▁eggs ▁ad here ▁to ▁plants , ▁alg al ▁m ats , ▁empty ▁muss el ▁shell s , ▁sand , ▁or ▁mud ▁at ▁sites ▁that ▁are ▁reached ▁by ▁water ▁only ▁at ▁high ▁spring ▁t ides . ▁E gg s ▁therefore ▁develop ▁while ▁exposed ▁to ▁mo ist ▁air , ▁and ▁they ▁h atch ▁when ▁the ▁next ▁high ▁spring ▁t ides ▁reach ▁them . ▁The ▁eggs ▁cannot ▁h atch ▁in ▁air , ▁nor ▁can ▁they ▁do ▁so ▁in ▁moving ▁water ; ▁h atch ing ▁is ▁initi ated ▁by ▁a ▁lack ▁of ▁o xygen , ▁something ▁that ▁can ▁happen ▁in ▁the ▁boundary ▁layer ▁of ▁relatively ▁still ▁water ▁surrounding ▁the ▁met abol ically ▁active ▁egg ▁at ▁high ▁t ide , ▁but ▁not ▁in ▁air ▁or ▁in ▁moving ▁water . ▁ ▁As ▁opposed ▁to ▁their ▁northern ▁counter parts , ▁the ▁southern ▁sub species ▁have ▁eggs ▁that ▁lack ▁fil aments ▁( ad hes ive ▁ch or ionic ▁f ibr ils ) ▁and ▁they ▁often ▁depos it ▁those ▁eggs ▁inside ▁empty ▁muss el ▁shell s . ▁The ▁two ▁sub species ▁are ▁also ▁distinguished ▁based ▁on ▁slight ▁morph ological ▁and ▁genom ic ▁differences . ▁ ▁Most ▁m umm ich ogs ▁become ▁sex ually ▁m ature ▁when ▁two ▁years ▁old , ▁around ▁ ▁in ▁length . ▁Normal ▁lif es pan ▁is ▁four ▁years . ▁ ▁Par as ites ▁ ▁M umm ich ogs ▁are ▁hosts ▁to ▁a ▁par as it ic ▁flu ke , ▁Hom al omet ron ▁p all id um , ▁which ▁has ▁a ▁complex ▁lif ecycle ▁involving ▁the ▁aqu atic