Echinolittorina granosa (Philippi, 1848)

Reid, David G., 2011, 2974, Zootaxa 2974, pp. 1-65 : 37-43

Echinolittorina granosa (Philippi, 1848)

( Figures 16, 17, 18A, B, 19)

Litorina granosa Philippi, 1848: 65 , Litorina pl. 7, fig. 14 ( Liberia and Gabon; lectotype ( Rosewater 1981: 44, pl. 2H) Philippi 1848: Litorina pl. 7, fig. 14; Fig. 16A herein).

Tectarius granosus —H. Adams & A. Adams, 1854: 315. Dautzenberg, 1912: 47. Tomlin & Shackleford, 1914: 251. Dautzenberg, 1927a: 504. Nicklès, 1947: 4. Nicklès, 1949: 114. Nicklès, 1950: 49, fig. 40. Nicklès, 1952: 144. Buchanan, 1954: 34. Barnard, 1963: 191 (in part, includes E. reticulata ( Anton, 1838)) . Edmunds, 1978: 28, fig. 4B. Bernard, 1984: 28, pl. 3, fig. 19. Fernandes & Rolán, 1993: 34. Ardovini & Cossignani, 2004: 21 (figure p. 81 is incorrectly localized Tectarius antonii ( Philippi, 1846)) . Robin, 2008: 118, fig. 6.

Littorina granosa —Reeve, 1858: Littorina sp. 106, pl. 18, fig. 106. Troschel, 1856 –1863: 135, pl. 11, fig. 3, 3a (radula). Hoyle, 1887: 340.

Tectarius miliaris var. granosus — Tryon, 1887: 259, pl. 48, figs 69, 77.

Nodilittorina granosa — Rosewater, 1978: 32–33. Reid, 2002a: 259–281.

Nodilittorina (Granulilittorina) granosa — Rosewater, 1981: 31–32, pls 1H, I, 2H, pl. 3I (operculum), pl. 4C (radula), 4H (penis).

Nodilittorina (Echinolittorina) granosa — Reid, 1989: 99.

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

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

Litorina striata — Dunker, 1853: 10–11 (in part, includes Tectarius striatus ). Watson, 1886: 575–576 (in part, includes Tectarius striatus ).

Littorina striata — Nobre, 1909: 34 (in part, includes Tectarius striatus ).

Littorina glans Reeve, 1857 : Littorina sp. 62, pl. 12, fig. 62a, b (no locality, Mus. Cuming; ‘ holotype BMNH 1859.4.6.10’ given by Rosewater 1981: 31, but the 2 specs in this lot are from HMS Rattlesnake and are not syntypes, so inferred lectotype designation is invalid; 3 possible syntypes BMNH 20110146 from Cape Palmas, ex Cuming Colln).

Litorina glans —Weinkauff, 1882: 62, pl. 8, figs 5, 6. Weinkauff, 1883: 214.

Tectarium miliare — Lamy, 1907: 149 (in part, includes Tectarius striatus ; not Quoy & Gaimard, 1833).

Nodilittorina miliaris — Vermeij, 1972a: 694 (not Quoy & Gaimard, 1833). Vermeij, 1972b: 93 (not Quoy & Gaimard, 1833). Lawson & John, 1982: 42 (not Quoy & Gaimard, 1833).

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

Littorina (Melarhaphe) striata var. affinis — Dautzenberg, 1927b: 117 (in part, includes Tectarius striatus ; as Melaraphe ; not L. affinis d’Orbigny, 1839 = T. striatus ).

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

Taxonomic history: Philippi (1848) described this species based on material from Liberia supplied by von dem Busch and from Gabon supplied by Largilliert. No material is present in the collection of the Geoscience Department of the University of Bremen (where the collection of von dem Busch is housed; Kuster-Wendenburg 2008) or in the MNHN (which holds material from Largilliert, including some seen by Philippi; Reid 1986). In the absence of original material, Rosewater (1981: 44) designated Philippi’s (1848) figure as lectotype.

For most of its history this has been recognized as a valid species, because of its distinctive shell. Authors with a broad species concept have often synonymized it with E. miliaris ( Tryon 1887; Lamy 1907; Vermeij 1972a, b; Rosewater 1975; Lawson & John 1982). There has also been confusion with nodulose forms of Tectarius striatus ( Dunker 1853; Watson 1886; Dautzenberg 1927b).

Diagnosis: Shell sculptured with 5–7 closely spaced cords with rounded, dark nodules, usually in axial alignment. Senegal to Congo; Islands in Gulf of Guinea. COI: GenBank AJ623005 , AJ623006 .

Material examined: 70 lots (including 8 penes, 2 sperm samples, 13 pallial oviducts, 4 radulae).

Shell ( Fig. 16): Mature shell height 5.9–21.2 mm. Shape turbinate to high turbinate (H/B = 1.10–1.68, SH = 1.42–2.10); spire whorls rounded; suture distinct; spire profile straight to slightly convex, concave near apex; periphery of last whorl rounded or slightly angled. Columella short, hollowed and slightly pinched at base; eroded parietal area. In shells with fine, well-preserved sculpture ( Fig. 16B–E, G, H), 5–7 nodulose spiral cords from just below periphery to suture, with (0)1–2(3) threads and fine spiral microstriae in spaces between cords; most shells severely eroded, with 5–7(11) equally developed rows of nodules from just below periphery to suture, the nodules rounded and usually well aligned axially in prosocline series ( Fig. 16F, J, K, N); the most strongly sculptured shells are small, tall, with 3-5 rows of rugose nodules ( Fig. 16P–R); base with 4–5 weakly nodulose ribs. Protoconch 0.26–0.28 mm diameter, 2.8–3 whorls. Ground colour grey brown, in weakly sculptured shells the ribs are brown with whitish nodules; strongly nodulose shells mainly black with paler base; in eroded shells nodules usually black against grey background; aperture dark brown with pale band at base and sometimes a second band at shoulder; columella purple brown.

Animal: Head black; tentacle pale around eye and across base, with two longitudinal grey to black stripes, fusing just behind pale tip; sides of foot black. Operculum: opercular ratio 0.52–0.67, central part thickened (thinner operculum and lower ratio, 0.39–0.45, in a sample of weakly sculptured shells). Penis ( Fig. 17A–F): filament 0.5– 0.6 total length of penis, with annular wrinkles for most of its length (so not clearly differentiated from wrinkled base), tapering or slightly blade-shaped, sperm groove ends terminally; mamilliform gland small, about one-fifth size of large penial glandular disc, borne together on stout projection of base; penis unpigmented. Euspermatozoa 65–70 µm; paraspermatozoa ( Fig. 17H, I) containing 1–2 parallel-sided rod-pieces 14–20 µm, with rounded or truncated ends, slightly projecting from cell, which is packed with large round granules. Pallial oviduct ( Fig. 17G): copulatory bursa separates at posterior end of straight section and extends back to albumen gland; 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. 18A, B): Relative radula length 2.63–8.24. Rachidian: length/width 1.39–1.67; major cusp long, tip pointed to rounded. Lateral and inner marginal: 4 cusps, tip of major cusp rounded. Outer marginal: 9–12 cusps.

Range ( Fig. 19): Senegal to Congo, islands in Gulf of Guinea. Range limits: Cape Vert, Senegal ( Sourie 1954); Casamance, S Senegal ( Nicklès 1947, 1950); Conakry, Guinea ( BMNH; MNHN; USNM 803310); 25 km E of Accra, Ghana ( BMNH); Cotonou, Benin ( USNM 707159); Limbe, Cameroon ( BMNH); Port-Gentil, Gabon ( MNHN); Bioko I., Equatorial Guinea ( BMNH; MNHN; ZMA); Annobón I., Equatorial Guinea ( BMNH; MNHN); Praia das Conchas, São Tomé ( BMNH; MNHN); Pointe-Noire, Congo ( Collignon 1960).

The records from Senegal ( Nicklès 1950; Sourie 1954) have not been verified; there is a small possibility that these could be extralimital occurrences of sculptured forms of Tectarius striatus , but that species has not been definitely recorded from the mainland of Africa ( Reid 1996, as L. striata ). Lawson (1956) reported E. granosa to be absent from the coast of Ghana to the east of Cape Three Points, but subsequently found it to be sporadic there ( Lawson 1966). It does appear to be rare between Accra and western Cameroon, with only a single record (Cotonou, Benin) from the intervening region. This is a coast dominated by mangroves ( Lawson 1966) where suitable habitat is scarce.

Habitat: In upper littoral fringe, on basalt, granite, laterite, sandstone and shale, mainly in moderately sheltered situations. In Ghana the species was most common under overhangs, between boulders and in shade of overhanging trees; occasionally it occurred on soil and salt-tolerant plants such as Sesuvium and grasses (personal observation). Although found on the relatively oceanic shores of Annobón and São Tomé, it is also tolerant of brackish conditions near river mouths on the continental shore ( Sierra Leone, Ghana, Cameroon).

Authors have recorded this species from the top of the eulittoral and in the littoral fringe ( Buchanan 1954; Lawson 1955, 1956, 1957; Longhurst 1958; Vermeij 1972a, 1973), reaching up to 3 m above MHWS ( Bassindale 1961). It is found on a range of substrates, including soft shale ( Vermeij 1972b), laterite ( Marchal 1960) and schist ( Vermeij 1973). Lawson (1966) observed that it is especially common in areas of high rainfall and scarce where rainfall is lower (e.g. eastern Ghana); animals have been observed to cluster at freshwater seepages on cliffs (personal observation: Ghana). Although recorded from sheltered and exposed shores ( Gauld & Buchanan 1959) it exhibits a preference for moderately exposed and sheltered coasts ( Collignon 1960; Bassindale 1961). In Ghana it is less common than co-occurring E. pulchella ( Lawson 1956; Edmunds 1978), but on coastlines influenced by river outflows it is the dominant species, as in Sierra Leone ( Lawson 1957), Cameroon and Gabon ( Lawson & John 1982). Where both species are found together, E. granosa occupies the higher level ( Lawson 1956, 1966; Gauld & Buchanan 1959; Lawson & John 1982; John & Lawson 1991), but occasionally also extends slightly lower into the barnacle zone ( Longhurst 1958). A density of 198 per 0.25 m 2 has been recorded in Sierra Leone ( Lawson 1957). It has been found up to 6 miles from the mouth of the Sierra Leone river ( Longhurst 1958) and at a site where salinity falls to 21‰ at Conakry, Guinea ( Marchal 1960). There is an upshore increase in size ( Vermeij 1972a).

Remarks: There is variation in shell shape from turbinate to tall, and in sculpture from weakly to strongly nodulose ( Fig. 16). At Matrakni Point, Ghana, there was a contrast between the large, turbinate, rounded, weakly nodulose shells found on a sheltered shore on the shaded sides of granite boulders ( Fig. 16B, E, H) and the small, highconical, angular, strongly nodulose shells ( Fig. 16M, P, Q) on a moderately exposed shore nearby. This could be explained by a connection between strong sculpture and small size in unfavourable microhabitats where growth is slow, as has been suggested in Tectarius striatus ( Reid 1996) . Transfer experiments with E. australis ( Gray, 1826) have yielded experimental evidence of the phenotypic plasticity of sculpture and of the adaptive value of nodulose shells that cool more quickly in full sun ( Johnson & Black 1999; Yeap et al. 2001).

The spiral form of the operculum shows more variation than in other congeners, the opercular ratio ranging from 0.39–0.67 and the thickness increasing with a tighter spiral. The thinnest and most paucispiral opercula were observed in shells with weak sculpture, suggesting that this form might likewise be produced when growth is rapid in favourable habitats. In typical nodulose shells the operculum is more tightly wound than in other eastern Atlantic Echinolittorina species. Thick, multispiral opercula are considered to be adaptive to resist desiccation at the highest shore levels ( Bandel & Kadolsky 1982).

Of the 13 pallial oviducts examined, only one showed evidence of a small expansion of the lower chamber (as in E. helenae , Fig. 23F); in the others no expansion was visible when viewed in standard orientation ( Fig. 17G). This character has only been noted in members of the E. granosa group and may be a synapomorphy of the clade.

The geographical distribution along the mainland coast of Africa and habitat range extending into estuarine environments, suggest that this is a continental species. Nevertheless, the distribution also includes the islands of São Tomé and Annobón in the Gulf of Guinea. These islands lie in oceanic water of low productivity, but are also influenced by the plume of the Congo and Niger rivers in the wet season ( Measey et al. 2007), which may account for the occurrence of E. granosa . The K2P genetic distance for COI between a specimen from São Tomé and one from Cameroon was only 0.42% ( Williams & Reid 2004) so there is no evidence for significant genetic divergence between island and mainland populations.

Shells of the typical nodulose forms of E. granosa ( Fig. 16A, J, K, N) cannot be confused with those of any other Echinolittorina , because the 5–7 rows of closely spaced, blackish nodules in axially aligned series are diagnostic. However, in the uncommon weakly sculptured forms ( Fig. 16B–E, G, H) the nodulose cords are reduced in width, pale in colour and separated by interspaces 2–3 times as wide; these shells resemble weakly sculptured forms of E. miliaris ( Fig. 20H, K). There is no consistent difference, but both the cords and the threads between them may be slightly more numerous in E. granosa ( Table 2). These weakly sculptured forms are only superficially similar to Tectarius striatus ( Reid 1996: fig. 10); in that species the spiral ribs are closely set, of similar width, and intermediate threads are virtually absent.