Comprehensive Description

provided by Smithsonian Contributions to Zoology
Paradexamine pacifica (Thomson)

Dexamine pacifica Thomson, 1879:238, pl. 10B: fig. 4.—Thomson and Chilton 1886:149.—Thomson 1889:262.

Paradexamine pacifica.—Stebbing 1899b: 210.—Chilton 1909:632.—Stebbing 1910a:602 [key].—Chilton 1911: 308.—Thomson 1913:243.—Stephensen 1927:345-347, figs 21, 22; 1938:246-247.—Sheard 1938:176-178, figs. 5, 8M.—J. L. Barnard, in press.

Not Paradexamine pacifica.—Chilton 1912:501-502 [=P. fissicauda, fide K. H. Barnard, 1930, and Stephensen, 1938]; 1925:179.—K. H. Barnard 1930:389-390, fig. 49 a-c [=P. barnardi Sheard].

DESCRIPTION (of female). — Lateral cephalic lobe with sharp anterior cusp, head lacking anteroventral definition at base of antenna 2, rostrum short but subacute; article 1 of antenna 1 with ventral spines thin and arranged in 2 groups of 3-4 each, article 2 about 1.33 times as long as article 1, apically simple and bearing set of thin setal spine (s) ventrally, flagellum about 3.0 times as long as peduncle; flagellum of antenna 2 about 1.8 times as long as peduncle, multiarticulate; mandibles with 2 long thin spines on right, 3 on left, molar moderately to poorly ridged, mainly fuzzy, ragged seta on each side, ordinary setae on right side only, accessory bulges weak, rounded; outer lobe of lower lip bearing 1 medium, 1 short cone, mandibular lobes thin, shortly upturned; palp of maxilla 1 large, of normal breadth, exceeding outer plate, bearing apical, medial, and lateral setae and 4 strong-to-weak apical cones, inner plate of normal size, thin, bearing 2 apicosubapical setae; inner plate of maxilla 2 much narrower than outer, reaching slightly more than 80 percent along outer, both appressed, inner with apex very oblique, outer with several submarginal setae on inner face, outer weakly curved; inner plate of maxilliped of medium size, broad, bearing several apical, apicolateral, medial, and facial setae, outer plate of ordinary size, moderately thin, spines small to medium, simple, palp robust, slightly exceeding outer plate, article 4 of short kind in this genus; coxa 1 apically widened, naked anteriorly, ventral margin setose and weakly scalloped, coxae 2-3 rectangular, 2 slightly rounded ventrally, neither with large spines, coxae 2-4 poorly setose ventrally, 5-7 spinose ventrally; gnathopod 1 with article 6 about 0.92 times as long as article 5, on gnathopod 2 about 0.84 times, gnathopods ordinary to thin, palms oblique, medial faces of hands with 6-7 pectinate setae in oblique row and 3 rows of anterior setae, palms and dactyls strongly pectinate; pereopods 1-5 thin, with sharp spines except on article 6 of pereopods 1-2, ratio of articles 4-7 on pereopods 1-2 about 18:15:23:13; article 2 of pereopod 3 of ordinary stoutness, posteroventral lobe broad and deep, article 2 of pereopod 4 pyriform, posteroventral lobe obsolescent but spinose, posterior margin with several spines; article 2 of pereopod 5 thinly pyriform, posterior margin weakly serrate and spinose, ratio of articles 4-7 about 21:35:29:15; pleonal epimera 1-2 with lateral ridge, small sharp tooth on epimeron 1, medium sharp on epimeron 2, epimeron 3 with medium-to-long sharp tooth, posterior margins of epimera smooth, epimeron 1 with facial row of 5 spines with spines and setae in tandem on anteroventral margin, epimeron 2 with facial row of 10 spines and 2 ventral spinules, epimeron 3 with approximate formula, rear to front, of 5-3-2-2-1 or 5-4-3-2-1; pleonite 1 dorsally smooth, pleonites 2-3 with sharp dorsal tooth and sharp tooth on ridge of each side, middle tooth of pleonite 3 somewhat anteriad, pleonite 4 with sharp, subprostrate dorsal tooth, no lateral tooth but with spine on weak lateral ridge, pleonites 5-6 (fused) with 2 dorsolateral spines on each side; dorsal margin of peduncle on uropod 1 evenly spinose; rami of uropod 3 lacking setae, peduncle with incipient distal pair of spines, 1 large spine always present, medial to it 1 wire-like seta in specimens smaller than 4.5 mm, larger than that with small spine becoming progressively larger with each instar; telson weakly crested, apices broad, with 8-9 irregular serrations, some of them bifidations, 1 small spine in notch space, lateral margins of each lobe with about 5-6 medium spines in tandem; cuticle of posterior body segments smooth or faintly spiculate.

MALE (about 4.2 mm, not strongly developed). — Eyes enlarged, setular tufts on ventral margin of article 1 on antenna 1, dorsal margins on articles 4-5 of antenna 2, article 2 of antenna 1 and article 4 of antenna 2 elongate, article 5 of antenna 2 short relative to article 4, flagella elongate; gnathopod 1 like female but article 5 of gnathopod 2 elongate, thus article 6 of gnathopod 2 only 0.76 times as long as article 5, each oblique row on hand face with 7 setae, posterior margins with 5 and 4 setae each (gnathopods 1 and 2 respectively), anterior facial setae, distal to proximal, formula: 2-2-1 on gnathopod 1, 3-3 gnathopod 2; article 2 of pereopod 3 slightly more slender than in female; uropod 3 with only wire-seta in accessory distal position on peduncle, besides main distal spine; spines on urosome slightly smaller than in female.
bibliographic citation
Barnard, J. L. and Drummond, M. M. 1978. "Gammaridean Amphipoda of Australia, Part III. The Phoxocephalidae." Smithsonian Contributions to Zoology. 1-551. https://doi.org/10.5479/si.00810282.103