Comprehensive Description
provided by Smithsonian Contributions to Zoology
Metaphoxus yaranellus
DESCRIPTION OF MALE.—Head about 17 percent of total body length, greatest width about 66 percent of length; rostrum reaching middle of article 2 on antenna 1, unconstricted, tapering evenly, apically rounded. Eyes medium to medium-large, eosin in color, clear of occluding pigment, ommatidia ovate or elliptical in small-eyed males, becoming elongate in terminal males. Article 1 on peduncle of antenna 1 about 1.2 times as long as wide, twice as wide as article 2, apicoventral margin poorly setulose, produced dorsal apex with one setule, medial face densely fuzzy, fuzz apparently composed of thick aesthetascs; article 2 about 0.65 times as long as article 1, apicoventral lateral face with 4–5 setae, article 2 slightly overriding article 3 on medial surface; accessory flagellum slightly shorter than primary flagellum, 3-articulate; primary flagellum 4-articulate, bearing one calceolus each on articles 1 or 1–2 and several aesthetascs. Spine formula on article 4 of antenna 2 = 1–2–2–3 or 1–2–2–4, set 3 with one accessory setule, set 4 with 1–3 accessory setules, spines thin, dorsomedial margin densely fuzzy, fuzz composed of thick aesthetascs, proximoventral margin with 2–3 penicillate setules, distally with pair of setae, ventral apex, with spine and 3 setae; article 5 about 0.8 times as long as article 4, facial spine formula = 2, no accessory setule, dorsodistal corner with 2 spine-setae, dorsal margin with 0–1 calceolus and 1–2 groups of male setae, ventrodistal apex with one spine-seta, pair of short setule-spinules, ventral margin with pair of setules; flagellum elongate, flagellar formula = (15–17), 1, 2, 4, 6, 8 only or 1, 3, 5 only or 1, 3, 5…15 (from 9 onward calceoli rudimentary), or 1, 2, 3, 5 only, or article 2 only. Prebuccal complex convex anteriorly, poorly extended forward, epistome and upper lip mostly fused together, ventral margin of upper lip weakly bisinuate. Palpar hump of mandible medium, broad; right incisor basically tridentate, with fourth tooth adjacent to tooth 2; left basically bidentate, distal branch strongly tri- or quadridentate; right lacinia mobilis flabellate, proximal branch distinct from serrate distal branch, face naked; left lacinia mobilis flabellate, 5-toothed; right rakers 3 plus 1–3 rudimentaries; left rakers 3 plus one rudimentary; molar conical, setulose; palp article 2 with inner subbasal setule and 2–3 subapical long setae, article 3 about 0.65 times as long as article 2, oblique apex with 8 setae. Each outer lobe of lower lip with cone, mandibular lobes long, weakly attenuate and apically rounded, inner lobes cleft about one-third. Inner plate of maxilla 1 of medium size, ovate, bearing one apicomedial setule; outer plate with 7 spines; palp slightly exceeding apex of outer plate, bearing 2 apical and one apicolateral setae, occasionally a fourth apicomedial seta. Inner plate of maxilla 2 slightly broader and much shorter than outer plate; medial margin of inner plate with one disjunct medial seta plus 5–7 other apicad setae of which one very stout; outer plate with 2 apicolateral, 6 apical and 2 medial setae. Inner plate of maxilliped with one mediofacial spine, one apicomedial spine, and 2–3 apical spines; outer plate with 3 apicomedial spines, one elongate basomedial spine; article 2 of palp with sparse, stout medial setal-spines, article 3 lacking facial setae, article 4 long, apical spine of medium length, bearing 2 accessory setules, first setule elongate. Coxa 1 scarcely expanded; long setal formula of coxae 1–4 = (2–5)–(4–5)–(3–5)–(0), each with tiny additional posteroventral setule; coxa 4 quadratiform, posterodorsal excavation medium–small, V-shaped, posterodorsal corner rounded, ratio of width to length = 7:9. Gnathopod 2 stouter and longer than gnathopod 1; long posterior setae on article 2 of gnathopods 1–2 = 1 and 1; article 5 small and triangular; article 6 elongate, twice as long as wide, palm weakly oblique, defining hump medium to large, defining spine large, dactyl fitting palm, apex of dactyl with flake, posterior margin of article 6 with 1–2 setae; length ratios of articles 5–6 on gnathopods 1–2 = 48:87 and 46:98, width ratios = 24:47 and 26:54. Pereopods 1–2 similar to each other; long posterior setae on article 2 of pereopods 1–2 = 2 and 2; article 4 with one long apicoanterior seta, no apicofacial setae, posterior margin with sets of 3 and 2 setae on pereopod 1, 4 and 3 on pereopod 2; article 5 with one apicofacial seta, long posterodistal spine reaching M. 80 on article 6, with small contiguous spinule at base; article 6 bearing one posterior seta and apical sets of 3 and 2 spines of medium length; dactyl with apical immersed nail, appearing to have apicofacial meatus, thin inner setule on weak acclivity, inner margin and lateral face bearing minute rows of nodules. Coxae 5–7 posteroventral setule formula = 1–4–4. Articles 4–5 of pereopods 3–4 thin, facial spines absent, pereopods 4–5 with one anterior facial ridge; width ratios of articles 2, 4, 5, 6 of pereopod 3 = 48:24:18:8, of pereopod 4 = 72:25:17:9, of pereopod 5 = 110:20:15:7, length ratios of pereopod 3 = 68:27:29:32, of pereopod 4 = 91:49:46:42, of pereopod 5 = 128:28:28:16; article 2 of pereopod 5 especially large, reaching middle of article 5, posterior margin with small setule acclivities, ventral margin with weak setule scallops; apex of article 6 finely combed. Epimeron 1 with facial ridge, absent on epimeron 2 (illustration showing ventral margin of next instar), each with rounded posteroventral corner and weakly convex posterior margin bearing 2 setules, epimeron 3 with deeply convex and notched posterior margin, posteroventral corner with setule notch, epimeron 2 with 2–4 facial setae in horizontal tandem. Urosomite 1 bearing one setal spine midventrally on each side. Peduncle of uropod 1 naked basofacially, lateral apex with one medium spine, medial apex with longer spine, medial margin with 1–2 additional spines, rami of uropods 1–2 naked dorsally, apices grossly naked and apparently lacking immersed nail (probably fully absorbed), inner rami often with apical flake, outer rami rarely so, inner ramus of uropod 1 with small mediobasal setule-spinule, rami of uropod 1 extending equally, peduncle of uropod 2 with 2 dorsal spines, medial apex with one spine, apex of peduncle on uropods 1–2 with lateral comb. Uropod 3 elongate, inner ramus strongly setose medially but not fully elongate (not fully adult), peduncle with 4–5 ventrolateral spines, medially with short spine and longer seta, dorsolaterally with setule, inner ramus extending to M. 75 on article 1 of outer ramus, apex with one long seta, one setule, article 2 of outer ramus elongate, 0.50, bearing 2 minute apical setules, lateral margin of article 1 with 3 acclivities; seta formula = 1(short)–1–1–1, spine formula = 0–1–1–1 (variable, setae = 1–1–1–0, spines = 0–1–1–2, or setae = 1–1–1–1 and spines = 0–1–1–2), medial apex with one spine, one seta. Telson highly elongae, length–width ratio about 7:4, apices tapering, narrow, apically truncate, bearing one short spine in middle of apex and one apicomedial setule, dorsal pair of plusetules alike, near middle of each lobe close to base, dorsal cuticle of telson covered with fuzz except for basal triangle bearing chisel shaped denticles in subcircular group, other stout setules distally. Cuticle covered with fuzz easily visible under medium and low power microscopy and scattered bulbar setules.
VARIATIONS.—Apical flakes on rami of uropods 1–2 variable in occurrence, usually borne only on inner rami, often absent, very rarely on outer rami; male “b” with apicomedial spine position on peduncle of uropod 1 bearing pair of spines; only males “a” (holotype) and “d” with oddly elongate ommatidia.
ILLUSTRATIONS.—Head of holotype slightly flattened laterally; holotype telson shown flattened, telson of male “n” shown flattened; body and appendages including uropods and telson almost fully covered with cuticular fuzz but, in those illustrations showing fuzz, only highlights actually depicted, except for naked triangle on base of telson.
HOLOTYPE.—AM, male “a,” 2.54 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 “b,” 2.61 mm; male “n,” 2.63 mm (illus.); male “d,” 2.40 mm; and male “e,” 2.41 mm. Female unknown.
RELATIONSHIP.—This species differs from Metaphoxus tuckatuck in the unshortened outer ramus of uropod 1, the very narrow coxa 4, fuzzy cuticle, enlarged article 2 of pereopod 5, elongate telson with apical setule on medial side of main spine, the greater spinosity on the lateral face of article 4 on antenna 2, the poorly expanded coxa 1 and the shapes of gnathopods 1–2.
Metaphoxus yaranellus bears the vaguest resemblance to M. frequens J. L. Barnard, 1960, from the northern hemisphere, but differs in numerous characters involving gnathopod 2, epimeron 3, mouthparts, telson, coxae, uropods, and pereopod 5.
MATERIAL.—AM, one sample (5).
DISTRIBUTION.—South Australia, Kangaroo Island, neritic.
