Birubius wirakus Barnard & Drummond 1978

Birubius wirakus

DESCRIPTION OF FEMALE.—Head about 21 percent of total body length, greatest width about 66 percent of length; rostrum weakly constricted, broad, not reaching apex of article 2 on antenna 1. Eyes small, weakly occluded with pigment or clear. Article 1 on peduncle of antenna 1 about 1.6 times as long as wide, about 1.7 times as wide as article 2, ventral margin with about 6 setules, weakly produced dorsal apex with two setule-setae; article 2 about 0.9 times as long as article 1, with ventral cycle of 5 setae; primary flagellum with 9 articles, bearing several aesthetascs; accessory flagellum with 7 articles. Spine formula on article 4 of antenna 2 = 2–4–4 or 3–4–4, dorsal margin with notch bearing 2 long and short setae, ventral margin with 3 groups of 2–3 mainly long setae, one ventrodistal long spine; article 5 about 0.75 times as long as article 4, facial spine formula = 1–2, dorsal margin naked, ventral margin with one set of setae, ventrodistally with one medium spine, 2 long spines, one long seta, one setule, subdistal facial spine; flagellum about 1.33 times as long as articles 4–5 of peduncle combined, with 10 articles. Mandibles with weak palpar hump; right incisor with 3 teeth; left incisor with 4 humps in 2 branches; right lacinia mobilis bifid, distal branch much shorter than proximal, distal branch broad, subbifid, proximal branch simple, pointed, with marginal denticles, humps; left lacinia mobilis with 4–5 teeth, middle teeth shortened; right rakers 6–8 plus one or more rudimentaries; left rakers 7–9 plus one or more rudimentaries; molar in form of weak hump demarcated mainly by spines, right molar with 5 primarily long spines plus one short spine strongly disjunct, left molar with 4–5 primarily long spines plus one short spine strongly disjunct (except on holotype), each molar with plume; palp article 1 short, article 2 with one long inner apical seta and 1–2 other short inner setae, article 3 about 1.1 times as long as article 2, oblique apex with 6–8 spine-setae, basofacial formula = 0. Inner plate of maxilla 1 large, bearing one long apical pluseta, one shorter similar apicomedial seta, 2 apicolateral much shorter setae; palp article 2 with 3–4 apicalmedial spines and 3 submarginal setae. Plates of maxilla 2 extending equally, outer slightly broader than inner, outer with 3 apicolateral setae, inner with one medial seta. Inner plate of maxilliped with 2 large thick apical spines, 3 apicofacial setae, 3 medial setae; outer plate with 5–7 medial and apical spines, one apicolateral seta; palp articles 1–2 lacking apicolateral setae, medial margin of article 2 strongly setose, article 3 not protuberant, with 3 facial setae, nail of article 4 long, with 2 accessory setules. Coxa 1 scarcely expanded distally, anterior margin weakly convex, main ventral setae of coxae 1–4 = 5–6–(5–6)–(4–5), posteriormost seta of coxae 1–4 elongate; anterior and posterior margins of coxa 4 almost parallel, posterior margin oblique, almost straight, posterodorsal corner rounded, posterodorsal margin weakly concave, width–length ratio of coxa 4 = 17:20. Long posterior setae on article 2 of gnathopods 1–2 and pereopods 1–2 = 1–2–(0–2)–4, short anteriors = 1–1–1–0, long anteriors = 0–4–0–0, no others. Gnathopods generally ordinary; width ratios of articles 5–6 on gnathopods 1–2 = 25:34 and 27:36, length ratios = 70:65 and 61:64; palmar humps small, palms weakly oblique; article 5 of gnathopod 1 weakly elongate, ovate, posterior margin rounded–flat; article 5 of gnathopod 2 ovate, posterior margin rounded–flat. Pereopods 1–2 similar, facial setae formula on article 4 = (2–4) and (2–3), on article 5 = 3 and 4; main spine of article 5 almost extending to M. 80 on article 6, article 5 with one proximoposterior spine on pereopod 2 (rarely pereopod 1); spine formula of article 6 = 4 + 4, rarely 4 + 5, plus middistal seta, some spines especially long; acclivity on inner margin of dactyls of pereopods 1–2 sharp, produced as tooth, emergent setule very short, almost fully immersed, midfacial pluseta ordinary. Coxae 5–7 posteroventral setule formula = 3–3–3. Articles 4–5 of pereopods 3–4 of ordinary width, facial spine rows moderately developed, facial ridge formula on article 2 of pereopods 3–5 = 0–2–2; width ratios of articles 2, 4, 5, 6 of pereopod 3 = 39:37:34:17, of pereopod 4 = 58:32:22:10, of pereopod 5 = 71:20:19:9, length ratios of pereopod 3 = 64:25:34:34, of pereopod 4 = 71:43:38:50, of pereopod 5 = 80:22:22:25; article 2 of pereopod 5 reaching apex of article 4; medial apex of article 6 weakly scalloped. Posteroventral corner of epimeron 1 narrowly rounded, posterior margin weakly convex, with setule, anteroventral margin with 2–4 short setae, posteroventral face with 1–2 long setae vertically paired; posteroventral corner of epimeron 2 subquadrate, with or without setule, posterior margin almost straight, facial setae = 5–6, occasionally posteriormost pair set vertically; posteroventral corner of epimeron 3 weakly protuberant, with setule sinus, posterior margin almost straight, ventral margin with 2 setae; epimera 1–3 with small to large seta on posterodorsal margin set in weak to strong notch. Urosomite 1 with lateral ventral setule at base of uropod 1, articulation line almost complete; urosomite 3 unprotuberant dorsally. Rami of uropods 1–2 with articulate enlarged apical nails, rami of uropods 1–2 lacking accessory nails, outer ramus of uropod 1 with 3 dorsal spines, inner with 2, outer ramus of uropod 2 with 2 dorsal spines, inner with one dorsomedial spine; peduncle of uropod 1 with 2 apicolateral spines and 2 basofacial setae, medially with 3 marginal spines, apicalmost enlarged; peduncle of uropod 2 with 4 dorsal spines. Peduncle of uropod 3 with 4 ventral spines, dorsally with one lateral spine, one medial spine; rami feminine, inner extending to M. 65 on article 1 of outer ramus, apex with 1–2 short setae, article 2 of outer ramus elongate, 0.31, bearing 2 setae, apicomedial margin of article 1 with one long seta, lateral margin with 3 acclivities, spine formula = 1–1–1–1, setal formula = 0–1–1–1. Telson ordinary, length–width ratio = 1:1, almost fully cleft, each apex wide, rounded, lateral acclivity broad, weak, bearing ordinary lateral setule, spine next medial much longer than setule, midlateral setules diverse. Cuticle with ordinary sparse bulbar setules.

OBSERVATIONS.—Female “n,” 3.76 mm: Epimeron 2 more densely setose than in holotype (see illustration) but following features of weaker development: spine formula of article 4 on antenna 2 (lesser count stated in description), fewer setae on coxae 3–4, on article 4 of pereopod 1, and on inner ramus of uropod 3, setule count on coxae 5–7 = 4–2–2.

DESCRIPTION OF MALE (subadult, male “nn,” 3.93 mm).—Scarcely distinct from female; eyes enlarged, of medium size, darkly pigmented; facial spine formula on article 4 of antenna 2 = 1–3–4–3, on article 5 = 0–2, flagellum with 11 articles, basal article stout and proliferating; disjunct spine on right mandibular molar absent; formula of long setae on coxae 1–4 = 6–6–6–3; length ratios of articles 5–6 on gnathopods 1–2 = 69:72 and 60:69; epimeron 1 with 5 anteroventral setae, posteroventral face with 2 setae in tandem, epimeron 2 with 7 facial setae in tandem, posteriormost pair crowded together; uropod 3 masculine, inner ramus slightly exceeding apex of article 1 on outer ramus, apex with 3 setae, outer ramus with 2 lateral acclivities, setal formula = 1–1–2, spine formula = 1–1–1, medial apex and margin with 2 setae in tandem, peduncle with 5 ventral spines; main spine on each lobe of telson shorter than in female; other characters like female, especially right lacinia mobilis, mandibular palp, antenna 1, dorsal margin of article 4 on antenna 2, pereopods 1–5, epimeron 3, uropods 1–2 except where mentioned, mouthparts other than mandibles not examined.

DESCRIPTION OF JUVENILE (juvenile male “t,” 3.32 mm).—Article 4 of antenna 2 with facial spine formula of 1–3–3–1, article 5 with facial spine formula of 0–2; both pereopods 1–2 with posteroproximal spine on article 5 (unusual); epimeron 1 with 2 anteroventral setae, 2 posterofacial setae in tandem, epimeron 2 with 8 facial setae, epimeron 3 with 2 ventral setae, posterior margin like adult but with 3 setules in tandem just below dorsal seta in crotch; outer ramus of uropod 1 with 2 dorsal spines, of uropod 2 with one dorsal spine, peduncle of uropod 2 with 3 dorsal spines; peduncle of uropod 3 with 4 ventral spines, inner ramus of uropod 3 as long as article 1 of outer ramus, bearing 3 apical setae. Other external features like female; mouthparts not examined.

ILLUSTRATIONS.—Species generally similar to variant-phenotype of Birubius mayamayi (11) (figures 118, 119), and otherwise similar to main phenotype of that species, following illustrations therefore omitted for B. wirakus: lateral head, antennae 1–2, prebuccal mass, upper lip, palpar hump and palp of mandibles, lower lip, maxillae 1–2, maxilliped, urosome, coxae 1–3, cuticle. Following exceptions for B. wirakus noted in description: spine formula on article 5 of antenna 2, basofacial setae of mandibular palp article 3, spines and setae of maxilliped fewer, nail of dactyl of maxilliped more elongate, uropodal spine formulas; view of left mandible heavily flattened, with fourth molar spine and smaller raker spines hidden in view as shown, apex of that molar illustrated separately in 2 views.

Additional specific items not illustrated: midapex on article 1 of antenna 1 with one setule, of article 2 with 3 setules, of article 3 with 4 apical and 2 ventral setules; article 3 of antenna 2 with one long, one short facial setae, proximal facial spine groups on article 4 of antenna 2 with accessory setule, with 2 subbasal penicillate setules on ventral margin, article 5 of antenna 2 much narrower than article 4, dorsodistal apex with several setules; prebuccal complex convex and moderately extended anteriorly, epistome and upper lip amalgamated, anterior margin of upper lip with crescentic rugosity, ventral margin truncate or weakly concave; lower lip with one cone on outer lobe, mandibular lobes rounded apically; outer plate of maxilla 1 with 11 spines, spine 2 broader; outer plate of maxilliped with cusp at base of second apicomedial spine (but absent on one side of holotype); inner ramus of uropod 1 with normal inner basofacial seta; urosomites 1–2 amalgamated but articulation line complete.

HOLOTYPE.—NMV, female, “a,” 4.3 mm.

TYPE-LOCALITY.—CPBS B4/2, 14 Nov 1964, Western Port, Victoria, Australia, 10.7 m, fine sand, mud.

VOUCHER MATERIAL.—PPBES 968/1, female “n,” 3.76 mm (illus.); EBS 32, male “nn,” 3.93 mm; EBS 31, juvenile male “t,” 3.32 mm.

RELATIONSHIP.—This species closely resembles B. mayamayi (11) and is difficult to distinguish except on small characters requiring careful dissection and observation. The main character of easily observable condition is the presence of a stout proximoposterior spine on article 5 of pereopod 2, absent in B. mayamayi. The following characters also distinguish B. wirakus from B. mayamayi: the blunter cornered and squarer coxa 4, more robust pereopod 4, very slightly greater length of article 5 on gnathopod 1 in female, absence of a posterodistal tooth on epimeron 2 in female, longer article 2 on outer ramus of uropod 3, presence of a disjunct spine on molar in female, and proportional differences of articles on pereopods 3 and 5 (see illustrations).

The holotype is a well advanced subadult female, with brood lamellae almost fully grown but naked. Immaturity is marked by poorly developed eyes, paucity of setation, and feeble armament of uropod 3. A small number of subadults and juveniles of B. mayamayi do have a shorter rostrum or a short article 6 of pereopod 4 or both but detailed comparison of B. wirakus with such subadults (of comparable size and development) shows that specimens of B. mayamayi have better developed eyes and more heavily setose appendages. Their mandibles, coxae, gnathopods and pereopods are virtually indistinguishable from those of the terminal adult. They lack a posteroproximal spine on article 5 of pereopod 2, a characteristic of B. wirakus. The inner ramus of uropod 3 is longer and article 2 of the outer ramus is shorter in B. mayamayi.

MATERIAL.—PPBES, 2 samples (2); CPBS, one sample (1); EBS, 2 samples (4).

DISTRIBUTION.—Victoria: Port Phillip Bay and Western Port, 8–11 m, sand. New South Wales: Jervis Bay, Murray's Beach, 6 m, Halophila.