48 |
A Handbook of Biology
Reproduction
Asexual
(fragmentation)
& sexual,
hermaphrodite,
internal
fertilization,
development is
indirect
Polyp reproduces
asexually
(budding) and
medusa sexually,
most are separate
sexes, external
fertilization,
development is
indirect
Only sexual,
hermaphrodite,
external
fertilization,
development is
indirect
Unique
features
Water canal
(water transport)
system,
(AIPMT 1999)
Water enters
through millions
of ostia into
spongocoel &
canals are lined
with choanocytes
(collar cells),
(NEET 2017) body
is supported by
spicules and
spongin fibres
Tentacles with
cnidoblasts,
a gastro-
vascular cavity
(coelenteron)
with an opening
(mouth) on
hypostome, polyp
& medusa forms
are seen, some
shows alternation
of generation,
(AIPMT 2015) corals
have skeleton
composed of
(CaCO3)
Locomotion is
by 8 vertical
external rows of
ciliated comb
plates, tentacles
present, shows
bioluminescence
Examples
Sycon (Scypha),
Spongilla (fresh
water sponge),
Euspongia (Bath
sponge)
Hydra, Obelia,
Aurelia, Physalia
(Portugese man
of war), Adamsia
(Sea-anemone),
Pennatula (Sea
pen), Gorgonia
(Sea fan), (Brain
coral) etc.
Ctenoplana,
Pleurobrachia
Hydra : In hydra nerve cells are present but brain is absent. (AIPMT 2002)
Alternation of generation (Metagenesis): The phenomenon in which
polyps produce medusae asexually and medusae form the polyps
sexually. E.g. Obelia.
Hermaphrodite: Male and female sex organs are seen in same individual.
Tentacles: Finger-like structures which surrounds the mouth of
coelenterates. Used for food capture & defense.