BIO190: The Class: Radiate Animals: Lesson 14

The Radiate Animals

The two phyla Cnidaria and Ctenophora make up the radiate animals.

Phylum Cnidaria

The phylum Cnidaria contains more than 9000 species. The following is a list of characteristics of the phylum.

• stinging

• radial symmetry

• exoskeleton present in some (Ca)

• two germ layers=dipooblastic

1. ectoderm
2. endoderm
3. (some have a 3^rd layer-however, it is derived from the ectoderm)

• gastrovascular cavity

1. lined with gastrodermis
2. moth only/no anus

• most have tentacles

• some sense organs are present

1. statocysts (equilibrium)
2. ocelli (photosensitive)

• locomotion

1. some muscular contraction
2. currents

1. wind
2. water

• all acquatic (mostly marine)

• polymorphisms

1. medusa (free-swimming) (fig, 14-2)
2. polyps (sessile: fig. 14-2)

• nematocysts (stinging cells: read p. 255-256; fig. 14-3)

1. over 20 types (important to taxonomy)
2. operculum
3. cnidocyte
4. cnidocil

• nerve "nets" (read p. 256-257)

• regarded as basal stock of metazoan linage

• fossil record over 700 million years

• Class Hydrozoa

The majority of hydrozoa are marine and colonial in form, and the typical life cycle includes, both the asexual polyp and the sexual medusa stages.

Browse this website: Cnidarians: Class Hydrozoa

1. Hydra (pp. 257-259)

• Class Scyphozoa

Includes most of the larger jellyfishes, or "cup animals."

Browse this website: Cnidarians: Class Scyphozoa

1. Medusa/sessile medusa (fig. 14-17)
2. Bell
3. Rhopadium (ocelli)
4. Tentacles
5. Oral arms from mount (fig. 14-18)

• Class Cubozoa

1. Cube animal (fig. 14-20<)
2. Polyp/medusa morphs in the class
3. Read blue boxed area pg. 265

• Class Anthozoa

The anthozonans, or "flower animals" are polyps with a flowerlike apperance.

Visit the website: Cnidarians: Class Anthozoa

1. Sea anemones, corals, sea fan (pp. 266-270)
2. Tentacles
3. Only polyp morphs known
4. Fig. 14-24
5. Coral reefs (pg. 270-272)

Browse the following websites for more information on coral reefs.

Ctenophora is composed of fewer than 100 species. All are marine forms occurring in all seas but especially in warm waters.
The following is a list of phylum characteristics.

• complete digestion tract (mouth to anus)

• locomotion

1. ciliary comb plates
2. currents (see Cnidaria)

• no polymorphism

• some have tentacles

• sense organs (see Cnidaria)

• gern layers (see Cnidaria)

• nerve "nets"

• colloblasts (adhesive organelles)

Taxonomy

• Class Tentaculata

• Class Nuda

*Be sure to see comparisons of both phyla on page 273 of your textbook.

Ctenophora (p. 275-blue boxed area)

Ctenophores are fragile and beautiful creatures. Their transparent bodies glisten life fine glass, brilliantly iridescent during the day and luminescent at night.

Phylogeny (see hypothesis pg. 275)

The origin of the cnidarians and ctenphores is obscure, although the most widely supported hypothesis today is that the radiate phyla arose from a radially symmetrical, planula-like ancestor.

Adaptive Radiation (pg. 276)

In their evolution neither phylum had deviated far from its basic plan of structure.

Once you have completed the lesson, you should go to Assignment 14-1.

E-mail Sylvester Allred at Syl.Allred@nau.edu

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