Lecture 5+6 (Bio-2040)

Classification of Cnidarians

• Hydrozoa → both medusa and polyp are important

• Scyphozoa → mostly medusa as the most important shape

• Anthozoa → polyp form only

Hydrozoa

• Both body types are important

• Hydra → Non-colonial model

• Obelia → A colonial model (specialization of polyps)

Scyphozoa

Both body shapes are present, but Medusa is more prominent, with lower diversity (about 200 species). These are larger but lack velum.

Anthozoa

• only polyp, all marine animals, highest diversity (about 4000 species)

• soft coral and reefs form diverse habitats, not only in coral, but other species

The Coral Triangle

The most diverse region on earth

Hexacorallia

Sea anemones and hard corals live in symbiosis with zooxanthellae algae. has 6 compartments

Octocorallia

soft coral and sea fans, 8 compartments. Polyps with 8 radial symmetry. No exoskeleton, only a soft endoskeleton derived from mesoglae

Ctenophores

• named after the ctenes for locomotion

• Despite similarities, they aren’t derived from Medusa’s

• colloblasts instead of nemacytes

Ctenes 

8-row comb plate in Ctenophores used for locomotion

Colloblasts

sticky cells on the tentacles to catch prey

Ctenophores Feeding

• predatory - carnivorous

• feed on plankton using tentacles and colloblasts

Ctenophores Reproduction

• hermaphroditic

• larva is cydippid

Cydippid

larve of Ctenophores

Bilateral Symmetry

• polarity development (anterior and posterior ends)

• Centralization of sensory cells/organs

Cephalization

Centralization of sensory organs/cells

Rhabdites

• rod-like structures “mucus producers”

• Unique and helps with locomotion and prevention of disiccation

• in flatworms

Feeding of flatworms

• incomplete gastrovascular system (No anus)

• Intestine with diverticula (side extensions)

Excretion of flatworms

• by diffusion and proto-nephridia

Flame-cells

in proto-nephridia

• filter and get rid of residuals

• primitive kidney cells

asexual reproduction of flatworms

by fission with high capacity of regeneration

sexual reproduction of flatworms

Hermaphrodites with cross-fertilization capacity (have both testes and ovaries)

Flatworms Nervous Systems

• ganglionar system with lateral nerve cords

• concentration of organs (light-sensitive ocelli on “head”)

single-host parasites

one life phase in host + free-living phase

Multiple host parasite

Different stages in different host + free-living phase

intermediate host

host holds the egg or larval stage

Final Host

The host holds the adult parasite

Turbellaria

free-living freshwater and marine

Monogenea

Ectoparasite on fish gills (1 host)

• attached on the opisthapor by external hooks

Digenea or Trematoda

Endoparasites of vertebrates (>1 host)

• Epidemis modified to a syncytial tegument. attach by suckers

Cestoda

Endoparasite of vertebrates (>1 host)

• Attached by scolex

• when infected, removal of the scolex kills the worm, not removal of the proglottids.

• syncytial tegument

Proglottid

• subunit with its own reproductive machinery

• comes with a gravid proglottid full of eggs.