, ▁and ▁only ▁one ▁ext inct ▁na util oid ▁genus ▁is ▁known ▁to ▁have ▁bor ne ▁anything ▁similar . ▁N aut ilus ▁does , ▁however , ▁have ▁a ▁le ath ery ▁head ▁shield ▁( the ▁h ood ) ▁which ▁it ▁uses ▁to ▁cover ▁the ▁opening ▁when ▁it ▁retre ats ▁inside . ▁ ▁There ▁are ▁many ▁forms ▁of ▁a pty chus , ▁varying ▁in ▁shape ▁and ▁the ▁sculpt ure ▁of ▁the ▁inner ▁and ▁outer ▁surfaces , ▁but ▁because ▁they ▁are ▁so ▁rarely ▁found ▁in ▁position ▁within ▁the ▁shell ▁of ▁the ▁am mon ite ▁it ▁is ▁often ▁unclear ▁to ▁which ▁species ▁of ▁am mon ite ▁one ▁kind ▁of ▁a pty chus ▁belongs . ▁A ▁number ▁of ▁a pty chi ▁have ▁been ▁given ▁their ▁own ▁genus ▁and ▁even ▁species ▁names ▁independent ▁of ▁their ▁unknown ▁own ers ' ▁genus ▁and ▁species , ▁pending ▁future ▁discovery ▁of ▁verified ▁occurr ences ▁within ▁am mon ite ▁shell s . ▁ ▁So ft - part ▁an atom y ▁Although ▁am mon ites ▁do ▁occur ▁in ▁exception al ▁l ager stat ten ▁such ▁as ▁the ▁Sol n hof en ▁lim estone , ▁their ▁soft ▁part ▁record ▁is ▁surprising ly ▁ble ak . ▁Bey ond ▁a ▁tent ative ▁in k ▁sac ▁and ▁possible ▁dig est ive ▁org ans , ▁no ▁soft ▁parts ▁are ▁known ▁at ▁all . ▁ ▁They ▁likely ▁bore ▁a ▁rad ula ▁and ▁be ak , ▁a ▁marg inal ▁si ph un cle , ▁and ▁ten ▁arms . ▁ ▁They ▁operated ▁by ▁direct ▁development ▁with ▁sexual ▁reprodu ction , ▁were ▁car