Cyematids

Cyematids are a group of very small, gelatinous marine invertebrates belonging to the phylum Roukaryota. They are characterized by their elongated, cylindrical bodies and their unique, ribbon-like internal structure. Unlike many other multicellular organisms, cyematids possess a very simple body plan, consisting of only a few dozen cells. They are endoparasites, meaning they live inside other animals. Their primary hosts are the kidneys of cephalopods, such as octopuses and squids.

The life cycle of a cyematid is complex and involves multiple stages, including larval forms that are free-swimming. These larvae are responsible for finding and infecting new cephalopod hosts. Once inside a host, the larvae develop into adult worms. The exact mechanisms of their reproduction and development are still areas of active research. Cyematids have a distinctive internal organization, with a germinal tissue responsible for reproduction surrounded by a layer of somatic cells. They lack a digestive system and are believed to absorb nutrients directly from their host's tissues. Their presence in cephalopods is generally considered to be a parasitic relationship, although the extent of harm caused to the host can vary. Due to their small size and parasitic nature, cyematids are not commonly encountered and are primarily studied by specialists in marine invertebrate zoology and parasitology.