ocy em ata ▁contains ▁all ▁the ▁members ▁of ▁the ▁Re pt ant ia ▁( including ▁c rab s , ▁lo bst ers , ▁c ray fish , ▁and ▁others ), ▁as ▁well ▁as ▁the ▁St en op od idea ▁( which ▁contains ▁the ▁so - called ▁" box er ▁sh rim p " ▁or ▁" bar ber - pole ▁sh rim p "), ▁and ▁Car idea , ▁which ▁contains ▁the ▁true ▁sh rim p . ▁Ple ocy em ata ▁compr ises ▁the ▁following ▁inf ra orders : ▁St en op od idea ▁Car idea ▁A sta cide a ▁G ly phe idea ▁A xi idea ▁Geb i idea ▁Ach el ata ▁Pol ych el ida ▁An om ura ▁Bra chy ura ▁ ▁These ▁tax a ▁are ▁un ited ▁by ▁a ▁number ▁of ▁features , ▁the ▁most ▁important ▁of ▁which ▁is ▁that ▁the ▁fert il ised ▁eggs ▁are ▁inc ub ated ▁by ▁the ▁female , ▁and ▁remain ▁stuck ▁to ▁the ▁ple op ods ▁( sw imming ▁legs ) ▁until ▁the ▁z oe a ▁lar va e ▁are ▁ready ▁to ▁h atch . ▁It ▁is ▁this ▁characteristic ▁that ▁gives ▁the ▁group ▁its ▁name . ▁Ple ocy em ata ▁also ▁possess ▁a ▁l am ell ar ▁g ill ▁structure ▁as ▁opposed ▁to ▁the ▁branch ed ▁found ▁in ▁D end rob ranch i ata . ▁ ▁The ▁earliest ▁foss il ▁representative ▁is ▁the ▁Dev onian ▁Pala e op ala emon . ▁ ▁References ▁ ▁External ▁links ▁ ▁Category : Dec ap ods ▁Category : Ext ant ▁Dev