Cerithideopsis malayensis, Reid & Claremont, 2014

Reid, David G. & Claremont, Martine, 2014, The genus Cerithideopsis Thiele, 1929 (Gastropoda: Potamididae) in the Indo-West Pacific region, Zootaxa 3779 (1), pp. 61-80 : 72-73

Cerithideopsis malayensis new species

( Figures 2F–H, N, O , 3B , 4 )

? Cerithidea fortunei — Casto de Elera, 1896: 329 (not A. Adams, 1855).

Cerithidea (Cerithidea) largillierti — Hasegawa, 2000: 133 (in part, includes C. largillierti , C. australiensis ).

Cerithidea largillierti —Lozouet, 2008: 286, pl. 88, fig. 4 (not Philippi, 1848).

Cerithideopsis largillierti — Lozouet & Plaziat, 2008: 57, 112, pl. 20, figs 4–6 (in part, includes C. largillierti , C. australiensis ).

Types. Holotype NHMUK 20100434 /1 ( Fig. 2N ) and 6 paratypes NHMUK 20100434 /2 ( Fig. 2F, O ), Kradeh , Kanchanadit, 20 km NE Surat Thani, Thailand.

Etymology. From its distribution, centred on the Malay Peninsula.

Taxonomic history. The record of ‘ Cerithidea fortunei ’ from Mindoro by Casto de Elera (1896) could possibly apply to this species. Also from the Philippines, it has previously been identified and figured as C. largillierti (Lozouet 2008; Lozouet & Plaziat 2008).

Diagnosis. Shell small (to 26 mm), brown with one pale spiral band above periphery; animal blackish, yellow edge to foot, 2 yellow bands across snout, yellow tentacles; Malay Peninsula , southern South China Sea, Philippines; COI: HE680619 – HE680622 , HE680624 , HE680625 .

Material examined. 18 lots.

Shell ( Fig. 2F–H, N, O ): H = 11.0– 26 mm. Shape elongated conical (H/B = 2.40–2.63, SH = 3.00–3.40); not routinely decollate, 7–11 whorls remaining in well preserved shells, but apex and protoconch always eroded. Spire whorls moderately rounded, suture distinct; spire profile slightly convex, slightly concave towards apex; periphery rounded; relatively delicate. Adult lip only slightly thickened, not flared; sometimes 1 previous lip on final whorl; apertural margin sinuous in side view; anterior canal a weak notch. Sculpture on spire of straight axial ribs, usually becoming curved (opisthocyrt) on last 2–3 whorls, ribs rounded, ribs and interspaces of similar width, 20–27(33) ribs on penultimate whorl, ribs becoming weaker and irregular on final whorl; smallest apical whorls with 3 spiral cords if well preserved, increasing to 6 by whorls 5–6, then becoming weak or disappearing, so that only a trace of 8–10 spiral elements is visible above periphery on penultimate whorl; base with 8–10 cords, of which 2 at periphery slightly enlarged, with marked groove between. No ventrolateral varix, but 0–3 indistinct or prominently raised and rounded varices may be present at any point on last whorl ( Fig. 2F ). Surface with spiral microstriae on thick periostracum; short periostracal fringe or bristles remaining on larger striae (i.e. 8–10 striae macroscopically visible above periphery) if well preserved; surface sometimes covered by thick black concretion. Colour: brown, with broad cream band above periphery, often concealed by periostracum; band visible by transparency within aperture.

Animal ( Fig. 3B ): sides of foot dark grey, broad yellow margin; head black, snout black with 2 broad transverse yellow stripes (one at tip), tentacles and tentacle bases yellow (examined in two samples from Kedah and Surat Thani). Yellow coloration not preserved after storage in ethanol, but pattern visible as absence of black pigment.

Range: Malay Peninsula, southern South China Sea , Philippines. Records : Burma: Kadan Kyun (King I.) ( NHMUK 1887.3.10.189). Thailand: Ao Nam Bor, Phuket I. ( NHMUK) ; Kradeh, Kanchanadit, 20 km NE Surat Thani ( NHMUK 20100434 ) . Malaysia: Bugang jetty, Merbok estuary, Kedah ( NHMUK 20080700 ) ; Pulau Lumut, Selangor ( USNM 661026 ) . Indonesia: near Bengkalis, Sumatra (T. Goulding & B. Dayrat); Cirebon , Java ( NNML) ; Mempawah, Borneo ( MZB) . Vietnam: Chilins, Vung Tau ( ANSP 330740 ) . Philippines: Abatan R., Bohol ( MNHN) ; Ponson I., Camotes I. ( USNM 287982 ) .

Habitat and ecology. In Malaysia and Thailand this species was found on firm, peaty mud and in shallow pools with leaf litter, in deep shade at the landward side of the Rhizophora belt. In the Abatan River mangal ( Philippines) Lozouet & Plaziat (2008) recorded it on mud in puddles in the shaded inner reaches of the mangrove forest, where it was rare.

Remarks. This species is small, usually scarce and difficult to find in its shaded, muddy habitat among leaf litter. It appears to have been overlooked in previous studies of the mangrove-associated molluscs of Southeast Asia (e.g. it was not mentioned by von Martens 1897, Van Benthem Jutting 1956 or Brandt 1974).

Molecular samples were available only from the Andaman Sea and Gulf of Thailand coasts of the Malay Peninsula. These showed no phylogeographic structure, in contrast to some other shallow-water marine gastropods in which a genetic break persists between the Indian and Pacific Oceans in this vicinity, consistent with repeated isolation of the two ocean basins during sea-level fluctuations associated with Plio-Pleistocene glaciations ( Reid et al. 2006). This could suggest that expansion to the Andaman Sea from the western Pacific (where its sister species C. largillierti occurs) is relatively recent. No molecular samples from the Philippines were available, but this is an area of endemicity in the potamidid genus Cerithidea ( Reid et al. 2013) . Shells from the Philippines do not differ obviously from those from the rest of the range but, in view of the limited morphological distinction between the three species of the C. largillierti complex, the conspecificity of the population in the Philippines should be tested with molecular data.

For comparison between the three species of Cerithideopsis in the Indo-West Pacific, see Remarks on C. australiensis below and Table 2 .

Figures

FIGURE 2. Shells of Cerithideopsis species. A–E. C. largillierti. F–H, N, O. C. malayensis n. sp. I–M, P–T. C. australiensis n. sp. A. China (Philippi 1849: Cerithium pl. 1, fig. 7). B. Cerithium (Potamides) largillierti Philippi, 1848, neotype and Cerithidea fortunei A. Adams, 1855, lectotype, Shanghai, China (NHMUK 20130431/1). C, D. Cerithidea fortunei A. Adams, 1855, paralectotypes, Shanghai, China (NHMUK 20130431/2, 3, respectively). E. Daehang-ri, Byeonsan-myeon, Buan-gun, Jeollabuk-do (NHMUK 20070408). F, O. C. malayensis n. sp., paratypes, Kradeh, Kanchanadit, 20 km NE Surat Thani, Thailand (NHMUK 20100434/2). G, H. Bugang jetty, Merbok estuary, Kedah, Malaysia (NHMUK 20080700). I, J. Cocoa Creek, Cleveland Bay, Queensland, Australia (NHMUK 20130433; 2 views of same specimen). K. Cockle Bay, Magnetic I., Queensland, Australia (NHMUK 20130434). L, M. C. australiensis n. sp., holotype, Cockle Bay, Magnetic I., Queensland, Australia (AM C.478294). N. C. malayensis n. sp., holotype, Kradeh, Kanchanadit, 20 km NE Surat Thani, Thailand (NHMUK 20100434/1). P, Q. Moreton Bay, Queensland, Australia (NHMUK 20130436). R–T. Broome, Western Australia (NHMUK 20130437; R, S, 2 views of same specimen).

FIGURE 3. Living animals (A–C) and periostracum (D) of Cerithideopsis species. A. C. largillierti, Kumamoto City, Kumamoto Pref., Kyushu, Japan (photograph: H. Fukuda; from Fukuda, 2000). B. C. malayensis n. sp, Merbok estuary, Kedah, Malaysia. C. C. australiensis n. sp, Wickham Point, Northern Territory, Australia (photograph: A.J. Bourke). D. C. australiensis n. sp., holotype, Cockle Bay, Magnetic I., Queensland, Australia (AM C.478294).

FIGURE 4. Distribution of Cerithideopsis largillierti (triangles), C. malayensis n. sp. (circles) and C. australiensis n. sp. (squares). Solid symbols, specimens examined; open symbol, literature record: A, Kamimura et al. (2010).