Echinoderms, Cnidarians, & The Gastropods That Parasitize Them

The recent Invertebrate Wars reminded me of spectacular, but often ignored, group of gastropods. The parasites! This is a group that I have totally geeked out on in the past. In my previous work I have focused on the Ptenoglossa likely a paraphyletic or polyphyletic group, established originally of unspecified rank by Gray (1853). It is generally agreed upon that the group is above the level of family and generally is defined as a suborder (Bouchet & Rocroi 2005). The group includes usually includes the families Cerithiopsidae, Triphoridae, Janthinidae, Epitoniidae, Aclidae, and the Eulimida. Most ptenoglosates possess radulae distinctive to the group (Ponder & Lindberg 1997).

Most eulimids are highly specialized and exclusively ectoparasitic (external parasites) on echinoderms. Most are permanently attached to a single host, although some species may transfer between hosts repeatedly during their lifespan. However a few species have undergone numerous morphological adaptations, including anatomical reductions, to exploit hosts as endoparasites particularly on the sea cucumbers! Shell morphology can be extremely variable, reflecting specialization for parasitism, with males typically smaller than females. Epitoniids are generally considered to be ectoparasites, although some authors have defined this group by various degrees of commensalism and predation (Smith 1998). In contrast to eulimids, epitoniids are exclusively ectoparasitic on cnidarians, primarily anemones and corals, and reside in the sediment near their hosts. A modified radula and jaw are used to bite pieces of their hosts. The host specificity of aclids is less clear is not known. Cerithiopsidae and Triphoridae feed on sponges possibly in a manner that could be construed as parasitic. The Janthinidae, or violet snails, are parasites on the various pelagic Cnidarians like Portuguese Man-‘O-War, Porpita, and Velella.

So its obvious once again that Mollusks, specifically Gastropods, are better than cnidarians and echinoderms (capitalization, or lack thereof, is intended)

See below for pictures.

Janthina globosa feeding on Porpita
Eulimid on crinoid

Examples of Epitoniids (Wentletraps)

Eulimid snail on Ophiothrix sp

Parasitic Eulimid Shell on a Fire Urchin

Dr. M (1801 Posts)

Craig McClain is the Executive Director of the Lousiana University Marine Consortium. He has conducted deep-sea research for 20 years and published over 50 papers in the area. He has participated in and led dozens of oceanographic expeditions taken him to the Antarctic and the most remote regions of the Pacific and Atlantic. Craig’s research focuses on how energy drives the biology of marine invertebrates from individuals to ecosystems, specifically, seeking to uncover how organisms are adapted to different levels of carbon availability, i.e. food, and how this determines the kinds and number of species in different parts of the oceans. Additionally, Craig is obsessed with the size of things. Sometimes this translated into actually scientific research. Craig’s research has been featured on National Public Radio, Discovery Channel, Fox News, National Geographic and ABC News. In addition to his scientific research, Craig also advocates the need for scientists to connect with the public and is the founder and chief editor of the acclaimed Deep-Sea News (, a popular ocean-themed blog that has won numerous awards. His writing has been featured in Cosmos, Science Illustrated, American Scientist, Wired, Mental Floss, and the Open Lab: The Best Science Writing on the Web.