Ecdysozoa

[CladeArthropoda]

This isn't necessarily pet related, but I think it's fun to know nonetheless. Arthropods nematodes, and several other groups are classified together as the super group 'ecdysozoa'. They are united by a layered cuticle that they molt as they grow, hence ecdysis means molting. They also lack cillia and produce amoeboid sperm. Now who are the members of this group?

First off, there's the arthropods. We are all quite familiar with them so these guys need no introduction.

I'm pretty sure a good deal of us know these guys as well. For those who of you who don't, velvet worms are animals very closely related to arthropods, but exhibit a few key differences. Their cuticle isn't a sclerotized exoskeleton as it is in arthropods, and their legs are stubby and not jointed. Their most prominent feature is the ability to shoot a glue like substance to catch prey.

Tardigrades are also relatively famous. They are microscopic animals related to velvet worms and arthropods. They are most noted for their ability to survive harsh conditions in a state of cryptobiosis, though they tend to get exaggerated. They are also a lot of more diverse than people think.

Then we have nematodes. These guys, are everywhere. Well, almost everywhere. They are strangely absent in pelagic ecosystems for some reason. But what they do best is burrowing. A single acre of soil can have millions of nematodes. They are also extremely successful as parasites, upon both plants and other animals. Most are microscopic, but some parasitic forms like Ascaris can grow to be quite large.

These are the groups that are relatively well known. Next post, I'll cover the more obscure groups.

 

[CladeArthropoda]

Alright, now for the more obscure groups.

Nematomorpha, also called Gordian worms, are a group of animals closely related to nematodes. They are a lot less diverse, but they have rather freaky life cycles. They are parasites of arthropods, from crickets to cockroaches to even crabs. After reaching sexual maturity, it hijacks the mind of it's arthropod host and makes it go into a body of water. It is there that the host dies and the worm emerges from the body. The adult worms get into these tight balls called Gordian knots, and mate. They lay their eggs and the cycle repeats.

Khinorhyncha, or mud dragons as they are sometimes called, are a small group of tiny, segmented animals. They are mostly eat detritus or diatoms. They dwell in marine sand at varying depths and are part of the meiobenthos. Unlike other similar sized animals which use cillia to move, khinorhynchs use spines on the body to move.

Priapulids are a small group of burrowing worm-like animals. They are called also penis worms, due to their comical appearance. These mud dwelling creatures feed with a proboscis.

Loriciferans are small animals that live between sand grains. They secrete a protective outer case called a lorica. They are among the most recently described animal groups, being discovered in 1983.

Lobopods are a collection of paleozoic worm like animals with legs. They aren't a group, but rather an evolutionary grade from which arthropods, velvet worms and tardigrades evolved from.

Dinocarids are also a grade, sometimes considered a subset of lobopods. This grade represents the step from the typical lobopod body plan to the arthropod body plan. Though these creatures have soft, lobopod like bodies, they do have fully 'arthropodized' forelimbs and more advanced forms have compounds eyes. Examples include the famous anomalocaris.

Palaeoscolecids are an assemblage of worm like animals from the early paleozoic. They are most likely stem priapulids.

 

[VolkswagenBug]

Those mud dragons are really cool. I'm actually surprised - I've never heard of those before!

 

[schmiggle]

They are strangely absent in pelagic ecosystems for some reason.

I wonder if this has partly to do with natural history. If nematodes are best at burrowing, they might do badly without a substrate. This would exclude all but the parasites, of which most have yet to be described. Given how sparse the pelagic ecosystem is anyway (in terms of density), I would imagine parasitic pelagic nematodes are hard to find, and they don't generate that much interest.

 

[CladeArthropoda]

I wonder if this has partly to do with natural history. If nematodes are best at burrowing, they might do badly without a substrate. This would exclude all but the parasites, of which most have yet to be described. Given how sparse the pelagic ecosystem is anyway (in terms of density), I would imagine parasitic pelagic nematodes are hard to find, and they don't generate that much interest.

Parasitic nematodes still burrow through substrate. Soft tissues.

 

[schmiggle]

Parasitic nematodes still burrow through substrate. Soft tissues.

I know, that's exactly what I mean. Sampling nematodes planktonically might not turn up much if the nematodes are predominantly or entirely parasitic.