DIVERSITY OF LIFE

THE PARAZOA (SOLLAS 1884)

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Parazoa (pair-uh-ZO-uh) is derived from two Greek roots that mean next to [=para (παρά)] and animals [=zoa (ζώο)].  The reference is to their separation from the other animals because of their simple organization without organ systems.  Both Huxley (1875) and Sollas (1884) suggested that the sponges were different enough to be separated from the rest of the animal kingdom (Thomas 1976).  Sollas (1884) coined Parazoa as a formal name to distinguish them from the Metazoa (the other animals).  

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 HOMOSCLEROMORPHA

Corticium, Oscarella, Plakina, Plakortis, Plakinolopha, Plakinastrella, Pseudocorticium.

CLASS DEMOSPONGIAE (15 ORDERS)

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.

  
Huxley, T. H. 1875. Remarks on the Classification of the Animal Kingdom. Journal of the Linnean Society. 12: 199-226.

Sollas, W. J. 1884. On the development of Halisarca lobularis (O. Schmidt). Quart. J. Microsc. Sci. 24: 603-621.

Thomas, P. A. 1976. The history of Spongology of the Indian Ocean. J. Mar. Biol. Ass. India. 18(3): 610-625.

 

By Jack R. Holt and Carlos A. Iudica.  Last revised: 08/28/2016