Echinolittorina Habe, 1956

Reid, David G., 2011, 2974, Zootaxa 2974, pp. 1-65 : 36

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; one or two white lines in aperture. 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. (Diagnosis modified from Reid 2009.)

Remarks: Genetic data show that the three eastern Atlantic members of this subgenus, the E. granosa group ( E. granosa , E. miliaris , E. helenae ), form a clade ( Williams & Reid 2004; Williams & Duda 2008; Reid 2009). There has been a history of taxonomic confusion between them and, together with E. vermeiji ( Bandel & Kadolsky, 1982) , all have at times been considered subspecies or synonyms of the first species to be named, E. miliaris . Their distributions are allopatric and, despite intraspecific variation, their shells are generally distinct. Anatomical differences among them are minimal; their penes are similar, but E. miliaris has a uniquely large lower chamber of the spiral part of the pallial oviduct. Tectarius striatus is another striate or granulose littorinid from the eastern Atlantic archipelagos, and has been confused with the members of the E. granosa group. Occasionally all the nodulose Echinolittorina species and T. striatus have been synonymized as Nodilittorina tuberculata ( García-Talavera 1983) , which is a Caribbean species.

Like other nodulose members of the genus Echinolittorina ( Reid, 2002b, 2007, 2009) these three species each show a remarkable range of intraspecific variation. The most extreme nodulose forms are usually smaller with a taller spire, whereas those with weak or absent nodules (including non-nodulose ‘striate’ forms in E. helenae ) are larger and broader. The parallels with shell variation in other Echinolittorina species (especially E. australis ( Gray, 1826) ; see review by Reid 2007) suggest an ecophenotypic basis and a likely correlation of nodulose sculpture with slow growth in open sunny conditions without strong wave splash. A similar range of variation is found in the distantly related Tectarius striatu s from the Cape Verde Islands, Canary Islands and Azores ( Reid 1996), and shells of E. helenae can be almost indistinguishable from that species. The characters of all four are compared in Table 2.

There is a superficial similarity between the nodulose shell forms of the eastern Atlantic E. ( Echinolittorina ) species and those of some members of E. ( Granulilittorina ) in the Indo-West Pacific. One useful feature for rapid discrimination between these groups is the presence of two pale bands in the aperture (the universal basal band and another at the shoulder) in many (but not all) shells of E. ( Echinolittorina ); the shoulder band is never present in the subgenus Granulilittorina .