Choanopoma

Watters, G. Thomas, 2014, A revision of the Annulariidae of Central America (Gastropoda: Littorinoidea), Zootaxa 3878 (4), pp. 301-350 : 342-343

“ Choanopoma ” cygni Pilsbry, 1930

Figure 11 A–C

Type material. ANSP 150938, holotype (figs. 11 A–C).

Type locality. “ Swan Island; rocks south of the radio tower.”

Type figured. Pilsbry, 1930: text fig. 6.

Chresonymy.

Choanopoma cygni Pilsbry, 1930: 241 –243, text fig. 6; Solem, 1961: 199; Baker, 1964: 169; Richardson et al., 1991: 42; Watters, 2006: 225.

Annularisca (Annularella) cygni ( Pilsbry, 1930) . Watters, 2006: 56, 225.

Distribution and habitat. Known only from the type locality. The holotype, the only known specimen, was found in leaf litter. Swan Island is part of the Islas de la Bahía Department of Honduras.

Description. See “Original description” below.

Remarks. This species is based on a single immature, weathered specimen lacking an operculum. The holotype is the only known specimen. Watters (2006) placed it in Annularisca (Annularella) , a Cuban group, based on overall shell shape. However, the specimen could just as well be an immature poteriid although Torre et al. (1942) did not list any poteriids from the island. Clapp (1914), in a review of the Swan Island terrestrial snails, listed ten species. None of them appear to be this species, even as an immature individual.

Swan Island (named for privateer Captain Swan) has seen an unusual amount of traffic for a 3.1 km 2 island: first as a coconut palm plantation, next a weather station, a quarantine station for Latin American cattle, a navigation beacon, and finally a military base. There seems ample opportunity for this snail to have been transplanted to the island from elsewhere. The identity of this taxon must await further collections of better preserved specimens.

Original description. “The immature shell consists of 3 ½ whorls, of which the first 1 ½ are smooth and form a mammilar summit. The next whorl has sculpture of fine, smooth and even, close-set riblets, about 9 in 1 mm. On the face of the last whorl, but becoming finer, about twice as numerous, on its latter part, where there are also traces of 5 or 6 very weak spiral cords between periphery and suture. The perspective umbilicus occupies one-forth of the basal diameter. The aperture is slightly longer than wide. Peristome simple, as in young pomatiasids generally.”

Etymology. L. cygnus, swan—Swan Island.

Figures

FIGURE 11. A – C. “ Choanopoma ” cygni Pilsbry, 1930. ANSP 150938, holotype, 6 mm width, photo courtesy of ANSP. D – F. Annularisca pleurophora (Pfeiffer, 1852). UMMZ 79565, 8.2 mm. G – H. Diplopoma turritum (Pfeiffer, 1852). UMMZ 77930, 13.2 mm.