Cerithideopsis Thiele, 1929

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 : 67-68

Genus Cerithideopsis Thiele, 1929

Cerithidea (Cerithideopsis) Thiele, 1929: 206 (type species by original designation Cerithidea iostoma (Pfeiffer) = Potamides iostomus Pfeiffer, 1839 = C. pliculosa ( Menke, 1829)) .

Taxonomic history. Thiele (1929) introduced Cerithideopsis as a subgenus of Cerithidea on the basis of the short, rather square, rachidian tooth and other small differences from the radula of Cerithidea decollata (L.). As originally conceived, the new subgenus included species now assigned to the genus Cerithideopsilla (itself described as a new section of the subgenus by the same author, on the basis of its shell characters and IWP distribution). Pirenella was retained as a distinct genus, for forms of P. conica (Blainville) . In his original sense, Thiele’s (1929) nominate section Cerithideopsis included only American species. Subsequently, Cerithideopsis was generally treated as a purely American subgenus of Cerithidea ( Wenz 1938; Bequaert 1942; Houbrick 1984). As a result of the molecular phylogenetic analysis by Reid et al. (2008), Cerithideopsis was raised to generic rank and the IWP species of the C. largillierti complex were added.

Diagnosis. Shell: moderately large (to 48 mm), delicate to solid, elongate, spire not decollate; sculpture of axial ribs, weakening on body whorl; 1–2 swollen varices may be present anywhere on body whorl (not routinely in a ventrolateral position) and others scattered over spire whorls; spiral ridges present on base, outermost 1–2 strongest with deep groove between, ridges absent or sometimes present above periphery; aperture circular, peristome sometimes flared and thickened in adult, planar or sinuous in side view, with weak anterior canal and slight posterior groove; columella straight or very slightly twisted, lacking folds; colour dark with peripheral white band and sometimes other spiral lines. Radula: rachidian tooth broad, square to pentagonal, with long central cusp and 2 denticles on each side; lateral tooth with long lateral extension; outer marginal with numerous small cusps and wide flange on outer side of basal shaft ( Bright 1958: C. californica ; Houbrick 1984: C. scalariformis ).

Remarks. The comparative morphology of Cerithideopsis , Cerithidea and Cerithideopsilla has been described in detail by Houbrick (1984). Their respective monophyly was established in the molecular study by Reid et al. (2008), who also gave brief morphological diagnoses. A more detailed taxonomic account of Cerithidea was given by Reid (2014).

The three western Atlantic species of Cerithideopsis are C. pliculosa , C. costata and C. scalariformis ; these are relatively well known ( Bequaert 1942; Abbott 1974). Traditionally, six species have been accepted on the American west coast ( Keen 1971; Abbott 1974), but a recent molecular study ( Miura et al. 2010) has suggested that this should be reduced to three: C. californica , C. montagnei and C. pulchra (C.B. Adams, 1852) . Molecular discrimination of the American species is complicated by two cases of dispersal across the Panamanian Isthmus and subsequent introgression of mitochondrial haplotypes ( Miura et al. 2012).

The six Cerithideopsis species from the eastern Pacific and western Atlantic, and the three from the IWP described here, form two sister clades ( Reid et al. 2008; Miura et al. 2010; Fig. 1 ). Several morphological characters are restricted to the IWP species, including the thick periostracum, the absence of a strongly thickened and flared peristome, and the yellow markings of the living animal—contrasting with the brown to black animals described by Bright (1958) in C. californica and Houbrick (1984) in C. scalariformis . The deeper phylogeny of the family ( Reid et al. 2008) suggests that these are likely synapomorphies.

Spawn and larval development have been reported in several species. The American Cerithideopsis species lay strings of eggs on mangrove roots, fallen leaves, algae or the mud surface ( Houbrick 1984; Miura, Frankel & Torchin 2011). In the western Atlantic, C. scalariformis ( Houbrick 1984) and C. pliculosa ( Miura et al. 2011) hatch as late swimming-crawling veligers without a planktonic stage. In the eastern Pacific, C. californica in California either settles immediately upon hatching ( Miura et al. 2011, quoting unpublished thesis by MacDonald 1967) or emerges at the crawling stage ( Race 1981). However, in Panama C. californica shows a planktonic phase of up to 19 days ( Miura et al. 2011). Development of the IWP species has not been recorded.

The eastern Pacific and western Atlantic species of Cerithideopsis are all found at high tidal levels on sheltered sedimentary shores, often in estuaries and lagoons. They frequently shelter beneath mangroves and salt marsh plants, and all have been recorded to climb on vegetation at least occasionally, particularly to avoid submersion during high tide ( Houbrick 1984; Cantera, Thomassin & Arnaud 1999; D.G. Reid unpublished observation of C. montagnei ). However, they do not appear to display the regular climbing on mangroves and other emergent vegetation (involving avoidance of submergence and downward migration to feed) that is characteristic of Cerithidea species ( Reid 2014) . Climbing behaviour appears to have been independently derived in these two genera ( Reid et al. 2008). Burrowing into the mud during cold spells has been recorded in C. californica ( Race 1981) . The IWP Cerithideopsis species have never been seen to climb on vegetation and appear to have no aversion to being submerged in shallow pools; C. australiensis is known to bury in the mud during neap tides (see below).

Figures

FIGURE 1. A. Molecular phylogeny of Cerithideopsis species produced by Bayesian analysis of partial COI sequences, using Telescopium telescopium as the outgroup. Localities are abbreviated and followed by the last three or four digits of the registration or reference number (for full details see Table 1). Support values are posterior probabilities; only values ≥ 0.90 are shown. Significant clusters determined by GMYC function in SPLITS (Ezard et al., 2009) are indicated by thickened stems. B– D. Molecular phylogenies produced by Bayesian analysis of 16S rRNA, 28S rRNA and all genes combined (COI + 16S rRNA + 28S rRNA), showing only the clade that includes all three Indo-West Pacific species of Cerithideopsis.