This document discusses theories about the early development of invertebrate animals. It mentions the trocophore theory proposed by Hatschek that certain animal phyla like Annelida and Mollusca share a common larval form called a trochozoon. It also discusses Haeckel's Recapitulation Law that ontogeny recapitulates phylogeny, with some crustaceans sharing ancestry to a nauplius-like form. Additionally, it notes the dipleurula and pentactula larva are coelomate, bilateral, and free-swimming forms. Finally, it states the tornaria larva is related to echinoderm larvae.

8. Trocophore theory: Hatschek (1878); trochozoon; Annelida,
Mollusca, etc.
Haeckel’s Recapitulation Law: Ontogeny repeats to some
extent phylogeny. Nauplius-like ancestor in crustaceans.
 Dipleurula & Pentactula larva: coelomate, bilateral & free
swimming.
Tornaria larva’s affinity to echinoderm larvae

9. Invertebrates by R. L. Kotpal
Invertebrate Zoology by Jordan & Verma