Comprehensive Description

provided by Smithsonian Contributions to Zoology
Birubius gallangus

DESCRIPTION OF MALE.—Head about 15 percent of total body length, greatest width about 70 percent of length; rostrum constricted, short, apex narrow, reaching almost to middle of article 2 on antenna 1. Eyes medium, clear of opaque pigment, but eosin colored. Article 1 on peduncle of antenna 1 about 0.90 times as long as wide, about 2.5 times as wide as article 2, ventral margin with about 12 setules, weakly produced dorsal apex with 2–3 setules, medial face with patch of fuzz; article 2 about as long as article 1, with ventral cycle of 4 setae; primary flagellum with 9 articles, about 0.85 times as long as peduncle, bearing one calceolus each on articles 1–4, no aesthetascs; accessory flagellum with 6 articles. Spine formula on article 4 of antenna 2 = 3–4–3, dorsomedial margin fuzzy, ventral margin with 3 groups of 2 medium setae, one ventrodistal medium spine; article 5 about 0.9 times as long as article 4, facial spine formula = 2, dorsal margin bearing 3 sets of male setae and 2 calceoli, ventral margin with 2 sets of 1–2 short to medium setae, 2 ventrodistal spines and setule; flagellum elongate, flagellar formula = (23–24), 1–3, 5, 7,…23 or 2–4, 6, 8…20. Mandibles with strong palpar hump; right incisor with 3 teeth and accessory notch; left incisor with 4 humps in 2 branches; right lacinia mobilis bifid, distal branch much shorter than proximal, weakly expanded but pointed, proximal branch simple, pointed, with marginal denticles; left lacinia mobilis with 4 teeth; right rakers 5–7, plus rudimentaries; left rakers 6–7 plus 0–1 rudimentary; molar in form of elongate plaque, right and left molars with 5–6 primarily long spines plus one short spine strongly disjunct; palp article 1 slightly elongate, article 2 with one long inner apical seta and 2 other shorter inner setae, article 3 about 0.9 times as long as article 2, oblique apex with 6 spine-setae, basofacial formula = 0–1. Inner plate of maxilla 1 ordinary, bearing one long apical pluseta, one similar medial seta, 2–3 apicolateral much shorter setae; palp article 2 with 4 apicalmedial marginal spines and 3 submarginal setae. Plates of maxilla 2 extending equally, outer slightly narrower than inner, with 3 apicolateral setae, inner with 2 medial setae. Inner plate of maxilliped with one short apical spine set in middle (unusual), 5 mostly apicofacial setae; outer plate with 4 medial and apical spines, no apicolateral setae; palp articles 1–2 each with apicolateral seta, medial margin of article 2 moderately setose, article 3 protuberant, with 2 facial setae, one lateral seta, nail of article 4 medium, with 2 accessory setules. Coxa 1 expanded distally, anterior margin almost straight; main ventral setae of coxae 1–4 = 6–6–3–0 and 0–(1–3)–(1–3)–1 rudimentaries, posteriormost seta of coxae 1–2 shortened; anterior and posterior margins of coxa 4 divergent, posterior margin almost straight, posterodorsal corner subsharp, posterodorsal margin long, weakly concave, width-length ratio of coxa 4 = 17:19. Long posterior setae on article 2 of gnathopods 1–2 and pereopods 1–2 = 1–2–3–3, others not noted. Gnathopods ordinary; width ratios of articles 5–6 on gnathopods 1–2 = 28:36 and 28:39, length ratios = 72:75 and 66:65; palmar humps ordinary, palms oblique; article 5 of gnathopod 1 elongate, ovate, posterior margin rounded-flat; article 5 of gnathopod 2 elongate, ovate, posterior margin rounded. Pereopods 1–2 similar, facial setae formula on article 4 = 4 and 4, on article 5 = 4 and 4; main spine of article 5 extending to M. 100 on article 6, article 5 with one proximoposterior spine; spine formula of article 6 = 3 + 3 plus middistal seta; acclivity on inner margin of dactyls of pereopods 1–2 weak, obsolescent, emergent setule long, midfacial pluseta highly distad. Coxae 5–7 posteroventral setule formula = 1–1–1. Articles 4–5 of pereopods 3–4 of ordinary width, facial spine rows sparse, facial ridge formula on article 2 of pereopods 3–5 = 1–2–2, width ratios of articles 2, 4, 5, 6 of pereopod 3 = 47:38:34:16, of pereopod 4 = 61:38:27:11, of pereopod 5 = 80:20:17:8, length ratios of pereopod 3 = 72:24: 35:40, of pereopod 4 = 80:42:39:46, of pereopod 5 = 107=27:24:23; article 2 of pereopod 5 almost reaching apex of article 4; medial apex of article 6 bearing digital processes. Posteroventral corner of epimeron 1 rounded, posterior margin deeply convex, anteroventral margin with 3 long setae, posteroventral face with 3 long setae; posteroventral corner of epimeron 2 rounded-quadrate, posterior margin strongly convex, facial setae = 6–7 crowded anteriorly; posteroventral corner of epimeron 3 with small-medium upturned tooth with setule sinus, posterior margin convex, with 1–2 setule notches, posteroventral face with 1–2 setae; epimera 1–3 with small setule on posterodorsal margin set in weak notch. Urosomite 1 with ventrolateral setule at base of uropod I, articulation line complete; urosomite 3 weakly protuberant dorsally. Rami of uropods 1–2 with articulate enlarged apical nails, inner ramus of uropod 1 with one accessory nail, outer ramus of uropod 1 with 2–3 dorsal spines, inner with one, outer ramus of uropod 2 with 1–2 dorsal spines, inner with one dorsomedial spine; peduncle of uropod 1 with 3 apicolateral spines, basofacial setae absent, medially with 0–1 marginal enlarged spine; peduncle of uropod 2 with 7–8 dorsal spines, medially with one medium apical spine. Peduncle of uropod 3 with 4 ventral spines, dorsally with one lateral spine, one medial spine; rami masculine, inner extending to M. 110 on article 1 of outer ramus, apex with 2 setae, medial and lateral margins setose, article 2 of outer ramus short, 0.13, bearing 2 long setae, medial margin of article 1 setose, lateral margin with 4 acclivities, spine formula = 1–1–2–2–2, setal formula = 1–1–1–1–1. Telson elongate, length-width ratio = 7:5, fully cleft, each apex protrusive, rounded, lateral acclivity deep, bearing ordinary lateral setule, spine next medial slightly shorter than setule, midlateral setules scarcely diverse, each lobe with dorsal row of denticles. Cuticle with very sparse ordinary bulbar setules.

VARIATIONS.—Head of male “q” with almost blunt, poorly protuberant preocular corner (see illustration); male “y” lacking distal branch on right lacinia mobilis (see illustration), left lacinia mobilis only trifid; left lacinia mobilis of male “n” poorly 4-dentate; male “q” with spine formula on article 4 of antenna 2 = 3–5–3 (otherwise males with 3–4–3), 4 apicolateral spines on peduncle of uropod 1, outer ramus of uropod 2 with 2 spines in 3 specimens, facial setae of epimeron 2 arranged in zigzag fashion.

ILLUSTRATIONS.—Dorsal view of head of male “y” bearing only outline of eyes; palp of maxilla 1 as illustrated, not flattened, and normal basal cusp proximal to palp not shown; setule on coxa 6 and epimeron 2 missing.

HOLOTYPE.—AM, male “a,” 3.26 mm.

TYPE-LOCALITY.—AM P.18125, 12 Dec 1939, Antechamber Bay, Kangaroo Island, South Australia, with light in net at night.

VOUCHER MATERIAL.—Type-locality: male “n,” 3.14 mm (illus.); male “q,” 3.50 mm (illus); male “y,” 3.11 mm (illus.); male “e,” 3.34 mm. Female unknown.

RELATIONSHIP.—Birubius gallangus fits Key B of Birubius in the simplicity of the distal branch on the right lacinia mobilis, but the presence of an accessory apical nail on uropod 1 suggests affinity with species 1–9 in Key A in which the distal branch of the right lacinia mobilis is complex and uropod 1 bears accessory nails. See remarks with B. lorus (2).

This species appears to have more characters in common with B. muldarpus (9) than any other species but differs from B. muldarpus in the reduced setation on epimeron 3, crowded setae on epimeron 2, different positions and lengths of facial ridges on pereopod 5, presence of a ridge on pereopod 3, shorter rostrum and no true apical spine on the inner plate of the maxilliped.

Birubius gallangus might have a point of origin near B. panamunus (1) and B. cartoo (7) but differs in the small tooth and poor setation of epimeron 3, and the narrower rostrum. Birubius gallangus differs from the greater B. myallus-B. kareus (4–5) group in the reduced setation and sharper tooth of epimeron 3.

DISTRIBUTION.—South Australia, Kangaroo Island, Antechamber Bay, neritic.