KINGDOM ANIMALIA
| SYSTEMATIC BIOLOGY |
KINGDOM ANIMALIA |
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| PHYLUM PHORONIDA | |||||
Phoronida (fo-RON-i-da) is derived from a single Greek word that means Isis, the Egyptian goddess [Phoronis (φορονισ)].
The phoronids are filter-feeding benthic invertebrates that have a lophophore system similar to that of the brachiopods. They live in a tube that is buried in loose substrate; so, only the anterior end emerges when feeding (Figures A&B). Brusca and Brusca (2003) and Margulis and Schwartz (1998) assume that the relationship between the lophophorate groups (bryozoans, brachiopods, and phoronids) is natural. However, Nielsen (2001) considers the lophophorate condition to be ancestral in the clade of the Bilateria. Indeed, Tudge (2000) includes them in a protostome group called the Lophotrochozoa. If this is true, the lophophorates cannot exist as a natural unit. As with the brachiopods, the developmental history of the phoronids is more like that of the deuterostomes such that Nielsen (2001) and Margulis, Schwartz (1998), and Brusca and Brusca (2003) place them into that group (this is consistent with most of the earlier work on brachiopods). Certainly more extensive developmental, structural, and molecular studies will be required to sort this out.
A. A field of Phoronopsis with only their anterior ends above the substrate. |
B. Phoronopsis removed from their tubes. |
| Images taken from: A: http://www.horta.uac.pt/species/Phoronida/Phoronopsis_harmeri/Phoronopsis_harmeri.htm B: http://www.ucmp.berkeley.edu/brachiopoda/phoronida.html |
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SYNOPTIC DESCRIPTION OF THE PHYLUM PHORONIDA
| The following information came from Margulis and Schwartz (1998), Buchsbaum (1938), Barnes (1980), Barnes (1984), Brusca and Brusca (2003), Hickman (1973), Meglitsch and Schramm (1991), Ruppert and Barnes (1991), Storer and Usinger (1965), and Tudge (2000). |
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I. SYNONYMS: phoronids. II. NUMBER: >14 species known. III. PHYLUM CHARACTERISTICS: A. Structure Symmetry: Bilateral Body Cavity: True coelom. Internally, the body is divided into three regions: a small preoral lobe or epistome that overhangs the mouth; a short mesosome that bears the lophophore; and a long cylindrical trunk. The trunk, mesosome (and possibly epistome) all have enterocoelic body cavities. The coelom runs into the tentacles of the lophophore. Body Covering: Outer epithelium that secretes and inhabits a chitinous tube. Support: Hydrostatic skeleton. Digestive System: Feeding by ciliated tentacular organ called a lophophore. Food tube U-shaped. Mouth in the center and the anus outside of lophophore. Circulatory System: Closed. Hemoglobin in corpuscles. Locomotion: Animals sedentary, inhabiting a tube in the sediment; tentacles covered with cilia to move water. Excretory System: Metanephridia, but protonephridia in larvae. Nervous System: Anterior nerve ring around the mouth and a single lateral nerve. Endocrine System: None. B. Reproduction: Reproductive System: Hermaphroditic, external fertilization. Development: Zygote develops by radial cleavage and forms a planktonic actinotroch larva that can reproduce asexually. C. Ecology: Benthic marine organisms. Filter-feeders as adults. |
HIERARCHICAL CLASSIFICATION OF THE PHORONIDA
| These enigmatic organisms seem to represent a remnant of a large Paleozoic diversity. As such, the remaining diversity is not sufficient to provide a taxonomy in which higher taxa can be agreed upon. Nevertheless, I give a provisional taxonomy with one class (I call Phoronata) and a single order. |
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This page maintained by Jack R. Holt. Last modified: 01/07/08