Echinolittorina Habe, 1956

Reid, David G., 2009, The genus Echinolittorina Habe, 1956 (Gastropoda: Littorinidae) in the western Atlantic Ocean 2184, Zootaxa 2184 (1), pp. 1-103 : 67-68

Subgenus Echinolittorina Habe, 1956

Nodilittorina (Echinolittorina) Habe, 1956: 96–99 (type by original designation Litorina tuberculata Menke, 1828 ; as Echinolittiorina in error, p. 96).

Diagnosis: Shell nodulose and spirally striate, occasionally a pseudumbilicus. Penis bifurcate, with penial glandular disc and 1–2 mamilliform glands. Pallial oviduct: additional glandular material present in a swelling around egg groove at anterior end of straight section; copulatory bursa opens at posterior end of straight section. Tropical Atlantic and eastern Pacific.

Remarks: No synapomorphic morphological characters have previously been discovered for the six members of this subgenus ( Reid 2002a), but in molecular phylogenetic analyses it is strongly supported ( Williams & Reid 2004; Williams & Duda 2008; Fig. 1 ). In the present study a unique synapomorphy has been found: the additional gland at the anterior end of the straight section of the pallial oviduct is present in all six members. If the topology of Figure 1 is accepted, the posterior position of the copulatory bursa (as coded by Reid 2002a) can be reconstructed as an equivocal synapomorphy of this subgenus, which is shared with most members of Amerolittorina .

The nodulose shells are convergent with those of Tectarius striatus ( King & Broderip, 1832) (from the Cape Verde Islands, Madeira and Azores; Reid 1996, as Littorina striata ) and Nodilittorina pyramidalis ( Quoy & Gaimard, 1833) (from eastern Australia; Reid & Williams 2004). Among other members of Echinolittorina closely similar nodulose shells are found in some Indo-West Pacific species of the subgenus Granulilittorina , in the E. natalensis and E. malaccana groups ( Reid 2007). Since almost all Granulilittorina species show either granulose or nodulose sculpture, and if the topology of the most recent molecular phylogeny is accepted ( Williams & Duda 2008; Fig. 1 ; but note that support for sister relationship between subgenera Granulilittorina and Echinolittorina is not strong, posterior probability = 89%) then it is likely that nodulose or granulose sculpture has arisen only once in the genus, in the common ancestor of these two subgenera. This in turn casts some doubt on the time calibration of the molecular phylogenies of Williams & Reid (2004) and Williams & Duda (2008). The only fossil used for calibration was E. lozoueti ( Dolin & Pacaud, 2000) , a nodulose species from the uppermost Lutetian stage of the Middle Eocene of France (41Ma), which was used to estimate the age of the entire genus. If this fossil had instead been used to estimate the divergence between Echinolittorina and Granulilittorina , the calibration scale would have been older. Nodulose sculpture is interpreted as an adaptation for convective heat loss in these species that are exposed to high temperatures in the littoral fringe ( Vermeij 1973a).

Figures

FIGURE 1. Molecular phylogeny of all 60 known species of worldwide Echinolittorina (after Williams & Duda 2008), with geographical distributions and subgeneric groups. This is a chronogram, produced by BEAST analysis of sequence data from 28S, 12S and COI genes, which employs Bayesian inference and an uncorrelated, relaxed, log-normal clock; error bars are 95% highest posterior density intervals, and numbers are Bayesian posterior probabilities (see Williams & Duda 2008 for methods). The time calibration of the phylogeny may be underestimated; see Remarks on subgenus Echinolittorina.