INTRODUCTION TO THE PARAZOA

The parazoan level of organization is a loose association of cells and structural elements that behave almost as a cellular aggregate rather than a multicellular organism.  Still, the two phyla likely share only primitive characters.  Furthermore, Trichoplax, the sole genus in the Phylum Placozoa, likely is secondarily simplified.  Either way, this subkingdom is a paraphyletic group.  The affinities between the Porifera and choanoflagellates are more clear.  Please consult The Major Clades of the Animal Kingdom for some views on the relationships of the parazoan phyla with each other and with the other phyla of the animal kingdom. 

PHYLUM PLACOZOA (ONE OR TWO GENERA IN A SINGLE ORDER)

Trichoplax.

PHYLUM PORIFERA

CLASS HEXACTINELLIDA (4 ORDERS DISTRIBUTED IN 2 SUBCLASSES)

SUBCLASS HEXASTEROPHORA

Aphrocallistes, Caulophacus, Euplectella, Hexactinella, Leptophragmella, Lophocalyx, Rosella, Sympagella.

SUBCLASS AMPHIDISCOPHORA

Hyalonema, Monorhaphis, Pheronema.

CLASS CALCAREA (7 ORDERS DISTRIBUTED IN 2 SUBCLASSES)

SUBCLASS CALCINEA

Clathrina, Dendya, Leucascus, Leucetta, Murrayona, Soleniscus.

SUBCLASS CALCARONEA

Amphoriscus, Grantia, Leucilla, Leucoselenia, Petrobiona, Scypha (Sycon).

CLASS DEMOSPONGIAE (15 ORDERS)

SUBCLASS HOMOSCLEROMORPHA

Corticium, Oscarella, Plakina, Plakortis, Pseudocorticium.

SUBCLASS TETRACTINOMORPHA

Acanthochaetes, Asteropus, Chondrilla, Chondrosia, Cliona, Cryptotethya, Geodia, Merlia, Polymastia, Rhabdermia, Stelletta, Superites, Tethya, Tetilla.

SUBCLASS CERACTINOMORPHA

Adocia, Agelas, Aplysilla, Aplysina (Verongia), Asbestopluma, Astrosclera, Axinella, Axociella, Calcifibrospongia, Callyspongia, Ceratoporella, Clathria, Coelosphaera, Goreauiella, Halichondria, Haliclona, Halisarca, Hispidopetra, Hymeniacidon, Ircinia, Lissodendoryx, Microciona, Mycale, Myxilla, Spongia, Spongilla, Stromatospongia, Tedania, Valceletia.

This page maintained by Jack R. Holt.  Last modified: 02/01/09