Nyctobadistes hamatus sp. nov.

(Figs 1 – 3)

Material examined. Holotype, male (3.2 mm), off Freycinet Peninsula, Tasmania, Australia, station SLOPE 46, 42°0.20’S, 148°37.70’E, 27 July 1986, WHOI epibenthic sled, 720 m, RV Franklin, coarse shelly sand (NMV J18840). Paratypes, 1 female (5.0 mm), 1 male (3.0 mm), 2 fragments, type locality (NMV J54111). 1 male (3.6 mm), off Freycinet Peninsula, Tasmania, Australia, station SLOPE 45, 42°2.20’S, 148°38.7’E, 27 July 1986, WHOI epibenthic sled, 800 m, RV Franklin, coarse shelly sand (NMV J18839).

Description of male. Body (Fig. 1 A, B) length about 2.4 times pereonite 2; cuticle smooth. Cephalon (Fig. 1 A–D) with 2 dorsal spines, anterolaterally with 4 pairs of smaller spines. Pereonite 1 (Fig. 1 A, B, D) with 8 spines, 3 pairs dorsal and 1 pair anterolateral; pereonites 2–3 with 6 spines; pereonites 4–5 with 4 spines; pereonite 6 with 2 spines; pereonite 7 with 3 spines. Ventrally (Fig. 1 E, F) pereonite 6 with 4 spines, two hook-like; pereonite 7 with two spines. Pleonite 1 (Fig. 1 A) with 1 pair of dorsal spines. Pleon (Fig. 1 A, B, E) length 1.5 times proximal width, posterior end square, with pair of tubercles.

Antenna 1 (Fig. 1 H) of 21 articles; article 1 length 1.4 times width, with 2 RS and 1 distal penicillate seta; article 2 length 1.7 times width, distomesial margin with 1 SS and 1 penicillate seta; article 4 mesial margin with 2 penicillate setae; from article 8 onwards, each article has 1 aesthetasc and many articles with additional SS.

Pereopod 6 (Fig. 2 G) basis length 4.6 times width, inferior margin with 18 SS, lateral surface with 1 SS, superior margin with 3 penicillate seta and 7 SS; ischium length 4.2 times width, inferior margin with 21 SS, superior margin with 5 SS; merus length 1.6 times width, inferior margin with 2 SS, distosuperior margin with 9 SS; carpus length 3.8 times width, inferior margin with 4 SS, lateral surface with 1 SS, superior margin with 1 sensillate RS; propodus length 7.5 times width, inferior margin with 2 SS, distosuperior margin with 3 SS and 1 penicillate seta; dactylus length 8.1 times proximal width, distosuperior margin with 2 SS.

Pereopod 7 (Fig. 3 A) basis length 5.8 times width, inferior margin with 11 SS and 1 RS, superior margin with 1 penicillate seta and 5 SS; ischium length 3.8 times width, inferior margin with 11 SS, lateral surface with 1 SS; merus length 1.5 times width, inferior margin with 7 SS, distosuperior margin with 2 SS; carpus length 4.4 times width, superior margin with 4 SS; propodus length 10.0 times width, distoinferior margin with 1 SS, superior margin with 5 SS (4 in clump at distal end, 1 very long); dactylus length approximately 7.3 times width, superior margin with 3 SS.

Pleopod 1 (Fig. 3 C, D) length 5.3 times proximal width, with 9 SS, 5 RS and distally with 13 SS. Pleopod 2 (Fig. 3 E) protopod length 3.6 times width, lateral margin with 6 SS (proximal half) and row of 9 plumose setae, surface with 16 SS, distally with lamellar extension and few fine SS, mesial margin with 2 plumose setae; exopod length 0.1 times protopod, with fine SS; stylet short, length 0.6 times protopod, not hooking up into proximal part of protopod; sperm duct length 0.5 times stylet.

Description of female. Antenna 1 (Fig. 1 G) of 6 articles; article 1 length 2.1 times width, mesial margin with 1 SS, mesial square-like extension with 3 blunt RS and 1 penicillate seta, surface with 1 penicillate seta, lateral margin with 1 SS; article 2 length 0.4 times article 1 and 2.9 times width, with 2 SS and 1 penicillate seta; article 4 with 2 penicillate setae; terminal article with 2 SS and 1 distal aesthetasc. Antenna 2 (Fig. 1 I) damaged; article 1 triangular, lateral margin with 1 RS; article 2 length 1.7 times article 1, with short spine; article 3 length 2.2 times article 1, scale with 5 SS, distomesial margin with 2 RS and 1 SS; article 4 length 1.5 times article 1, with 1 SS.

Mandible (Fig. 2 A, B) lacinia mobilis reduced, smooth and rounded; spine row damaged on left mandible, right mandible spine row with 4 spines; molar large, distally with 1 SS (on left mandible, absent on right) and 4 biserrate setae; mandibular palp article 1 with 3 SS, article 3 with 3 terminal SS. Maxilla 1 (Fig. 2 C) lateral and mesial margins with fine SS; lateral lobe width 2.1 times mesial lobe, distal margin with few fine SS, 3 RS, 7 pectinate RS and 2 pectinate dentate RS, mesial lobe distally with 5 SS and 2 long pectinate setae. Maxilla 2 (Fig. 2 D) lateral lobe margins with fine SS, distally with 4 long pectinate setae; middle lobe width 1.4 times lateral lobe, distally with 4 long pectinate setae; mesial lobe width 3.4 times lateral lobe, margins and surface with fine SS proximally, mesial margin also with 17 long bi-serrate setae, distally with 5 blunt SS, 5 toothed setae and 1 pectinate setae (broken off). Maxilliped (Fig. 2 E, F) coxa rectangular, length 1.1 times width; basis length 2.9 times width, with 11 SS; endite with 5 coupling hooks, distally with 4 blunt SS, 3 sub-marginal SS, 6 fan setae and many fine SS; palp article 1 rectangular, distolateral margin with 4 SS, distomesial margin with 1 SS; article 2 length 2.8 times article 1, lateral margin with 6 SS, mesial margin with 8 distally pappose setae; article 3 length 1.4 times article 1, lateral margin with 1 SS, surface with 3 SS and 2 distally pappose setae, mesial margin with 16 distally pappose setae; article 4 length 0.7 times article 1, lateral margin with 2 SS, distal margin with 1 SS and 7 distally pappose setae; article 5 narrow, length 0.8 times article 1, with 4 SS and 2 distally pappose setae; epipod length 1.7 times width, margins with cuticular scales, surface with scattered SS.

Pereopod 1 (Fig. 1 J, K) basis length 3.8 times width, inferior margin with 9 sensillate RS and 1 SS, superior margin with 11 SS and 1 penicillate seta; ischium length 2.6 times width, inferior margin with 7 SS, lateral surface with 5 SS, superior margin with 2 RS; merus length equals width, inferior margin with 9 RS, distosuperior margin with 3 SS; carpus length 3.5 times width, inferior margin with 10 RS and 7 SS, superior margin with 1 SS; propodus length 5.7 times width, inferior margin with 7 SS, lateral surface with 2 SS, distosuperior margin with 2 SS; dactylus length 2.7 times proximal width, superior margin with 3 SS.

Operculum (Fig. 3 B) length approximately 2.9 times proximal width, distally with medial excision and veined lamellar extension, medial keel with row of RS and SS, surface with scattered SS, margins anterolaterally with SS, laterally and distally with row of plumose setae. Pleopod 3 (Fig. 3 F) exopod length 1.1 times length of endopod, distally with 7 long plumose setae and 1 distal SS; endopod length 2.0 times as long as wide, with 3 long plumose setae. Pleopod 4 (Fig. 3 G) exopod distally with 3 long plumose setae; endopod length 1.7 times width. Pleopod 5 (Fig. 3 H) length 2.2 times width.

Remarks. See remarks section for genus.

Distribution. Off Freycinet Peninsula, Tasmania, Australia, between the depths of 720–800 metres.

Etymology. Hamatus is a Latin word meaning with hooks; here alluding to the hook like spines on the ventral side of pereonite 6.