6926475875

150

Arquivos dc Zoologia

op,    opcrculum; or, ovopositor; os, osphradium; ov, oviduct; pa, posterior aorta; pc, pericardial chamber; pd, pedał gland; pe, pallial spermoduet;

pg,    pedał gland anterior furrow; pi, pre-intestinal gastric fold; pk, posterior kidney lobe; pl, pallia! cavity; po, pedał ganglion; pr, pleural ganglion; ps, pedał sole; pt, pedał tentacle; pu, posterior furrow of pedał sole; ra, radular ribbon; re, receptaculum seminis; rf, right furrow of head-foot; m, radular nucleus; rp, receptaculum aperture; rs, radular sac; rt, rectum; sa, dorsal sorting area; sc, subradular cartilage; sd, sa]ivary gland duet; se, salivary gland aperture; sf, satellite osphradian fold; sg, salivary gland; si, siphonal inflexure; su, snout; so, statocyst; sp, style sac aperture; sr, adrectal sinus; as, style sac; st, stornach; sv, seminal vesicle cf; te, cephalic tentacle; to, tissue of esophagus on odontophore; tr, tissue on middle region of radula; tv, transversal vessels between gili and adrectal sinus; up, union of m5 with its pair; va, seminal vesicle aperture; vd, vas deferens; ve, ventricle; yw, ventral wali of buccal mass.

Systematics

Family Thiaridae Genus Aylacostoma Spix, 1827

(Type species: A. glabrum Spix, 1827 = Melania scalaris Wagner, 1827)

Aylacostoma eioplicata new species (Figs 1-3,51,72, 82,83,114-135)

Types: Holotype MZSP 28694. Paratypes: MZSP 28695,1 specimen; MZSP 29697,1 specimen; MZSP 28346,63 specimens; USNM 890885, AMNH 292172, ANSP A18961,2 specimens each. Ali from type locality.

Type locality: Brazil; Pari; Tlicurui, Caraipć River (xi/1982, Motta, C.S. col., sta. INPAmol-100)

Diagnosis: osphradium about 1/9 of gili length, satellite fold at left of osphradium; gili with broad, sharp pointed filaments; vessels in area between gili and rectum present; anus posterior to pallial oviduct anterior end; stornach central pad with broad posterior and narrow anterior regions, two gastric dorsal rounded folds.

Description:

Shell (figs 1 -3). Medium size (up to 25 mm), turriform, apex eroded, elear brown with some sparse, spiral, reddish dark brown, minutę spots. Protoconch only present in young specimens (from brood pouch), with two whorls almost smooth, convex, rounded; gradually spiral ribs begins, becoming strong on next whorls. Junction of protoconch and teleoconch difficult to determine. Teleoconch with about five whorls; sculpture of broad spiral cords, uniform in size, about eight in penultimate whorl; with a narrow and shallow furrow between. Aperture elliptical, angled posteriorly, with shallow anterior canal. Peristome glossy, cream in color. Umbilicus absent.

Head-foot. Pigmented by dark txansverse bands around snout, tentacles (figs 122-123) and dorsal region of foot. Head protruding. Snout large, dorso-ventrałly flattened (figs 114-116), anterior margin somewhat bilobed Tehtacles long, stubby, eyes dark on a smali elevation near outer base. Foot of medium size, without divisions; a furrow present in front maiginof anterior pedał gland (figs 114-116). Several specimens with posterior region of head bulging by developed embryos mto brood pouch (fig. 116), its aperture a smali slit situated ventrally close to right fusion of mantle (figs 115-116). Columellar muscle of about one and half whorls.

Operculum (fig. 51). Ovate, comeous, nucleus sub-terminal, externally lamellate, occupies partially aperture. Muscle scar elliptic, near inner margin.

Mantle organs (figs 117, 118, 120, 121). Entire mantle border with smali lobed tentacles, morę developed in both extremities. Mantle cavity rather deep, about two whorls. Osphradium very-long, ridge-like, lies on left margin of pallial cavity at about 9/10 of gili length. Anterior extremity of osphradium posterior to that of gili. Satellite fold at left side of osphradium, with about its same length (figs 118,121: sf). Gili very long, about same length as pallial cavity; filaments triangular, Iow, tip sharp pointed tumed to right; ctenidial vein well developed. Between gili and^ rectum a proportionally broad area with well spaced vessels connected with a large ad-rectal sinus (figs 118, 121); hypobranchial gland thin, between gili and ad-rectal sinus. Ad-rectal sinus broad, rectum running free within it. Anus siphoned, in right