(Figures 2I–M, P–T, 3C, D, 4)
Cerithidea largillierti — Hedley, 1909: 357. Hinton, 1978: pl. 7, fig. 1. Hinton, 1979: pl. 6, fig. 1. Healy, 1983: 57–75, figs 50– 53, 55, 63, 69, 95–98 (euspermatozoa). Wells & Bryce, 1986: 55, pl. 11, fig. 129. Jarrett, 2011: 40, fig. 96 (all not Philippi, 1848).
Cerithidea ? largillierti — Houbrick, 1984: 16 (in part, includes C. largillierti).
Cerithidea (Cerithidea) largillierti — Wilson, 1993: 133, pl. 15, fig. 12 (not Philippi, 1848). Hasegawa, 2000: 133 (in part, includes C. largillierti, C. malayensis).
Cerithideopsis largillierti — Reid et al., 2008: 680–699, fig. 2 (phylogeny and shell; in part, includes C. largillierti). Lozouet & Plaziat, 2008: 112 (in part, includes C. largillierti, C. malayensis). Willan, 2013: 78, fig. 9 (not Philippi, 1848).
Types. Holotype AM C.478294 (Fig. 2L, M) and 2 paratypes NHMUK 20130435, Cockle Bay, Magnetic Island, Queensland, Australia.
Etymology. From its distribution, largely confined to Australia.
Taxonomic history. Previously, this species has always been known under the specific name largillierti. Reid et al. (2008) first suggested that C. largillierti s. l. consisted of two species, from Japan and Australia respectively, with a relatively high genetic (K2P) distance for COI of 15%.
Diagnosis. Shell relatively large (to 48 mm), brown with 1–2 pale spiral bands, or white with 1–3 brown bands; animal black with dense yellow spots; tropical Australia and Gulf of Papua; COI: AM 932790, AM 932791, HE680615 – HE680617.
Material examined. 42 lots.
Shell (Fig. 2I–M, P–T): H = 15.2–48.2 mm. Shape elongated conical (H/B = 2.30–2.64, SH = 3.13–3.48); not routinely decollate, 10–14 whorls remaining in well-preserved shells, but apex and protoconch always eroded. Spire whorls rounded, suture distinct; spire profile very slightly convex, slightly concave towards apex; periphery rounded; relatively solid. Adult lip only slightly thickened and flared; sometimes up to 3 previous lips and strong growth lines near end of final whorl; apertural margin sinuous in side view; anterior canal a weak notch. Sculpture on spire of straight axial ribs, becoming curved (opisthocyrt) on last 2–3 whorls, ribs rounded, ribs and interspaces of similar width, 15–24(29) ribs on penultimate whorl, ribs becoming weaker and irregular on final whorl; smallest apical whorls with 2–3 spiral cords if well preserved, increasing to 5 by whorls 5–6, then disappearing, so that only a trace of 8–10 spiral elements is visible above periphery on penultimate whorl, stronger posteriorly; 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, up to 7 in total on last 3 whorls (Fig. 2J, M, Q, S). Surface with spiral microstriae on thick periostracum (Fig. 3D); short periostracal fringe or bristles remain on larger striae (i.e. 8–10 striae macroscopically visible above periphery) if well preserved. Colour: brown, with broad cream band above periphery, sometimes additional pale band at suture; pattern often concealed by periostracum; in northwestern Australia shells are white with 1–2 brown bands above periphery and sometimes a brown line between 2 strong outermost basal grooves (Fig. 2R–T); bands visible by transparency within aperture.
Animal (Fig. 3C): sides of foot and snout black with dense yellow spots, 2 larger yellow spots near tip of snout; tentacle bases yellow (Fig. 3C from Northern Territory). Yellow coloration not preserved after storage in ethanol, but pattern visible as absence of black pigment (examined in two lots from Proserpine and Thirsty Sound, Queensland).
Range: Tropical Australia and Gulf of Papua. Records: Western Australia: Cossack (AM C.439257); Lookout Hill, Broome (NHMUK 20130437); Buccaneer Archipelago (AM C.042509). Northern Territory: Ludmilla Creek, Darwin (NHMUK); Bing Bong station (AM C.412930). Queensland: Forsyth I. (AM C.108447); Mapoon (AM C.014282); Missionary Bay, Hinchinbrook I. (NHMUK); Cockle Bay, Magnetic I. (NHMUK 20130435); Plum Tree, Thirsty Sound (AM C.419622); Russell I., Moreton Bay (AM C.410423); Lota Creek, Waterloo Bay, SW Moreton Bay (NTM P.49902). Papua New Guinea: 30 miles E Port Moresby (AM C.82943).
Wells & Bryce (1986: 55) recorded this species from “North West Cape, W.A. to Queensland ”. The southernmost records are from Moreton Bay, southern Queensland. Hinton (1979: caption of pl. 7) observed that this species was “reasonably common in Gulf of Papua ”.
Habitat and ecology. In northern Queensland it is found on mud and in shallow pools with leaf litter, in the shade of Ceriops trees on the edges of saltpans in mangrove areas. The snails bury themselves in the mud during neap tides. In Broome, Western Australia, it was found on soft mud beneath Avicennia trees in a wide belt of this tree fringing a coastal mudflat. Willan (2013) reported that it inhabits the middle and lower tidal zones of mangrove forests where the mud is soft, and remains in pools when the tide recedes.
Remarks. Shells from Western Australia are always pale in colour and of unusually thick texture (Fig. 2R–T). This marine region is known for its high endemicity and the mangrove-associated gastropods include the endemic Cerithidea reidi Houbrick (Reid 2014), Littoraria cingulata (Philippi) and L. sulculosa (Philippi), besides several distinctive regional forms with low genetic divergence (Reid 1986; Reid, Dyal & Williams 2010). White shells with brown lines (2 above periphery and 2 below) are occasionally found as far east as Darwin (NTM P.009694). Genetic study is required to test the status of the western form of C. australiensis.
The three species of Cerithideopsis in the Indo-West Pacific are extremely similar in shell characters and there are no entirely diagnostic characters by which to separate them (Table 2). In overall size, C. malayensis is typically small (not exceeding 26.0 mm in shell length), while C. australiensis reaches largest size (up to 48.2 mm in shell length). Their shapes and rib counts show broad overlap. In shell colour, C. largillierti typically has two pale bands above the periphery, while C. malayensis has one and colour is more variable in C. australiensis, but this feature is not useful when the shell is encrusted with mud and algae, covered by a thick periostracum or when severely eroded. The headfoot of C. largillierti is black with yellow tentacle bases and tip of snout when living; that of C. malayensis is black with two yellow stripes across the snout and a yellow edge to the foot, while that of C. australiensis is black with yellow spots. In ethanol-preserved specimens the yellow coloration fades almost to white, but the black pigmentation remains. Available information indicates that these colour patterns are speciesspecific, but this requires confirmation. The distributions of the three species are entirely allopatric (Fig. 4) and this provides the simplest means of identification.
Cerithideopsis australiensis is of small size relative to edible potamidids such as species of Terebralia, Telescopium and Cerithidea, and has not been found in densities that would appear sufficient to warrant collection for food. Willan (2013) noted that C. australiensis is never consumed by Aboriginal people in Australia. However, this has not always been the case; the species dominates many middens dated to around 2000–2500 BP on the coast of Papua New Guinea southeast of Port Moresby (Petchey et al 2012; specimens from Caution Bay examined).