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Vol. 36(2), 2001

Family Vermetidae Genus Serpułorbis Sasso, 1827 (Typc species: V arenaria Linne, 1758)

Serpułorbis decussatus (Gmelin, 1791)

(Figs 43, 79, 112, 113,423-439)

Synonymy sec Clessin, 1904: 99. Complement: Serpułorbis decussata: Warmke & Abbott, 1961: 66 (pi. 12, fig. d).

Serpułorbis decussatus: Rios, 1970: 40 (pl.8); Abbott, 1974: 101 (fig.); Rios, 1975: 45 (pi. 12, f. 164); 1985:47 (pl. 18, f. 214); Jong & Coomans, 1988: 43; Rios, 1994: 67 (pl. 22, f. 259).

Descńption.

Shell (fig. 43). Irregularly uncoiled as nor-mai vermetid, relatively large, about 100 mm. Sculptured by irregular longitudinal and transver-sal Iow ridges, both predominating, producing a reticulation. Aperture simple, not notched. Morę details in Clessin (1904: 99-100).

•. Head-Foot (figs 423-427). Scarcely pigmented by brown spots, most pale cream. Head greatly protruding and clearly broader than other regions. Snout large, as an extension of head, without elear limit, cylindrical. Mouth ample, longitudinal, in anterior-ventral snout region. Tentacles shorter than snout and situated ventrally near foot. Eyes smali, dark, on smali ommatophores situated in ventral-basal region of tentacles. Foot very smali and complex. Pedał sole a deep concavity. Anteri-or region of foot thick and probably main extensible stmeture; ventral surface smooth; dorsal region with following structures: laterally insertion in ven-tral base of head by a pair of flaps (figs 424-427: pl); in median-anterior region a glandular pad (p2) with 7-8 longitudinal, Iow folds and a concavity in posterior region, covering these folds; between flaps and posterior to glandular pad a pair of well developed foot tentacles (figs 423, 424, 427: pt), eachone based broad and tip sharp; a longitudinal, opened furrow in almost they entire length, except near median linę (just where duet of pedał gland opens). Pedał glands enormous (fig. 425), elliptical, long, situated in ventral region of haemocoel, intemally two bands of glandular, obliąue folds, separated by a narrow space which runs longitudinal ly in middle region; duet of pedał gland broad, penetrates in median region of foot muscle jointed with a pair of nerve, opens between both pedał tentacles (fig. 427). Ventral insertion of mantle very posterior. Food groove runs in left region of head-foot complex, posterior and anteri-or extremities oniy shallow furrows, its middle region with tali, thick borders; near head towards right and contours its right region, finishes ventrally near mouth. Columellar muscle very long, morę than half of total shetl length, anterior 2/3 thick and broad, suddenly becomes narrow and thin in its posterior 1/3. Operculum absent.

Mantle oigans (figs 428,430,431). Mantle border thin, with minutę, sparse papillae, somewhat regularly disposed; color pale brown, white near papillae. Mantle cavity deep, about half of soft parts length. Osphradium very long and narrow, slightly far from gili and from left extremity of mantle cavity; anterior extremity curved and anterior to that of gili; total length about 8/10 of that of gili. Gili very long, little shorter than pallial cavity length, filaments triangular, narrow; tip very long and pointed; anterior gili end very posterior from mantle border. Ctenidial vein of somewhat uniform width; relatively long posterior region free from gili. Between gili and rectum a broad anterior and narrow posterior area. Rectum extremely broad, thin walled. Anus siphoned, posterior from mantle border. Gonoduct running in right margin described below. From both insertions of mantle in head, several nerves radially disposed clearly visible; some of them (from left side) insert in osphradium, while others run medially and anteriorly near mantle bordeT (fig. 430: nv).

Circulatory and excretory Systems (fig. 428). Heart proportionally smali, situated in left-dorsal region of pallial cavity posterior extremity; pericardium connected to anterior region of stornach. Kidney very simple and smali, somewhat elliptical, situated between pericardium and rectum in posterior region of pallial cavity. Intemally a solid and flattened renal tissue. Nephrostome a slit situated in middle region of membranę between kidney and pallial cavity.

Digestive system (figs 425, 426, 428-432, 435-439). Mouth in ventral-anterior region of snout, ample. Buccal mass large, slightly spherical, occupying almost entire space of head and snout. Peribuccal and jaws muscles well developed, almost same size of odontophore. Jaws (figs 79,