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Vol. 36(2), 2001

Remarks. The anatomy of T. hookeri differs from thatof T. communis (cf. Randles, 1900; Johansson, 1946 and Fretter & Graham, 1962: 366, fig. 189) by having the bursa and receptacle closed; capsule gland thin; devcloped pallial food groove covering osphradium region; and ovopositor less developed. The brood strategy of T. hookeri - some large capsules aligned in pallial cavity, appears to be different from that of the Caribbean T. variegata L. (Flores & Macsotay, 1972). This species has extemal posturę with almost one thousand smali capsules. However, according to data by Houbrick (1988), the strategy of T. hookeri is the normal of the family.

Family Modulidae

Genus Modułus Potiez & Michaud, 1838 (Type species: Trochus modulus Linne, 1758)

Modulus modulus (Linne, 1758)

(Figs 21-24, 63,98, 99, 299-313)

For synonymic list see Abbott (1944): 2. Complement:

Modulus modulus: Warmke & Abbott, 1961: 70 (pl. 11, fig. j); Rios, 1970: 41; Flores & Macsotay, 1972: 49; Abbott, 1974: 102 (fig. 976); Rios, 1975: 44 (pl. 12, f. 163); Houbrick, 1980a: 117-142; 01iveira et al., 1981: 98; Abbott & Dance, 1983: 63 (fig ); Rios, 1985: 48 (pl. 18, f. 217); Jong & Coomans, 1988: 43 (pl. 34, fig. 202); Leal, 1991: 361; Rios 1994:61 (pl.21, f. 233); Aplodon modulus: Morretes, 1949: 78.

Description.

Shell (figs 21-24). Turbinoid, heavy, umbiiicated, described several times in literaturę (e.g., Abbott 1944: 2; Houbrick 1980a: 118>120 + figs 1 a-h). A considerable shell variation occurs, specimens from Sao Paulo coast (figs 21,23) have nodes taller, morę spaced, and cxtemal keel less developed than those of northem waters (figs 22, 24) (op. cit. and person, obs.). When broken, shell wali considerably thick, columella without folds, inner surface white in color with violet spot in upper regions of each whorl. Protoconch and other details in Houbrick (1980a: 119, figs ld-h).

Head-foot (figs 299-301). Color pink in all anterior structures. Head protruding. Snout large, cylindrical, strongly bilobed anterior-ventral margin. Mouth longitudinal, cited deeply in snout furrow. Tcntacles long, eyes dark, situated about in its middle region on smali ommatophores. Foot relatively large, without divisions, with deep anterior furrow of pedał glands. Musculature around haemocoel dorsally thick (fig. 300), outer layer of obliąue muscle fibers, two very thick middle layers of radial muscle fibers, and an inner layer of circu-lar fibers around haemocoel; another thin layer of circular fibers between outer and middle muscular layers in region of columellar muscle. Columellar muscle of about half whorl; anterior-right third with a thickness of fibers obliąuely disposed; in poste-rior third suddenly become thin. Female ovopositor described below. Other details in Houbrick (1980a: 120-121, fig.2).

Operculum (fig. 63). Circular, comeus, palcispiral to multispiral, occupies almost entire aperture, nucleus central.

Mantle organs (figs 302, 303, 306). Mantlc border pink in color, entirely papillated, papillae not uniform in size; left border thick muscular. Mantle cavity of almost one whorl. Osphradium ridge-like, in situ with about same length than gili, but longer than gili if straightened; anterior osphradium region with a zigzag. Gili very long, almost same length than pallial cavity, filaments triangular, narrow, very tali. Between gili and rectum a proportionally broad area with hypobranchial gland well-developed, color pink, bearing several transversal chambers and several apertures in surface, finishes near anus. Rectum and genital ducts described below. Anus siphoned, posterior in cavity. Other details of mantle oigans in Houbrick (1980a: 121-124, figs. 1 a-d).

Cireulatory and excretory systems (figs 305, 306). Heart large, similar to those described for preceding species. Aorta runs attached to style sac. All examined specimens with pericardium filled by a hard greenish transparent substance resembling a cartilage consistence, its dissection is necessary for heart exposure. Kidney short, about 1/10 whorl, with single lobe, white in color, solid, without chambers. Nephrostome slit-like in middle region of wali between kidney and pallial cavity. Other details in Houbrick (1980a: 132).

Digestive system (figs 302-313). Buccal