Echinolittorina marisrubri, Published, 2007

Reid, David G., 2007, The genus Echinolittorina Habe, 1956 (Gastropoda: Littorinidae) in the Indo-West Pacific Ocean, Zootaxa 1420 (1), pp. 1-161 : 28-31

Echinolittorina marisrubri new species

( Figures 6E, F , 10 , 11 , 12 )

Nodilittorina (Granulilittorina) subnodosa — Rosewater, 1970: 495–496, pl. 383, figs 7–10, pl. 383a (map) (in part, includes E. subnodosa , E. arabica ; not Philippi, 1847).

Nodilittorina (Nodilittorina) subnodosa — Sabelli & Taviani, 1984: 95–100, pl. 1 (radula, penis), figs 3–5 (not Philippi, 1847).

Nodilittorina subnodosa — Sharabati, 1984: pl. 6, figs 4, 4a (not Philippi, 1847). Verbinnen & Dirkx, 2005: 112, fig. 5 (not Philippi, 1847).

Nodilittorina arabica — Dekker & Orlin, 2000: 20 (not El Assal, 1990). Reid, 2002a: 259–281 (in part, includes E. arabica ; not El Assal, 1990).

Echinolittorina arabica — Williams et al., 2003: 83 (in part, includes E. arabica ; not El Assal, 1990).

Echinolittorina arabica B—Williams & Reid, 2004: 2227–2251.

Types: Holotype BMNH 20030885 ( Fig. 11G ); 10 dry and 36 alcohol paratypes BMNH 20030886 ( Fig. 12A, B, E, F ); Port Safaga , Egypt.

Etymology: Latin, from the Red Sea.

Taxonomic history: Together with E. arabica this species was included with E. subnodosa by Rosewater (1970). Sabelli & Taviani (1984) and Verbinnen & Dirkx (2005) correctly distinguished the two nodulose species in the Red Sea, but misidentified E. subnodosa as N. natalensis and E. marisrubri as N. subnodosa . Following the description of E. arabica by El Assal (1990), that name was applied to E. marisrubri also (Dekker & Orlin 2000; Reid 2002a), and the two were only distinguished with molecular data (Williams & Reid 2004).

Diagnosis: Shell conical; 3 rows of nodules at and above periphery, with 1 beaded rib and smaller threads between; cream, yellow or orange, nodules white; Red Sea. COI: GenBank AJ622979 , AJ622980 .

Material examined: 22 lots (including 5 penes, 2 sperm samples, 6 pallial oviducts, 3 radulae).

Shell ( Fig. 11 ): Mature shell height 6.7–11.8 mm. Shape high turbinate to conical (H/B = 1.29–1.52; SH = 1.53–1.87); spire whorls flat or slightly rounded, suture distinct; spire profile slightly convex, often concave at apex; periphery of last whorl weakly angled. Columella short, concave, slightly hollowed at base; no eroded parietal area. Sculpture of last whorl: usually 3 rows of pointed nodules at periphery, shoulder and near suture, with single beaded rib (occasionally 2 or more) and 1 or more threads in each interspace, in total 8–13 ribs and threads at and above periphery; posterior row of nodules may be absent; suture and adjacent posterior part of last whorl usually rugose; in smoothest shells ( Fig. 11D ) 8 subequal granulose ribs at and above periphery and nodules absent; spiral microstriae cover entire surface; base with 3–7 nodulose ribs, 1–2 threads in interspaces. Protoconch 0.29–0.30 mm diameter. Colour: cream, pale yellow, orange or grey; spire whorls brownish; nodules paler or white; sometimes a faint spiral pattern of brown marks between nodules and granules on ribs; aperture brown with pale band at base; columella cream to dark brown.

Animal ( Fig. 12 ): Head pale to dark grey, with or without unpigmented stripe across snout, tentacle pale around eye, with two longitudinal grey to black lines; sides of foot grey to black. Opercular ratio 0.51–0.61. Penis ( Fig. 12A–E ): filament blade-shaped, tip rounded, base narrowed, filament 0.7–0.8 total length of penis, sperm groove extends to tip; mamilliform gland and glandular disc of similar size, borne on short projection of base; penis unpigmented or slightly pigmented at base. Euspermatozoa 86–100 µm; paraspermatozoa ( Fig. 12G, H ) oval, with 1–3 rod-pieces 14–27 µm, either slightly projecting and straight with rounded ends, or strongly projecting and slightly curved, cytoplasm filled with large round granules. Pallial oviduct ( Fig. 12F ): bursa opening at midpoint of straight section and extending back to albumen gland. Spawn a pelagic capsule 250 µm diameter, 150 µm high, cupola-shaped upper side sculptured by 3 concentric rings, containing single ovum 70 µm diameter (Hulings 1986; as N. subnodosa but probably this species). Development planktotrophic (Hulings 1986).

Radula ( Fig. 6E, F ): Relative radula length 2.60–3.12. Rachidian: length/width 1.32–1.52; tip of major cusp pointed. Lateral and inner marginal: major cusp on each of similar size, tips rounded. Outer marginal: 5– 6 cusps.

Range ( Fig. 10 ): Red Sea and western Gulf of Aden. Range limits: Suez Canal, Egypt (BMNH 1928.3.26.76); Eilat, Israel (BMNH 20030883); Djibouti (MNHN); Conquest Bay, Aden, Yemen (BMNH). The coast of Somalia is poorly sampled, but absence of this species from the Arabian Sea coast east of Aden is believed to be genuine.

Habitat and ecology: Substrate records include rocks on both sandy and muddy beaches, coral limestone cliffs and piers; it is found in the upper eulittoral zone or littoral fringe. In the Gulf of Aqaba this species occupies a zone above that of E. millegrana ; its rate of water loss has been measured and it survived out of water for 17 days in the field (Hulings 1987, as N. subnodosa , but average size = 7.3 mm, so probably this species). Reproduction occurs from June to September in the Gulf of Aqaba (Hulings 1986, as N. subnodosa ). Most available samples show high frequencies of repaired shell breakage ( Fig. 11F, G ), probably attributable to attempted predation by crabs.

Remarks: The new species is closely related to its sister taxon E. arabica (Williams & Reid 2004; see Remarks on that species for discrimination).

This species is poorly represented in museum collections; it is apparently not rare, but may have been overlooked in favour of the larger and superficially similar E. subnodosa with which it is sympatric. Shells of E. subnodosa are larger (to 18.7 mm) and broader, also with three rows of nodules, but the rows are widely spaced and the intervening threads are not granulose; there are brown lines connecting the nodules ( Fig. 19 ). Males may be separated by the shape of the penial filament, smooth and strap-shaped in E. marisrubri ( Fig. 12A–E ), but tapering and with annular wrinkles in E. subnodosa ( Fig. 20A–D ). The new species just overlaps with E. omanensis at Aden; shells of the latter are grey or blackish with three rows of white nodules, of which those in the anterior row are axially elongate, and the intervening threads are not granulose ( Fig. 17 ). From the western Indian Ocean, E. natalensis displays similar features to E. omanensis , but is less elongate ( Fig. 13 ).

There have been few observations of the habitat of this species. It occurs throughout the Red Sea, and therefore in both the oligotrophic northern part and in the more nutrient-rich south that is under the influence of water from the Gulf of Aden (Sheppard 2000). Absence from the Arabian Sea coast of Arabia might be due to the monsoon-driven summer upwelling of cool water (Wilson 2000).

During glacial low sea-level stands the water depth in the shallow Bab el Mandab seaway at the mouth of the Red Sea was reduced to a mere 15 m. Evaporation then exceeded inflow from the Gulf of Aden so the Red Sea became hypersaline; salinities in the central and northern parts are estimated to have exceeded 50 ‰ (Siddall et al. 2003). Most marine organisms would not have been able to survive such extremes and the most recent recolonization took place following the last glaciation, about 15000 years ago (Sheppard et al. 1992). It follows that species now endemic to the Red Sea, such as E. marisrubri , must either have survived in refugia in the very south of the Red Sea or in the Gulf of Aden, or otherwise must have originated very recently. The age of separation of E. marisrubri and E. arabica can be estimated as 1.3–2.4 Ma (COI K2P distance = 6.24% and using evolutionary rates from Williams & Reid 2004). The present distribution of E. marisrubri ( Fig. 10 ) suggests that only a very small refugium may have existed outside the mouth of the Red Sea. However, during glacial intervals the strength of the upwelling along the southern coast of Arabia was much reduced (Sheppard et al. 1992) and the distribution of E. marisrubri may then have been more extensive in the Gulf of Aden.

Figures

FIGURE 6. Radulae of Echinolittorina species (two views of each radula, flat and at 45°). A, B, E. radiata; Kinkasan I., Miyagi Pref., Japan (BMNH 20050563; shell H = 8.7 mm). C, D, E. arabica; Hamriya, Sharjah (BMNH 20030871; shell H = 8.4 mm). E, F, E. marisrubri new species, paratype; Port Safaga, Egypt (BMNH 20030886; shell H = 10.6 mm). G, H, E. omanensis new species, paratype; Wadi Sayq, Jabal Qamr, Dhofar, Oman (BMNH 20040220; shell H = 14.2 mm). Scale bars = 50 µm.

FIGURE 10. Distribution of Echinolittorina arabica (solid circles) and E. marisrubri (open circles).

FIGURE 11. Echinolittorina marisrubri new species. A, Little Aden, Yemen (BMNH 20030882). B, C, Safaga, Egypt (NNML). D, Eilat, Israel (BMNH 20030883). E, H, Red Sea (BMNH 20030884). F, paratype (BMNH 20030886). G, holotype, Port Safaga, Egypt (BMNH 20030885). I, Hind Kadam, Sudan (BMNH 1891.1.31.49).

FIGURE 12. Echinolittorina marisrubri new species. A–E, penes. F, pallial oviduct. G,H, paraspermatozoa. A, B, E, F, paratypes; Port Safaga, Egypt (BMNH 20030886; shell H A = 10.7 mm, B = 10.4 mm, E = 9.3 mm, F = 10.3 mm). C, D, G,H, Ras Mohammed, Sinai, Egypt (BMNH 20030887; shell H C = 9.6 mm, D = 10.2 mm). Shading conventions as in Figure 3.

FIGURE 13. Echinolittorina natalensis. A–C, Tiwi Beach, Kenya (BMNH 20040209). D, J, K, North Pier, Durban, South Africa (BMNH 20040210). E, F, Ankarena, Île Ste Marie, Madagascar (BMNH 20030679). G, H, no locality [probably eastern Madagascar] (MNHN). I, L, N, Libanona Beach, Tolagnaro, Madagascar (BMNH 20030691). M, Litorina natalensis Krauss in Philippi, 1847, lectotype, Natal, South Africa (SMNS ZI.0050942).

FIGURE 17. Echinolittorina omanensis new species. A, B, Merca, Somalia (HUJ 30002). C, F, M, Mirbat, Dhofar, Oman (BMNH 20040213). D, Mughsayl I., Dhofar, Oman (BMNH 20040214). E, Karachi, Pakistan (BMNH 20040215). G,H, W Mughsayl I., Dhofar, Oman (BMNH 20040217). I, Karachi, Pakistan (BMNH 20040216). J, holotype, Wadi Sayq, Jabal Qamr, Dhofar, Oman (BMNH 20040218). K, L, Mukalla, Aden, Yemen (BMNH 20040221).

FIGURE 19. Echinolittorina subnodosa. A, no locality [Red Sea] (BMNH 20040224). B, C, Hammam-Fara’un, Gulf of Suez, Egypt (BMNH 20040225). D–F, Mukawwar I., Sudan (BMNH 20040226). G, I, S of Port Sudan Harbour, Sudan (BMNH 20040227). H, Litorina subnodosa Philippi, 1847, lectotype figure, Red Sea (Philippi, 1847, Litorina pl. 3, fig. 9). J, no locality [Red Sea] (BMNH 20040228).

FIGURE 20. Echinolittorina subnodosa. A–D, penes. E, paraspermatozoa. F, pallial oviduct. G, head. A, El-Qalawi, 30.5 km S Port Safaga, Egypt (BMNH 20040229; shell H = 12.5 mm). B, C, F, Mukawwar I., Sudan (BMNH 20040226; shell H B = 13.0 mm, C = 12.3 mm, F = 13.1 mm). D, E, G, Ras Mohammed, S Sinai, Egypt (BMNH 20040230; shell H = 10.3 mm). Shading conventions as in Figure 3.