Birubius nauarchuncus, Horton, 2008

Horton, Tammy, 2008, Amphipoda from marine caves of Hong Kong Island, Journal of Natural History 42 (9 - 12), pp. 825-854 : 841-846

Birubius nauarchuncus sp. nov.

( Figures 8–10 )

Type material

Holotype female, 3.7 mm, NHM Reg. No. 2005.34.

Material examined

Long Kei Wan, control site Z, (21/10/02), unique holotype.

Description

Female, 3.7 mm. Head 16.8% of total body length, rostrum constricted, narrow, exceeding apex of peduncle article 1 of antenna 1. Eyes, large, pigmented. Antenna 1: peduncle article 1 length to width ratio 1:1, twice as wide as article 2, ventral margin with six setules; peduncle article 2 as long as article 1 with four ventral setae; primary flagellum with eight articles, 0.75 times as long as peduncle, lacking aesthetascs; accessory flagellum with seven articles. Antenna 2: peduncle article 4 robust setal formula51-3-4-5 (see Barnard and Drummond 1978); dorsal margin with notch bearing one robust seta and one slender seta; ventral margin with ten slender long and short setae and one ventrodistal robust seta; peduncle article 5 about 0.8 times as long as peduncle article 4, facial robust setal formula50–2, dorsal margin naked, ventral margin with two groups of 1–3 slender setae, three ventrodistal robust setae; flagellum 1.2 times as long as peduncle articles 4 and 5 combined, with nine articles. Mandible: weak palpar hump; left mandible incisor with three teeth; lacinia mobilis with four teeth, six plumose accessory setae; molar a short protrusion with three robust setae; right mandible incisor with two teeth and eight plumose accessory setae; palp article one short, article 2 with one long apical seta and two medium inner setae, article 3, 0.82 times as long as article 2, apex oblique with seven robust to slender setae, without basiofacial setae. Maxilla 1: inner plate, narrow with two long apical plumose setae, two shorter apical simple setae; outer plate with 11 spine teeth; palp article 2 with one apical robust seta and five slender setae; Maxilla 2: inner and outer plates subequal in length; inner plate with five plumose setae and five simple setae; outer plate with six simple setae increasing in size to the apex, and two short subapical setae. Maxilliped: inner plate with one apical robust seta, six medial plumose/simple setae, and one subapical simple seta; outer plate with four apicomedial and medial plumose robust setae, decreasing in size proximally; palp articles 1 and 2 with one apicolateral seta, one lateral simple seta on article 2, and 14 medial simple setae, article 3 subovate, slightly expanded distally, with five medial simple setae, four apicolateral simple setae and two facial setae, article 4 long, about 1.15 times as long as article 3, unguis present, long, about one third of total length. Coxae: coxa 1 strongly expanded distally; coxa 4 tapering distally, rounded posterodistal corner; posteroventral setal formula of coxae 1–456-7-7-5; coxae 5–7 posteroventral setal formula54-2-1. Setal formulae on basis of gnathopods 1–2 and pereopods 3–4; long posteriors51-2-2-2, short posteriors50-0-0-0, long anteriors52-5-0-0, short anteriors51-2-4-0. Gnathopods: carpus of medium length, width ratios of carpuspropodus51:0.75, 1:0.75, length ratios51:1.1, 1:0.95; palmar humps ordinary, palms oblique. Pereopods 3–4: similar; facial setae on merus54 and 3, on carpus54 and 3; main spine of carpus extending to M95 and M88; robust setal formula of propodus56 and 7; acclivity on inner margin of dactyls, weak. Pereopods 5–7: merus-carpus of pereopods 5–6 medium to narrow, facial robust setae rows poorly developed, facial ridge formula on basis50-1-2; width ratios of basis, merus, carpus, propodus of pereopod 5524:25:21:9, of pereopod 6540:25:13:6, of pereopod 7545:15:11:6; length ratios of basis, merus, carpus, propodus of pereopod 5540:20:20:22, of pereopod 6547:30:22:30, of pereopod 7557:16:12:12; pereopod 7 basis reaching apex of carpus. Epimera: epimeron 1, posteroventral corner rounded, anteroventral margin with one plumose seta; epimeron 2 posteroventral corner rounded, with six plumose facial setae, and one simple marginal seta; epimeron 3, posteroventral corner without tooth, posterior margin rounded with two short simple setae, oblique row of four plumose facial setae, ventral margin with two simple setae. Urosomite 1 naked; urosomite 3 with large dorsal hook. Uropod 1, peduncle with two apicolateral robust setae, two basiofacial simple setae, three slender medial setae and one apicomedial enlarged robust seta; outer ramus with two dorsal robust setae, inner with one dorsomedial robust seta; uropod 2, peduncle with five dorsal robust setae; outer ramus with two dorsal robust setae, inner with one robust seta; uropods 1–2, apicolateral corners of peduncles without comb, both rami with articulate enlarged apical ‘‘nails’’. Uropod 3 unreduced, peduncle with three ventral robust setae, two dorsal robust setae; rami feminine, outer ramus longer than peduncle, inner extending to M50 on article 1 of outer ramus, apex with one long seta, medial and lateral margins naked; outer ramus, article 2 short, 0.2 times article 1, with two long plumose setae, apicomedial margin of article 1 with two long plumose setae, lateral margin with four acclivities, robust setal formula51-1-1-1, slender setal fomula51-1-1-0. Telson, length-width ratio51:1, not fully cleft, each apex wide, rounded, lateral acclivity, shallow, bearing a lateral setule, and a single shorter simple seta, two mid-lateral setules, one long and one short.

Male

Unknown.

Remarks

This species closely resembles Birubius wallisae Taylor and Poore, 2001 , from Moreton Bay in Australia (27 ° 029S, 153 ° 209E), but can be easily distinguished from this species by the setation of the uropods and telson. Uropod 1, outer ramus with two dorsal robust setae, uropod 2 peduncle with 5 dorsal robust setae, outer ramus with two robust setae, compared with six, ten and four, respectively for B. wallisae . The telson of Birubius nauarchuncus also differs in having one very small seta and one setule apically and two setules dorsally on each lobe compared to one large robust seta and one setule apically, and one setule dorsally per lobe for B. wallisae . The species is currently placed in Birubius following the work of Taylor and Poore (2001).

Etymology

From the Latin, nauarchus, meaning captain (of a ship) and uncus, meaning hook, in reference not only to the prominent hook on urosomite 1 but also to the pirate theme of the expedition.

Figures

Figure 8. Birubius nauarchuncus sp. nov.

Figure 9. Birubius nauarchuncus sp. nov.

Figure 10. Birubius nauarchuncus sp. nov.