Ctenophora

Outlines

PHYLUM CTENOPHORA

Class Tentaculata (Tentaculate ctenophores)

Order Cydippida
Order Platyctenida
Order Thalassocalycida
Order Lobata
Order Cestida

Class Nuda (no tentacles)

Order Beroida

PHYLUM CTENOPHORA

Body Plan

two (possibly three) layers: epidermis and gastrodermis. Middle layer ("mesoderm") is a cellular mesenchyme, containing true muscle cells (hence the "mesodermal" designation). Biradial symmetry (unless secondarily modified) . Gut is a branched gastrovascular cavity, with a mouth and one or more "anuses". Phylum characteristic is presence of comb plates for motility.

Locomotion

Elastic mesenchyme provides "skeletal" support, with muscle cells providing tonus for body shape. Neutrally bouyant, but swim using comb rows with ctenes (transverse bands of partially or wholly fused cilia beating as a unit).

Feeding and Digestion

All ctenophores are predatory. Prey captured by tentacles equipped with colloblasts which discharge a sticky filament. Mesenchymal muscle cells aid in ingesting prey into pharynx where it is exposed to enzymes and moved about by ciliary action. Digestion extracellular. Breakdown products are distributed via branches of the gastrovascular cavity. Undigested food expelled through mouth and anuses.

Sense Organs

Both "unspecialized" mechanoreceptive and chemoreceptive nerve endings in epidermis and gastrodermis. Special sense organs include statocysts and ocelli.

Nervous System

Nerve net. No centralization, although there are plexuses beneath the combs, in which cells form nervelike strands. Neurons are bare and nonpolar. Calcareous statolith provides orientation.

Respiration and gas exchange

Cellular. Uses simple diffusion. Gas exchange at gastrovascular or epithelial surface.

Circulation

No specialized system.

Osmoregulation

Cellular level. Largely osmoconformers. All are marine.

Reproduction

Although powers of regeneration are great, no evidence for asexual reproduction by fission. Reproduction considered to be entirely sexual. Most species are hermaphroditic, but some gonochoristic. In most, gametes shed through mouth, fertilization and development external.

Body Plan	two (possibly three) layers: epidermis and gastrodermis. Middle layer ("mesoderm") is a cellular mesenchyme, containing true muscle cells (hence the "mesodermal" designation). Biradial symmetry (unless secondarily modified) . Gut is a branched gastrovascular cavity, with a mouth and one or more "anuses". Phylum characteristic is presence of comb plates for motility.
Locomotion	Elastic mesenchyme provides "skeletal" support, with muscle cells providing tonus for body shape. Neutrally bouyant, but swim using comb rows with ctenes (transverse bands of partially or wholly fused cilia beating as a unit).
Feeding and Digestion	All ctenophores are predatory. Prey captured by tentacles equipped with colloblasts which discharge a sticky filament. Mesenchymal muscle cells aid in ingesting prey into pharynx where it is exposed to enzymes and moved about by ciliary action. Digestion extracellular. Breakdown products are distributed via branches of the gastrovascular cavity. Undigested food expelled through mouth and anuses.
Sense Organs	Both "unspecialized" mechanoreceptive and chemoreceptive nerve endings in epidermis and gastrodermis. Special sense organs include statocysts and ocelli.
Nervous System	Nerve net. No centralization, although there are plexuses beneath the combs, in which cells form nervelike strands. Neurons are bare and nonpolar. Calcareous statolith provides orientation.
Respiration and gas exchange	Cellular. Uses simple diffusion. Gas exchange at gastrovascular or epithelial surface.
Circulation	No specialized system.
Osmoregulation	Cellular level. Largely osmoconformers. All are marine.
Reproduction	Although powers of regeneration are great, no evidence for asexual reproduction by fission. Reproduction considered to be entirely sexual. Most species are hermaphroditic, but some gonochoristic. In most, gametes shed through mouth, fertilization and development external.