Echinolittorina soroziczac, Reid, 2011

Reid, David G., 2011, 2974, Zootaxa 2974, pp. 1-65 : 33-36

Echinolittorina soroziczac new species

( Figures 8, 11G, H, 14, 15)

Littorina (Melarhaphe) punctata — Lamy, 1907: 149 (as Melaraphe ; not Gmelin, 1791).

Littorina punctata — Tomlin & Shackleford, 1914: 251 (not Gmelin, 1791). Alvarado & Alvarez, 1964: 267 (in part, includes E. punctata ). Fernandes & Rolán, 1993: 34 (not Gmelin, 1791).

Littorina (Austrolittorina) punctata — Rosewater, 1970: 423, pl. 367 (map) (in part, includes E. punctata , E. caboverdensis , E. pulchella and probably Afrolittorina knysnaensis and L. saxatilis ). Rosewater, 1981: 24–26 (in part, includes E. punctata , E. caboverdensis , E. pulchella ).

Nodilittorina aff. ziczac — Reid, 2002a: 259–281.

Echinolittorina aff. ziczac — Williams et al., 2003: 83.

Echinolittorina ziczac B— Williams & Reid, 2004: 2227–2251, fig. 6B (map). Williams & Duda, 2008: fig. 1 (phylogeny).

Echinolittorina (Amerolittorina) ziczac B— Reid, 2009: figs 1, 37 (phylogeny).

Echinolittorina sp. Robin, 2008: 114 , fig. 13.

Littorina sp. Robin, 2008: 117 , fig. 11.

Types: Holotype BMNH 20110127 ( Fig. 14A); 7 dry paratypes BMNH 20110128 ( Fig. 14E–F); 21 alcohol paratypes BMNH 20110129; Praia das Sete Ondas , São Tomé.

Etymology: combination of soror, Latin sister, and ziczac, Latinized zigzag, in reference to relationship to E. ziczac .

Taxonomic history: This species has rarely been mentioned or figured. In lists of the molluscs of São Tomé ( Lamy 1907; Tomlin & Shackleford 1914; Fernandes & Rolán 1993) and Annobón ( Alvarado & Alvarez 1964) it has been referred to as L. punctata . It was first noted as distinct in a morphological cladistic analysis by Reid (2002a) and this has been supported by subsequent genetic analyses ( Williams & Reid 2004; Williams & Duda 2008; Reid 2009). It was figured twice, without a specific name, in a recent popular book by Robin (2008).

Diagnosis: Shell with 22–43 incised spiral lines above periphery; pale to dark brown with white spots, often in spiral zones or axial zigzags; aperture brown with two pale bands. Penis bifurcate, with very large mamilliform penial gland occupying most of base. Pallial oviduct with projection of renal oviduct in centre of spiral of albumen gland. Islands in Gulf of Guinea. COI: GenBank AJ622973 , AJ622974 .

Material examined: 15 lots (including 8 penes, 10 pallial oviducts, 4 radulae).

Shell ( Fig. 14): Mature shell height 5.1–17.9 mm (20.3 mm, Robin 2008). Shape high turbinate to tall (H/B = 1.41–1.74, SH = 1.55–1.96); spire whorls rounded; suture distinct; spire profile slightly convex; periphery of last whorl rounded or slightly angled. Columella slightly hollowed and pinched at base; eroded parietal area slight or absent. Sculpture of 8–10 primary spiral grooves visible on spire whorls; these remain as narrow incised lines, increasing (by division and interpolation) to (17)22–43 above periphery of last whorl; periphery marked by a wider space without lines, not raised as a rib; 14–27 fine lines below periphery; sculpture sometimes faint from shoulder to suture; spiral microstriae usually absent, sometimes 1-3 microstriae in wider grooves. Protoconch not seen. Ground colour pale to dark brown, often with indistinct pale and dark spiral bands; smaller shells darker, with regular opisthocline array of white spots, sometimes fusing to give regular axial zigzag lines; spots may disappear except at periphery and on base in larger shells; colour pattern often interrupted or altered by darker growth lines on final whorl; aperture brown with external pattern showing through towards margin, pale band at base and at shoulder; columella white to purple brown.

Animal: Head black, no unpigmented stripe across snout; tentacle with two longitudinal black lines, sometimes fused, pale around eye; sides of foot black. Opercular ratio 0.32–0.38. Penis ( Fig. 15A–E): filament narrowly leaf shaped, tapering to tip, 0.5–0.6 total length of penis, separated from wrinkled base by a constriction, medial lip of sperm groove enlarged, groove ends terminally; mamilliform gland very large, entirely filling lateral projection and much of base; penial glandular disc relatively small; penis unpigmented. Sperm not seen. Pallial oviduct ( Fig. 15F): copulatory bursa separates at posterior end of straight section and extends back to albumen gland; renal oviduct enlarged, first loop posterior to seminal receptacle, another smaller loop projecting into centre of spiral loop of albumen gland before joining with albumen gland and duct from seminal receptacle at presumed point of fertilization; seminal receptacle small, elongate, in a more anterior position than in most congeners. Spawn not known; pelagic capsules predicted from form of pallial oviduct ( Reid 2002a).

Radula ( Fig. 11G, H): Relative radula length 1.93–15.0. Rachidian: length/width 1.38–1.80; major cusp long, tip rounded. Lateral and inner marginal: 4 cusps, tip of major cusp rounded or bluntly rounded. Outer marginal: 8– 10 cusps.

Range ( Fig. 8): Islands in the Gulf of Guinea. Range limits: Bioko I. ( Fernando Po), Equatorial Guinea ( ZMA); Annobón I. (Pagalu), Equatorial Guinea ( BMNH; MNHN); Praia das Conchas, São Tomé ( BMNH; MNHN); Bom Bom I., Príncipe, São Tomé and Príncipe ( BMNH).

Habitat: Only one collection has habitat information: bare basalt at high tide level ( BMNH 20110129, São Tomé, leg. T. Gascoigne). Crevices in splash zone ( Alvarado & Alvarez 1964).

Remarks: In studies of the molluscs of São Tomé and Annobón this species has been listed as L. punctata (see Synonymy above), although Alvarado & Alvarez (1964) noted that “the largest shells are whitish and appear at first glance to belong to another species”. It was first recognized as ‘ E. aff. ziczac ’ by Reid (2002a), who pointed out that it shared the unique synapomorphy of a greatly enlarged mamilliform penial gland with the western Atlantic E. ziczac , but that details of penis and shell were distinct. Genetic data demonstrate a close phylogenetic relationship between the two; reciprocal monophyly is shown by analyses of mitochondrial COI and 12S rRNA sequences, but this is not fully supported, and there is no support from analysis of the nuclear 28S rRNA gene ( Williams & Reid 2004). The average K2P distance for COI between E. ziczac and E. soroziczac is only 2.61%, among the lowest for any pair of accepted biological species of Echinolittorina ( Reid 2009) . Nevertheless, there are morphological differences that suggest some nuclear genetic differentiation. The shells are almost always distinct, that of E. soroziczac showing more rounded whorls (and therefore less acute posterior apertural angle), stronger spiral striae, a preponderance of brown coloration and only rarely a zigzag pattern of lines (cf. the generally white shell with narrow brown lines and zigzags in E. ziczac ; Reid 2009: fig. 14). In addition, the penis of E. soroziczac has a smaller mamilliform gland, which is not bent into a U-shape to fit into the penial base (cf. Reid 2009: fig. 15A–E). Approximately 7000 km separates the two species on either side of the Atlantic Ocean, far exceeding the maximum potential for larval dispersal in Echinolittorina (1200 to 2100 km; Reid 2002b, 2007), so that continuing gene flow between them is very unlikely.

This species has been recorded only from islands off the African coast, suggesting a typical oceanic distribution. Primary productivity maps show that the three islands that lie furthest offshore ( Príncipe, São Tomé and Annobón) lie in oceanic waters (Rutgers University Primary Productivity Study). However, Bioko lies on the continental shelf and during the rainy season between about September and February is influenced by water of high productivity. When rainfall is high the plume of the Congo and Niger rivers lowers the surface salinity to 30‰, and also affects the more distant islands ( Measey et al. 2007). It appears, therefore, that E. soroziczac may have some tolerance of continental conditions, at least for part of the year.

Some specimens show abrupt changes in shell colour pattern following growth interruptions ( Fig. 14D), suggesting that environmental conditions influence shell colour.

The shell is similar to those of the three members of the E. punctata group ( Figs 6, 9, 12), but in E. soroziczac the grooves above the periphery of the final whorl are more numerous (22–43) and there are two pale spiral bands within the aperture ( Table 1). There are no records of sympatric occurrence with E. pulchella , which is restricted to the African mainland.