SYNOPTIC DESCRIPTION OF THE PHYLUM ACOELOMORPHA
| EUKARYA>UNIKONTA>OPISTHOKONTA>ANIMALIA>METAZOA>BILATERIA>ACOELOMORPHA |
PHYLUM ACOELOMORPHA LINKS
| The following information came from Brusca and Brusca (2003), Nielsen (2001), Pechenik (2005), Ruppert et al. (2004), and Walker and Anderson (2001). |
- I. SYNONYMS: flatworms, acoels.
- II. NUMBER: >200 species known.
- III. PHYLUM CHARACTERISTICS:
- A. Structure
- Symmetry: Bilateral
- Body Cavity: Not present. Organ systems in parenchymatous mesoderm (text with tooltip) Parenchymatous mesoderm is connective tissue that fills the space between the musculature and the gut in acoelomates. .
- Body Covering: Ciliated epithelium.
- Support: Hydrostatic skeleton.
- Digestive System: Very simple. Mouth is ventral. The digestive region within the Acoela is a syncytium with no definite boundary. The Nemertodermata also have a simple system but have a permanent boundary layer of cells. Many species have intracellular algae.
- Circulatory System: None.
- Locomotion: Ciliated epithelium and muscular contractions.
- Excretory System: none.
- Nervous System: 4-6 major lateral nerve cords (text with tooltip) A nerve cord is a major nerve that runs the length of most bilaterian animals. They are ventral in the protostomes and usually dorsal in the deuterostomes. without a ganglion. Have statocyst with 1 (Acoela) or 2 (Nematodermata) statoliths.
- Endocrine System: None.
- B. Reproduction:
- Reproductive System: Oviparous (text with tooltip) An oviparous (adj.) animal is one that releases eggs in its life cycle. They may be fertilized internally or externally. and hermaphroditic (text with tooltip) An animal that bears both male and female gonads. . Sperm with 9+2 flagella (the flatworms have 9+1 flagella). Some reproduce asexually by budding.
- Development: Initial development by a simple spiral cleavage (text with tooltip) Spiral cleavage is typical of the Protostomata and is characterized by the division planes of early cytokinesis products of the zygote being oblique to the plane of the polar axis. This produces unequal cells in the developing blastula. Usually spiral cleavage is determinant. . Some with asexual (text with tooltip) As the name implies, asexual reproduction is the formation of offspring without the union of gametes. Usually, asexual reproduction involves the production of specialized cells or multicellular structures that can give rise to new individuals. stages.
- C. Ecology: Marine.
- A. Structure
| LITERATURE CITED Brusca, R. C. and G. J. Brusca. 2003. Invertebrates. Sinauer Associates, Inc. Sunderland, Mass. Nielsen, C. 2001. Animal Evolution: Interrelationships of the Living Phyla. 2nd Edition. Oxford University Press. Oxford. Pechenik, J. A. 2005. Biology of the Invertebrates. McGraw-Hill. New York. Ruppert, E. E., R. S. Fox, and R. D. Barnes. 2004. Invertebrate Zoology: A Functional Evolutionary Approach. Seventh Edition. Thomson, Brooks/Cole. New York. pp. 1-963. Walker, J. C. and D. T. Anderson. 2001. The Platyhelminthes, Nemertea, Entoprocta, and Gnathostomulida. In: Anderson, D.T., ed. Invertebrate Zoology. Oxford University Press. Oxford, UK. pp. 59-85. [L] |
| By Jack R. Holt. Last revised: 02/01/2011 |
