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Arquivos de Zoologia

Melanoides tuberculatus is an alien species in South America, coming from Eurasia, introduced in Brazilian basins maybe by aquarists or studies for competition with planorbids. This species is spreading by several macrobasins competing directly with native cerithioideans. They live probably in the same niche of native cerithioideans - water with some energy degree - rather than planorbids, which are animals of water with lower energy. In locals where M. tuberculatus occurs, the native cerithioideans are found in a despicable number (person, obs.), showing direct competition and danger of exlinction.

Family Planaxidae Genus Supplanaxis Thiele, 1929 (Type species: Purpura nucleus Bruguiere, 1789)

Supplanaxis nucleus (Bruguere, 1789)

(Figs 17-19, 56. 74, 88, 189-206)

Synonymy: see Houbrick, 1987a: 25. Complement: Planaxis nucleus: Warmke & Abbott, 1961: 70 (pl.

13 fig. a); Abbott, 1974: 102 (fig. 975);

Abbott & Dance, 1983: 62 (fig.); Jong &

Coomans, 1988: 43.

Description.

Shell (figs 17-19). Elliptical outline, spire sharp. Periostracum velvet-like, whitish. Ostracum black. Aperture opistłiocline, peristome ample, dark purple, complex scultured, with several inner ribs and strong canal. Other details described by Houbrick (1987a: 25-27, fig. 17).

Head-Foot (figs 189-192). White with gray spots in dorsal region of foot, dorsal and lateral regions of head, snout and tentacles. Tcntacles gray spots disposed in longitudinal bands in lateral regions of foot spots disposed in oblique bands (fig. 190). Ommatophore smali, eye dark, rclatively smali. Snout sub-cylindrical, with piane, white anterior extrcmity, mouth approximatcly in center. Malc with a elear groove in outer region of right tentaclc, running ventrally ncar foot, white intemally, dark gray in margins. Femaie with porę of brood pouch in middle region between right tentacle and columellar muscle; a elear furrow mns from aperture of pallial oviduct to brood pouch aperture. Brood pouch described below. Other details see Houbrick (1987a: 27, figs. 19-21).

Operculum (fig. 56). Yellowish-brown, semi-transparent, nucleus sub-terminal, outline elliptical, occupies entire aperture.

Mantle organs (figs 193-195). Mantle border simple, without tcntacles, gray with a mosaic of elear spots; right side thickened and notched. Mantle cavity of about 1.5 whorl. Osphradium long, ridge-like, with about same gili length; anterior extremity of osphradium morę anterior than that of gili and disposed parallel to mantle border. Gili elliptic, leaflets many, triangular, lip long, somewhat sharp. Between gili and rectum a proportionally broad area. Hypobranchial gland thin, only visible in posterior region of cavity. Rectum, anus and pallial gonoducts described below. Other details of manile organs in Houbrick (1987a: 27, fig. 22).

Circulatory and excretory systems (figs 194, 200). Heart similar to those described for preccding species. Aortas attached to style sac and intestine. Kidney proportionally short, about 1/6 whorl, intemally a solid white tissue. Nephrostome a slit in middle region of wali between kidney and pallial cavity.

Digestive system (figs 192-194, 196-198, 201-206). Buccal mass similar to preceding species, distinctive features follow. Jaws almost vestigial, a pair of smali triangular plates not fixed directly in dorsal peri-buccal wali, but in a thin, transparent membranę (figs 74, 201). Four narrow longitudinal folds in inner dorsal surface of buccal cavity, two broader, close odontophore, and two median (fig. 201). Dark spots in lateral-anterior region of buccal cavity (fig. 201: ds). Aperture of salivary glands in middle-inner margin of broader folds (fig. 201: se). Odontophore (figs 202-206) also similar to those of preceding species, but with radula very long, sometimes coiled. A dark spot always present in dorsal region of radular sac just anterior to radular nucleus (figs 201,202). Radular sac siack, keeping radular ribbon firce within it. Odontophore distinctive features: 1) mil pair narrow, originating in middle region of inner surface of subradular membranę, inserting in vcntral region of radular sac, in its outer surface; 2) mila, other accessory pair of muscles origin lateral to mil, runs anteriorly, presenting a smali connection with anterior extrcmity of cartilages, afterwards unitę with