Caecum paradoxum de Folin 1867

Caecum paradoxum de Folin, 1867 Figures 63 A–F, 64A–F, 65A–B, 126N Caecum paradoxum de Folin, 1867c: 48, pl. II, fig. 7, holotype MNHN-IM-2000-4589, Panama. Caecum paradoxum — Tryon, 1886: 218, pl. 67, fig. 78; Kisch, 1959a: 33; Keen, 1971: 397; Lightfoot, 1993b: 85. Material examined. In addition to the type material the following lots were examined. NHMLAC: LACM 1965 - 21.71, Otoque Island, Panama Prov., Panama Bay, Panama, 9–37 m, 2 sh; LACM 1972 - 54.59, Herradura Bay, Puntarenas Prov., Costa Rica, 37 m, 1 sh; LACM 1972 - 43.20, Ballena Bay, Puntarenas Prov., Costa Rica, 11 m, 1 sh; LACM 1967 - 15.20, Banderas Bay, Jalisco, Mexico, 10–21 m, 1 sh; LACM 1967 - 17.49, Libertad Port, Sonora, Mexico, intertidal, 5 sh; LACM 1960 - 24.14, 40 miles S of Mazatlan, Sinaloa, Mexico, 30–36 m, 2 sh. SBMNH: SBMNH 452538, Isla Jaltemba, Nayarit, Mexico, 10–25 m, 2 sh; SBMNH 128134, Isla Lobos, Mazatlan, Sinaloa, Mexico, intertidal, 1 sh. BCD: Navidad Bar, Colima, Mexico, 15–30 m, 4 sh. Original diagnosis. “C. testa cylindrica, arcuata, subtranslucida, apicem versus albida, fulgens, dein grisea seu cornea; primum annulis validis, tribus cincta, annulis primis 2 rotundatis superne paululum planatis; annulo tertio majore, rotundato, subito transeunte ad laevem superficiem; interstitiis latis, subconcavis, subplanatis; dein laeve; septo magno, prominente, globuloso; margine laterali concavo, dorsali paulum uncinato, dorsum versus reverso. Operculum?” de Folin (1867a: 48). Description. Protoconch and teleoconch I unknown. No clear separation observed between Teleoconchs II and III (Fig. 64A), both sculptured with weak longitudinal, sinuous striae (Fig. 64B). Mucro spade-like, positioned along dorsal margin (Fig. 64A), transition to teleoconch IV marked by suture, followed by 2–3 well-developed annuli (Fig. 65A). Teleoconch IV sculptured with fine axial growth lines that strengthen aperturally, crossed by fine close-set longitudinal sinuous lines throughout (Fig. 64E), mucro knob-like, positioned centrally (Fig. 64D). Aperture sculptured with deep sulcus followed by varix, then sharply constricted (Fig. 64D). Transition to teleoconch V marked by varix (Fig. 65A). Teleoconch V (last growth stage) small for genus [Tol 1.84–2.00 mm], tubular, moderately arched [Larc: 0.72–0.80 mm; Arc: 0.21–0.24 mm], subcylindrical, semi-translucent to opaque white (Fig. 63A). Teleoconch V sculptured (when not worn) with axial growth lines that strengthen aperturally, crossed by close-set, longitudinal, sinuous lines (Fig. 64E). Posterior [Dpe: 0.35–0.40 mm] with rounded shoulder, constricted, with 1–2 well-developed annuli (Fig. 64F). Septum mucronate, pronounced (Fig. 64F). Mucro covered by septum (Fig. 64F). Aperture [Da: 0.40–0.45 mm] sculptured with deep sulcus followed by varix (Fig. 64F), then sharply constricted (Fig. 64F). Apertural varix well-defined, abrupt large swelling, marked with 3–5 rings (Fig. 64F). Lip smooth, with moderately deflected peristome (Fig. 63C). Periostracum not observed. Operculum unknown. Conceptual reconstruction of growth stages, Fig. 65A. Distribution and Habitat. From Sonora, Mexico to Panama Bay, Panama. Intertidal to 37 m. Uncommon on sand and gravel substrates. Remarks. The holotype of Caecum paradoxum (MNHN-IM-2000-4589) is a posterior end fragment of a late subadult (Fig. 63F). Caecum paradoxum goes though a significant change from its highly recognizable subadult stage (Fig. 63E) to the rarely seen adult stage (Fig. 63D). Worn adult specimens that do not display any posterior annuli (Fig. 63A) are sometimes mistaken for C. semilaeve.Published as part of Raines, Bret K., 2020, A Rosetta Stone for eastern Pacific Caecidae (Gastropoda: Caenogastropoda), pp. 1-146 in Zootaxa 4827 (1) on pages 85-86, DOI: 10.11646/zootaxa.4827.1.1, http://zenodo.org/record/440230