Pacific Brook Lamprey

Adults: 9.8-17.5 cm TL. Body proportions, as percentage of TL (based on 39 specimens measuring 9.8-17.3 cm TL): prebranchial length, 8.9-12.8; branchial length, 8.9-11.3; trunk length, 44.7-53.5; tail length, 24.3-35.0; eye length, 1.4-3.0; disc length, 4.1-7.2. Urogenital papilla length, as a percentage of branchial length, in ten spawning males measuring 11.2-13.3 cm TL, 17.8-36.4. Trunk myomeres, 53-58. Dentition: supraoral lamina, 2 unicuspid teeth; infraoral lamina, 6-9 unicuspid teeth, usually 8; usually 3 endolaterals on each side, occasionally 2 on one side; endolateral formulae highly variable with the first two teeth 1-3 and the third 1-2; 1-2 rows of anterials; first row of anterials, 6 unicuspid teeth (in spawning specimens, the teeth in the anterior field may be lost); exolaterals absent; posterials absent; transverse lingual lamina, undetermined number of minute unicuspid teeth on either side of an enlarged median one; longitudinal lingual laminae cusps too small to count. Velar tentacles, 3-6, with tubercles. Body coloration (preserved), dark gray on dorsal and lateral aspects, whitish on ventral aspect. Lateral line neuromasts unpigmented. Extent of caudal fin pigmentation, 1% to

Freshwater; creeks and rivers. Metamorphosis occurs in October in Oregon and California.Adults nonparasitic. Based on the dates of collection of spawning individuals in the original description, the spawning period probably occurs between mid-April and August in Oregon, while in California spawning probably occurs between the end of April and the beginning of May (Ref. 89241).