The Abyss - Part V - More Invertebrates



Written by Jonathan C. Wojcik - Photo credits unknown or from public news articles unless otherwise

noted. If you know their sources and need them credited or removed, please e-mail me.



Gastropods



Holothurians or "sea cucumbers" are an especially common sight on the floor of the

abyss, walking on tubular feet and grazing on bacteria-rich sediment with a ring of oral

tentacles. Many sea cucumbers defend themselves from predators by regurgitating their

own sticky intestines, which will quickly regenerate.



In these images by researcher Stefano Schiapaelli ( CAML ), we can get a good look

at a Scotoplane or "sea pig" and a newly discovered species of parasitic snail.



Stalked, filter-feeding Crinoids or "sea lilies" were once abundant at all aquatic

depths, but have been largely restricted to the abyss for millions of years. Some

species are able to detach and swim short distances, or even walk on two or more

tentacles in a bizarrely anthropomorphic fashion.



Marine slugs and snails typically spend their early days as free-swimming, planktonic

larva before settling down to a life of sluggish slithering. Some groups, however, are

holoplanktonic , which means that they retain their swimming form throughout their

lifespan. These gelatinous, flapping "sea butterflies" or "pteropods" may filter-feed

on microscopic plankton, trap food in dangling webs of mucus or actively hunt other

invertebrates. Their shells can be external, internal or completely absent, and some

may display bioluminescence. Holoplanktonic mollusks are found throughout our

oceans, but seem to be more common in much colder waters.



Sponges



Xenophyophores



I can't remember when it was that I first learned of these humble little creatures, but

I've yet to fully overcome the shock of their existence, and by now, I'm sure you know

that this is saying quite a bit. Liesurely creeping along the muck of the sea floor,

these gelatinous globules collect tiny fragments of shells, sponges and other animal

remains to build a hollow casing or "test" (what we see in these photos) around their

delicate bodies. Different species favor different building materials, and many form

tests of their own hardened excrement. They secrete a blanket of mucus as they sift

for tiny particles of food in the surrounding mud, engulfing it in one more amorphous

pseudopodia.



So, where's the shocking part? With some species reaching the size of a human fist,

Xenophyophores are, by an immense margin, the world's largest single-celled

organisms. They are protozoans, related to the amoeba.



Giant germs that wear their feces are as high a note as I could ever end on, so with

that, I'll bring this crappy little e-tour to a close. Every year, science is surprised anew

by what we dredge up from these stygian pits, and we can no doubt look forward to

ever-weirder zoological discoveries in our lifetimes.



Echinodermata



A flesh-eating beast you are unlikely to find in a pineapple, the surface of this innocuous-looking

deep-sea organism functions as a sort of flypaper for small crustaceans, entangling their jointed

limbs in a velcro-like pattern of microscopic hooks. Special cells in the sponge's body migrate

around the prey to form a temporary orifice, where its lipid content is absorbed and carried to

the sponge's core.



Many other sponges feed in a similar fashion, but Chondrochladia lampadiglobus , pictured here,

is one of the most visually striking. Nearly all are found in the deep-sea abyss, arctic waters and

underwater caves where sunlight and plankton are relatively scarce.

