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PHYLUM ECTOPROCTA

INTRODUCTION TO THE ECTOPROCTA

Ectoprocta (ek-to-PROK-ta) is formed from two Greek roots that mean outside anus [outside -ectos (εκτός); and anus -proktos (πρωκτός)]. The reference is to the anus located outside of the ring of ciliated tentacles (lophophores).

The entoprocts and ectoprocts collectively are known as the bryozoans. These are sessile organisms that usually live in dendritic colonies. Because many of them produced calcified structures and lived in large, reef-forming colonies, they have left an impressive fossil record. The ectoprocts have cup-shaped zoids which have ciliated tentacles (lophophores) that function to filter out food particles. They resemble the entoprocts, but the ring of lophophores in the ectoprocts encloses only the mouth (not the anus as in the entoprocts). Also, the ectoprocts are eucoelomic unlike the entoprocts. The two groups resemble each other, but their relationships are not very clear. Brusca and Brusca (2003) consider them to occupy separate phyla, Tudge (2000) and Margulis and Schwartz (1998) do not. Nielsen (2001) does not believe that they (both groups) are related to the brachiopods and phoronids (the other lophophorates). He does, however, suggest that the two groups might have a sister group relationship. Anyway, I have kept them as separate phyla.

A. Plumatella at low magnification showing the dendritic growth pattern of the colony.

B. Archimedes, an extinct bryozoan was given its latin name because of its resemblance to Archimedes' screw.

C. Bugula, a higher power view of zoids with their lophophores unfurled.

Images taken from:
A: http://www.thaibryozoans.com/content_eng/bryozoans/species_pc_en.shtm
B: http://faculty.evansville.edu/ck6/bstud/archimedes.html
C: http://www.marlin.ac.uk/species/Bugulaflabellata.htm

SYNOPTIC DESCRIPTION OF THE PHYLUM ECTOPROCTA

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).

I. SYNONYMS: "bryozoans", polyzoa.

II. NUMBER: >4,000 species known.

III. PHYLUM CHARACTERISTICS:

A. Structure

Symmetry: Bilateral

Body Cavity: True coelom. The body cavity is bounded by the peritoneum, but it is formed neither as a schizocoel nor an enterocoel. It seems to be formed de novo during metamorphosis of the larvae.

Body Covering: Zooids secrete a gelatinous, horny or calcareous shell. The lophophore extends through an opening in the shell.

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, a condition opposite from Entoprocta.

Circulatory System: Absent.

Locomotion: Animals sessile; tentacles covered with cilia to move water. Lophophores connected to retractor muscles.

Excretory System: Absent.

Nervous System: Simple anterior nerve ring from which nerves emanate.

Endocrine System: None.

B. Reproduction:

Reproductive System: Most are hermaphroditic, external fertilization. Budding is common in these colonial animals.

Development: Zygote develops by radial cleavage and often are brooded, although a planktonic larval stage may occur.

C. Ecology: Most are marine, but some are freshwater. Colonial and sessile filter-feeders as adults.

HIERARCHICAL CLASSIFICATION OF THE ECTOPROCTA

I took this taxonomy from Brusca and Brusca (2003).

CLASS PHYLACTOLAEMATA (1 ORDER)

Monomorphic, freshwater; large cylindrical zooids in non-calcareous colonies; polyps with body wall musculature, large horseshoe-shaped lophopohre, well-developed epistome with a coelomic compartment, and resting buds (statoblasts) which overwinter, disperse and "germinate" when conditions improve. Coelomic compartments of different individuals intercommunicate. Some colonies mobile.

Cristatella, Hydinella, Pectinatella, Lophopus, Lophopodella, Plumatella.

CLASS STENOLAEMATA (1 ORDER)

Marine, cylindrical zooids in tubular, calcareous shells; circular terminal aperture without an operculum; without an epistome; circular lophophore not protruded by deformation of the calcareous covering but by hydrostatic pressure and muscular action; limited polymorphism; polyembryony is common (often more than 100 embryos develop from one zygote).

Actinopora, Crisia, Diaperoecia, Disporella, Idmodronea, Tubulipora.

CLASS GYMNOLAEMATA (2 ORDERS)

Polymorphic, mostly marine; with non- or partially-calcified walls, which when deformed protrude the lophophore; without epistome or body wall musculature; lophophore circular; lophophoral orifice closable; interconnecting pores in polyp walls plugged by special cells.

Aethozoon, Alcyonidium, Alcyonium, Amathia, Bowerbankia, Flustrellidra, Nolella, Tubiporella, Victorella.

Bugula, Callopora, Carbasea, Cellaria, Clavopora, Conopaeum, Cornucopina, Cribilaria, Cryptosula, Cupuladria, Electra, Eurystomella, Flustra, Hippothoa, Membranipora, Metrabdotus, Microporella, Pentapora, Pherusella, Porella, Pyripora, Rhamphostomella, Schizoporella, Thalamoporella, Tricellaria.

This page is maintained by Jack R. Holt. Last modified: 01/07/08.