Shell small, thin, semitranslucent, generally very elongated, curved and covered with the pale brownish periostracum; umbo situates near the anterior end of the dorsal margin, gently curved and slightly elevates beyond the dorsal line ; two obtuse ridges run out from the umbo, one to the antero-ventral corner and another to the postero-ventral; anterior and posterior ends rounded and ventral margin concavely curved ; surface marked by the growth lines only.
Height 2. 6 mm., length 9. 2 mm. and breadth 2. 3 mm. (type specimen)
Height 2.1 mm., length 8. 0 mm. and breadth 1.8 mm. (paratype no. 1)
Height 2.4 mm., length 7.5 mm. and breadth 1.8 mm. (paratype no. 2)
Height 2. 7 mm., length 9. 7 mm. and breadth 2. 5 mm. (specimen from Tanabe Bay)
Height 3.4 mm., length 9. 4 mm. and breadth 3. 0 mm. (specimen from Tanabe Bay)
Type locality: Off Chikuzen-Okinoshima, Fukuoka pref., Kyushu (85 m in depth).
Distribution: Nagasaki, Kyushu: Tosa Bay, Shikoku and Tanabe Bay, Wakayama Pref., and off Owase, Mie Pref., Honshu.
Remarks: This new species is generally found in the holes of the submarine timber bored by the ship worms. " Modiola " parasitica Deshayes from Reunion is quite close to this new species, but the former differs from the latter in having the more elongated and less curved shell which is covered with the velvet-like periostracum.