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Arquivos de Zoologia

Hemisinus (Yerena) tenuilabris tenuilabris:

Morretes, 1949: 78.

? Aylacostoma behni: Henry & SimSo, 1986: 507-516 (non Reeve, 1860).

Aylacostomaglabrum: Nuttall, 1990: 259-261 (figs 290, 291) (part, not Spix, 1827). Aylacostoma tenuilabris tenuilabris: Vaz et al._f 1987:373.

Types: The Natural History Museum, London, Zoology Department, BMZD 1984222, sintypes with lectotype designed by Nuttall (1990). (Not scen.)

Description.

Shell (figs 7, 8, 31,45). Large size (up to 40 mm), turriform, apex eroded, brown in color with several sparse reddish spots. Protoconch (fig. 45) present only in young specimens (from brood pouch), similar to those of preceding species except in being taller. Protoconch with two first whorls smooth and almost in same piane, next whorls gradually becoming larger and tumed down. After third whor! thin and Iow spiral sculpture appears, bcaring dark spiral spots regularly spaced (fig. 31). Teleoconch with up to six whorls, last whorl outstandingly latge in relation to spire. Sculpture narrow spiral cords, uniform in size, about five in penultimate whorl; a somewhat broad, shaJlow furrow between. Some specimens present Iow, axial ribs in two or three first whorls. Aperture long, elliptical, angled posteriorly, shallow anterior ca-nal. Umbilicus absent.

Head-foot (figs 150, 163). Head-foot structures very similar to those of preceding species, including pigment, Iow ommatophore and brood pouch aperture smali, close to right fusion of mantle.

Operculum (fig. 53). Differs from preceding species only by somewhat long outline, nucleus also sub-tenninal.

Mantle organs (figs 151, 152, 155, 156). Mantle border with smali, lobed, well-spaced tentacles, morę developed in both extremities. Osphradium very long, ridge-like, with about 7/10 of gili length; anterior extremity somewhat bulged, posterior to gili beginning; posterior extremity sharp, anterior to gili end. Gili very long, about same length than pallial cavity, filaments triangu-lar and Iow; tip of each filament shaip, tumed to left; gili anterior extremity sharp and near mantle border. Ctenidial vein narrow anteriorly, gradually becoming broader in posterior gili half, almost same width than gili; broad insertion in auricle. Between gili and rectum a very broad space in anterior half of cavity, and narrow in posterior half; entirely covered by visible vessels; in anterior region longitudinal vessels, posteriorly they curve to left; in posterior region only transversal, sometimes dichotomic vessels. Hypobranchia! gland yellowish-transparent, very thin, situated in area between gili and rectum; in posterior region discretely thicker. Ad-rectal sinus extremely broad, rectum running free within its space, gradually ad-rectal sinus narrows anteriorly. Anus siphoned, near mantle border. Pallial oviduct narrow, white, running between adrectal sinus and right margin of pallial cavity, fmishes posterior to anus, morę details below.

Circulatory and excretory systems (figs 152, 156). Heart similar to those of preceding species, with aortas attached to style sac. Circulatory distinctive characters are broad ad-rectal sinus and broad posterior region of ctenidial vein. Kidney very large and complex, almost a half whorl in length. Kidney composed by two lobes separated with each other by a thin irregular septum (fig. 152: ks). Left lobe lying pericardium, bearing several hollow chambers not uniform in size, disposed somewhat transversal to pericardium wali; a smali portion bulges into pallial cavity. Right lobe broad, triangular, lying at right of intestine; has two regions, a ventral with hollow chambers similar to those of left lobe, and a dorsal solid-glandular. Nephrostome smali, slit-like, in right extremity of membranę between kidney and pallial cavity, close ad-rectal sinus. Blood in fixed specimens white, jelly-like.

Digestive system (figs 151, 156-168). In generał similar to those of preceding species. Distinctive features follow. Jaws.with elevated, cuspided anterior margin. Inner dorsal wali of buccal mass (fig. 162) with two broad and Iow lon-gitudinal folds running to esophagus. Odontophore (figs 164-168) with well developed muscle fibers in its ventral surface, provided by ventral wali of buccal mass, they contours radular ribbon and inserts part with m7 and part in ventral region of mouth (fig. 165: ml3). Pair of m5 and horizontal muscle proportionally short. Pair of mil