Caecum shaskyi, Raines, 2020

Raines, Bret K., 2020, A Rosetta Stone for eastern Pacific Caecidae (Gastropoda: Caenogastropoda), Zootaxa 4827 (1), pp. 1-146 : 131-133

Caecum shaskyi species novum

Figures 114 A–I, 115A–E, 116A–B, 128E

Fartulum farcimen — Shasky, 1984: 27, [non Carpenter, 1857].

Type material. Holotype, SBMNH 637732 ; paratypes, SBMNH 637733 (4 figured).

Additional material examined. NHMLAC: LACM 1938 - 218.5 , 18 miles SE of Foca Island , Piura Dept., Peru, 21 m, 2 sh . SBMNH: SBMNH 637731 , Salango Island , Manabí Province, Ecuador 11–27 m, 1 sh. BCD: N. side of La Plata Island, Ecuador, 12–30 m, 1 sh .

Type locality. La Plata Island , Manabí Province, Ecuador .

Diagnosis. Teleoconch subcylindrical, with increase in diameter from posterior end to aperture. Surface smooth and glossy, yellowish-orange to orange in color. Septum mucronate, with pronounced finger-like, blunt mucro. Aperture with slight swelling and pronounced axial rings. Periostracum sculptured with dense, sinuous striae.

Description. Protoconch and teleoconchs I, II unknown. Teleoconch III surface smooth with weak axial growth lines ( Fig. 115B ), transition to teleoconch IV marked by slight axial constriction ( Fig. 115A ). Teleoconch IV surface smooth, glossy, with occasional axial growth lines ( Fig. 115C ), transition to teleoconch V marked by slight axial constriction ( Fig. 115A ). Teleoconch V with identical characters as previous stage, transition to teleoconch VI marked by axial constriction ( Fig. 115D ). Teleoconch VI (last growth stage) large for genus [Tol 3.41–3.60 mm], tubular, thick, robust, moderately and regularly arched [Larc: 1.22–1.41 mm; Arc: 0.30–0.35 mm], subcylindrical with increase in diameter from posterior to aperture, yellowish-orange to orange ( Fig. 114B ). Surface smooth, glossy ( Fig. 115C ). Posterior [Dpe: 0.60–0.61 mm] with thick edge, squared shoulder ( Fig. 114E ). Septum mucronate, deeply recessed ( Fig. 114E ). Mucro finger-like, conical, blunt, positioned near dorsal margin, straight to slightly curved toward dorsal margin ( Fig. 114E ). Aperture [Da: 0.72–0.79 mm] with slight swelling followed by rapid constriction, with 4–5 distally spaced axial rings, interspace narrowing with constriction ( Figs. 114E , 115E ). No varix. Lip smooth, with deflected peristome ( Fig. 114E ). Periostracum rather thick, with dense, sinuous striae, yellow-orange ( Figs. 114A, C, F ). Operculum thin, light brown; exterior surface with 5–6 concentric rings ( Figs. 114 H–I). Conceptual reconstruction of growth stages shown in Fig. 116A .

Etymology. The species is named in honor of the late Donald R. Shasky (1925–2002), for his work on eastern Pacific molluscs.

Distribution and Habitat. Known from La Plata Island, Manabí Province, Ecuador to Foca Island, Piura Dept., Peru. Subtidal, 11– 30 m. Uncommon on sandy substrates.

Remarks. Caecum shaskyi cannot be mistaken for any other eastern Pacific caecid. Its robust, glossy, yelloworange teleoconch along with its blunt finger-like mucro has no contenders. While several western Atlantic species such as C. floridanum Stimpson, 1851 , C. lineicinctum de Folin, 1880 , and C. carolinianum Dall, 1892 also have recessed, blunt, finger-like mucros, only C. carolinianum is comparable. Both C. shaskyi and C. carolinianum have smooth, glossy teleoconchs with longitudinal striae on the periostracum. Both species are rather robust with apertural swelling. Where C. shaskyi differs from C. carolinianum is in microsculpture, size and coloration. Caecum shaskyi lacks surface microsculpture, while C. carolinianum has both axial growth lines and longitudinal striae. The only axial rings present on C. shaskyi are those on the apertural swelling. Caecum shaskyi has a yellow-orange teleoconch with an average size of 3.5 mm. Caecum carolinianum is creamy white with a larger average size teleoconch of 4.2 mm.

Figures

FIGURE 114. Caecum shaskyi sp. nov. A. Holotype, profile view with periostracum (SBMNH 637732). B. Paratype, profile view without periostracum (SBMNH 637733). C. Holotype, profile view (SBMNH 637732). D. Paratype, profile view (SBMNH 637733). E. Paratype, ventral view (SBMNH 637733). F. Close-up of periostracum (SBMNH 637733). G. Close-up of surface without periostracum (SBMNH 637733). H. Operculum, exterior surface (SBMNH 637733). I. Operculum, interior surface (SBMNH 637733).

FIGURE 115. Caecum shaskyi sp. nov. shells at different growth stages. A. Teleoconchs III to IV (SBMNH 637733). B. Surface of teleoconch III (SBMNH 637733). C. Teleoconchs IV to VI (SBMNH 637733). D. Surface of teleoconchs IV to VI (SBMNH 637733). E. Teleoconch VI (SBMNH 637733).

FIGURE 116. Caecum shaskyi sp. nov. A. Conceptual reconstruction of growth stages. B. Species distribution map.