Lecture 7: Other Cnidaria

Question 1

What are Hydrozoa?

Answer 1

Colonial hydroids, smaller jellyfish, siphonophores

Probably sister group to Scyphozoa

Question 2

Theca

Answer 2

Thin secreted organic material from epidermis (protonaceous and collagenous or chitin)

Question 3

Three types of polyp

Answer 3

Trophozooid: tentacles and cnidae that capture prey and move them through network of stolons

Dactylozooid: Defensive that develop tentacles for stinging, with long basal extenstions

Gonozooid: reproductive polyps that give rise to buds that eventually detach from colony to medusae

Question 4

Jet Propulsion in Athecata and Thecata medusae

Answer 4

Space between bell and manubrium is filled with water, simultaneous muscle contraction of myoepithelium compresses the water out of the oral space

Question 5

Velum

Answer 5

Shelf around base of medusae decreases the cross sectional area through which the water is being forced out; increases speed of jet propulsion

Question 6

Tubularia, Athecata

Answer 6

Benthic colonial polyp form dominates life cycle; medusoids stay attached to benthic polyp colony

Question 7

Hydra

Answer 7

Freshwater medusa colony entirely suppressed in little “gonad”
No tentacles, no extensions of gastrovascular canals

Question 8

Aglaura

Answer 8

Polyp stage entirely suppressed, entire life is pelagic

Question 9

Siphonophores

Answer 9

Large clade of hydrozoans, entirely pelagic, grow as colonies of polyps

Question 10

Siphonophore Polymorphism

Answer 10

Extreme polymorphism;

a few polyps become non-feeding structures in which the gastrovascular cavity forms a gas chamber and gastrovascular cells secrete gasses to float (Pneumatophore!!)

A few polyps for Dactylozooids

Question 11

Scyphozoa’s 3 stages

Answer 11

Scyphistoma (polyp phase): shared gastrovascular cavities, no specialization of non-feeding polyp types

Strobilate (transverse division): polyp drops tentacles and distal end is serially sectioned to get a stubbed disk (ephyra)

Ephyra (young medusae)

Question 12

Scyphozoan traits

Answer 12

Polyps, stolons, NO polymorphism, sexual medusa

Question 13

How do Scyphozoans and Hydrozoans differ?

Answer 13

S: Along radial canal, gastrovascular cavity of medusa form gonads that develop gametes (like Anthozoans). No jet propulsion, has Ocellus.

H: Develops gametes from stem cells in the epidermis

Question 14

Scyphozoan Swimming

Answer 14

Flap their epithelial dorsal edges like fin motions, movement is muscular but movement to normal shape is mechanica by the mesoglea’s opposing of the muscular contraction

Question 15

Ocellus in Scyphozoans

Answer 15

Statolith in epithelial space, sensory cilium tells change of orientation, firing an action potential to neurons

Ocellus + Statocyst = Rhopalium

Question 16

Anthozoa’s Phylogeny

Answer 16

Anthozoa is the sister group to all other Cnidaria

Question 17

Myxozoans

Answer 17

Parasites of fished, spores are cellular and surrounded by epithelial cells, syncytium and nematocysts which were called “polar capsule cells” attach to host

Question 18

Buddenbrockia

Answer 18

Bryozoan parasite: 2 epithelial layers, no mesoglea but connective tissue layer with myocytes
Epithelial cells develop cnidae
Gastrodermis just for spores