The Mesozoa and Parazoa




BIO190: The Class: Mesozoa and Parazoa: Lesson 13

Origin of Metazoa

Unraveling the origins of the multicellular animals has presented problems for zoologist. There are three prevalent hypotheses in current use:

Phylum Mesozoa (p. 241)

Van Beneden who believed that the group was a missing link between protozoa and metazoa coined the name Mesozoa.

Phylum Placozoa (p. 242)

The plylum Placoza was proposed in 1971 by K. G. Grell to contain a single species, Trichoplax adhaerens.

Phylum Porifera=Sponges (p. 242-251)

Visit this web site to learn more about sponges:
Sponges

The following is a list of sponge characteristics.

Types of Sponge Cells

pinacocytes
body covering /lining
myocytes

choanocytes (collar cells)
flagellum
water currents
trapping food
reproduction (sperm)

archaeocytes
amoeboid-like
digestion
secrete spicules

Skeletal Components
calcium carbonate
silicon dioxide

Sponge Physiology
no tissues/no organs
nervous system essentially absent
sessile as adults

Reproduction

1. asexual
budding (external)
germules (internal)
(freshwater sponges)

2. sexual
ova/sperm
produce ciliated larva

Form and Function

The following is a list the unique functions of the Mesozoa and Parazoa.

Pores, the only body opening for these animals

Canal types (from simplest to complex) (fig. 13-5)

Sponge physiology, all the life activities of the sponge depend on the current of water flowing through the body.

Taxonomy

For more on taxonomy browse this website:
Porifera

spicules if present.

(silicon dioxide)

freshwater sponges

bath sponges

95% of all sponges are members

few species known

calcareous skeletons (=coralline sponges)

cryptic habitats

Phylogeny/Adaptive Radiation (pg. 250)

The sponges originated before the Cambrian period.

Once you have completed the lesson, you should go to Assignment 13-1.

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