Kalmar "subclass Opisthobranchia" tana nufin matsayi na haraji a cikin rarrabuwar dabbobi. Kalmar "opisthobranch" ta fito ne daga kalmomin Helenanci "opistho" ma'ana "a baya" ko "a baya," da "reshe" ma'ana "gills." Wannan yana nufin matsayin gyambon da ke bayan jiki.Opisthobranchs an san su da nau'i-nau'i iri-iri kuma galibi masu launin launuka, kuma sun haɗa da sanannun ƙungiyoyi irin su nudibranchs da teku. kuraje. Ana siffanta su da ƙwanƙwasa, sau da yawa elongated jiki, kuma ba su da harsashi na waje. Maimakon haka, sau da yawa suna da gyare-gyare iri-iri don tsaro, irin su spicules, kari na alkyabba, ko kariyan sinadarai.Opisthobranchia subclass yana ɗaya daga cikin rukunoni uku na ajin Gastropoda, wanda kuma ya haɗa da Pulmonata da Prosobranchia.