New records and distribution extension of Nassarius persicus ( Martens , 1874 ) and N . tadjallii Moolenbeek , 2007 ( Mollusca : Gastropoda : Nassariidae ) to India

We report new findings of live specimens of Nassarius persicus (Martens, 1874) and N. tadjallii Moolenbeek, 2007, extending their range to the Gulf of Kachchh, Gujarat, India. The known distribution of both species was limited: N. persicus was distributed in the Persian Gulf, Gulf of Oman, and Karachi in Pakistan; N. tadjallii was reported from the Persian Gulf and the Gulf of Oman. We also provide comprehensive taxonomic descriptions of both species, along with additional morphological and ecological information.


INTRODUCTION
Nassarius Duméril, 1805 (Gastropoda: Nassariidae) is the most diverse genus within the subfamily Nassariinae and limited to the Indo-West Pacific (Galindo et al. 2016;Dekker et al. 2016). Information on the members of this genus from the Indian subcontinent, a major ecoregion of the Western Indo-Pacific, however, is scarce (Nerurkar et al. 2020). In this paper, for the first time, we report the occurrence of many living specimens of Nassarius persicus (Martens, 1874) and Nassarius tadjallii Moolenbeek, 2007 from the intertidal reef associated mud-flats of the Gulf of Kachchh, Gujarat, India. We also provide a complete taxonomic description for both species, along with additional information about morphological characters which are previously unknown (radula and operculum) for further reference.
Nassarius persicus was earlier reported from the Persian Gulf and the Gulf of Oman, a single record from Aden, Yemen, should be confirmed as it is out of the expected range for this species. This species is also found in Karachi, Pakistan (Cernohorsky 1984). This species is a conspicuous member of the intertidal reef community within the Gulf of Kachchh, Gujarat; however, it was misidentified as N. arcularia plicatus (Röding, 1798) (Ghosh 2008: pl. 1, figs. 5-6)  Nassarius tadjallii is currently known only from the Persian Gulf and the Gulf of Oman. This species is very similar to N. marmoreus (A. Adams, 1852), N. javanus (Schepman, 1891), andN. thachorum Dekker et al., 2016.

MATERIALS AND METHODS
Taxon sampling: Specimens of both species were found and handpicked at low tide during the present study, intertidally, up to 1 m depth, at different localities in the district Devbhumi Dwarka, Gujarat, India. Live animals were photographed in the field before collection (IMAGE 1). Animals were preserved in 96-98% ethanol and voucher specimens are housed in the museum of Bombay Natural History Society (BNHS).
Morphological analyses for primary identification: A stereomicroscope (Carl Zeiss ZEISS Stemi 2000C, Germany) was used to observe shell and operculum morphology for each specimen included in the study. A digital vernier (accurate to 0.1 mm) was used for shell measurements. Shells were photographed using SX520 HS Canon digital single-lens reflex camera. For SEM imaging, radulae were mounted on carbon conducting tape and sputter coated with Au-Pd. The scanning electron microscope (SEM) images of radulae were

Diagnosis
Shell: Shell up to 23 mm in length (20.8 mm in holotype), elongate-ovate, with high, conical spire (Figs. 2A-B); very thin periostracum clearly visible in the live animal. Protoconch of three glassy-white whorls (Figs. 2E-F). Teleoconch of 6.5-7.25 weakly convex whorls, sculptured with strong axial ribs. Axial ribs are angulate and weakly constricted by a sharp, subsutural spiral line, to form weak nodes at the suture (same as that of holotype); ribs numbering from 12-14 on the penultimate and 12-19 on the body whorl, ribs becoming moderately obsolete in the center of the body whorl; only body whorl sculptured with very weak spiral striae, 3-4 basal spiral threads more prominent, siphonal fasciole with cords. Colour of shell is yellowish to olive green in live animals while dry shells look strawyellow or pale grey. A creamy, pale colored spiral band is clearly visible on the shell with a nebulous darker band in the background of dorsal side of body whorl. The body whorl ends with four to five shallow axial ribs followed by a strong varix. Colour of varix is same as that of the shell. Aperture white, ovate, narrow, with 3 brown bands interiorly; outer lip thickened, edge slightly turned backwards; interior of outer lip with 7-8 lirate denticles (same as that of holotype). Columella heavily calloused, white, columellar shield large and extending up to body whorl suture; columella plicate with one strong plication at the base and 5-8 small folds. Anterior or siphonal canal short, distinct, wide and marked with 4-5 oblique basal cords. Posterior or anal canal distinct, deep, "U" shaped and marked by an intense posterior columellar ridge.
Operculum (Image 2G): Operculum corneous, yellowish to light brown in colour, serrate at the margins. Roughly trapezoidal in shape with curved bases, simple, flattened with terminal basal nucleus which is slightly turned to left. Information on operculum of holotype is not available.
Radula (Image 2K): Approximately, 62-70 rows of teeth, rachidian teeth with concave crescentic base, cutting edge is fringed with 11 or 12 sharp pointed, conical denticles with symmetrical arrangement. Corners of rachidian plate wide and smooth. Accessory intermediate lateral plates present in between each rachidian tooth and left lateral and right lateral tooth, respectively. Lateral teeth with two arched, narrow, elongated and pointed hook-like cusps, basal cusp is shorter than the upper cusp; the inner cutting edge of the basal cusp (between the two cusps) is finely serrate. The outer edge of the basal cusp (below the basal spur) is serrate with small five to six sharp, pointed denticles.

1874.
Nassa  Habitat: Intertidal, up to 1 m depth, within degraded reef-flat with coral sand and silt.
Remarks: Nassarius persicus occur abundantly in its habitat and observed to be a dominant member of the intertidal fauna in intertidal reef-flats of Poshitra, Gujarat. It is a new record for India and a valuable addition to the fauna of Gulf of Kachchh Marine Sanctuary, Gujarat. Formerly, this species was misidentified (Ghosh 2008; Dave & Mankodi 2008), but a thorough investigation of its morphological characters clarifies its correct identity. The shell of N. persicus is similar to the western Indian Ocean species N. arcularia plicatus (Röding, 1798) in having large shield like columellar callous extending up to the penultimate whorl, creamy-yellow to pale grey colour of shells, a narrow brown band or dark brown spots or a nebulous darker band between sutural coronations of shells of both the species. But N. persicus can be easily distinguished from N. arcularia plicatus in having a slender shell with high spire, N. arcularia plicatus has a globous shell with moderate spire and spiral sculpture. Misidentification of N. persicus as N. olivaceus could be only due to the 'olive green' colour of the shell in live condition, else not any morphological similarity exists between these two species.

Nassarius tadjallii Moolenbeek, 2007 (Images 1B; 2C-D, H-J & L)
Vernacular name: Tadjalli's Nassa.  J TT spiral grooves gradually disappearing; remaining whorls smooth with only one, rather strong sub-sutural groove. Suture prominently channeled. Between the suture and the sub-sutural groove, the area is slightly nodulose and consists of alternate creamy white and dark brown dots. Shell colour is white or cream in the background with light and dark brown patterned patches. These patches are arranged in two light and three dark alternate bands, visible on the body whorl (shell colour in holotype is light brown, with darker brown patches). This banding pattern is not mentioned in the original description. The body whorl ends with three to four minor axial ridges followed by a strong varix. Varix is creamy white in colour and bears three distinct brown patches as extensions of the three dark patterned bands of the body whorl (Varix orange brown in holotype. This brownish hue caused by its intact periostracum). Aperture whitish, ovate, moderately wide, interior of outer lip with about nine lirate denticles. Columella plicate with two or three fine folds. Columellar callus thin, smooth, white, spreading slightly on body whorl and extending outwards at siphonal canal forming anterior ridge. Anterior or siphonal canal short, distinct, wide and marked with five spiral grooves or basal cords which ends as five denticles on outer lip. Posterior or anal canal distinct, moderately deep and marked by a strong posterior columellar ridge and a strong denticle on the top of the outer lip. Parietal denticle also prominent. Shell of BNHS NASSA 324 has three to four prominent repair scars on penultimate and body whorls.
Operculum (Image 2J): Operculum of BNHS NASSA 324 is corneous, yellowish brown in colour. Trapezoidal, elongate, simple, flattened with smooth inner margin, crenate outer margin and terminal nucleus. Information on operculum of holotype is not available.
Radula (Image 2L): Radula consists of 62-68 rows of teeth; rachidian teeth with concave crescentic base and cutting edge fringed with 9-11 sharp, pointed, conical denticles in symmetrical arrangement; corners of rachidian plate wide and smooth; accessory intermediate lateral plates present in between each rachidian tooth and left lateral and right lateral tooth, respectively. Lateral teeth with two arched, narrow, elongated and pointed hook-like cusps, the basal cusp being shorter than the upper cusp; the inner cutting edge of the lateral teeth (between the two cusps) is smooth. The outer edge of the basal cusp (below the basal spur) is also smooth. Basal spur is prominent. Information on radula of holotype is not available.
Distribution (Figure 1) Localities within India: Previously none. New localities within India (Figure 1): All three localities namely, Narara, Poshitra from Gulf of Kachchh and Shivrajpur (Arabian Sea), falls under district Devbhumi Dwarka, Gujarat, on northwestern coast of India.
Habitat: Intertidal, up to 1 m depth, within degraded reef-flat with coral sand and silt.
Remarks: Nassarius tadjallii Moolenbeek, 2007 is a new record for India which extends the distribution eastwards and is an addition to the marine fauna of Gujarat. This species shows morphological similarities and can be confused with N. marmoreus (A. Adams, 1852), N. javanus (Schepman, 1891) and N. thachorum Dekker et al., 2016. N. marmoreus from Oman is smaller and much darker in colour compared to N. tadjallii. N. javanus, which can be found in India (Tamil Nadu), is smaller and has a much more globose body whorl. N. thachorum from Vietnam differs from N. tadjallii in having a much weaker or lacking subsutural groove, the presence of a ridge consisting of small denticles on the columella, and has a darker colour of the shell (Dekker et al. 2016).

DISCUSSION
Prior to this work, Nassarius persicus and N. tadjalli had not been reported from India (Nerurkar et al. 2020) and thus, the present records extend the known range of these species from the Arabian Peninsula to Gujarat, India. Both these species of Nassarius currently are found only at Narara, Poshitra (Gulf of Katchchh) and Shivrajpur (Arabian Sea but close to Gulf of Katchchh) and not seen along the rest of the Indian coasts.
Marine fauna changes considerably in the northern part of the Gujarat State, especially in the Gulf of Katchchh. In the north, the fauna is influenced by the Arabian Sea upwelling which appears to have significant influence on the faunal change from Gulf of Katchchh across Mekran and into the Arabian Gulf. But we know little about it as faunal barrier. Williams et al. (2011) while discussing continental ark idea, observed a similar pattern in the case of dispersal of Lunella coronata (Gmelin, 1791) morph B along the continental coastline, from Arabian Peninsula to Porbunder, Gujarat, India.