Tryonia imitator (Pilsbry 1899)

Tryonia imitator (Pilsbry, 1899)

Paludestrina imitator Pilsbry, 1899:124 [type locality, Santa Cruz, California].—Taylor, 1966b: 197.

Paludestrina curta Arnold, 1903:305 [type locality, San Pedro bluffs (California), Upper San Pedro Series (Pleistocene)].—Woodring et al., 1946:66 [synonymized with Hydrohiaprotea=Tryonia protea].—Taylor, 1966b:197 [synonymized with T. imitator].

Hydrobia imitator.—Berry, 1948:59 [reassignment].

Amnicola imitator.—Baily and Baily, 1952:51 [reassignment].

Tryonia imitator.—Taylor, 1966b:197 [reassignment]; 1981:153 [distribution].

DIAGNOSIS.—Shell medium- to large-sized, ovate-conic. Penial ornament of 2 distal and 1 basal papillae on inner edge.

DESCRIPTION.—Shell (Figure 23E,F) 2.5–5.5 mm tall. Shell apex shown in Figure 5B. Whorls, 4.25–6.0, medium convexity, teleoconch sculptured with 10–15 strong spiral lines interspersed between weaker threads. Aperture ovate, lip complete, thin, adnate; umbilicus rimate. Operculum ovate, inner side with weak rim along border. Ctenidial filaments about 35, pleated. Stomach with small posterior caecum. Radula with about 45 rows of teeth, length/width of ribbon 580%. Lateral margins of central radular teeth weakly flared (teeth almost square), dorsal edge medium indented, basal tongue slightly convex to V-shaped, central cusp broad, spoon-like, lateral cusps, 6–9, basal cusps 1 or 2, weakly developed. Lateral teeth (Figure 8C) having 3 or 4 cusps on inner side and 5–7 cusps on outer side; outer wing well flexed, length 150% of tooth-face width. Inner marginal teeth with 21–25 cusps, outer marginal teeth with 26–33 cusps.

Prostate gland small, ovate, pallial section 33% of total length, pallial vas deferens broad. Distal penis pigmented, well-developed swelling along inner edge, penial duct weakly undulating (Figure 26E). Oviduct loop anterior-oblique, pigmented. Brood-pouch opening subterminal, raised (Figure 3C); brooded embryos 25 to 30. Albumen gland largely posterior to bursa copulatrix. Bursa copulatrix small, ovate, pigmented; seminal receptacle a little smaller than bursa copulatrix, ovate or elongate (Figure 3D). Sperm-duct opening to distal portion of bursal duct. Sperm-tube opening in posterior 33% of pallial cavity.

DISTRIBUTION.—Southern California coast.

MATERIAL EXAMINED.—UNITED STATES. California: Pleistocene deposits, San Pedro Bluffs, USNM 162542 (holotype, Paludestrina curta); Santa Cruz, Santa Cruz County, ANSP 62670 (lectotype, Paludestrina imitator); Morro Bay, San Luis Obispo County, USNM 892057.

The California brackish water snail, also known as the mimic tryonia, scientific name Tryonia imitator, is a species of very small brackish water snails that have an operculum, aquatic gastropod mollusks in the family Hydrobiidae.

This species is endemic to the United States.