Proseriata is an order of free-living

flatworms Platyhelminthes (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") is a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrates commonly called ...

in the class

Rhabditophora Rhabditophora (from ''rhabdito''-, rhabdite + Greek -φορος ''phoros'' bearer, i.e., "rhabdite bearers") is a subphylum (previously a class) of flatworms. It includes all parasitic flatworms (clade Neodermata) and most free-living species ...

with over 400 species described worldwide.

Description

Proseriate flatworms are minute aquatic organisms, usually with an elongate body. There are no strong

synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to ...

for the group, but it is supported by molecular studies. The suggested synapomorphies include the lack of lamellated rhabdites, an otherwise synapomorphy of Rhabditophora, and some features of the

ultrastructure Ultrastructure (or ultra-structure) is the architecture of cells and biomaterials that is visible at higher magnifications than found on a standard optical light microscope. This traditionally meant the resolution and magnification range of a c ...

of the protonephridia and the

cilia The cilium (: cilia; ; in Medieval Latin and in anatomy, ''cilium'') is a short hair-like membrane protrusion from many types of eukaryotic cell. (Cilia are absent in bacteria and archaea.) The cilium has the shape of a slender threadlike proj ...

of epidermal cells.

Ecology

Most proseriates occur in marine environments, at the coastal zones, and are particularly common in high-energy habitats with medium to coarse sediments, sometimes being the dominant animal group in such areas. They are also common in brackish water, but few species occur in freshwater. Most proseriates are carnivores or scavengers, but some species are

ectoparasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The en ...

on marine

crustacea Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

ns. As they occur in very high densities in some habitats, they may have a considerable impact on the population of other meiofaunal organisms.

References

{{Authority control Rhabditophora