Practice question

Poriferan embryology reveals diverse larval morphotypes including parenchymella solid stereoblastula and amphiblastula. Amphiblastula distinctive of calcareous sponges Class Calcarea and some Demospongiae characterized as hollow blastula with polarity one hemisphere composed small flagellated micromeres animal pole opposite large non-flagellated macromeres vegetal pole giving half-flagellated appearance. Free-swimming undergoes gastrulation by invagination of flagellated half then attaches metamorphoses into juvenile sponge. Polarity reflects axial specification. Presence exemplifies primitive holoblastic unequal cleavage lecithotrophic dispersal phase before sedentary adult filter-feeding existence demonstrating early evolution of larval strategies in earliest diverging animals with minimal tissue organization and cellular totipotency and settlement.