Echinolittorina helenae (E.A. Smith, 1890)

Reid, David G., 2011, 2974, Zootaxa 2974, pp. 1-65 : 47-50

Echinolittorina helenae (E.A. Smith, 1890)

( Figures 18E, F, 19, 22, 23)

Littorina striata — Jeffreys, 1872: 262 (not King & Broderip, 1832 = Tectarius striatus ). Melliss, 1875: 125 (not King & Broderip, 1832).

Litorina striata — Watson, 1897: 291 (in part, includes T. striatus ).

Littorina helenae Melliss, 1875: 125 (nomen nudum).

Littorina helenae ‘Melliss’ E.A. Smith, 1890a: 283–284, pl. 21, fig 19 (St Helena; lectotype ( Rosewater, 1981: 35, pl. 2L) BMNH 1889.10.1.2546, seen, Fig. 22M herein; 8 paralectotypes BMNH 1889.10.1.2547–2554, Bandel & Kadolsky 1982: fig. 51, seen).

Nodilittorina miliaris helenae — Rosewater, 1978: 32–33.

Nodilittorina (Granulilittorina) miliaris helenae — Rosewater, 1981: 34–36, pl. 1L, M, 2L, M, pl. 3F (operculum), 4E (radula), 4O (penis).

Nodilittorina (Nodilittorina) helenae — Bandel & Kadolsky, 1982: 37, fig. 51.

Nodilittorina helenae — Reid, 2002a: 259–281.

Echinolittorina helenae — Williams et al., 2003: 83. Williams & Reid, 2004: 2227–2251, fig. 6F (map). Williams & Duda, 2008: fig. 1 (phylogeny).

Echinolittorina (Echinolittorina) helenae — Reid, 2009: figs 1, 37 (phylogeny).

Littorina miliaris —E.A. Smith, 1890a: 283 (in part, includes E. miliaris ).

Nodilittorina (Granulilittorina) miliaris — Rosewater, 1975: 10–11, fig. 3 (in part, includes E. granosa , E. miliaris , E. vermeiji , T. striatus ).

? Nodilittorina (Echinolittorina) miliaris — Reid, 1989: 99 (in part, includes E. miliaris , doubtfully E. vermeiji ).

Nodilittorina tuberculata — García-Talavera, 1983: 44–45, map (in part, includes E. tuberculata , E. vermeiji , E. miliaris , E. granosa , T. striatus ).

Taxonomc history: In the first report on the molluscs of St Helena, Jeffreys (1872) misidentified the sole littorinid species from the island as L. striata , which is the species now known as Tectarius striatus from the more northern island groups of Cape Verde, Canaries, Madeira and Azores. Shells of the two are closely similar (see Remarks below). The name L. helenae was first used by Melliss (1875) in a general account of St Helena, for “a small periwinkle, found abundantly alive and sticking to the rocks all around the sea-coast at and above high-water mark”. Without a morphological description, this must be considered a nomen nudum. In addition, he listed L. striata , “also found alive with the other species”. Smith (1890a) concurred that two species were present on the island, but identified the larger, smoother form as L. miliaris rather than L. striata , which shows his careful observation. He associated Melliss’ L. helenae with smaller, conical, tuberculate shells with angled periphery, and gave a formal description to validate the name. In fact these two forms are extremes of the wide range of E. helenae .

Rosewater (1975) classified all the littorinids from the Atlantic islands ( E. miliaris , E. vermeiji , E. helenae , T. striatus ) as a single species, Nodilittorina miliaris . The specific name helenae does not appear to have been used until Rosewater (1978, 1981) considered it as a subspecies of N. miliaris , while Reid (1989) listed it as a doubtful synonym of the latter. Bandel & Kadolsky (1982) regarded it as a full species on morphological grounds, as did Reid (2002a). Genetic data have since supported this status ( Williams & Reid 2004; Williams & Duda 2008; Reid 2009).

Diagnosis: Shell sculptured with 12-20 low spiral ribs of varying width with microstriae between; 4 largest ribs sometimes bear small nodules. Oviduct with small expansion of muscular chamber between albumen gland and posterior end of bursa. St Helena. COI: GenBank AJ623009 , AJ623010 .

Material examined: 23 lots (including 10 penes, 10 pallial oviducts, 4 radulae).

Shell ( Fig. 22): Mature shell height 4.1–17.8 mm. Shape turbinate to high turbinate (H/B = 1.30–1.66, SH = 1.47–1.91); spire whorls slightly rounded; suture usually distinct; spire profile straight, sometimes slightly concave near apex; periphery of last whorl rounded or occasionally angled. Columella short, hollowed and slightly pinched at base, with or without an anterior lip; eroded parietal area. Sculpture of non-nodulose (‘striate’) forms ( Fig. 22A– C, G–I, L): 12-20 low spiral ribs and threads (including base) varying in width and prominence, larger ones slightly rugose; interspaces up to same width as ribs, with spiral microstriae. Sculpture of nodulose forms ( Fig. 22D–F, J, K, M, N): 3 largest ribs on spire whorls bear small nodules; 4 largest ribs at and above periphery of last whorl bear small nodules, of which two anterior rows may fuse to give large nodules at angular periphery ( Fig. 22M); often eroded. Protoconch 0.36 mm diameter, 2.4 whorls. Ground colour grey, ribs pale brown or flecked with brown; aperture dark brown with pale band at base and sometimes a second band at shoulder, in pale shells brown lines of the ribs show through at margin; columella purple brown.

Animal: Head black; tentacle pale around eye and sometimes across base, with two longitudinal grey to black stripes, often fused; sides of foot black. Operculum: opercular ratio 0.43–0.61. Penis ( Fig. 23A–D): filament 0.5– 0.6 total length of penis, with annular wrinkles for most of its length (so not clearly differentiated from wrinkled base), smooth only at slightly pointed tip, sperm groove ends terminally; mamilliform gland small, about one-fifth size of large penial glandular disc, borne together on stout projection of base; penis pigmented at base. Spermatozoa not seen. Pallial oviduct ( Fig. 23E, F): copulatory bursa separates at two-thirds length of straight section and reaches back to touch spiral of albumen gland; a small expansion of basal chamber usually visible between bursa and seminal receptacle ( Fig. 23F); additional glandular material present in a swelling around egg groove at anterior end of straight section. Spawn not known; pelagic capsules predicted from form of pallial oviduct ( Reid 2002a).

Radula ( Fig. 18E, F): Relative radula length 2.35–3.87. Rachidian: length/width 1.38–1.79; major cusp long, tip rounded. Lateral and inner marginal: 4 cusps, tip of major cusp rounded. Outer marginal: 9–10 cusps.

Range ( Fig. 19): Island of St Helena only. Records: James Bay ( BMNH 20110164); Jamestown jetty ( BMNH 20110157); Rupert’s Bay ( ZMA); Sandy Bay ( USNM 634135).

Habitat: Common in littoral fringe, on bare rocks and in small pools; up to 70 feet (21 m) above water level (label of BMNH 1892.8 .19.70 by W.H. Turton) .

Remarks: Among Echinolittorina species this shows an unusually wide range of variation in shell shape and sculpture ( Fig. 22), which was at first interpreted as the coexistence of two species ( Jeffreys 1872; Melliss 1875; Smith 1890a). In contrast to other two members of the E. granosa group, the striate shell form of E. helenae is more common than the nodulose form. This could reflect genetic differentiation or possibly, in view of the likely ecophenotypic effects acting on shell form (see Remarks on subgenus Echinolittorina and on E. granosa ), a difference in shore topography or climate within St Helena. As in other Echinolittorina species , the correlation of small size, nodulose sculpture and tall spire implies that the nodulose form may be a consequence of slow growth in an unfavourable microhabitat. Despite the wide range of shell form, no pronounced variation was detected in the four radulae examined (cf. normal and narrowed forms of other Echinolittorina species , e.g. E. punctata , E. caboverdensis ; see Reid 2009: 83–85).

The sister species of E. helenae is E. miliaris (see Remarks on the latter).

Among Echinolittorina species , the striate shells of E. helenae are distinctive and unlike any other. However, they show remarkable convergence with shells of Tectarius striatus , a littorinid endemic to the more northerly Atlantic islands of the Cape Verde, Canary Island and Azores archipelagos. The turbinate form, flattened or weakly rounded spire whorls, sometimes concave spire profile, tendency to develop small nodules, and external coloration are identical in each. Close inspection reveals that in T. striatus the sculpture is of 15–20 evenly sized ribs (counting over the whole of the last whorl, since the periphery is not distinct) that are triangular in section and closely spaced, without intervening threads ( Reid 1996: fig. 10). Furthermore, the aperture never contains two pale bands, but only the single basal band that is present in most littorinines. In the striate shells of E. helenae ( Fig. 22A–C, G– I, L) the 12–20 ribs are low, of unequal size, sometimes minutely rugose and there are 1–3 threads between each; both species have microstriae between the ribs. In nodulose shells, those of T. striatus show three rows of small nodules, whereas in those of E. helenae there are four rows ( Fig. 22D–F, J, K, M, N). Anatomical features of penis and oviduct distinguish these two species unequivocally ( Table 2). In rare cases ( Fig. 22J) the shell of E. helenae is extremely similar to those of weakly sculptured forms of E. miliaris and E. granosa (compare with Figs 16, 20).