Caecum limnetes Long, 1972

Raines, Bret K., 2020, A Rosetta Stone for eastern Pacific Caecidae (Gastropoda: Caenogastropoda), Zootaxa 4827 (1), pp. 1-146 : 112-115

Caecum limnetes Long, 1972

Figures 90 A–G, 91A–I, 92A–B, 127N

Caecum (Micranellum) limnetes Long, 1972: 291 , figs. 1–2, holotype CAS 088040 and 6 paratypes CAS 088041 , AMNH 162063 , SDMNH 55551 , FMNH 172334 , NHMUK 197012 , LACM 1446 , Estuaries of Bahia de Adair , Sonora, Mexico.

Caecum (Micranellum) limnetes — Skoglund, 1992: 28.

Brochina limnetes — Lightfoot, 1993b: 81, fig. 28.

Fartulum limnetes — Hertz et al. 1994: 93, figs. 7a–c.

Material examined. In addition to the type material the following lots were examined. NHMLAC: LACM 1961 - 2.12 , San Carlos Bay , Guaymas, Sonora, Mexico, intertidal, 2 sh ; LACM 1968 - 14.31 , Estero Soldado, NW of Guaymas , Sonora, Mexico, intertidal to 3 m, 110 sh ; LACM 1968 - 12.10 , Guasimas Bay , Guaymas, Sonora, Mexico, intertidal, 32 sh ; LACM 1973 - 5.51 , Estero Soldado, NW of Guaymas , Sonora, Mexico, intertidal, 75 sh ; LACM 1969 - 21.25 , El Muerto Island , Puertecitos, Baja California, Mexico, 15–27 m, 1 sh ; LACM 1965 - 34.53 , Puertecitos, Baja California, Mexico, intertidal to 10 m, 3 sh . SBMNH: SBMNH 620189 , Estero Morua , Sonora, Mexico, intertidal, 1 sh ; SBMNH 114904 , Bahia La Choya , Sonora, Mexico, intertidal, 30 sh ; SBMNH 118949 , Empalme, Empalme, Sonora, Mexico, intertidal, 2 sh ; SBMNH 114906 , Bahia La Choya , Sonora, Mexico, intertidal, 3 sh ; SBMNH 619738 , Bahia La Choya , Sonora, Mexico, 8 sh ; SBMNH 619784 , Estero Morua, Sonora, Mexico, intertidal, 4 sh ; SBMNH 619785 , Estero Morua, Sonora, Mexico, 10–25 m, 5 sh ; SBMNH 129779 , Agua de Chale , Baja California [Norte], Mexico, intertidal, 5 sh ; SBMNH 126596 , Playa Las Almejas, San Felipe, Baja California [ Norte ], Mexico, intertidal, 2 sh ; SBMNH 118496 , Playa Las Almejas, San Felipe, Baja California [ Norte ], Mexico, intertidal, 20 sh ; SBMNH 620165 , Puerto Penasco, Sonora, Mexico, 1 sh ; SBMNH 620591 , Santa Clara, Sonora, Mexico, intertidal, 10 sh ; SBMNH 116670 , Miramar, Sonora, Mexico, intertidal, 10 sh ; SBMNH 621308 , Estero Morua, Sonora, Mexico, intertidal, 12 sh ; SBMNH 621410 , Puerto Lobos, Sonora, Mexico, intertidal, 1 sh ; SBMNH 621502 , Estero Morua, Sonora, Mexico, intertidal, 25 sh ; SBMNH 116243 , Bahia Tortugas, Baja California Sur, Mexico, 5 m, 1 sh. BCD: Marua Estero , SE of Penasco Point, Sonora, Mexico, intertidal, 26 sh; Pelican Pt. , Cholla Bay , Sonora, Mexico, intertidal, 4 sh; San Felipe , Baja California, Mexico, intertidal, 8 sh; 25 miles S of Guaymas, Sonora, Mexico, intertidal, 1 sh; San Carlos Bay, Guaymas, Sonora, Mexico, intertidal, 9 sh .

Original diagnosis. “Teleoconch white, semitransparent, arcuation and diameter increasing only slightly toward the anterior. Annuli variable, consisting of about 40 or more raised, closely appressed rings, separated by fine incised grooves. Septum approximately hemispherical but with a right dorsal irregularity or protuberance rising in a straight line, apically, ending at the level of maximum elevation of mamillate portion of septum. Aperture never constricted. Operculum circular, horny, slightly concave, sinistral; composed of 6 to 8 rings plus a nucleus about 1/3 the total diameter of the operculum. In younger animals, diameter as well as degree of distinction between annuli increases with growth somewhat more than in older animals. Body of animal white, semitransparent, with concentrations of black pigment granules on head, beginning just dorsal to eyes and extending dorsally to edge of mantle. Mantle margin and dorsal surface of foot, beneath operculum, also with black pigment granules. Bolsters of radula black, visible through body surface. Both cephalic tentacles blunt, each with about 5 long stiff sensory cilia on tips. Tentacles with ciliated tracts along length. On right tentacle, dorsal tracts beats in a proximal direction while ventral tract beats in a distal direction. On left tentacle, the directions of beat for the tracts are reversed. Left tentacle sometimes with an undulated left lateral margin along proximal 1/2 of length.” Long (1972: 291).

Description. Protoconch unknown. No clear separation observed between teleoconchs I and II ( Fig. 91A ), surface sculptured with rudimentary axial ribs covered by weak striae ( Fig. 91B ), transition to teleoconch III marked by change in sculpture ( Fig. 91A ). Teleoconch III sculptured with low rounded axial ribs covered by longitudinal striae ( Fig. 91C ), transition to teleoconch IV marked by slight axial incised line ( Fig. 91A ). Teleoconch IV sculptured with rounded axial ribs covered by numerous, overlapping, longitudinal striae ( Fig. 91E ), transition to teleoconch V marked by rapid increase in diameter ( Fig. 91C ). Teleoconch V sculptured with low, flattened axial ribs covered by dense, conspicuous, longitudinal striae ( Fig. 91F ), transition to teleoconch VI marked by suture ( Fig. 91H ). Teleoconch VI (last growth stage) small for genus [Tol 1.55–2.10 mm], larger than previous stage, tubular, mildly and regularly arched [Larc: 0.51–0.66 mm; Arc: 0.10–0.14 mm], subcylindrical with increase in diameter from posterior to aperture, semi-translucent to opaque white ( Figs. 90 A–C). Axial sculpture of 30–40 low, wide ribs closely arranged and regularly spaced ( Fig. 91I ). Axial interspaces shallow, narrower than ribs to nearly obsolete ( Fig. 91F ). Surface sculptured with dense, conspicuous, longitudinal striae on axial ribs and interspaces ( Fig. 91F ). Posterior [Dpe: 0.32–0.38 mm] with thin edge, squared to rounded shoulder ( Fig. 90D ). Septum mucronate, pronounced ( Fig. 90 D ). Mucro blunt, rather wedge-shaped, positioned on dorsal margin ( Fig. 90D ). Aperture [Da: 0.38–0.50 mm] thick, simple ( Fig. 90D ). No varix. Lip smooth, weakly developed, with slightly deflected peristome ( Fig. 90D ). Periostracum thin, smooth, light brown ( Fig. 90A ). Operculum thin, light brown; exterior surface with 6–8 concentric rings ( Figs. 90 E–F). Conceptual reconstruction of growth stages shown in Fig. 92A .

Distribution and Habitat. Restricted to the northern Gulf of California, from Cholla Bay to Guaymas, Mexico. Intertidal to 27 m. Common in estuaries on sand and mud substrates.

Remarks. The paratype at NHMLAC is a partial adult specimen (LACM 1446, Fig. 90G ). Although the holotype (CAS 088040) was available for examination it was not figured, because it is broken into five pieces.

Figures

FIGURE 90. Caecum limnetes. A. Profile view with periostracum (LACM 1968-14.31). B. Profile view of smooth form without periostracum (LACM 1968-14.31). C. Profile view of ribbed form without periostracum (LACM 1968-14.31). D. Ventral view (SBMNH 114904). E. Operculum, exterior surface (SBMNH 114904). F. Operculum, interior surface (SBMNH 114904). G. Paratype, LACM 1446.

FIGURE 91. Caecum limnetes shells at different growth stages. A. Protoconch and teleoconchs I to IV (LACM 1973-5.51). B. Surface of teleoconchs I to II (LACM 1973-5.51). C. Surface of teleoconch III (LACM 1973-5.51). D. Teleoconchs IV to V (LACM 1973-5.51). E. Surface of teleoconch IV (LACM 1973-5.51). F. Surface of teleoconchs V to VI (SBMNH 114904). G. Teleoconch V (LACM 1968-14.31). H. Teleoconchs V to VI (SBMNH 114904). I. Teleoconch VI (SBMNH 114904).

FIGURE 92. Caecum limnetes. A. Conceptual reconstruction of growth stages. B. Species distribution map.