Various galeommatoidean bivalves, including free-living species (A, C, T) and species symbiotic with their host invertebrates (B, D, E–S, U, V). (A) Galeomma sp. attached to the undersurface of a rock; (B) Ephippodonta gigas living in the burrow of the thalassinidean shrimp Callianidea typa; (C) Scintilla aff. hydatina attached to the undersurface of a rock; (D) Arthritica japonica attached to the intertidal crab Xenophthalmus pinnotheroides; (E) Pseudopythina subsinuata attached to the abdomen of the mantis shrimp Oratosquilla oratoria; (F) Pseudopythina macrophthalmensis attached to the intertidal crab Macrophthalmus sp.; (G) Pseudopythina ochetostomae with its echiuran host Listriolobus sorbillans; (H) Peregrinamor ohshimai attached to the abdomen of the thalassinidean shrimp Upogebia major; (I) Pseudopythina aff. nodosa attached to the peanut worm Siphonosoma cumanense; (J) Byssobornia yamakawai living in the burrow of the spoon worm Ochetostoma erythrogrammon; (K) Pseudopythina aff. ariake with its holothurian host Patinapta ooplax; (L) Scintillona stigmatica attached to the heart urchin Brissus latecarinatus; (M) Salpocola philippinensis attached to the peanut worm Sipunculus nudus; (N) Litigiella pacifica attached to the peanut worm S. nudus; (O) Nipponomysella subtruncata attached to the peanut worm S. cumanense; (P) Devonia semperi attached to the sea cucumber Protankyra bidentata; (Q) Anisodevonia ohshimai attached to the sea cucumber P. bidentata; (R) Neaeromya rugifera attached to the abdomen of the thalassinidean shrimp Upogebia pugettensis; (S) Curvemysella paula collected from an empty shell carried by the hermit crab Spiropagurus spiriger; (T) Mysella aff. bidentata living in sand; (U) Nipponomontacuta actinariophila attached to the sea anemone Telmatactis sp.; (V) Basterotia sp. living in the burrow of the spoon worm O. erythrogrammon.