Practice question

Defining autapomorphy of phylum Nemertea is presence of rhynchocoel separate fluid-filled coelomic chamber located dorsal to alimentary canal extending most body length not connected to digestive lumen, housing within anterior portion eversible proboscis apparatus isolated from gut. Proboscis remains invaginated and coiled within rhynchocoel when retracted attached posterior by retractor muscle to wall. During prey capture contraction of body wall and rhynchocoel circular muscles raises hydrostatic pressure rapidly everting proboscis through anterior rhynchopore above mouth. Rhynchocoel fluid acts as hydraulic skeleton for protraction retraction cycle structure absent in all other metazoan phyla.