Sponges
From Paleos
Contents |
Phylum Porifera
(Latest Vendian to Recent)
The most primitive form of multicellular animal life, it is thought that sponges evolved independently of metazoan animal life. In many respects they are little more than colonial choanoflagellate protozoa. Over 5000 recent species are known, and many more fossil species. All are benthic, sessile, suspension-feeders which inhabited a wide variety of exclusively marine environments, from the early Cambrian to the present day.
Sponges make their skeleton out of both organic fibers (primarily a material called spongin (the stuff of an natural bath sponges), secreted by spongocyte cells and inorganic spicules (calcium carbonate or opalline silica needle-like structures secreted by sclerocyte cells).
The major fossil record of these animals consists of the resistant spicules. After death, spicules are scattered across the sea floor and may be found as disarticulated microfossils.
Classification
There are four main classes:
Class Calcarea Class Demospongiae Class Sclerospongiae Class Hexactinellida
Two fossil groups are often included - the Stromatoporoidea and the Archaeocyatha. The former are most likely Porifera (possibly Sclerospongiae or Demospongiae), while the precise relationships of the latter remain controversial.
Organization of the Poriferan Body Plan
The basic body form of sponges consists of numerous small incurrent canals called ostia (sing. ostium) and one or more large excurrent opening called oscula (sing. osculum). Organization of chambers and channels varies however from simple to quite complex
| asconoid structure image | syconoid structure image | leuconoid image |
| asconoid | syconoid | leuconoid |
Levels of Porifera organization, from simplest (left) to most complex (right
Phylogeny
<===o PORIFERA
| ?--o Archaeocyatha |--o Demospongiae [Demospongea] | |--o Homoscleromorpha | |-- Tetractinomorpha | `-- Ceractinomorpha |--o Sclerospongiae | |?-o Stromatoporoida | |--o Ceratoporellida | `--o Merliida |-- Calcarea `-- Hexactinellida
References and Links
Parker, Sybil P. (ed.), 1982: Synopsis and Classification of Living Organisms New York: McGraw-Hill Book Co., 2 vols.
Invertebrate Zoology by Edward E. Ruppert, Robert D. Barnes
Curt Smecher Home Page - a lot of excellent info on Sponges, including a comprehensive systematic review with description of each taxon.
Les porifères - a Belgian page on fossil sponges
Porifera - short intro to recent and fossil groups
Porifera - Sponges - when last checked, had references and links but no essay. Classification down to subclass only
