Acanthocephala

Acanthocephala, related to the rotifers, is a clade of endoparasitic worms. These worms lack a mouth or a digestive system, instead, they absorb nutrients through their epidermis. The anterior region of acanthocephalans consists of an eversible proboscis covered in hook-like spikes which are thought to be ciliary in origin (relating to the rotifers). The mechanism used to propel and contract the proboscis is two sacs, called lemnisci, located on either side of the proboscis sac and act as a hydraulic system.
As can be seen in the diagram below, the Acanthocephalans have a unique circulatory system called the lacunar system. It is comprised of longitudinal canals through the cytoplasm of the syncitial epidermis. lateral pathways are found throughout the epidermis.
The life cycle of a typical acanthocephalan consists of two hosts: an intermediary host (usually an arthropod) during the juvenile stage, and a vertebrate host for adulthood. Unlike the Rotifers, Acanthocephalans are dioecious, requiring sexual reproduction. Eggs are laid by the female which are excreted by the vertebrate host. Organisms such as isopods and other crustaceans will pick up the eggs while ingesting the detritus. The acanthocephalan hatches and develops into a cystacanth within the intermediary host. eventually the intermediary host is consumed by the potential vertebrate host and the cystacanth infects the vertebrate, everting its proboscis and attaching to a tissue wall.