Cnidarians
(coming from the Greek CNIDOS= stinging
needle) are incredibly diverse in form
but come in two fundamental shapes,
polypoid and medusoid shapes. The main
characteristic feature is the presence
tentacles set in a radial symmetry with
their digestive system in the middle. On
these tentacles are found the
nematocysts (stinging cells that can be
ejected at a prey if they come close
enough) used to subdue and capture food
by the use of a toxin, that can be
sometimes even lethal to man. Cnidarians
can be found as single element or in
colonies (like coral)
There are
9000 species (400 in the Mediterranean) of cnidarians
organized in four major groups: Anthozoa, which includes
true corals, anemones, and sea pens; Cubozoa, the
amazing box jellies with complex eyes and potent toxins;
Hydrozoa, the most diverse group with siphonophores,
hydroids, fire corals, and many medusae; and Scyphozoa,
the true jellyfish.
Anthozoa:
Asteroides
Clycularis
Calliactis Parasitica
Alicia
Mirabilis
Condy Lactis Aurantiaca
Scyphozoa (jelly Fish)
Aurelia
Aurita
Rhizostoma Pulmo
Hydrozoa
:
Velella
Vellella
COTHYLORIZA TUBERCULATA - CASSIOPEIA - FRIED EGG JELLY
FISH
Belongs to
the Order Rhizostomae. Family Cepheidae. One of the most
common jellyfish in the Mediterranean sea and definitely
the most colorful of all. The animal can grow to 35 cm
in diameter and in contrast to most jellyfishes has an
ability to move on its own. It migrates vertically while
various juvenile fishes are associated with it.
This species feeds on Microplankton and has separate
sexes. The eggs are fertilized internally, the larvae
kept in pockets and then are released in the open water
where they developed into sessile polyps.
Ctenophores - Comb Jelly
Ctenophores (Greek for "comb-bearers") have eight
"comb rows" of fused cilia arranged along the sides
of the animal, clearly visible along the red lines
in these pictures. These cilia beat synchronously
and propel ctenophores through the water. Some
species move with a flapping motion of their lobes
or undulations of the body. Many ctenophores have
two long tentacles, but some lack tentacles
completely.
Ctenophores, variously known as comb jellies, sea
gooseberries, sea walnuts, or Venus's girdles, are
voracious predators. Unlike cnidarians, with which
they share several superficial similarities, they
lack stinging cells. Instead, in order to capture
prey, ctenophores possess sticky cells called
colloblasts. In a few species, special cilia in the
mouth are used for biting gelatinous prey.
Leucothea
The
phylogenetic position of ctenophores has been, and
still is, in dispute. Ctenophores have a pair of
anal pores, which have sometimes been interpreted as
homologous with the anus of bilaterian animals
(worms, humans, snails, fish, etc.). Furthermore,
they possess a third tissue layer between the
endoderm and ectoderm, another characteristic
reminiscent of the Bilateria. However, molecular
data has contradicted this view, although only
weakly. Therefore, this is an active area of
research.
