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Arquivos de Zoologia

Family Litiopidae Genus Alaba H. & A. Adams, 1853 (Type species: Rissoa melanura C.B. Adams)

Alaba fncerta (Orbigny, 1842)

(Figs 68, 80, 106, 107, 362-376)

Eulima incerta Orbigny (in Sagra), 1842: 218 (pl. 26, figs 7-9).

Rissoa tervaricosa C. B. Adams, 1845: 6. Cerithium melanura C. B. Adams, 1850: 116. Alaba tervaricosa: Smith, 1890b: 320; Dali, 1889a: 258; 1889b: 146: Morretes, 1949:78.

Alaba incerta: Warmke & Abbott, 1961: 74 (pl. 13, fig. r); Rios, 1970: 44; Robertson, 1971: 51 (pis. 2-3); Abbott, 1974: 110 (fig. 1121); Rios, 1975: 49 (pl. 13, f. 181); 1985: 51 (pl. 19, f. 227); Houbrick, 1987b: 9-17 (figs. 1-3, 5, 7, 10-12,15-20); Jong & Coomans, 1988: 45; Leal, 1991: 360; Rios, 1994: 63 (pl. 21, f. 240).

Description.

Shell. Smali (up to 15 mm), tumform, thin, white, up to 12 whorls. Protoconch of four whorls, first whorl smooth, others with numerous axial riblets; anal slit present (see also Robertson, 1971: 51, pis. 2-3; Houbrick, 1987b: 12, fig.10). Periostracum transparent, thin. Teleoconch with convex whorls, deep suture. Sculpture six to seven spiral, Iow and broad furrows. Last whorl with nonę or up to 4 strong axial threads. Aperture ample, elliptical, simple, canal weak; outer lip generally thick. No inner chitinous layer detectable. Other details in Houbrick (1987b: 10, figs 10-11); Rios (1994).

Head-foot (figs 362-366). Homogeneous pale cream in color, without spots. Head protruding, somewhat broad. Snout short but broad, dorso-ventrally flattened, bilobed anterior margin. Tentacles very long (morę than double of snout length), slender. Eyes dark, proportionally smali, near tentacles base, without ommatophore. Foot somewhat large; a furrow of pedał glands in anterior maigin; its superior margin extends beyond foot limit in both sides as a pair of propodial tentacles. Other furrow of pedał gland in median-posterior region of foot sole, longitudinal, finishes before posterior foot margin. Epipodium present, lying

lateral-dorsal region of foot and inner opercular surface (fig. 365); epipodial edge entire with tentacles; those of lateral region longer and laiger, three or four in each side; those tentacles around operculum shorter, lobed, being two posterior discretely laiger. Female with ovopositor described below. Columellar muscle of about one whorl. Other details in Houbrick (1987b: 10-11, figs 2-3).

Operculum (figs 68,364). Elliptical, comeus, yellowish, semi-transparent; nucleus excentric, near inferior margin. Muscle scar proportionally smal I, sub-elliptical, close inner margin; surrounded extemally by a well-developed ridge (fig. 364: k3). Most part of | operculum free, only leaned on epipodium dorsal surface. Other details see Robertson (1971, pl. 4, f. j 16) and Houbrick (1987b: 10-11, fig. 1).

Mantle organs (figs 369,370, 376). Mantle border smooth, somewhat thick, white. Mantle ■ cavity of about 1.5 whorls. Osphradium long, about i 2/3 ofgill length, pectinate, Iow; anterior extremity j morę anterior than that of gili; posterior region clearly narrower. Satellite fold of osphradium present, Iow, running left, anterior and right sides i of osphradium; finishes posteriorly morę or less i where osphradium also finishes. Anterior half of osphradium and satellite fold somewhat parallel to mantle bórder, at some distance of this (except anterior extremity, which arrives close to mantle border). Gili very long, about same length than pallial cavity, nanow; bears several long, tali, tri-angular filaments; tip of each filament sharp, somewhat central. Ctenidial vein narrow, slight uniform width. Between gili and rectum a relatively narrow area. Hypobranchial gland thin. Rectum narrow, edging left margin of pallial gonoducts; intemally some fecal pellets obliąuely disposed. Anus siphoned, near mantle border. Gonoducts running in right margin commented below. Other details in Houbrick (1987b: 13).

Circulatory and excretory systems (figs 370, 376). Heart characters and site similar to those of preceding species, aortas attached to style sac. Kidney short, about 1/6 whorl; intemally a solid, white tissue compressed between rectum and pericardium in anterior half, and between rectum and stornach in posterior half. Nephrostome a smali slit in middle region of membranę between kidney and pallial cavity.

Digestive system (figs 366-368, 371-376). Mouth in anterior and ventral region of snout furrow,