6926475897

152

Arquivos de Zoologia

a large, elliptic, flattened fold in ventral side (central pad) with anterior half narrow and posterior half broad with a median compression; another smaller fold surround posterior half of central pad (crescentic ridge). Duet to digestive gland single, situated ventrally in middle-right region of central pad, partially surrounded also by anterior-left region of crescentic ridge. Esophageal aperture at left of duet to digestive gland; near this another longitudinal, Iow, narrow fold in left maigin of stornach wali (fig. 135: gf). Gastric shield smali and thin, between right anterior region of central pad and right margin of gastric wali. Dorsal gastric wali with differentiated, somewhat elliptic sorting area in left side, bearing sigmoid, Iow, successive folds; in right-posterior region two broad folds, each one with posterior region rounded and broad, and anterior region narrowing gradually; left anterior region of dorsal wali smooth. Stornach still having anteriorly a smali smooth chamber bearing two anterior apertures, at left intestine origin, at right origin of style sac. Style sac large, about half of stornach size. Intestine origin preceded by two tali folds (fig. 135), posterior fold triangular and short, anterior fold rounded, tapers gradually in ventral surface of intestine becoming an intestinal typhlosole; between both folds a furrow which communicates intestine with style sac. Stornach and style sac inner surfaces almost entire covered by thin, yellowish iridescent chitin. A broad furrow in ventral region of style sac inner surface. Style elliptic, yellowish-transparent. Digestive gland surrounds posterior half of ventral surface of stornach and two whorls posterior to it (fig. 119). Intestine long, narrow, surrounds style sac ventrally (figs 117, 119, 135), other loop in dorsal-anterior region of this, after towards anteriorly edging right margin of pallial cavity; after kidney suddenly becoming broad. Rectum with successive oblique, broad, somewhat uniform inner folds in its dorsal surface (fig. 117). Several fecal pellets inside rectum, aligned and compacted parallel to folds. Near anus, inner folds thinner and morę numerous. Anus siphoned, posterior firom mantle edge.

Genital system. Only females found. Ovary developed in largest specimens; occupies superior regions of each whorl on digestive gland (fig. 119). Oviduct yellowish, thick walled, somewhat broad, lies on columella; in pallial cavity suddenly expands. Pallial oviduct posteriorly closed at about 1/6 of its length (fig. 133). Inner lamina thin and broad, keeping a furrow close to columellar muscle. Outer lamina very thick mainly in its posterior half. Bursa, a smali long and sub-elliptical furrow in middle region of pallial oviduct, bordered at left by a smali fold. Anterior extremity of pallial oviduct, anterior to anus and near columella, close to smali, sphincter-like aperture of brood pouch. Two folds penetrate in brood pouch aperture, one of them ffom inner lamina and other attached to thick outer lamina (fig. 115). Brood pouch a sac with thin walls (figs 122-124), situated behind head at right and dorsal to esophagus, free in haemocoel except for its thick walled anterior extremity. Internally several Iow radial folds around its aperture, one of them very large, with irregular surface (fig. 124); this fold may be protracted (fig. 115); remainder inner surface smooth; sometimes brood pouch compress m2 muscle of buccal mass (fig. 123). Up to five young specimens can occur within brood pouch in different growth stages, ffom one to five whorls. Young specimens imbibed in yellow mucus.

Measurements (figured specimens, in mm). Holotype: 21.8 by 9.0; MZSP 28695: 22.9 by 9.9; MZSP 28696: 16.1 by 7.0.

Distribution. Only known firom type locality.

Etymology: the specific name refers on protractible fold of brood pouch aperture.

Aylacostoma ci new species (Figs 4-6,44, 52, 73, 84, 85, 136-149)

Types: Holotype MZSP 28691. Paratypes: MZSP 28392,1 specimen; MZSP 28693,1 specimen; MZSP 28345,65 specimens; USNM 890886, 2 specimens. Ali ffom type locality.

Type locality: Brazil; Rondónia; U.H.E. Samuel, Jamari River, (20/viii/1987, Motta, C.S. col., sta. lNPAmol-118).

Diagnosis. Pigment of head-foot scantier. Tentacles of mantle border morę developed. Osphradium broad and short, less than half of gili length. Gili narrower with filaments tali. Broad space between gili and osphradium. Absence of well-developed vessels between gili and rectum except ad-rectal sinus. Stornach with a distinctive sorting area edged by a fold “Y” in shape. Rectum inner surface smooth. Pallial oviduct with a