Echinolittorina Habe, 1956

Reid, David G., 2007, The genus Echinolittorina Habe, 1956 (Gastropoda: Littorinidae) in the Indo-West Pacific Ocean, Zootaxa 1420 (1), pp. 1-161 : 13-15

Genus Echinolittorina Habe, 1956

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

Taxonomic history: The complex history of the generic classification of those littorinids now referred to the genus Echinolittorina has been reviewed in detail elsewhere (Reid 2002b; Reid & Williams 2004). Briefly, most nineteenth century authors employed the single genus Littorina (used in the emended form Litorina by some, mainly German, workers). H. Adams & A. Adams (1854) grouped species with elongate and patterned shells (together with the species now classified as Littoraria ) as Littorina subgenus Melarhaphe , while those with nodulose shells were placed in the genus Tectarius (emended by some authors as Tectaria or Tectarium , and incorrectly as Tectus), and a similar scheme was adopted by Weinkauff (1883) and Tryon (1887). In 1897 von Martens introduced Nodilittorina as a subgenus of Littorina , for nodulose species with a paucispiral operculum and no columellar tooth (thereby contrasting with Tectarius ). This subgenus was later transferred to Tectarius on the basis of radular similarities, while smooth-shelled species remained in L. ( Melarhaphe ) (Thiele 1929; Wenz 1938). Nodilittorina was first used as a full genus, for Indo-Pacific species, by Habe (1951). Abbott (1954) was the first to include details of the penis and spawn in his revision of littorinid genera; he classified the nodulose western Atlantic species as Nodilittorina tuberculata , but pointed out its anatomical similarity and close relationship to the smooth-shelled L. (Melarhaphe) ziczac (Gmelin, 1791) (i.e. E. ziczac ). Citing Abbott’s (1954) description of the radula of N. tuberculata, Habe (1956a) established the new subgenus Echinolittorina for this species, retaining Nodilittorina s.s. for Indo-Pacific species alone. Subsequently, the genus Granulilittorina was erected (Habe & Kosuge 1966a, b) on the basis of the unusual egg capsule of its type species, G. philippiana Habe & Kosuge, 1966 (= E. vidua ). In his monograph of Indo-Pacific littorinids, Rosewater (1970) described characters of penis and spawn, but still used shell sculpture as the basis of his generic classification. Smooth-shelled species currently included in Echinolittorina were distributed among five subgenera of Littorina , while Nodilittorina was divided into three subgenera: Nodilittorina with nodulose shells, Granulilittorina with granulose sculpture, and the monotypic Echinolittorina with nodulose shell and narrow rachidian tooth. Small changes were made by Ponder & Rosewater (1979) and later an additional subgenus, L. ( Fossarilittorina ), was introduced (Rosewater 1981).

A more natural (i.e. phylogenetic) classification of these species was attempted by Bandel & Kadolsky (1982), who pointed out the evolutionary convergence in characters of the littorinid shell, radula and operculum. Emphasizing penial and spawn characters, they grouped all current Echinolittorina species in two genera, Nodilittorina and Fossarilittorina . This scheme was largely supported by the first attempt at a formal cladistic analysis of littorinid genera (Reid 1986a), although a more thorough analysis (Reid 1989a) recognized only Nodilittorina , with three subgenera: Fossarilittorina , Echinolittorina and Nodilittorina . The evidence for the monophyly of the genus Nodilittorina was, nevertheless, weak and supported by the sole synapomorphy of tentacle coloration, while the subgenera Echinolittorina and Nodilittorina were separated only by the position of the copulatory bursa within the pallial oviduct. As taxonomic and anatomical data accumulated, it became clear that a small group of Nodilittorina species with smooth shells and southern-temperate distribution could be characterized by the structure of the pallial oviduct, and these were provisionally placed in the subgenus Austrolittorina (Reid 2002b) . A renewed attempt at a morphological phylogenetic analysis supported this southern-temperate clade, but failed to confirm the monophyly of Nodilittorina as a whole, because of pervasive homoplasy of morphological characters (Reid 2002a).

More recently, progress has been made by means of molecular phylogenetic analysis. It has been conclusively demonstrated that Nodilittorina (sensu Reid 1989a, 2002a, b) is polyphyletic (Williams et al. 2003). The southern-temperate species have been removed to the two monophyletic genera Austrolittorina and Afrolittorina (Williams et al. 2003; Reid & Williams 2004). The remaining species consist of a large tropical clade and the unrelated N. pyramidalis from southeastern Australia. The latter is the type species of Nodilittorina designated by Abbott (1954), and that genus is therefore now monotypic. The earliest available name for the remaining tropical species is Echinolittorina , with the western Atlantic E. tuberculata as its type (Habe 1956a).

Molecular support for the monophyly and divergence of Echinolittorina is strong, based on the combined sequence of two nuclear (28S and 18S rRNA) and two mitochondrial (12S rRNA and cytochrome oxidase I) genes, of which 28S provided the strongest signal (Williams et al. 2003; Williams & Reid 2004). Nevertheless, mapping of the known morphological characters of the subfamily Littorininae onto the molecular phylogeny failed to discover any unique morphological synapomorphy for the genus Echinolittorina (Reid 2002a; Williams et al. 2003). The characters enumerated in the following diagnosis are all either plesiomorphic within the subfamily Littorininae , or are homoplasies that are shared with other genera. Taken together, however, they diagnose the monophyletic taxon recognized by molecular analyses.

Diagnosis: Shell aragonitic; nodulose, granulose, spirally striate or entirely smooth; if smooth or striate then usually with dark axial stripes or axially aligned series of dashes; eroded parietal area may be present, sometimes a small pseudumbilicus; aperture dark with pale spiral band at base (i.e. anterior end) and sometimes another posteriorly. Cephalic tentacles with 2–3 longitudinal black lines, all black, or with broad transverse band at base distal to eye. Operculum paucispiral. Penis with blade-shaped filament (rarely swollen); base usually bifurcate (not so if mamilliform gland absent); usually a single mamilliform gland (sometimes absent, rarely 2); glandular disc of subepithelial glandular tissue usually present; penial vas deferens an open groove or rarely a closed tube. Rod-pieces of paraspermatozoa usually long and straight (rarely small and irregular, or curved). In pallial oviduct egg groove makes a simple loop through albumen gland, straight path through capsule gland and jelly gland; copulatory bursa opens in anterior or posterior position within straight section of pallial oviduct. Spawn a biconvex pelagic capsule with cupola-shaped upper side sculptured by concentric rings, containing single egg; development planktotrophic. Outer marginal radular tooth with flange at inside and at outside of base. Distribution worldwide tropical and warm temperate.

Remarks: As here defined, Echinolittorina is the largest genus of Littorinidae , with 59 recognized species worldwide (accepting the molecular ESUs of Williams & Reid 2004 as species).