Rhinoecetes caetus, 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 : 117-120

Rhinoecetes caetus sp. nov.

Figures 11–12

Type fixation. Holotype, ♂, here designated.

Etymology. The epithet is Latin for shark. It refers to the type location in Shark Bay

Material examined. Holotype, ♂, 3.1 mm, Monkey Mia, Shark Bay , Western Australia, 25°48’S 113°43’E, 1.5 m ( HW), silty sand with fine and coarse detritus, hand dredge, J. Just, 18 March 1984, stn AU12, WAM C73442.

Paratypes (about 100). Same sample as holotype, WAM C73443, (10 specimens and abodes). Same sample as holotype, NHMD-233139, (6 specimens) . Monkey Mia , Shark Bay, Western Australia, Australia, 25°48’S 113°43’E, 1.5 m ( HW), silty sand with much fine and coarse detritus, hand dredge, J. Just, 19 March 1984, stn AU14, WAM C73444, (5 specimens, 12 abodes) . Monkey Mia , Shark Bay, Western Australia, Australia, 25°48’S 113°43’E, 1.5m ( HW), silty sand with much fine and coarse detritus, hand dredge. J. Just, 19 March 1984, stn AU15, WAM C73445, (4 specimens, 2 of which in abodes) . Denham , Shark Bay, Western Australia, Australia, 25°56’S 113°32’E, ca. 200 m off shore, 1.5 m ( HW), sand and foraminiferans with some detritus, scattered sea grass, hand dredge, J. Just, 20 March 1984, stn AU16, WAM C73446 (ca. 90 specimens) . Denham , Shark Bay, Western Australia, Australia, 25°56’S 113°32’E, ca. 100 m off shore, 1.5 m ( HW), sand and foraminiferans with some detritus, hand dredge. J. Just, 20 March 1984, stn AU17, WAM C73447 (66 specimens + abodes) . Denham , Shark Bay, Western Australia, Australia, 25°56’S 113°32’E, ca. 50 m off shore, 0.75 m ( HW), sand and foraminiferans with scattered Penicillum and some detritus, hand dredge. J. Just, 20 March 1984, stn AU18, WAM C73448 (6 specimens + abodes) . Denham, Shark Bay , Western Australia, Australia, 25°56’S 113°32’E, near head of jetty (east side), along edge of dense Posidonia bed, 2 m ( HW), sand, foraminiferans, detritus, hand dredge. J. Just, 21 March 1984, stn AU19, WAM C73449 (45 specimens + abodes). Denham, Shark Bay, Western Australia, Australia, 25°56’S 113°32’E, ca. 200 m off shore, 1.5 m ( HW), sand and foraminiferans with some detritus, scattered sea grass, hand dredge, J. Just, 20 March 1984, stn AU16, NHMD-233145 (6 specimens) .

Description (♂). Head as long as pereonites 1 and 2 combined along dorsal midline; mid-anterior depression moderately deep, encompassing approximately 0.5 head length. Rostrum downward curved, acutely pointed, in dorsal view reaching beyond apices of eye lobes with about 0.6 of its length. Eye lobes broadly rounded in lateral view, lower distal margin with 1–2 simple setae.

Antenna 1 approximately as long as head and pereonites 1–4 and half of 5 combined, reaching to proximal 0.25 of antenna 2 peduncle article 5; flagellum of 6+ articles, as long as peduncle articles 2 and 3 combined, peduncle article 1 medial margin without proximal bulge. Antenna 2 approximately as long as head, pereonites 1–7 and pleonite 1 combined; ventral projection of peduncle article 2 approximately as long as broad at base, with broadly rounded apex, with a few short and long simple setae apically and laterally; peduncle articles 4–5 with dorsal, ventral and lateral groups of simple setae, more densely on 5; article 5 length 0.9 of article 4; flagellum articles 1 and 2 with many slender robust setae.

Mouthparts, mandible palp article 1 with 2 groups of mid-ventral setae and about 4 apical setae.

Gnathopod 1 propodus length 3.2 width, with 2 mid-posterior robust setae. Gnathopod 2 propodus length 1.7 greatest width. Pereopods 3–4 basis with several long and a few short setae along anterior margin, a few long setae in distal half of posterior margin; merus with mid-anterior and anterodistal long setae, posterior margin with 4–5 groups of unequally long setae. Pereopods 5–6 basis anterior margin with 4 groups of long setae in distal half, posterior margin with a few short setae.

Uropod 1 peduncle dorsolaterally with 2 slender robust setae, a few simple seta, and tuft of setae distally, some of which are specialised robust setae with bifid tip; ventral apical margin with half dentate half fimbriate corona; outer ramus approximately 0.65 dorsal length of peduncle, lateral margin with 2 robust setae (occasionally 3 in large specimens); inner ramus straight, slender, 0.7 length of outer ramus. Uropod 2 peduncle approximately half length of peduncle of uropod 1, with finely fimbriate corona; ramus 0.5 length of peduncle, 0.47–0.5 length of uropod 1 inner ramus, barely reaching apex of uropod 3 ramus. Uropod 3 peduncle with rounded median projection carrying a few simple setae apically; ramus with 3–4 long simple setae. Telson width approximately 1.35 length, apex evenly convex.

Female. Generally as male. Rostral curvature increasing with size (both sexes). Pereonite 7 ventrally with very short, forward pointing sternal papillae ( Fig. 12 Fsp). Ovigerous females with up to 5 eggs.

Size. Largest ♂, 4.9 mm; largest ♀, 3.4 mm.

Colour. Antennae transparent colourless except for faint white bands. Head and body light sandy mottled with brown entrails shining through in patches. Mandible palps, pereopods and urosome colourless semitransparent. Abodes were nearly all microprosobranch shells. Abode aggregates including 1 ♂ and 2 ♀ observed.

Distribution. Western Australia, Shark Bay, 0.75–2.0 m.

Remarks. Rhinoecetes caetus shares with R. setosus sp. nov. (below) uropod 1 peduncle with 2–3 robust setae and the ventral corona with small denticles, but differs from that species primarily by its curved rostrum, its much less setose antenna 2 and the ramus of uropod 2 not reaching beyond the ramus of uropod 3 as opposed to the latter species.

Figures

FIGURE 11. Rhinoecetes caetus sp. nov. Holotype, ♂, except F1, ♀, paratype, 3.4 mm, and F2, ♀, paratype, ovigerous, 2.7 mm. a2 flag, antenna 2 flagellum; cdv, cephalon dorsal view; clv, cephalon lateral view; md plp, mandible palp; vp, ventral projection of article 2 of antenna 2. Scale for habitus and F2: 1 mm.

FIGURE 12. Rhinoecetes caetus sp. nov. Holotype, ♂, except F, ♀, paratype. gp1, gnathopod 1; gp2, gnathopod 2; p4, pereopod 4; p6, pereopod 6; up 1–3 enl, uropods 1 to 3 enlarged; up ped vv, uropods 1 and 2 peduncles, ventral apical margin; us, urosome; sp, sternal papilla (right oblique lateral view); 6 and 7, pereonites 6 and 7.