Coelenterata is a phylum of aquatic animals that includes jellyfish, corals, sea anemones and hydroids. They are diploblastic with two main cell layers, a gelatinous mesoglea in between, and stinging nematocysts. They exhibit radial or biradial symmetry and polymorphism. Reproduction can occur asexually through budding or sexually through external fertilization and a planula larva stage. The phylum is divided into three classes: Hydrozoa, Scyphozoa, and Anthozoa.
2. 9000 living sps and many fossils since Ordovician
period
Marine , some are fresh watered
Proterospongia-link between Protozoa and
Coelenterata
Ctenoplana- link between Coelenterata and helminthes
Cyanea arctica - Big and Long jelly fish-7.5.m radius
with 120 yards long tentacles
Chirposalmus , Chironex jelly fishes are most
poisonous
Coelenterates are called stinging animalcules
COELENTERATA
3. PEYSONNEL (1773) called them as coral insects
Linnaeus, Lamark ,Cuvier included these in Radiata
Eschscholtz (1829) divided radiata into three groups like
Zoophyta, Ecalepha, Echinodermata. He studied
Ecalepha and later described Ctenophora and
Siphonophora medusae
Johnston (1939) separated Hydroidea class
Leuckart (1947)formed this phylum including sponges
and ctenophora
Hatschek (1888) divided it into Spongiaria, Cnidaria ,
Ctenophora
COELENTERATA- Historical Background
4. Metazoan multicellular animals
Tissue grade of organisation
Aquatic animals except Hydra all are marine.
Solitary or Colonial, sedentary or free living
Radial or bilateral symmetry
Two types of individuals- polyp (asexual
form) and free swimming medusa (sexual
form)
General characters- Coelenterata
5. Zooids - small animals in a colony .
Depending on function, the nature of
zooid changes thus shows polymorphism
Diploblastic body wall with two cellular
layers
1. Outer epidermis
2. Inner gastrodermis
3. Gelatinous mesoglea in between
Body layers are with special nematocysts –
more in tentacles- many types. Stinging
cells useful for killing and protection
General characters- Coelenterata
6. Acoelomate organisms
Digestive system is incomplete anus being
absent and mouth for ingestion and egetion.
Digestion is intra and extracellular
Mouth is with small, thin tentacles which are
useful for food capture, ingestion, locomotion
and protection
Gastro vascular cavity is often branched. It
opens outside through mouth
General characters- Coelenterata
7. Respiratory , circulatory and excretory systems
are absent
Muscular system of epithelio and endothelio
muscle cells is present. Independent fibres are
present in mesoglea.
Nerve nets of synaptic or non synaptic pattern
with diffuse conduction
Sense organs are simple or complicated. Some
are with ocellli and statocysts
General characters- Coelenterata
8. Asexual reproduction – budding/binary
fission
Sexual reproduction by gametes. Sexual
forms are monoecious or dioecious
Development exhibits planula larva
Life cycle is with alternation of
generations with polyp generation and
medusoid generation
General characters- Coelenterata
10. Solitary/ colonial, polyp and medusoid forms
Radial symmetry
Body wall –ectodermis,mesoglea and gastrodermis
Gastrocoel is spacious
Cnidoblasts are absent
Body has thick perisarc.in some animals this is very solid and called
coral
Polymorphism is seen
Alternation of generation
Sex cells are formed from ectoderm
Fertilization is external
Holoblastic cleavage
Planula larva
2700 genera included
Five orders
Ex: Hydra,Bougainvillea,Millipora,Physalia,Velella,Porpita,Helistemma
HYDROZOA
12. Solitary, medusoid
Medusa umbrella or bell shaped with/without stalk
Gastrocoel has gastro fibres, Gonads and bifurcated into four radial
septa. With tetra radial symmetry
umbrella structure is with more mesoglea
True velum is wanting.
Animal end is with lappets
Exumbrellar surface has median manubrium
Sex cells derive from gastro dermis and release gametes into
gastrocoel
Monoecious
200 genera included
Five orders included
Rhizostoma, Aurelia, Periphylla, Cassiopea, Lucernaria, Charybdea,
Pericolpa, Tomoya
SCHYPHOZOA
14. Solitary/colonial, polypoid marine forms
Hexamerous , octamerous ,polymerous, biradial or radio-bilateral
symmetric animals
Anterior region becomes wide to form oral disc to accommodate
tentacles
Mesoglea with tissue
Gastrocoel has septa formed by mesenteries
Epidermis secretes test of CaCo3 or horny material
Inner side of mesentery has cnidoblasts
Gonads derive from gastrodermis and developed from mesentery.
Gametes are released into gastrocoel
Fertilisation is external. Life cycle includes planula
It inncludes 6100 genera
2 sub classes and eleven orders
Pennatula, Metridium, Fungia ,Adamsia, Madripora, Meandrina,
Gorgonia, Alcyonium, Tubipora, Heliopora
ANTHOZOA