Ch.13 Textbook Review Questions

Question 1

Explain the utility of radial symmetry for sessile and free-floating animals

Answer 1

radial symmetry means all sides are the same, which is useful, as sessile and free-floating animals approach their environment (or the environment approaches them) from all sides equally.

Question 2

What characteristics of phylum Cnidaria are most important in distinguishing it from other phyla?

Answer 2

Cnidaria get their name from cells called cnidocytes, which contain the stinging organelles (cnidae) characteristic of the phylum. Cnidae come in several types, including the common nematocysts. Nematocysts are formed only by cnidarians.

Question 3

Name and distinguish the taxonomic classes in phylum Cnidaria

Answer 3

Hydrozoans Colonial jellies; velum in medusa; medusae produced by lateral budding

Scyphozoan-Bell/cup jellies; strobilation - asexual reproduction via division of the body into segments

Cubozoa-Box jellies; boxlike medusa; four evenly spaced tentacle clusters; complex, well developed eyes

Anthozoa- sea anemone no medusa stage; reproduce by budding; 3 subclasses: Hexacorallia, Ceriantipatharia, Octocorallia

Staurozoa- no medusa stage, solitary polyp on stalk, attach to objective w/ adhesive disc, sexually reproduce

Myxozoa-obligate parasites, life cycle has two hosts fish/annelid worm, polar capsules-homologous to nematocysts

Question 4

Distinguish b/t polyp and medusa form

Answer 4

Poly attached to something; sessile; asexual reproduction

Medusa is free swimming; looks like jelly fish; sexual reproduction

Question 5

In what way is a hydra atypical as a hydrozoan

Answer 5

Hydra is one of the few cnidarians to live in freshwater and, atypical for a hydrozoan, lacks both the planula larva and medusa stages

Question 6

Coral reefs generally are limited in geographic distribution to shallow marine waters. How do you explain this observation

Answer 6

Hermatypic corals and their zooanthellae that make up coral reefs require warmth, light, and salinity of undiluted seawater

Question 7

How do zooxanthellae contribute to the welfare of hermatypic corals?

Answer 7

a mutualistic relationship in which the zooxanthellae live in the coral tissues where they photosynthesize and fixate carbon dioxide which in turn furnishes food molecules for the coral

Question 8

What characteristics of Ctenophora are most important in distinguishing it from other phyla?

Answer 8

all marine, 8 rows of comb-like plates, free swimming, biradial symmetry

Question 9

Compare cnidarians and ctenophores, giving five ways in which they resemble each other and five ways in which they differ

Answer 9

5 ways Cnidarians and Ctenophores resemble each other:
- Tentacles
-Medusa shape in most
-Diploblast with gelatinous middle layer (Debatable)
- No coelomic cavity
- No Respiratory system

5 ways in which they differ:
- Ctenophores have a complete gut w excretory system
- Cydippid larva vs. Planula larva
- Colloblasts vs. Cnidocytes
-All marine vs. some freshwater/ some marine.
- Strictly medusa vs. polyp and medusa

Question 10

Cnidarians and Ctenophores are considered diploblastic, but why might some biologists label them triploblastic ?

Answer 10

They have cells within the gelatinous layer are problematic