to M. caerulea from Mauritius, in which the gnathopod 2 basis is slender and the propodus palm has a single distal tooth. The relatively plain male gnathopod 2 propodus is also found in M. latibrachium from Madagascar, the Maldives and the Gulf of Mannar, M. latibrachoides from Gulf of Mannar, and M. odontoplax , from Suluwesi, however the later three species have a broad basis and no palmar teeth. Mallacoota caerulea also has heavily setose coxae 1–4 ventral margins and uniform short robust setae on pereopods 5–7. The coxae 1 to 4 of M. Sirius s p. nov. have few setae while in M. caerulea the ventral margins of the coxae are lined with many long slender setae.

Distribution. Norfolk Island. Kingston Wharf (current study).