In this Presentation, Phylum Ctentophora, Comb Jellies is described. After watching this you will learn the characteristics and examples of Phylum Ctentophora. The detail description of Pleurobranchia along with reproduction, colloblasts, mesoglea, comb rows and nerve net. It is part of BS Zoology Course Animal diversity.
2. PHYLUM CTENOPHORA
Animals in the phylum ctenophora (gr. Kteno,
comb phoros, to bear) are called sea walnuts
or comb jellies.
The approximately 90 described species are
all marine (figure 9.22).
Most ctenophorans have a spherical form,
although several groups are flattened and/or
elongate.
3. • Characteristics
• 1. Diploblastic or possibly triploblastic, tissue-level
organization
• 2. Biradial symmetry
• 3. Gelatinous, cellular mesoglea between the epidermal
and gastrodermal tissue layers
• 4. True muscle cells develop within the mesoglea
• 5. Gastrovascular cavity
• 6. Nervous system in the form of a nerve net
• 7. Adhesive structures called colloblasts
• 8. Eight rows of ciliary bands, called comb rows, for
locomotion
PHYLUM CTENOPHORA
4.
5. Ctenophorans have traditionally been classified as having diploblastic
organization.
Their “mesoglea,” however, is always highly cellular and contains true muscle
cells. This observation has led some zoologists to conclude that the
Ctenophoran middle layer should be considered a true tissue layer, which would
make these animals triploblastic acoelomates.
Pleurobranchia has a spherical or ovoid, transparent body about 2 cm in
diameter.
It occurs in the colder waters Of the atlantic and pacific oceans (figure 9.22b).
Pleurobranchia, like most ctenophorans, has eight meridional bands of Cilia,
called comb rows, between the oral and aboral poles.
Comb rows are locomotor structures that are coordinated Through a statocyst at
the aboral pole and a subepidermal
Nerve net that is superficially similar to that found in members Of the cnidaria.
Pleurobranchia normally swims with its aboral pole oriented downward. The
statocyst detects tilting,
And the comb rows adjust the animal’s orientation.
Two long, branched tentacles arise from pouches near the aboral Pole.
6. Tentacles possess contractile fibers that retract the tentacles, And
adhesive cells, called colloblasts, that capture prey (figure 9.22c).
Ingestion occurs as the tentacles wipe the prey across The mouth.
The mouth leads to a branched gastrovascular canal system.
Some canals are blind; however, two small anal Canals open to the
outside near the apical sense organ.
Thus, unlike the cnidarians, ctenophores have an anal opening.
Some undigested wastes are eliminated through these canals, and
some are probably also eliminated through the mouth.
Pleurobranchia is monoecious, as are all ctenophores.
Two bandlike gonads are associated with the gastrodermis.
One of these is an ovary, and the other is a testis.
Gametes are shed through the mouth, fertilization is external, and a
slightly flattened larva develops.
