Rhodopidae
Rhodopidae is a family of sea slugs. Rhodopids are small, meiofaunal organisms with worm-like body plans that differ considerably from a typical gastropod body plan, to the point that Rhodope was at one point classified as a flatworm. They have no shell. Two genera are currently recognized within the family, Rhodope and Helminthope. Helminthope has been described as the most worm-like gastropod.
Etymology
Rhodope, the type genus of the family, is named for Rhodope, a figure in Greek mythology.Description
Rhodopids have worm-like bodies with no appendages. They often have red, orange, or purple bands, in varying pattern depending on the species, though some species are entirely white. The species range in length from 1.5 to 8 mm, although they are capable of considerably contracting themselves. The length-to-width ratios of the body while extended to crawl is around 9 in Rhodope and 25 in Helminthope. Their bodies contain spicules below the epidermis that may provide structural support for the animal. The nervous system of rhodopids has accessory ganglia, as in several other lineages of interstitial gastropod.Ecology
Some rhodopid species are epibenthic, while others, particularly the genus Helminthope, are fully interstitial organisms. They are found in temperate and warm oceans worldwide.Rhodopids are the only known predators of placozoans, which make up the primary component of their diet. At least some species, such as Rhodope placozophagus, can subsist entirely on a diet of placozoans; they are apparently not harmed by the toxins present in placozoans.