Caecum venustum de Folin, 1867

Figures 75 A–H, 76A–I, 77A–B, 128A

Caecum venustum de Folin, 1867a: 42, 2 syntypes MNHN-IM-2000-4581, Panama.

Caecum complanatum de Folin, 1867a: 41, 3 syntypes MNHN-IM-2000-4604, Panama. (syn. nov.).

Caecum mutabile de Folin, 1869: 132, pl. XX, figs. 3–4, holotype MNHN-IM-2000-4591, Panama. (syn. nov.).

Caecum venustum — Kisch, 1959a: 34; Pizzini et al. 2007: 6, fig. 3d.

Brochina farcimen — Lightfoot, 1993b: 80, fig. 27.

Material examined. In addition to the type material the following lots were examined. SBMNH: SBMNH 621345, Punta la Gringa, Bahia de los Angeles, Baja California [Norte], Mexico, 20–40 m, 4 sh; SBMNH 620479, Bahia Ballena, Puntarenas, Costa Rica, 17–23 m, 1 sh; SBMNH 620529, Bahia San Carlos, San Carlos Nuevo Guaymas, Sonora, Mexico, 15–30 m, 1 sh; SBMNH 620537, Bahia San Carlos, San Carlos Nuevo Guaymas, Sonora, Mexico, 15–30 m, 4 sh; SBMNH 619739, Punta Coyote, Baja California Sur, Mexico, 20–57 m, 1 sh; SBMNH 620533, Cabo Tepoca, Sonora, Mexico, 20–30 m, 5 sh; SBMNH 621398, Cabo Tepoca, Sonora, Mexico, 20–30 m, 40 sh; SBMNH 452436, Punta San Pedro, Sonora, Mexico, 10–25 m, 15 sh; SBMNH 452437, Isla Danzante, NE end, Baja California Sur, Mexico, 60–90 m, 6 sh; SBMNH 452505, Bahia Santiago, Colima, Mexico, 27–40 m, 4 sh; SBMNH 452522, Bahia de Culebra, Guanacaste, Costa Rica, 13–23 m, 20 sh; SBMNH 452528, Bahia Santiago, Colima, Mexico, 27–40 m, 1 sh; SBMNH 619527, Las Cocinas, Sonora, Mexico, 13 m, 1 sh; SBMNH 619564, Isla Jaltemba, Nayarit, Mexico, 10–25 m, 3 sh; SBMNH 619565, Bahia Santiago, Colima, Mexico, 27–40 m, 3 sh; SBMNH 619567, Isla Jaltemba, Nayarit, Mexico, 10–25 m, 1 sh; SBMNH 619568, Islas Viradores, Playas del Coco, Guanacaste, Costa Rica, 10–25 m, 2 sh; SBMNH 619740, Isla Danzante, Baja California Sur, Mexico, 83–100 m, 4 sh; SBMNH 619832, Isla Danzante, Baja California Sur, Mexico, 60–90 m, 10 sh; SBMNH 619902, Isla Danzante, Baja California Sur, Mexico, 83–100 m, 20 sh; SBMNH 619908, Punta San Pedro, Sonora, Mexico, 10–25 m, 15 sh; SBMNH 620534, Barra de Navidad, Jalisco, Mexico, 3–45 m, 3 sh; SBMNH 620536, Punta la Gringa, Bahia de los Angeles, Baja California [Norte], Mexico, 20–40 m, 2 sh; SBMNH 620538, Bahia Saladita, Sonora, Mexico, 12–20 m, 2 sh; SBMNH 620539, Playa Tamarindo, Guanacaste, Costa Rica, 5–15 m, 1 sh; SBMNH 620834, Bahia San Carlos, Sonora, Mexico, 18–22 m, 6 sh; SBMNH 621344, Barra de Navidad, Jalisco, Mexico, 3–45 m, 3 sh; SBMNH 621349, Bahia San Carlos, San Carlos Nuevo Guaymas, Sonora, Mexico, 15–30 m, 12 sh; SBMNH 621501, Isla Danzante, S of, Baja California Sur, Mexico, 45–75 m, 1 sh; SBMNH 621637, Isla San Pedro Martir, Sonora, Mexico, 120 m, 4 sh; SBMNH 621648, Isla de Coiba, Veraguas, Panama, 1 sh; SBMNH 622392, Isla San Pedro Nolasco, Sonora, Mexico, 17–23 m, 1 sh.

Original diagnosis. “Testa cylindrica, elongata, leviter arcuata, tenui, vitrea nitida, superne levi, inferne transversim et irregulariter plicata, aperturam versus paulo inflata, et annulis rotundatis ornata, deinde contracta; apertura vix declivi, marginata; septo submamillato, cylindraceo, prominente, apice ad dorsum curvo; margine laterali convexo; operculo?” de Folin (1867a: 42).

Description. Protoconch and teleoconchs I, II unknown. Teleoconch III sculptured by weak, wide, longitudinal wrinkles (Fig. 76B), transition to teleoconch IV marked by suture (Fig. 76A). Teleoconch IV sculptured by numerous, continuous, longitudinal striae (Fig. 76C), septum with squared rim, concave; mucro heel-like, positioned along dorsal margin (Figs. 76 A–B), transition to teleoconch V marked by suture immediately following slight apertural welling (Fig. 76D). Teleoconch V sculptured by numerous, diffuse, short longitudinal striae (Fig. 76H), transition to teleoconch VI marked by suture (Fig. 76G) Teleoconch VI (last growth stage) small for genus [Tol 1.84–1.93 mm], tubular, rather thick, moderately and regularly arched [Larc: 0.66–0.72 mm; Arc: 0.18–0.19 mm], larger than previous stage, subcylindrical, semi-translucent white (Figs. 75 A–B, 76I). Surface sculptured by numerous, diffuse, short longitudinal striae, and axial growth lines (Fig. 76H). Posterior [Dpe: 0.38–0.39 mm] with thick edge, rounded shoulder (Fig. 75C). Septum mucronate, rather flattened (Fig. 75C). Mucro heel-like, positioned on dorsal margin, usually covered by septum (Fig. 76I). Aperture [Da: 0.40–0.43 mm] with slight swelling and 6–9 fine axial rings, followed by abrupt constriction (Fig. 76I). No varix. Lip smooth, with moderately deflected peristome (Fig. 75C). Periostracum thin, smooth, yellowish (Fig. 75A). Operculum thin, light brown; exterior surface with 8–10 concentric rings (Figs. 75 D–E). Conceptual reconstruction of growth stages shown in Fig. 77A.

Distribution and Habitat. From Sonora, Mexico to Coiba Island, Panama. Intertidal to 100 m. Uncommon on coarse sand substrates.

Remarks. The type material of Caecum venustum consists of two adult specimens (MNHN-IM-2000-4581, Fig. 75F). Caecum complanatum (Fig. 75G), C. venustum and C. mutabile (Fig. 75H) are conspecifics. As first reviser, C. venustum has been selected to represent the species, because the type material is in better condition. Early subadult C. venustum develop temporary septa, which quickly wear away. However, while this temporary septum is present, specimens can easily be misidentified as young C. glabriforme.

Lightfoot (1993b: 80) misidentified Caecum venustum as Carpenter’s C. farcimen. Pizzini et al. (2007) followed Lightfoot’s position, and in doing so incorrectly considered C. venustum and C. complanatum to be junior synonyms of C. farcimen.

Lastly, Caecum venustum should not be confused with another one of de Folin’s species with a similar name, Caecum venosum de Folin, 1867, which is an unrelated species from Brazil. Gomes & Absalão (1996: 519, figs. 8–9) correctly illustrated and described C. venosum in detail.