Paradexamine fissicauda Chevreux 1906

Paradexamine fissicauda Chevreux, Phenotype B, Antarctica

DESCRIPTION (of female, 19.2 mm, AH 5-30). — Lateral cephalic lobe rounded-truncate anteriorly, head with weak anteroventral definition at base of antenna 2, rostrum short, blunt; article 1 of antenna 1 with 4 pairs of spines in tandem, or with 5 sets of 2-2-2-1-3, apex above terminal spine with small tooth, article 2 about equal in length to article J, apically simple and with 3 sets of ventral spines, flagellum about 2.2 times as long as peduncle; flagellum of antenna 2 about 1.3 times as long as peduncle, multiarticulate; mandibles bearing 2 medium spines on right, 3 on left, molars scarcely triturative, each molar with ordinary setae and ragged setae, ordinary setae of left slightly weaker than those on right; accessory bulges slightly sharpened; outer lobe of lower lip bearing weak accessory lobe, with 1 medium cone and 1 vestigial cone or 3 vestigial cones, mandibular lobes blunt, rounded; inner plate of maxilla 1 of normal size, bearing about 4 setae, palp exceeding outer plate, broad, medially and apically setose, apical cones vestigial; inner plate of maxilla 2 narrower than outer, reaching nearly 80 percent along outer, lobes appressed, outer scarcely curved, inner with weak apical truncation, both lobes with submarginal facial setae; inner plate of maxilliped large, broad, highly setose, outer plate ordinary, spines essentially simple, palp slightly exceeding outer plate, claw short; coxa 1 evenly wide along its full length, bearing only 3 marginal setae, 1 anterior, 2 ventral, 1 thick posterior seta and 1 thin posterior seta, coxa 2 with 1 ventral seta, posterior margin with stout spine, coxae 2-3 evenly rectangular, 3 with 2 stout posterior spines, 1 ventral seta, 1 stout posteroventral spine medially, coxa 4 with 1 ventral seta, coxae 5-7 with thin ventral spines; gnathopod 1 with article 6 about 0.90 times as long as article 5, on gnathopod 2 about 0.82 times, gnathopods of ordinary stoutness, palms very oblique, dactyls failing to extend palmar lengths, palms weakly castellate, dactyls smooth proximal to main tooth, oblique setal row with 17-22 pectinate setae, anterofacial areas with several sets of setae; pereopods slightly stout, pereopods 1-2 with ratio of articles 4-7 of 22:15:24:13; article 2 of pereopod 3 of ordinary width, with weak posteroventral lobe, article 2 of pereopod 4 narrowly pyriform, posteroventral lobe absent but corner spinose, article 2 of pereopod 5 thin, rectangular, spinose posteriorly and at posteroventral corner, ratio of articles 4-7 about 30:33:26:13; pleonal epimera 1-2 with lateral ridge, 1 with weak blunt tooth, 2 with long thin tooth, epimeron 3 with similar thin tooth, epimeron 1 with 8 facial spines and numerous spines and setae anteroventrally, epimeron 2 with 12 facial spines and 2 spine sets anteroventrally (2-1), epimeron 3 with 5 facial spines, then 4 facial spines, then 1 anteroventral spine (commencing from posterior); pereonites toothless, pleonites 1-3 with medium sharp dorsal tooth, medium (pleonite 1) to long (pleonite 3) side tooth, dorsal teeth of pleonites set anteriad, pleonite 4 with dorsal tooth fully erect and partially to strongly attenuate, lateral tooth absent, lateral spine present but no lateral ridge usually present, pleonites 5-6 (fused) with 1 anterolateral spine each side and 1-3 posterolateral spines in group each side; dorsal margin of peduncle on uropod 1 evenly spinose; uropod 3 with pair of very long apical spines on peduncle, rami with spines, no setae; telson long, flat, apices very narrow, each with notch and 1 spine, sides of each lobe with 2-3 pairs of large dorsal spines along distal half of margins beyond pair of small dorsal setae, cleft of telson incomplete; cuticle not spiculate but chitin very dense and opaque, surface with scattered, extremely weak slit-pits with extremely rare, short, immersed setae; for example, lateral surface of article 1 of antenna 1 with 2-3 of these ultrafine setae, dorsal margin of pleonite 3 with one of these setae, coxa 5 posterior margin with several.

JUVENILE (4.4 mm, associated with form B adults). — Very similar to adult and recognition unquestionable: Ventral spines of article 1 on antenna 1 thin and in 2 sets, thin and in 1 set proximally on article 2, with 1 middle seta also; article 3 of antenna 2 with small seta instead of spine dorsally; mandibular molars slightly better triturative than in adult; each lobe of lower lip with 1 long, 1 vestigial cone; inner plate of maxilla 1 with 2 setae; plates of maxilla 2 lacking submarginal setae; maxilliped inner plate highly setose like adult; coxa 1 also with only 3 setae, coxae 1, 2, and 3 each with stout posterior spine, coxa 3 lacking ventral setae, 4 with 1 ventral seta; gnathopods 1-2 with 5 and 6 pectinate spines in oblique row on face of hand, anterior facial rows on gnathopod 1 in distal to proximal order with formula of 0-3-3, on gnathopod 2: 1-3; epimeral spine formulae, posterior to anterior, epimeron 1: 3-1-1, epimeron 2: 4-1, epimeron 3: 3-1-1; pleonal teeth poorly developed, side teeth of pleonite 1 absent and dorsal tooth rudimentary, dorsal tooth of pleonite 3 short and blunt, pleonites 5-6 with only 1 posterior spine on each side and 1 anterior spine each side; distal spine pair on peduncle of uropod 3 normal; telson with only 2 pairs of lateral spines each side.

MATERIAL (of phenotype B). — AH-3 (1), AH4-20 (7), AH4-25 (9), AH4-30 (12), AH4-35 (3), AH5-30 (6).

Paradexamine fissicauda Chevreux, Typical Phenotype A, Antarctica

Paradexamine fissicauda Chevreux, 1906:88—93, figs. 51—53. —Chilton 1912:181.—Schellenberg 1931:210.—K. H. Barnard 1932:217.—Sheard 1938:185.—Stephensen 1938: 241; 1947:66.

Paradexamine pacifica Chilton.—1912:501-502 [not Thomson; fide K. H. Barnard, 1932].

NOMENCLATURE. — Except for the original description, which fits the material at hand, the references cited are unverified as to their identification.

DESCRIPTION. — These specimens fit the description of phenotype B (which follows) except that pereonites 6-7 each bear 1 dorsal tooth, coxa 1 bears about 11 medium-to-long setae and 1 stout posterior spine, coxa 2 bears about 6 ventral setae, coxae 3-4 each bear about 4 medium ventral setae, and the palp of maxilla 1 is longer and thinner than in phenotype B (compare same scale Figure 34x1 with Figure 34nLx1).

The inner plate of maxilla 1 has a point, the spines on the maxilliped are definitely bifid, and coxa 7 has a distinctly larger tooth posteroventrally, though this tooth varies in size; finally, the cuticle is more transparent and far better furnished with highly visible and elongate slit-pits (under medium power), many of them furnished with immersed setae; for instance, article 1 of antenna 1 has more than 15 of these ultrafine setules, dorsal margin of pleonite 3 has more than 8 of these setules, and coxa 5 has many of these setules quite enlarged.

These specimens are identified as phenotype A, with Chevreux’s original description, because of the teeth on pereonites 6-7. One specimen has a middorsal spine on the peduncle of uropod 2, but the other specimens lack the spine as typical of phenotype B.

MATERIAL (of phenotype A). — Hoseason Island, Palmer Peninsula (1); Eltanin 436 (3).