The Echinoblog: Melibe Ghostly Nudibranchs for Halloween! Happy #SeaSlugDay 2015

Image photographed by Martin Buschenreithner. Borrowed from the US Slug Site!

NUDIBRANCHS! Happy First Sea Slug Day!!

Given its proximity to Halloween and my propensity for sharing cool stuff about weird animals my post this week is about one of my favorite bizarre sea slugs: The ones in the genus Melibe!

Melibe (in the family Tethyiidae) includes 17 currently recognized species which are known Primarily from the tropical and temperate Pacific but with a minority of species from the Atlantic, including South Africa and the tropical west Atlantic (Bahamas, Florida, etc.)

Personal caveat: I am not an expert in nudibranchs and have gone with names used by the photographers. If you know better let me know and I will correct them.

Here's a "classic" Melibe leonina from the California coast to give you an idea of what the general body plan looks like...

This species is fairly well known. With nice brief write up by Monterey Bay Aquarium but many others as well.

When encountered, some species are often present in great abundance..

Although they appear to be mostly filter feeding in the pictures

some Melibe species can also be fairly effective predators.. here's a nice video from Japan showing prey capture..

Morphology on these animals is remarkable in that their body can be translucent to transparent and the internal anatomy can be visible just like those old "Visible Man" model kits!

A close up on the lobes on the body reveals these fine branching structures-the digestive glands! Which function in digestion of food

What happens when you take these digestive glands to the extreme? Along with a transparent body?
You get Melibe colemani, aka the "Phantom Melibe!" named for the photographer Neville Coleman, who was a noteworthy photographer, diver and natural historian from Australia.

What you are seeing in the picture below is its digestive glands!! The body is completely transparent!! This species was originally described from Malaysia. These images are from Lembeh (Indonesia) and other images have been identified from the Philippines, so I would imagine it occurs in roughly that tropical, central Pacific region.

Although not much is known about it, there's a pretty great article about this species on the Slugsite Here.

I know just looking at pictures doesn't look like its a sea slug, but check out this video!!

Melibe colemani from Travel Maniac on Vimeo.

They SWIM!!
Most of the species seem to crawl around or stay in one place, but given the motivation, some species can swim.. Here's what I think is Melibe viridis, based on this article in the Sea Slug Forum but kind of swimming in the water column..(identified as Melibe japonica, since synonymized)

Melibe diversity is fairly mind boggling.

This one from Lembeh, Indonesia. This one is also identified as Melibe viridis, but which seems to vary somewhat from the one from Japan. These can get quite large with some individuals reaching almost a foot long!

There's a nice write up on Melibe viridis here on the Slug Site. Here.