TWO NEW SPECIES OF MOLLUSCS ( NATICIDAE : GASTROPODA ) FROM INDIA

The genus Natica was established by Scopoli, 1777 with Nerita vitellus Linnaeus, 1758 and subsequent designation given by Anton (1839) as the type. Several authors worked on the genus Natica ( Sowerby, 1883, Reeve, 1885, Tryon 1886 and recently Cemohorsky, 1971,1972, ) which are distributed in the Indo-Pacific region. In India, Subba Rao and Dey (2000) listed 12 species of the genus Natica in their Catalogue of Marine Molluscs of Andaman and Nicobar Islands. Subba Rao (2003) enumerated 15 species under this genus in Indian Sea Shell (Part-I) Polyplacophora and Gastropoda. Of 91 species under the genus Natica reported globally, 41 species are from Indo-Pacific region and 19 species have been listed from various parts of India. While studying the molluscs of the family Naticidae, the authors came across with two new species of Naticidae from India. The type specimens are deposited in the National Zoological Collections, Zoological Survey of India, Kolkata.


INTRODUCTION
The Naticidae is a cosmopolitan family of burrowing Cenogastropods under the Phylum Mollusca.It is commonly known as moon shell.This family is well represented and morphologically homogenous group of marine gastropods, living in habitats from the intertidal zone to deep sea.
The genus Natica was established by Scopoli, 1777 with Nerita vitellus Linnaeus, 1758 and subsequent designation given by Anton (1839) as the type.Several authors worked on the genus Natica ( Sowerby, 1883, Reeve, 1885, Tryon 1886and recently Cemohorsky, 1971,1972, ) which are distributed in the Indo-Pacific region.In India, Subba Rao and Dey (2000) listed 12 species of the genus Natica in their Catalogue of Marine Molluscs of Andaman and Nicobar Islands. Subba Rao (2003) enumerated 15 species under this genus in Indian Sea Shell (Part-I) Polyplacophora and Gastropoda.Of 91 species under the genus Natica reported globally, 41 species are from Indo-Pacific region and 19 species have been listed from various parts of India.While studying the molluscs of the family Naticidae, the authors came across with two new species of Naticidae from India.The type specimens are deposited in the National Zoological Collections, Zoological Survey of India, Kolkata.

Fig. 1&4 (plate-1)
Diagnosis: Shell moderate in size 41.15 mm, shell width is larger than shell length, spire moderately high, whorls shallowly impressed below suture; suture broadly deep and deeply concave, subsutural area with a milky white band, protoconch obtuse, white with 1-1/2 whorls, umbilicus partly filled by a callus pad.Parietal callus distinctly divided into anterior and posterior lobes; anterior portion after joining with the columellar lip making a transverse"u" shaped notch; shell white with broad brown orange band, subsutural area with microscopic axial striae, body whorl smooth, umbilicus and callus pad light orange brown; operculum slightly concave with a single marginal rib; inner edge of the operculum with a row of dentic1es.
Description: Globose, spire moderately raised, shallow concavity between suture and periphery; suture distinct, surface polished with fine growth lines which are especially distinct below suture; body whorl with microscopic axial striation.Aperture and labium very evenly and shallowly concave.Parietal callus distinctly divided by two lobes.Anterior portion of the callus join with the columelar callus by making a transverse"U" shaped notch.Funicle well developed and entering into the umbilical groove vertically; anterior portion of the parietal callus, collumellar lip and umbilicus with light orange colour, base of the shell with labium forming lip like appearance.Teleoconch whorls 2, protoconch of about 2 whorls, first whorl fairly large.Ground colour white, protoconch white, started from protoconch a milky-white band encircles along the sub sutural area of the penultimate whorl.Angulation with the body whorl is slightly folded and less than 90°.
Operculum: Single marginal rib.It is remarkable that the ratio of length and width is directly proportional with the increase in size of the shell.Operculum is slightly concave with a thickened nuclear region, one marginal rib with a series of denticles along the labial edge is another significant character of the shell.

Columellar callus
Columellar callus almost straight Columellar callus slightly arched, and anterior portion of the parietal funicle present and joining with callus feeble and joining with the the inner wall of the umbilical wall of the umbilical callus. callus.

Angulation
Angulation of the aperture stared Angulation of the aperture stared from the body whorl is 90°.
from the body whorl is less than 90°.Diagnosis : Shell small in size, penultimate whorls 3; large body whorl, suture deep and encircle with much faint axial striae and restricted only to the subsutural region.Body colour light brown; deep brown maculation or pattern around the body whorl below the suture and it started from the 3 rd penultimate whorl.Umbilicus deep almost covering by the funicle leaving a comma shaped area.
Description: Shell nearly globose, nuclear whorl 2-suture distinct, deep, surface polished, with fine growth lines which are especially distinct below suture; body whorl with fine microscopic axial striation that continues only some portion of the body whorl.
R. Venkitesan and party, Regd.No. M 26222/5; Paratype, same as above, Regd.No. M 26223/5.Remarks: This species resembles Natica vitellus Linnaeus but differs from this species in several ways which are as follows: (Subba Rao and Dey, 2000)arietal callus Some authors erroneously included this species(Subba Rao and Dey, 2000)as N. adamsoni ( mispelt) adansoni but a careful observation of the N. andamanensis suggested it to be a new species to science and new record from India with geographical distribution from Andaman and Nicobar Islands only.