Hydrobia ulvae

(Pennant, 1777)

Description (shell):
Shell an elongate cone, length/breadth ratio 2:1, slightly transparent, glossy, with six to seven flat-sided or slightly tumid whorls, apex rounded; last whorl comprising >50 % of shell height, slightly angulate at periphery, especially in younger shells. Superficially smooth but with microsculpture of fine prosocline growth lines and finer spiral striae. Aperture slightly pear-shaped (more angulate in young shells), outer lip arising tangentially to last whorl, forming a slight spout basally where it meets columella; inner lip reflected over last whorl, leaving a small umbilical chink (H. ulvae-drawing).

Up to 6 x 3 mm.

Periostracum horn-coloured, underlying shell white; viscera showing through apical whorls gives living shells a darker appearance.

Body with long bifid snout, often with transverse band of dark pigment anteriorly and a triangular or shield-shaped pigmented area between cephalic tentacles; a single, small pallial tentacle projects from mantle edge near junction of last whorl and outer lip. Cephalic tentacles long, slender, setose, left slightly thicker than the right; eyes at base. A dark pigmented band placed at a distance greater than its own length from the tentacle tips. Penis large, a smooth sickle-shaped curve, with pointed tip (H. ulvae-animal).

A brackish water species favouring substrata of firm mud and muddy sand; most abundant above MTL, but found sublittorally down to 20 m.

Widely distributed from northern Norway to Senegal (Distr. H. ulvae).