The genera Snyderidia Gilbert, 1905 and Pyramodon Smith and Radcliffe, 1913 are both free-living members of the family Carapidae, the former represented by a single valid species, Snyderidia canina Gilbert, 1905, distributed circumglobally in tropical and subtropical waters, and the latter by four valid species in the Indo-Pacific region, two being known from Japan: Pyramodon ventralis Smith and Radcliffe, 1913, and Pyramodon lindas Markle and Olney, 1990. Three specimens (149.8–163.8+ mm total length: TL) of Snyderidia and two (111.1–182.9 mm TL) of Pyramodon were collected off the Pacific coast of Tohoku District, northern Japan, during bottom trawl surveys conducted in autumn from 2021 to 2024. The former, identified as S. canina based on the following combination of characters: pelvic fins absent; dorsal fin origin anterior to anal fin origin; 6 or 7 dorsal-fin rays anterior to anal fin origin; 24–27 pectoral-fin rays; 15 precaudal vertebrae; fang-like teeth (canines) present at symphysis of both jaws; and cardiform teeth absent, represent the first Japanese records of the species, a specimen collected off Iwate Prefecture (ca. 40˚N) being the northernmost record. The latter were identified as P. ventralis based on the following combination of characters: pelvic fins present; dorsal and anal fin posterior regions only pigmented, margins without black edge; cheek and pectoral-fin base pigmented; dorsal fin origin almost directly above anal fin origin; pectoral-fin rays 25 or 26; precaudal vertebrae 14 or 15; vertebrae to anal fin origin 6 or 7; and gnathoproctal length (snout to anus) 116.3–136.2% of head length. Since the distribution of P. ventralis has previously been restricted to the Indo-Pacific region south of Choshi, Chiba Prefecture, Japan, the specimen collected off Miyagi Prefecture (ca. 38˚N) represents the northernmost record of the species.
