Caecum semilaeve Carpenter, 1857

Figures 45 A–H, 46A–K, 47A–B, 126M

Caecum (Anellum) elongatum var. semilaeve Carpenter, 1857: 319, syntype NHMUK 1857.6.4.1526, Mazatlan.

Caecum (Anellum) elongatum var. semilaeve— Carpenter, 1858: 424.

Caecum semilaeve — Keen, 1968: 419, fig. 80; Keen, 1971: 397; Hertz, 1979b: 32, fig. 1; Shasky, 1984: 27; Shasky, 1989: 8; Skoglund, 1992: 28; Kaiser, 1997: 29; Finet et al. 2016: 28.

Brochina semilaeve — Lightfoot, 1993b: 81. fig. 29.

Brochina species #6— Lightfoot, 1993b: 82. fig. 31.

Material examined. In addition to the type material the following lots were examined. NHMLAC: LACM 1935 - 170.13, Port Utria, Colombia, 24 m, 1 sh; LACM 1935 - 171.11, Port Utria, Colombia, 64 m, 6 sh; LACM 1935 - 90.11, Secas Islands, Panama, 45 m, 10 sh; LACM 1935 - 134.10, Secas Islands, Panama, 25 m, 1 sh; LACM 1935 - 136.4, Secas Islands, Panama, 22 m, 3 sh; LACM 1971 - 83.57, Los Arcos, Banderas Bay, Jalisco, Mexico, intertidal to 3 m, 4 sh; LACM 1972 - 53.35, Herradura Bay, Costa Rica, 22 m, 10 sh; LACM 1934 - 126.13, Secas Islands, Panama, 1 m, 1 sh; LACM 1935 - 179.9, Octavia Bay, Colombia, 83 m, 5 sh; LACM 1960 - 19.5, Mazatlan, Sinaloa, Mexico, 37 m, 4 sh; LACM 1965 - 21.68, Otoque Island, Panama Bay, Panama, 9–27 m, 1 sh; LACM 1972 - 42.69, Ballena Point, Ballena Bay, Puntarenas Prov., Costa Rica, 3–16 m, 12 sh; LACM 1972 - 52.68, Ballena Point, Ballena Bay, Puntarenas Prov., Costa Rica, 3–16 m, 28 sh; LACM 1972 - 22.16, San Pedrito Island, Murcielagos Islands, Guanacaste Prov., Costa Rica, 3–4 m, 4 sh; LACM 1972 - 63.89, Cano Island, Puntarenas Prov., Costa Rica, 6–14 m, 30 sh; LACM 1976 - 46.66, Alcatraz Island, Tortugas Islands, Puntarenas Prov., Costa Rica, 2–8 m, 9 sh; LACM 1975 - 9.16, Los Angeles Bay, Baja California, Mexico, 30 m, 50 sh; LACM 1968 - 45.55, Cuastecomate Bay, Jalisco, Mexico, 18–37 m, 2 sh; LACM 1972 - 30.30, Santa Elena Point, Guanacaste Prov., Costa Rica, 13–17 m, 14 sh; LACM 1973 - 95.4, Los Cobanos, Sonsonate Dept., El Salvador, 2 m, 5 sh; LACM 1970 - 9.33, Salinas, Guayas Prov., Ecuador, intertidal, 5 sh; LACM 1972 - 17.47, Jobo Bay, W of Salinas Bay, Guanacaste Prov., Costa Rica, 2–8 m, 2 sh; LACM 1973 - 57.9, Zacatillo Island, La Union Prov., El Salvador, 2 m, 3 sh; LACM 1972 - 71.47, Dulce Gulf, Puntarenas Prov., Costa Rica, 2–16 m, 2 sh; LACM 1972 - 196.28, Espinoza Point, Fernandina Island, Galapagos Islands, 15–30 m, 19 sh; LACM 1937 - 206.7, Georges Island, Sonora, Mexico, 18 m, 4 sh; LACM 1972 - 81.23, S of Bocapan, Tumbes Dept., Peru, intertidal, 1 sh; LACM 1960 - 20.12, 40 miles S of Mazatlan, Sinaloa, Mexico, 33 m, 3 sh; LACM 1934 - 317.1, La Plata Island, Manabi Prov., Ecuador, 82–100 m, 1 sh; LACM 1937 - 223.5, Isabel Island, Nayarit, Mexico, 32 m, 2 sh; LACM 1967 - 15.16, Banderas Bay, Jalisco, Mexico, 18–27 m, 12 sh; LACM 1964 - 36.54, San Carlos Bay, Guaymas, Sonora, Mexico, 18–37 m, 16 sh; LACM 1975 - 22.33, San Carlos, Panama Prov., Panama, intertidal, 2 sh; LACM 1968 - 13.31, San Antonio, Sonora, Mexico, 17–27 m, 4 sh; LACM 1967 - 17.48, Libertad Port, Sonora, Mexico, intertidal, 30 sh; LACM 1964 - 31.24, Puertecitos, Baja California, Mexico, 8–18 m, 48 sh; LACM 1967 - 70.29, Magdalena Island, Magdalena Bay, Baja California Sur, Mexico, 2–6 m, 1 sh; LACM 1949 - 59.10, Entrada Pt, Magdalena Bay, Baja California Sur, Mexico, 32–34 m, 2 sh. SBMNH: SBMNH 215028, Isla Candelero, Sonora, Mexico, 27 m, 40 sh; SBMNH 132340, Bahia de los Angeles, Baja California [Norte], Mexico, 11–31 m, 2 sh; SBMNH 132338, Bahia de los Angeles, Baja California [Norte], Mexico, 11–31 m, 5 sh; SBMNH 110195, Acapulco, Guerrero, Mexico, 11–18 m, 7 sh; SBMNH 214998, Bahia Cuastecomate, Jalisco, Mexico, 9–30 m, 1 sh; SBMNH 452429, Puerto Lobos, Sonora, Mexico, 20–30 m, 4 sh; SBMNH 452430, El Submarino, Sonora, Mexico, 11 m, 1 sh; SBMNH 452431, Punta Doble, Sonora, Mexico, 30–45 m, 4 sh; SBMNH 452432, Ensenada San Francisco, Sonora, Mexico, 23–40 m, 4 sh; SBMNH 452434, La Puntilla, Salinas, Guayas, Ecuador, intertidal, 1 sh; SBMNH 452435, Punta San Pedro, Sonora, Mexico, 10–25 m, 1 sh; SBMNH 452438, Isla Danzante, NE end, Baja California Sur, Mexico, 60–90 m, 2 sh; SBMNH 452452, Isla Danzante, NE end, Baja California Sur, Mexico, 70–100 m, 1 sh; SBMNH 452517, Isla Jaltemba, Nayarit, Mexico, 10–25 m, 20 sh; SBMNH 452519, Roca Acero, Sonora, Mexico, 30–45 m, 4 sh; SBMNH 452520, Bahia de Culebra, Guanacaste, Costa Rica, 13–23 m, 5 sh; SBMNH 452564, Las Cocinas, Sonora, Mexico, 13 m, 20 sh; SBMNH 619526, Las Cocinas, Sonora, Mexico, 13 m, 15 sh; SBMNH 619534, Bahia Ballena, Puntarenas, Costa Rica, 13–15 m, 3 sh; SBMNH 619737, Roca Blanca, Nayarit, Mexico, 55–60 m, 1 sh; SBMNH 619899, Isla Jaltemba, Nayarit, Mexico, 10–25 m, 2 sh; SBMNH 128898, Punta Camaron, Mazatlan, Sinaloa, Mexico, intertidal, 1 sh; SBMNH 620159, Bahia San Carlos, Guaymas, San Carlos Nuevo Guaymas, Sonora, Mexico, 15–30 m, 25 sh; SBMNH 620162, Bahia Cuastecomate, Jalisco, Mexico, 12–30 m, 20 sh; SBMNH 620475, Bahia Ballena, Puntarenas, Costa Rica, 5–10 m, 3 sh; SBMNH 620614, Isla Taboga, Panama Prov., Panama, 1 sh; SBMNH 620668, Isla Venado, Panama Prov., Panama, intertidal, 2 sh; SBMNH 620769, Bahia Saladita, Sonora, Mexico, 10–25 m, 6 sh; SBMNH 620773, Bahia Saladita, Sonora, Mexico, 12 m, 1 sh; SBMNH 620781, Bahia Bocochibampo, Sonora, Mexico, 15–17 m, 1 sh; SBMNH 620787, Bahia Tenacatita, Cabo Tamarino, Jalisco, Mexico, 8–10 m, 3 sh; SBMNH 621311, Barra de Navidad, Jalisco, Mexico, 3–45 m, 6 sh; SBMNH 621357, Punta la Gringa, Bahia de los Angeles, Baja California [Norte], Mexico, 20–40 m, 12 sh; SBMNH 621513, Playa Venado, Panama Prov., Panama, intertidal, 2 sh; SBMNH 621666, Bahia Cuastecomate, Jalisco, Mexico, 9–30 m, 3 sh; SBMNH 622323, Punta Ancon, W side, Guayas, Ecuador, intertidal, 2 sh; SBMNH 622337, Punta Mala, Manabi, Ecuador, 10–25 m, 3 sh; SBMNH 622489, Bahia de los Angeles, Baja California [Norte], Mexico, 22 m, 2 sh. BCD: Navidad Bar, Colima, Mexico, 16–30 m, 9 sh.

Original diagnosis. “? var. semilaeve; t. huc et illuc annulata, huc et illuc laevi.” Carpenter (1857: 319).

Description. Protoconch paucispiral (about 1.7 whorls), planispiral, smooth (Fig. 46A), transition to teleoconch I marked by apertural varix (Fig. 46A). Teleoconch I short, smooth (Figs. 46 A–B, E), transition to teleoconch II marked by axial incised line (Fig. 46B). Teleoconch II about same length as teleoconch I, smooth (Fig. 46E), transition to teleoconch III marked by axial incised line (Fig. 46B). Teleoconch III smooth (Fig. 46E), mucro finger-like, curved, positioned along dorsal margin (Figs. 46 B–D), transition to teleoconch IV marked by axial constriction (Fig. 46C). Teleoconch IV with identical characters as previous stage, transition to teleoconch V marked by apertural swelling followed by constriction (Figs. 46H, 47A). Teleoconch V smooth or sculptured with axial rounded ribs throughout tube (Figs. 46F, H–J), transition to teleoconch VI marked by varix (Figs. 46I, 47A). Teleoconch VI (last growth stage) average size for genus [Tol 2.50–3.06 mm] (Fig. 46K), tubular, rather thick, mildly and regularly arched [Larc: 0.85–0.97 mm; Arc: 0.19–0.23 mm], larger than previous stage, subcylindrical, semi-translucent to opaque white (Figs. 45 A–B). Surface smooth (Fig. 46G). Posterior [Dpe: 0.46–0.60 mm] with thick edge, rounded shoulder (Fig. 45C). Septum mucronate, rather flattened (Fig. 45C). Mucro with low rounded point, positioned on dorsal margin (Fig. 45C). Aperture [Da: 0.53–0.70 mm] thick, with up to 3 axial rounded ribs, deep sulcus and abrupt swelling forming well-developed varix sculptured with 2–3 axial rings followed by strong constriction (Figs. 45 A–B, 46K). Lip smooth, with deflected peristome (Fig. 45C). Periostracum thin, smooth, yellowish (Fig. 45A). Operculum thin, light brown; exterior surface with 6–8 concentric rings (Figs. 45 G–H). Conceptual reconstruction of growth stages shown in Fig. 47A.

Distribution and Habitat. From Magdalena Bay, Baja California, Mexico to Tumbes, Peru, including the Gulf of California and the Galapagos Islands. Intertidal to 100 m. Common on coarse sand and rubble substrates.

Remarks. Carpenter (1857) originally described Caecum semilaeve from a one adult specimen and a posterior fragment. Unfortunately, the adult specimen is lost and the fragment is in such poor condition it is not recognizable (NHMUK 1857.6.4.1526, Fig. 45D). For taxonomic stability a neotype is herein designated for C. semilaeve (LACM 3758, Fig. 45E).

Lightfoot (1993b: 82) mentioned and illustrated a species that she dubbed “ Brochina species #6”. Her species is actually an early subadult of Caecum semilaeve. However, Lightfoot did not recognize it as such, because the varix at this stage is just a simple apertural swelling and quite different from that of the adult.

While studying the subadult stages of Caecum semilaeve, two observations were made. First, it appears that only in the teleoconch V stage does the species occasionally develop axial ribs on the tube beyond two or three (Fig. 46J). Second, C. semilaeve seems to form more aberrant specimens (Fig. 46I) than any other eastern Pacific caecid observed to date.