P is for Parasitic Snail! Enter: The Eulimidae!

From the Eulimidae EOL image gallery-Moorea Biocode

Last week, we saw some pics of big predatory snails feeding on starfish!  This week, we turn our attention to smaller snails with a more insidious means of feasting on their hapless echino-prey!

Behold the Eulimidae! A family of snails, whose primary means of nutrition is feeding on echinoderms...specifically as PARASITES! They pretty much attach themselves to every class within the living Echinodermata: urchins, crinoids, brittle stars, sea cucumbers (remember the sea pigs?) and today's subject... starfish!!

Eulimids are insanely diverse. There's over 85 genera and easily hundreds of species. With likely more being discovered as they are found on their hosts..

If you guys ever need a one-stop shop paper on the Eulimidae, you are in luck! This paper (behind a paywall) includes a summary of biology as well as an overview to all the genera.   The acknowledged world expert on these is Anders Waren,  a scientist at the Swedish Natural History Museum

Basically, eulimid snails feed by sticking their proboscis into their host and sucking the tasty, delicious juices out of them. This in itself is kind of interesting because most echinoderms use a kind of specially treated seawater (filled with body cells called coelomocytes) as a bodily fluid.

Apparently, its these cells-the coelomocytes upon which the snails feed... Note below, the extended probsocis...

This snail was described as Melanella with what appears to be its proboscis extended and gives you a general idea of how these snails operate...

Image from EOL's Eulimidae image gallery

Here is a snail in the genus Parvioris with its proboscis extended and the animal hard at work..

From the Eulimidae EOL image gallery-Moorea Biocode

From what I've been able to determine, certain snails DO tend to occur on certain hosts, but the pattern doesn't always seem to be consistent. Some specific species of snails apparently occur on different starfish hosts but some are specific to types of hosts, e.g. sea urchins or sea cucumbers.. Many of these are undersampled, and so it still remains to be seen how much host variation is observed..

1. Ectoparasites. Some eulimids are ectoparasites, that is they are attached, but only on the exterior.. Here's one hunkered down on the disk of the very gorgeous goniasterid Iconaster longimanus.

Here's another one attached to the sand star Archaster from Singapore, but several species of starfish are often hosts. Here's a short write up on their page about them..

Another well-known ectoparasite is the eulimid called Thyca crystallina...

These are famously parasites on the blue starfish Linckia laevigata where they are often found on the oral surface around the tube foot grooves..

We often see these snails well-camoflaged as the same distinctive color which identifies their host...

Some are not so well-hidden.. (and yes, sometimes Linckia laevigata is orange!)

2. Endoparasites!  On the OTHER hand..some eulimid snails, get pretty "dug in" and have literally buried themselves in their work!

They basically embed themselves in the host, attach their proboscis directly to the internal arm canals and just suck on em' all day....  This one, Parvioris fulvescens looks like its embedded itself in what looks like Ophidiaster (?)

From Femoreale Shells via EOL

Here..we have some which have embedded themselves in Neoferdina, a goniasterid... Note how they've pretty much buried themselves INTO the skeleton of the animal. The starfish are strongly calcified.. and since there's no clear damage, I wonder if  these get in as juveniles...

Here's one called Stylifer which has buried itself in the arm of the ophidiasterid Linckia multifora

3. Parasites of the Deep! 
and lest, you think that eulimids only parasitize shallow water reef species, let it be known that many deep-sea starfish are also parasitized by snails! Here is Asterophila japonicus as reported by Sasaki et al. in: Sasaki, T., Muro, K. & Komatsu, M. 2007. Anatomy and ecology of the shell-less endoparasitic gastropod, Asterophila japonica Randall and Heath, 1912 (Mollusca: Eulimidae).Zoological Science 24(7): 700-713.

This species seems to be a host in the astropectinid sea star Leptychaster,where it has burrowed UNDER the disk and lives right above the stomach!

Several of the deep-sea snail parasites are VERY unusual and some have bodies which are SO reduced that you can barely recognize them as snails..  One deep-sea snail parasite, Asterophila rathbunasteri described only in 1994! lives as a gall in the arms of the deep-sea, multi-armed asteroid which lives off the west coast of North America...

Which they were actually unable to ID to phylum until they realized, when it was spawning, that it was producing veligers (snail juveniles)!!

the HORROR!