Gray, 1843
An adult shell is lacking in this family; the larval shell is thrown off during metamorphosis. Like the carinariids, the body is elongate, basically cylindrical, and consists of a proboscis, trunk and tail. The body, however, is more slender and streamlined (Pterotrachea hippocampus). The visceral nucleus is compacted into a fusiform structure, oriented at approximately a 90° angle to the long axis of the body. This orientation serves to greatly reduce the surface area of this opaque structure when viewed from beneath, thus potentially reducing the visibility of the animal to upward-searching predators (Seapy and Young, 1986). The swimming fin is located about midway between the head region and visceral nucleus. A fin sucker is present only in males and has been assumed to function in mating, although this function is uncertain. Harbison (cited in Lalli and Gilmer, 1989) observed copulation behavior in Pterotrachea hippocampus; while the male and female were paired ventrally and head to head, the male's sucker was in contact with the female but could not be seen to actually hold the female. The radula in Pterotracheidae (type II) is comparatively smaller than in Carinariidae and has a much lower growth angle. Also, the number of tooth rows (24-30) is lower than in Carinaridae. The central tooth is basically polycuspid with a prominent central cusp (He 4d); the lateral and marginal teeth are monocuspid (for morphogenesis of radula and teeth see Richter, 1968).
Pterotracheids are particularly vulnerable to damage during net capture (particularly stretching) and to shrinkage and the distortion of body shape during preservation. Thus, measurements of body length are often not representative of a healthy, relaxed animal. To solve this problem, one can calculate body length from the diameter of the lens using a regression equation for the relationship between lens diameter and body length taken from undamaged animals (Seapy, 1985). An example of net damage is the holotype specimen of Pterotrachea minuta, which was examined in the above study and found to be severely stretched; measuring 38.8 mm total length. Based on the specimen's lens diameter, however, the true body length was estimated to be 20.5 mm. Recently, Seapy (2000) showed that Pterotrachea minuta Bonnevie, 1920 is not a valid species, and that it should be regarded henceforth as a junior synonym of Pterotrachea hippocampus.
Genus Firoloida
Firoloida desmaresti
Genus Pterotrachea
Pterotrachea coronata
Pterotrachea scutata
Pterotrachea hippocampus