Caecum cocoense Sibaja-Cordero, García-Méndez & Troncoso, 2013

Raines, Bret K., 2020, A Rosetta Stone for eastern Pacific Caecidae (Gastropoda: Caenogastropoda), Zootaxa 4827 (1), pp. 1-146 : 122-124

publication ID	https://doi.org/ 10.11646/zootaxa.4827.1.1
publication LSID	lsid:zoobank.org:pub:2CE528C2-DE07-4155-B37D-BE2C342A3901
DOI	https://doi.org/10.5281/zenodo.4457830
persistent identifier	https://treatment.plazi.org/id/03A3DF49-FF9B-FFFA-FF44-FDF4FE963AD6
treatment provided by	Plazi
scientific name	Caecum cocoense Sibaja-Cordero, García-Méndez & Troncoso, 2013
status

Treatment

Caecum cocoense Sibaja-Cordero, García-Méndez & Troncoso, 2013 View in CoL

Figures 102 View FIGURE 102 A–E, 103A–G, 104A–B, 128D

Caecum cocoensis View in CoL [ sic] Sibaja-Cordero et al. 2013: 144, figs. 24a–n, holotype MZUCR9740-01 , paratypes MZUCR9741-01 , MZUCR9742-01 , Isla del Coco, Costa Rica.

Material examined. In addition to the type material the following lots were examined. SBMNH: SBMNH 619898 View Materials , Isla Jaltemba , Nayarit, Mexico, 10–25 m, 3 sh ; SBMNH 620535 View Materials , Barra de Navidad , Jalisco, Mexico, 3–45 m, 1 sh .

Original diagnosis. “Shell length: 2.10 mm ±0.20; width min: 0.47 mm ± 0.01, and width max: 0.50 mm ± 0.03. The shell is slightly arched and translucent, with some tan colour ( Fig. 24a View FIGURE 24 ). The form of the septum is mammillate, tapering, and constant ( Figs. 24 View FIGURE 24 g–j). There is no mucro present in the specimens collected. The sculpture is formed by rings more widely spaced and well marked distally, becoming near the aperture narrower and less well marked. The shell presented some porosity with minute holes in the rings and marked pits in the inter ring spaces ( Figs. 24 View FIGURE 24 l–n). Moreover, subadult traits are present in some sections of the tube of the specimens, where the ringed sculpture appears to be interrupted by incised lines ( Figs. 24d, e, k, m View FIGURE 24 ), representing a transitional zone between the teleoconch growth stages. The aperture is smooth and underdeveloped, another indication of a subadult stage; and the operculum is brown, flat, and presents a heavy concentric sculpture ( Figs. 24b, c, f View FIGURE 24 ). Finally a hole or deep depression is present in the septum of the specimens ( Figs. 24 View FIGURE 24 g–j).” Sibaja-Cordero et al. (2013: 144).

Description. Protoconch and teleoconch I unknown. Teleoconch II short, sculptured with axial growth lines and weak longitudinal striae ( Fig. 103B View FIGURE 103 ), transition to teleoconch III marked by slight axial constriction ( Fig. 103A View FIGURE 103 ). Teleoconch III about four times length of teleoconch II, sculptured with sparse, thin, longitudinal striae ( Fig. 103C View FIGURE 103 ), transition to teleoconch IV marked by suture, followed by axial ribs ( Fig. 103A View FIGURE 103 ). Teleoconch IV sculptured with diffuse orange peel texture and flattened, axial ribs, irregularly spaced ( Figs. 103 View FIGURE 103 D–E), septum with squared rim, slightly concave ( Fig. 103D View FIGURE 103 ), transition to teleoconch V marked by incised axial line ( Fig. 103D View FIGURE 103 ). Teleoconch V (last growth stage) small for genus [Tol 1.64–1.95 mm], tubular, rather thick, mildly to moderately and regularly arched [Larc: 0.58–0.70 mm; Arc: 0.18–0.22 mm], subcylindrical, semi-translucent ( Figs. 102 View FIGURE 102 A–B). Axial sculpture of wide, flattened axial ribs, spacing and intensity rather irregular, becoming obsolete centrally ( Fig. 103G View FIGURE 103 ). Surface sculptured with diffused orange peel texture crossed by sparse, thin, longitudinal striae ( Fig. 103F View FIGURE 103 ). Posterior [Dpe: 0.30–0.32 mm] with moderately thick edge, rounded shoulder ( Fig. 102C View FIGURE 102 ). Septum mucronate, slightly recessed ( Fig. 102C View FIGURE 102 ). Mucro low, heel-like, positioned on dorsal margin, covered by septum ( Fig. 103G View FIGURE 103 ). Aperture [Da: 0.35–0.40 mm] thick, with one wide, flattened, axial rib ( Figs. 102C View FIGURE 102 , 103G View FIGURE 103 ). No varix. Lip smooth, weakly developed, with slightly deflected peristome ( Fig. 102C View FIGURE 102 ). Periostracum thin to obsolete, yellowish ( Fig. 102A View FIGURE 102 ). Operculum thin, light brown; exterior surface with 6–7 concentric rings ( Fig. 102D View FIGURE 102 ). Conceptual reconstruction of growth stages shown in Fig. 104A View FIGURE 104 .

Distribution and Habitat. Originally described from Cocos Island at 9– 14 m. However, one early subadult stage and three adult specimens have also been found on the mainland of Costa Rica and as far north as Nayarit, Mexico. Subtidal, 3– 45 m. Uncommon on coarse sand and gravel substrates.

Remarks. The type material of Caecum cocoense is comprised of three late subadult stages (holotype MZUCR9740-01, Fig. 102 E View FIGURE 102 ). Additional specimens located in the SBMNH collection allowed for a more complete description.