Echinodermata
Echinoderms are the closest relatives to Chordates. It may not seem so
at first, but looking closely at embryological evidence, it is believed
that chordates and echinoderms shared a common relative. This relative is believed to have been something along the lines of
sea urchin - an orgasnism a bit larger than a golf ball with spines extending radially like the guy from Hellraiser.
Interesting little creatures, they aren't especially intelligent. In fact, they don't do much of anything.
Keep in mind that "close" is a relative term. New York and Sydney are
close compared to the distance between the earth and Jupiter. It is all a
matter of context. In evolution, the context is a matter of many
millions of years.
Classification of Echinoderms
- Kingdom Animalia - they're animals
- Subkingdom Eumetazoa - echinoderms have organs
- Branch Bilateria - in their early early stages, they
all have bilateral symmetry.
- Grade Coelamata - they have body cavities
- Subgrade Enterocoela - the mesoderm pouches to form a
true body cavity
- Phylum Echinodermata - echinoderms
- Subphylum Crinozoa - radially symmetric as ADULTS, with
an upward mouth
- Class Crinoidea - Feather stars
- Subphylum Asterozoa - Radially symmetric as ADULTS,
star shaped mouth points down
- Class Stelleroidea
- Subclass Asteroidea - sea stars
- Subclass Ophiuroidea - Brittle stars
- Subphylum Echinozoa - globular or disc-shaped, mouth
points down.
- Class Holothuroidea - sea cucmumbers
- Class Echinoidea - sea urchins, sand dollars
- Class Concatricycloidea - Sea daisies
Please note, these are the classes we will be studying, it is not a
complete list of classes.
Things To Know About Echinoderms
Echinoderms are very varied. They range from a raquetball sized sea
urchin to 25-armed starfish to the eggplant-lookalike sea cucumbers. They
do however share certain characteristics:
- All echinoderms live in MARINE environments. No, that does not
mean they like Parris Island or Camp LeJeune. It means they live in salt
water environments. If they liked freshwater, they would be called
aquatic.
- Most echinoderms have spiny skin in some way or another. That's why
they are called echinoderms. "Echino-" = "hedgehog" / "derm" = "skin". Sea
urchins have pronounced spines, starfish have smaller bumps, sea cucumbers
have microscopic plates.
- Secondarily derived pentaradial symmetry. What does that mean? It
means that echinoderms tend to be pentaradially symmetric. The secondarily
derived portion of that means that they switch from being bilaterally
symmetric to radially symmetric as they mature. This is of no consequence
to taxonomists, they use the symmetry at the larval stage.
- Three different circulatory systems:
- Water vascular system - consists of the madreporite, the stone
canal, the ring canal, radial canals, ampullae and tube feet.
- Transport system - body fluids circulate throughout the
tissues
- Haemal system - doesn't do much in most echinoderms except sea
cucumbers. Its main function is to act as a "blood system".
- Ectoneural & entoneural systems - the ectoneural system tells the
animal what's going on outside (sensory) and the entoneural system is
how the animal controls its functions so its more of a motor system. It
doesn't have a brain!
- Echinoderms are monoecious, that means that the sexes are
separate. Males are males, females are females. There is no
ambiguity. However, with echinoderms, the sexes are not readily
aparent using the unaided eye.
Since the specimens we're looking at are so varied,I'll give you the
rundown on them individually - next to the pictures.
Since there are so many differences between the echinoderms, I'll give
you a complete rundown on them individually next to their pictures.
Dissected Specimens