Caecum paradoxum de Folin, 1867

Raines, Bret K., 2020, A Rosetta Stone for eastern Pacific Caecidae (Gastropoda: Caenogastropoda), Zootaxa 4827 (1), pp. 1-146 : 85-86

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 .

Figures

FIGURE 63. Caecum paradoxum. A. Profile view of an adult stage (LACM 1967-17.49). B. Profile view of late subadult stage (SBMNH 452538). C. Ventral view of late subadult stage (SBMNH 452538). D. Profile view of an adult stage (LACM 1967- 17.49). E. Profile view of late subadult stage (SBMNH 128134). F. Holotype, MNHN-IM-2000-4589.

FIGURE 64. Caecum paradoxum shells at different growth stages. A. Teleoconchs II to III (LACM 1972-43.20). B. Surface of teleoconchs II to III (LACM 1972-43.20). C. Surface of teleoconch IV (SBMNH 128134). D. Teleoconch IV (SBMNH 128134). E. Surface of teleoconch V (LACM 1967-17.49). F. Teleoconch V (LACM 1967-17.49).

FIGURE 65. Caecum paradoxum. A. Conceptual reconstruction of growth stages. B. Species distribution map.