Comprehensive DescriptionRead full entry
A relatively large, elongate aquatic salamander. All members of the Family Sirenidae (sirens and dwarf sirens) lack hind limbs and eyelids, have a horny beak on the upper and lower jaws, and retain gills throughout life (Martof 1974a b; Petranka 1998). Sirens have four toes on the forelimbs and three gill slits. There is a dorsal fin, restricted to the tail. Adult Siren intermedia attain lengths of 18-69 cm, total length (Petranka 1998). The tail is 28 - 40% of the total length in adults (Martof 1973). Males have enlarged jaw (masseter) muscles which cause the head, posterior to the eyes, to appear swollen. Males are also slightly longer than females. Hatchlings have large, bushy gills and a dorsal fin on the tail which extends onto the trunk region of the body (Martof 1973; Petranka 1998).. Hatchlings are 11 - 11.5 mm total length and the tail is about 19 - 25% of the total length (Martof 1973; Godley 1983). Limb buds are present at hatching (Godley 1983).
The dorsal ground color of adults is variable, ranging from olive green to grayish blue or black. Brown or black spots can be seen scattered on the dorsum of lighter colored individuals. The venter is lighter than the back and white or yellowish flecks may occur on the sides (Martof 1973; Petranka 1998). Hatchlings and juveniles are more brightly colored than adults, having light stripes along the body and yellow or red banding on the head (Martof 1973; Petranka 1998). The bright colors and stripes fade and the dorsal fin on the back is lost as animals age (Petranka 1998).
Two or three subspecies are recognized and can be distinguished based on distribution (see below), size, and coloration. Siren i. intermedia, the eastern lesser siren, is a dark colored form, sometimes having tiny black spots on the dark brown or black dorsum. The venter is also dark, without spots or mottling, and lighter than the dorsum. Maximum length is about 38 cm, and the modal number of costal grooves is 32-33. Siren i. nettingi, the western lesser siren, is olive green to gray with tiny black spots on the dorsum. The venter is also dark with numerous light flecks. Maximum length is 50 cm, with a modal number of 35 costal grooves. Siren i. texana, the Rio Grande siren, is the largest subspecies, reaching 69 cm total length, and having a modal costal groove count of 37. The dorsum is gray to brownish gray with tiny black spots and the venter is light gray. Descriptions from Petranka (1998)