(Lesson, 1830)
Larger of the two species in the genus, exceeding 110 mm in length (Lalli and Gilmer, 1989). Larval shell consists of three whorls. After metamorphosis a small teleoconch forms, which is represented by a narrow fringe at right angles to the larval shell aperture. With growth the shell becomes imbedded in the dorsal surface of the digestive gland, with only the top of the protoconch visible. The numerous gills (>20) form a distinctive, fan-like arc encircling the visceral nucleus. The tail terminates in 12, finger-like reddish-brown to black extensions or filaments, which form a fan-like structure that can be rapidly contracted when the animal is disturbed (Lalli and Gilmer, 1989). Both sexes with reddish-brown spots covering the trunk and proboscis; the spots are highly contractile, changing in size from 0.5 mm to 2 mm diameter (Lalli and Gilmer, 1989).
Of the two species of Cardiapoda, Tesch (1949) reported that Cardiapoda placenta was collected at stations close to land, while Cardiapoda richardi was collected from open ocean stations. In agreement with Tesch, Pafort-van Iersel (1983) termed the former species neritic and the latter oceanic.