Phylum Nemertea (Rhynchocoela)

Rhyncocoel
The proboscis pore leads to rhynchodeum (anterior
lumen), which is continuous with the epidermis, and to
proboscis canal
The rhynchocoel is a closed, fluid-filled space that is
squeezed by the surrounded muscles, causing the
eversible proboscis to be rapidly extended. Squeezing
increases the hydrostatic pressure of rhynchocoel.
Everted proboscis is retrieved by retractor muscle or
hydrostatically. The genus Gorgonorhynchus possess
an unusual, massively branched proboscis that takes
the appearance of a collection of medusa-like snakes,
called proboscides.
Most predators, some
scavengers, few ectoparasites
(e.g. Carcinonemertes errans
infects all Dungeness crabs)
a) A retracted and B) extended
proboscis of a hoplonemertean