Echinolittorina mespillum ( Mühlfeld, 1824 )

Reid, David G., 2009, The genus Echinolittorina Habe, 1956 (Gastropoda: Littorinidae) in the western Atlantic Ocean 2184, Zootaxa 2184 (1), pp. 1-103 : 22-27

Echinolittorina mespillum ( Mühlfeld, 1824)

( Figures 2H , 5C–F , 7–9 )

Helix mespillum Mühlfeld, 1824: 219 , pl. 8, fig. 8a, b (types not in NHMW, presumed lost; neotype here designated

BMNH 20080967, Cienfuegos, Cuba; Fig. 7A ). Littorina mespillum — Johnson, 1934: 102. Bequaert, 1943: 19–21, pl. 6, fig. 17–19. Abbott, 1954a: 133, pl. 19k.

Coomans, 1958: 62, pl. 8. Bandel, 1974a: 102, 107, 18–22 and 34–35 (radula). D’Asaro, 1986: 190–191, fig. 2c, d

(egg capsule). Sterrer, 1986: 407–408, pl. 135. Littorina (Neritrema) mespillum — Abbott, 1958: 34. Warmke & Abbott, 1961: 53–54, pl. 9m. Rehder, 1962: 122. Littorina (Melarhaphe) mespillum — Rosewater, 1970: 424 (as? Melarhaphe ). Abbott, 1974: 68, fig. 557. H.E. Vokes &

E.H. Vokes, 1983: 14, pl. 4, fig. 7 (as Melaraphe ). Díaz & Puyana, 1994: 125, pl. 34, fig. 405. Littorina (Fossarilittorina) mespillum — Rosewater, 1981: 30. Fossarilittorina mespillum — Britton & Morton, 1989: 86, fig. 4-5O. Nodilittorina (Fossarilittorina) mespillum — Reid, 1989: 98. Nodilittorina mespillum — Redfern, 2001: 28, pl. 14, fig. 116. Reid, 2002a: 259–281. Echinolittorina mespillum — Williams, Reid & Littlewood, 2003: 60–86. Williams & Reid, 2004: 2227–2251, fig. 6A

(map). Turbo minimus Wood, 1828: 19 , pl. 6, Turbo fig. 29 (no locality; 2 probable syntypes BMNH 1968369, seen). Littorina minima — Gray, 1839: 139. Reeve, 1857: sp. 86, pl. 16, fig. 86. Litorina minima —Philippi, 1847: 197, Litorina pl. 4, fig. 6. Weinkauff, 1878: 35, pl. 3, figs 23, 24 (pl. 3 by Küster 1856).

Weinkauff, 1883: 221. Clench, 1938: 113–114. Littorina (Melarhaphe) minima —H. Adams & A. Adams, 1854: 314 (as Melaraphe ). Mörch, 1876: 141 (as Melaraphe ).

Nevill, 1885: 138 (as Melaraphe ). Tryon, 1887: 252, pl. 45, fig. 11 (as Melaraphe ). Littorina mespillum var. minima — Usticke, 1959: 34.

Littorina (Neritrema) minima — Rehder, 1962: 121–122.

Littorina mespillum forma minima — Coomans, 1963. De Jong & Coomans, 1988: 20, pl. 32, fig. 83.

Littorina fusca L. Pfeiffer, 1840: 254 ( Cuba; 9 possible syntypes BMNH 20060796 , seen).

Littorina naticoides d’Orbigny, 1841: 214–215 , pl. 15, figs 21–23 (La Havane [La Habana], Cuba; 17 syntypes BMNH 1854.10 .4.138, seen).

Litorina mespilum Philippi, 1847: 16 , Litorina pl. 6, fig. 20 (unjustified emendation of Helix mespillum Mühlfeld, 1824 ). Küster, 1856: 15–16, pl. 2, figs 16, 17 (pl. 2 1853). Weinkauff, 1878: 30. Weinkauff, 1883: 219.

Littorina mespilum —Reeve, 1857: sp. 77, pl. 15, fig. 77.

Littorina (Melarhaphe) mespilum — Mörch, 1876: 141–142 (as Melaraphe ). Nevill, 1885: 139 (as Melaraphe ). Tryon, 1887: 252, pl. 45, fig. 16, 17 (as Melaraphe ).

Littorina (Neritoides) mespilum —Arango, 1880: 159.

Litorina (Litorina) mespilum — Dall, 1889: 146. Dall & Simpson, 1901: 430.

Litorina gundlachi Philippi, 1849 ( Cuba; as ‘ grundlachi ’, but given as ‘ gundlachi ’ in index p. vi; named for the collector Gundlach, therefore a justified emendation; types not traced). Weinkauff, 1882: 107. Weinkauff, 1883: 227.

Littorina (Melarhaphe) gundlachi —H. Adams & A. Adams, 1854: 314 (as Melaraphe ). Mörch, 1876: 142 (as Melaraphe ).

Neritina pupa — Lewis, 1960: 417, fig. 11J (egg capsule), K (veliger) (includes Puperita pupa (Linnaeus)) .

Taxonomic history: The figure provided by Mühlfeld (1824) is poor and misleading, showing a thin, globular shell with a narrow, twisted columella and no umbilicus, so that the identity of this species could be doubted. However, he described a somewhat thick, umbilicate shell with an everted and adnate columella lip and this, together with the given size (6.98 x 5.45 mm) and locality of the Antilles, indicate the present species. To obviate any doubt, a neotype is here designated.

The collection of L. Pfeiffer in the Stettin Museum was destroyed during the 1939–45 war ( Dance 1986), but possible syntypes of L. fusca have been located in BMNH; these shells may have been sent to H. Cuming by Pfeiffer (they are labelled simply ‘ L. fusca Cuba’).

Philippi (1849) received material of Litorina gundlachi from Gundlach, a collector in Cuba, and Dance (1986) reported that the Gundlach collection remains in Cuba in the University of La Habana. The name was introduced for a more acute-spired form of this species, because it was compared with Melarhaphe neritoides .

The shell described as Helix mespillum Mühlfeld, 1824 was of the brown variety, whereas Turbo minimus Wood, 1828 was of the white form with black spots. These were treated as distinct species throughout the nineteenth century (Philippi 1847; Weinkaiff 1878, 1883; Reeve 1857; Mörch 1876; Nevill 1885; Tryon 1887) and even by Rehder (1962). The former was invariably spelled mespilum , following the unjustified emendation of Philippi (1847). Clench (1938) first noted that the colour forms were no more than varieties, although he used L. minima as the valid name. This conspecificity was confirmed by Bequaert (1943), and the original spelling restored.

As pointed out by Bandel (1974a), the ‘beehive-shaped’ capsules identified by Lewis (1960) as those produced by Puperita pupa are almost certainly of E. mespillum , with which P. pupa frequently occurs.

Diagnosis: Shell small; smooth except for microstriae and one incised peripheral line; narrow pseudumbilicus usually present; brown, cream or white, with or without black spots. Penis simple, tapering, no glands, closed sperm duct. Islands in Caribbean Sea, Bahamas, E Florida, Bermuda. COI: GenBank AJ622955 , AJ622956 .

Material examined: 78 lots (including 10 penes, 4 sperm samples, 6 pallial oviducts, 4 radulae).

Shell ( Fig. 7 ): Mature shell height 2.8–9.4 mm (occasionally to 12.5 mm, USNM 773840). Shape globular to turbinate (H/B = 1.06–1.38, SH = 1.16–1.38, occasionally to 1.67); whorls rounded; suture distinct; spire profile slightly to strongly concave; spire whorls often eroded away; last whorl may be slightly compressed laterally, shoulder sometimes thickened, periphery rounded. Columella short, broad, slightly pinched at base; narrow pseudumbilical slit usually present, sometimes inconspicuous, occasionally as wide as columella; no eroded parietal area. Sculpture absent but for fine spiral microstriae over entire surface and usually a single incised line just above periphery; periostracum dull, but surface shiny if worn. Protoconch 0.26 mm diameter, 2.5 whorls. Colour red brown, blackish brown, yellow brown, pinkish cream or white; brown shells usually unmarked but may bear a few inconspicuous small dark brown spots ( Fig. 7C, F ); cream shells sparsely and irregularly spotted ( Fig. 7H ); white shells are more heavily spotted with black ( Fig. 7G ); aperture brown with external pattern showing through, sometimes a pale zone at base (not forming a distinct band); columella brown.

Animal: Head ( Fig. 8A ) black to grey, with an unpigmented stripe across snout; tentacle unpigmented, rarely with two short longitudinal black stripes just distal to eye, usually a black dot at tip; sides of foot with grey to black band. Operculum ( Fig. 2H ): opercular ratio 0.31–0.41. Penis ( Fig. 8A–F ): wrinkled base merges into simple blade-like filament with rounded to pointed tip; vas deferens closed as a superficial duct (running from anterior end of open prostate, across right side of head, to tip of penial filament); penis unbranched and lacking mamilliform glands or penial glandular disc; penis unpigmented. Euspermatozoa 50–57 µm; paraspermatozoa ( Fig. 8K, L ) containing single (occasionally divided) elongate rod-piece 31–39 µm with rounded ends, projecting from cell, which is packed with round granules. Pallial oviduct ( Fig. 8H–J ): short copulatory bursa separates at anterior one third length of straight section; posterior half of straight section constricted and flexed into U-shaped loop that contains an opaque cream or reddish gland around the egg groove (this is not an extension of the small translucent capsule gland). Spawn ( Fig. 8G ): an asymmetrically biconvex pelagic capsule 250–260 µm diameter by 150 µm high with broad peripheral rim slightly overhanging base, dome-shaped upper side sculptured by 1–2 concentric rings, containing single ovum 80–110 µm diameter ( Lewis 1960, as Puperita pupa : Barbados; D’Asaro 1986: Bahamas).

Radula ( Fig. 5C–F ): Relative radula length 1.70–3.40. Rachidian: square ( Fig. 5C ) to elongate ( Fig. 5E ), length/width 1.14–2.93; major cusp broad, tip pointed. Lateral and inner marginal: 4 cusps, tip of major cusp pointed; major cusp may be enlarged, becoming more rounded, other cusps then reduced in size ( Fig. 5E ). Outer marginal: 6–8 cusps; no flange on outer side of base; may be narrowed ( Fig. 5E ).

Range ( Fig. 9 ): Islands throughout Caribbean Sea, Bahamas, SE Florida, Bermuda. Range limits: Jupiter Blowing Rock , Palm Beach Co., Florida ( USNM 706883 ; Bingham, 1973); West Summerland Key , Florida ( USNM 820412 ) ; Tea Street, Bermuda ( USNM 773841 ) ; Green Turtle Key, Bahamas ( USNM 709129 ) ; Great Inagua I., Bahamas ( USNM 390227 ) ; Puerto Sosua, Santo Domingo, Dominican Republic ( ZMA) ; Little Bay , St Maarten ( ZMA) ; St Vincent ( BMNH 1840.8.24.206); Barbados ( USNM 54653 ) ; La Orchila I., Venezuela ( USNM 656007 ) ; Aruba, Netherlands Antilles ( ZMA) ; Morant Reef, Jamaica ( BMNH 20080973 ) ; Priory, Jamaica ( BMNH 20080974 ) ; Cayman Brac, Cayman Is ( BMNH) ; Santiago, Cuba ( USNM 663176 ) ; Gibara, Cuba ( MNHN) ; Cienfuegos, Cuba ( BMNH 20080968 ) ; Veradora, Cuba ( BMNH) ; Punta Cajón, Cuba ( USNM 435438 ) ; San Miguel, Cozumel, Quintana Roo, Mexico ( USNM 736568 ) ; Cancun, Quintana Roo, Mexico ( USNM 794784 ) .

This species is frequent on oceanic islands in the region. In addition, there are numerous records from all around Cuba, three from the Dominican Republic and three from the north coast of Jamaica. Abbott & Jensen (1967) first reported this species from Bermuda, and Sterrer (1986) suggested that it was ‘a recent (1950–1960) introduction’. There are just two records from mainland coasts, one from the east coast of Florida ( Bingham 1973) and one at the northeastern tip of the Yucatán Peninsula, both in areas of oceanic conditions. Dall (1889) mentioned it from Texas and Britton & Morton (1989: 86) describe it as rare in the Gulf of Mexico, but records have not been confirmed and established populations are unlikely. Bequaert (1943) doubted a record by L.M. Perry from Sanibel, on the west coast of Florida, and this does seem highly unlikely. A figure ( Perry & Schwengel 1955: pl. 25, fig. 129), perhaps of this specimen, is indeterminate but apparently not this species.

Habitat: Abundant in shallow pools on moderately exposed platforms of coral limestone, from the littoral fringe down to the mid eulittoral. Frequently with the neritid Puperita pupa .

Most authors describing the zonation of this species have found it to be characteristic of the upper part of the eulittoral yellow zone on limestone platforms, usually submerged in small pools, but it can also be found in splash pools in the black zone higher on the shore ( Clench 1938; McGinty 1939; Newell et al. 1959; Usticke 1959; G.L. Voss & N.A. Voss 1960; Bandel 1974a; D’Asaro 1986; Brattström 1992, 1999; Britton 1992; Lang et al. 1998). Most of these workers have mentioned that Puperita pupa occupies the same pools. Occurrence has also been noted among moss-like algae of the low littoral fringe ( Vermeij 1973a, b), on algal rocks in the lower eulittoral ( Bingham 1973) and even just below low water ( Bandel 1974a). It can occupy exposed sites ( Bingham 1973; Redfern 2001). The heat coma temperature is 45.6–45.8°C, similar to that of littorinids from the highest littoral fringe ( Fraenkel 1968; Britton 1992; McMahon 2001), and it tolerates emersion for at least 12 days ( Britton 1992). Lewis (1960) recorded eggs in July and August in Barbados, while D’Asaro (1986) collected spawn in late February and early March in the Bahamas.

Remarks: This species shows a striking colour polymorphism. The majority of shells are brown ( Fig. 7A–F ), in shades from pale yellow brown, to red brown and blackish brown, and some of these shells show small, sparse, dark spots that, because of the dark ground colour, are inconspicuous ( Fig. 7C, F ). However, in the Lesser and Netherlands Antilles almost all shells are white with a regular pattern of small black spots ( Fig. 7G ); this is the form that was described as Turbo minimus Wood, 1828 . Although the periostracum is thicker than is usual in Littorinidae , it does not contribute to the coloration of the shell. Only occasionally are both colour forms found at the same locality, and then there are in addition rare examples of shells with cream shells sparsely spotted with brown, which appear to be intermediates ( Fig. 7H ). Such mixed samples have been recorded from: West Summerland Key, Florida (USNM 820412); South Bimini, Bahamas (BMNH 20080972); Bermuda (USNM 773841); Santo Domingo, Dominican Republic (ZMA); Bonaire (USNM 709128, 848544); Morant Reef, Jamaica (BMNH 20080973); Priory, Jamaica (BMNH 20080974); Cozumel, Mexico (USNM 736559, 736568). In addition, brown shells have been recorded from Barbados (USNM 54653) and at Los Roques, Venezuela ( De Jong & Coomans 1988) in the geographical range dominated by the white form. The supposed lack of intermediates between the two forms persuaded Rehder (1962) to regard them as distinct species. In contrast, Bequaert (1943) reported both forms, and intergrades, from ‘nearly every one’ of the localities sampled in Cuba, Hispaniola and the Bahamas (he may, however, have considered presence or absence of spots, rather than pale or dark gound colour, as more characteristic of the extreme forms).

This pronounced geographical division into brown northern and white southern populations, with mixed populations mainly (though not exclusively) between the two, suggests a likely genetic determination of colour pattern. Geographical patterns in shell colour in littorinids have sometimes been interpreted in terms of climatic selection for dark colours at higher latitudes ( Hughes 1979; Reid 2002b; Reid & Williams 2004), but this is unlikely in a tropical setting. Another possibility is that visual predators might impose selection for crypsis. The brown morph resembles in shape, size and colour a unicellular green alga with which it occurs in intertidal pools in the Bahamas (pers. obs.). The neritid Puperita pupa is slightly larger but similar in shape and has a white shell with black reticulation; this is often found together with E. mespillum and the white morph bears a resemblance to it. There is as yet no evidence for this hypothesis. However, among other members of the Littorinidae there is a strong association between visual predation and shell colour polymorphism (e.g. Reid 1987, 1996).

This is the most oceanic of all the western Atlantic Echinolittorina species. It has been recorded from only two locations on the American mainland, and all localities are sites of clear, oceanic water. Its occurrences and those of the continental species E. interrupta are almost mutually exclusive (see remarks on the latter). The tolerance of heat and emersion is high for a small species, perhaps connected with its occurrence in shallow pools on the upper shore, and this may be compared with the greater sensitivity of E. meleagris that is generally found slightly lower on the shore.

Radula variation in this species ( Fig. 5C–F ) is comparable to that in E. tuberculata and E. jamaicensis , and the form with narrowed rachidian has not been observed previously.

Figures

FIGURE 2. Opercula of Echinolittorina species. A–C, E. angustior, St Ann’s Bay, Jamaica (BMNH 20081038; shell H A = 17.2 mm, B = 17.9 mm, C = 17.9 mm; OR A = 0.57, B = 0.62, C = 0.74). D, E. interrupta, Fort Charlotte, Lucea, Jamaica (BMNH 20081006; shell H = 14.0 mm; OR = 0.41). E, E. tuberculata, Brewer’s Bay, St Thomas (BMNH 20081062; shell H = 12.0 mm; OR = 0.60). F, G, E. tuberculata, 5 km S Tulum, Quintana Roo, Mexico (BMNH 20081041; shell H F = 15.0 mm, G = 18.0 mm; OR F = 0.62, G = 0.76). H, E. mespillum, Eight-mile Rock, Grand Bahama I., Bahamas (BMNH 20080969; shell H = 5.9 mm; OR = 0.34). Abbreviations: ol, operculum length; ds, diameter of spiral part of operculum. Opercular ratio OR = ds/ol.

FIGURE 5. Radulae of Echinolittorina species (two views of each radula, flat and at 45°). A, B, E. meleagris; Sebastian Inlet, Brevard Co., Florida, USA (BMNH 20080958; shell H = 5.5 mm). C–F, E. mespillum. C, D, normal form; Morant Reef, Jamaica (BMNH 20080973; shell H = 5.3 mm). E, F, narrowed form; Priory, Jamaica (BMNH 20080974; shell H = 4.7 mm). Scale bars = 50 µm.

FIGURE 7. Echinolittorina mespillum. A, Helix mespillum Mühlfeld, 1824, neotype, Cienfuegos, Cuba (BMNH 20080967). B, Cienfuegos, Cuba (BMNH 20080968). C, Eight-mile Rock, Grand Bahama I., Bahamas (BMNH 20080969). D, Black Bat Cave, Nassau, Bahamas (BMNH 20080970). E, Jamaica (BMNH 20080971). F, G, S Bimini, Bahamas (BMNH 20080972). H, Morant Reef, Jamaica (BMNH 20080973).

FIGURE 8. Echinolittorina mespillum. A, head and penis. B–F, penes. G, egg capsule (after D’Asaro 1986). H–J, pallial oviducts. K, L, paraspermatozoa. A, C, H, I, Priory, Jamaica (BMNH 20080974; shell H A = 3.9 mm, C = 3.5 mm, H = 4.7 mm, I = 5.1 mm). B, D, Morant Reef, Jamaica (BMNH 20080973; shell H B = 5.3 mm. D = 5.7 mm). E, Boca Raton Inlet, Palm Beach Co., Florida, USA (ANSP A8181b). F, J–L, Eight-mile Rock, Grand Bahama I., Bahamas (BMNH 20080969; shell H F = 5.8 mm, J = 5.9 mm). G, South Bimini, Bahamas. Shading conventions as in Figure 15.

FIGURE 9. Distribution of Echinolittorina mespillum.