Loxocorniculum purisubrhomboidea (Edwards ex Puri 1953)

Loxoconcha purisubrhomboidea Edwards, 1953

Loxoconcha subrhomboides Edwards, 1944, p. 527, pl. 88: figs. 28-32.—Swain, 1951, pp. 25–26, pl. 2: figs. 18, 19.

Not Loxoconcha subrhomboidea Brady, 1880.

Loxoconcha reticularis Edwards, Malkin, 1953, pp. 786—787, pl. 80: figs. 13–17.

Loxoconcha purisubrhomboides Edwards, in Puri, 1953a, p. 750.—McLean, 1957, p. 71, pl. 7: figs. 4a–e.—Puri, 1954, p. 274, fig. 10h, pl. 10: fig. 8.—Grossman, 1965, pp. 148–150, figs. 3, 20–36, pl. 2: figs. 1–11.

Loxoconcha matagordensis Swain, 1955, pp. 629–360, figs. 36b and 39, 7a–b, pl. 63: figs. 9a–b, pl. 64: figs, la–b, 7a–b.

SHAPE.—Male carapace outline in lateral view elongate-subrhomboidal to subovate; greatest height behind middle. Dorsal margin nearly straight with small convexity at posterior cardinal angle; ventral margin slightly concave in front of middle, broadly rounded in its lower portion and extended below, upper portion with nearly straight slope forming subtruncate, obtuse angle with dorsal margin; upper portion of posterior margin, truncate at posterior cardinal angle, extending as very short, straight to slightly concave slope until abruptly terminated by broadly rounded, extended, lower posterior margin to form a small posterodorsal caudate process. Carapace outline in dorsal view subovate, widest medially; posterior half more swollen than anterior, both ends pointed.

ORNAMENTATION.—Surface of valves covered by moderately small, circular pits in rows roughly subparallel to valve margins; pits largest near valve center and decrease in size toward margins. Moderately thick peripheral rim present; two low finely beaded submarginal ridges present behind anterior margin and subparallel to it. Small, slightly swollen portion of valve directly below posterior cardinal angle, not forming definite node or horn.

SIZE.—Right valve of adult male: length 0.66 mm; height 0.38 mm. Left valve of adult male: length 0.67 mm; height 0.39 mm.

INNER LAMELLA.—Moderately wide throughout, greatest width anteriorly, sinuous ventrally. Line of concrescence and inner margin separated anteriorly, ventrally, and posteroventrally; rather small anterior vestibule and very narrow, elongate ventral-posteroventral vestibule. Moderately strong selvage present parallel to and considerably removed from outer margin forming rather wide groove behind flange.

MARGINAL PORE CANALS.—Very few, more numerous anteriorly (about 7 or 8), least numerous posteriorly (2 or 3) and widely spaced; straight to very slightly curved; simple, long, and centrally enlarged; some short and wide intercalated false pore canals present.

HINGE.—Gongylodont. Hinge of right valve consisting of anterior small, rather deep socket; low, small, bluntly rounded tooth; very small postjacent socket; elongate, crenulate interterminal groove followed by low, blunt, trilobed tooth; long, flat socket; and rather high, long, rounded tooth. Hinge of left valve consisting of anterior elongate, shallow socket; moderately high, bluntly rounded tooth; postjacent small, square socket; elongate, crenulate, interterminal ridge; postjacent shallow, lobed socket; long, low, flat tooth; and posterior deep, rounded socket.

NORMAL PORES.—Moderate in number, scattered, large, sieve type.

MUSCLE SCARS.—Slightly downcurved row of 4 elongate adductors, upper 2 longer than lower 2; single, moderately large, bow-shaped, antennal scar in front of lower of top 2 adductors; 2 small, thin, elongate, aligned mandibular scars.

EYE SPOTS.—Moderately small, raised, hyaline eye spot present beneath anterior cardinal angle.

OVERLAP.—Valves nearly equal in size, left slightly larger; no noticeable overlap.

SEXUAL DIMORPHISM.—Pronounced, male carapace considerably longer than that of female and not as tumid.

MATERIAL.—In bottom samples 2,893 specimens collected from Redfish Bay, 1,833 from Laguna Madre, and 22 from Copano Bay.

OCCURRENCE.—The specimens illustrated are from Station 12 in Laguna Madre, collection number 092859–2. Loxoconcha purisubrhomboidea was the second most abundant and widely distributed ostracod species in the study area. It was rare to abundant in Redfish Bay and Laguna Madre and rare in Copano Bay.

TYPE-SPECIES.—Paradoxostoma dispar Fischer, 1855, p. 654.

OCCURRENCE.—Worldwide; brackish to epineritic normal marine waters, plant dwellers. According to van Morkhoven (1963), the representatives of this genus have the upper lip, hypostome, and mandible transformed into a device for sucking the juices of the plants on which they live.

Paradoxostoma? species

SHAPE.—Carapace outline in lateral view elongate-ovate; greatest height medially. Dorsal margin rather broadly and uniformly convex; ventral margin slightly sinuate in front of middle, very gently convex elsewhere. Anterior margin narrowly rounded, acuminate slightly below midheight. Posterior margin more broadly rounded, subtruncate above, producing slight irregularity at junction with dorsal margin. Carapace outline in dorsal view elongate-ovate, only moderately inflated; greatest width slightly in front of middle from whence valves taper anteriorly and posteriorly to narrowly rounded ends.

ORNAMENTATION.—Valves unornamented, smooth, thin, very fragile, and transparent.

SIZE.—Right valve of adult: length 0.43 mm; height 0.20 mm. Left valve of adult: length 0.44 mm; height 0.19mm.

INNER LAMELLA.—Quite wide throughout, slightly-widest anteroventrally and posteroventrally, but very little actual variation in width except above small anteroventral concavity, and there somewhat narrower. Inner margin and line of concrescence separated throughout, resulting in presence of wide, continuous vestibule anteriorly, ventrally, and posteriorly. Marginal zone very narrow. Selvage submarginal, weak; two rather widely spaced lists present.

MARGINAL PORE CANALS.—Very few, difficult to distinguish, about 7 anteriorly, 8 ventrally, and 4 posteriorly; all very short, simple, straight, and widely spaced.

HINGE.—Lophodont, very weakly developed. Hinge of right valve consisting of small, low, smooth anterior and posterior toothlets joined by long, smooth, shallow groove. Hinge of left valve consisting of small, socket-like, terminal indentations joined by low, smooth extension of dorsal margin of valve.

NORMAL PORES.—Moderately few, small scattered, open.

MUSCLE SCARS.—Quite strongly developed, consisting of a nearly vertical row of four adductor scars (lower three very elongate, top one more nearly circular); thin, small, crescent-shaped scar present slightly in front and above the top adductor; second, small, oval, frontal scar present at considerable distance anterodorsally from crescent-shaped scar; about three rather large, indistinct dorsal scars present high above adductors. No mandibular scars present.

OVERLAP.—Left valve slightly longer than right and overlapping it terminally, but right valve higher than left dorsally.

MATERIAL.—Five specimens collected in bottom samples from Laguna Madre.

MATERIAL.—Forty specimens collected in bottom samples from Redfish Bay, 10 from Laguna Madre, and 3 from Copano Bay.