Borneoecetes minimus, Just, 2019

Just, Jean, 2019, Siphonoecetini Just, 1983 (Crustacea, Amphipoda, Ischyroceridae) 13: Western Australian species of Bubocorophiina in Rhinoecetes, Cephaloecetes, Sinoecetes, Borneoecetes and Pararhinoecetes gen. nov., Zootaxa 4554 (1), pp. 101-140 : 129-131

Borneoecetes minimus sp. nov.

Figures 19–20

Type fixation. Holotype, ♀, here designated.

Etymology. The epithet indicates that this is a very small and fragile species.

Material. Holotype, ♀, 3.4 mm. North West Shelf , off Port Hedland, 19°30’S 118°52’E, 39 m, grab, CSIRO RV Soela, 28 June 1983, stn 03/83/G/B8, WAM C73455.

Paratypes (all: Western Australia, CSIRO, RV Soela, North West Shelf , between Dampier and Port Hedland). 19°05’S 118°51’E, 82 m, grab, 29 June 1983, stn 03/83/B5,G,R13, WAM C73456 (1 specimen). 19°04’S 118° 47’E, 84 m, grab, 29 June 1983, stn 03/83/B6/G, WAM C73457 (1) . 19°31’S 118°49’E, 39 m, grab, 28 June 1983, stn 03/83/B7/G, WAM C73458 (1♀) . 19°30’S 118°52’E, 39 m, grab, 28 June 1983, stn 03/83/G/B8, NHMD 284964 (1♀) . 19°05’S 118°47’E, 81 m, grab, 30 June 1983, stn 03/83/B10/G, WAM C73460 (1♂). Stn 05/83/B7/G, WAM C73461 (1).

Description (♀). Head as long as pereonites 1 and 2 combined along dorsal midline; mid-anterior depression shallow, encompassing approximately 0.3 head length; in dorsal view slender, base of antenna 2 not visible laterally. Rostrum slightly down curved, acutely pointed, in dorsal view reaching beyond apices of eye lobes with about half length. Eye lobes in dorsal view tapering to blunt apex, in lateral view rounded truncate, lower distal margin with 1 simple seta.

Antenna 1 approximately as long as head and pereonites 1–4 and half of 5 combined, reaching to apex of article 4 of antenna 2 peduncle; flagellum of 6+ articles, as long as peduncle articles 2–3 and half of 3 combined. Antenna 2 approximately as long as head, pereonites, 1–7 and pleonites 1–3 combined; ventral projection of peduncle article 2 approximately one third longer than broad at base, slightly tapering to rounded apex, with short fringe of long simple setae laterally and apically; peduncle articles 4–5 with scattered groups of short simple setae; articles 4 and 5 of equal length; flagellum articles 1 and 2 with 4–5 slender robust setae.

Mouthparts. Mandible palp article 1 with 3 midventral, 2 distoventral and a couple of medial long setae; vestigial article with long seta inserted medioapically.

Gnathopod 1 propodus length 3.0 width, with 2 mid-posterior robust setae. Gnathopod 2 propodus length 1.6 greatest width, posterior margin straight distal to robust setae. Pereopods 3–4 basis with about 5 long setae along middle of anterior margin, merus with anterodistal tuft of a few long setae, posterior margin with scattered unequally long setae. Pereopods 5–6 basis anterodistal margin with group of unequally long setae. Sternal papillae not observed.

Uropod 1 peduncle dorsolaterally with 4 robust setae, medial margin with 2 robust setae, with tuft of simple setae distally, ventral apical margin with finely fimbriate corona; outer ramus approximately 0.5 length of peduncle, dorsolaterally with 3 robust setae, with simple setae dorsally; inner ramus 0.7 length of outer ramus, straight, dorsomedially with single robust seta at base of terminal seta. Uropod 2 peduncle approximately 0.4 length of peduncle of uropod 1, with 1 or 2 simple setae; ramus about 0.3 length of peduncle, with single robust seta at base of apical robust seta and a few dorsal simple setae, reaching beyond uropod 3 ramus with about 0.5 of its length. Uropod 3 ramus with 4–5 unequally long simple setae. Telson width approximately 1.6 length, apex straight (not illustrated in dorsal view).

Male. The single small male is similar to female except uropods with fewer robust setae.

Size. Only known ♂, 2.4 mm; largest ♀, 3.4 mm; (1 ♀ of 2.4 mm with fully developed oostegites).

Colour and biology. No observations.

Distribution. Western Australia, North West Shelf, 39– 84 m.

Remarks. Borneoecetes minimus sp. nov. differs from the only known congener B. wongi (in parentheses) as follows: rostrum longer and eyelobes longer and apically truncate (short rostrum and very short, broad and rounded eyelobes); setae on the mandible palp are much longer, and article 2 is at the center of article 1; gnathopod 2 propodus nearly oval, cutting edge almost straight (more elongate, cutting edge concave); uropod 1 peduncle with dorsolateral and mediolateral robust setae (simple setae only dorsally).

Figures

FIGURE 19. Borneoecetes minimus sp. nov. Holotype, ♀. a2 flag, antenna 2 flagellum; cdv, cephalon dorsal view; md palp, mandible palp; mx1 plp, maxilla 1 palp; rlv, rostrum right lateral view; us, urosome; vp, antenna 2 article 2 ventral projection. Habitus scale: 1 mm.

FIGURE 20. Borneoecetes minimus sp. nov. Holotype, ♀. gp1 and 2, gnathopods 1 and 2; p4 and 6, pereopods 4 and 6.