Stenolaemata

(invertebrate zoology) A class of marine ectoproct bryozoans having lophophores which are circular in basal outline and zooecia which are long, slender, tubular or prismatic, and gradually tapering to their proximal ends.

(Marine bryozoans)

Class: Stenolaemata

Number of families: Approximately 25

Thumbnail description
Colonial marine animals, superficially plantlike in appearance, made up of many units that feed or perform other vital functions, and having rigid, calcified supportive skeletons.

Evolution and systematics

Phylum Bryozoa, also called phylum Ectoprocta, sorts itself into three classes: Stenolaemata, Gymnolaemata, and Phylactolaemata. Stenolaemata are exclusively marine bryozoans, while Gymnolaemate bryozoans are mostly marine, plus a few freshwater types, and Phylactolaemates bryozoans are entirely reshwater.

The fossil record of class Stenolaemata extends back as far as 400 million years, into the early Ordovician Era. The Stenolaemata have passed their peak of diversification and are now in decline. Stenolaemata comprises one extant order, Cyclostomata (also called Tubuliporida), which first appeared in the Ordovician and scraped by with small colonies and little diversification through the Paleozoic, then exploded into extraordinary diversity during the Cretaceous. Its diversity declined toward the end of the Cretaceous, the number of genera was whittled down from about 175 to about 50, and the order has maintained that level of diversity into the present. There are about 500 extant species.

Physical characteristics

Stenolaemata, like bryozoans in general, are colonial animals, with many species superficially resembling seaweeds or corals. A common sort of stenolaemate colony consists of a branching array of hollow, calcified tubes, which serves as a skeleton, the tubes studded along the lengths of the tubes with individual, functional units called "zooids." Stenolaemate colonies can take a variety of forms, including crustlike, rosette, cup-shaped, branching, lumpy, and leaf-shaped. Colonies may bear calcified structures arising from the support skeleton, called "maculae," that function in colony hygiene, directing "used" water, or water already sifted for food particles and carrying wastes, away from the colony for hygiene purposes.

A single colony may be less than a millimeter high, or grow as high as a few feet (1 m) or more. The individual zooids are microscopic or nearly so. Microscopes are standard and necessary tools for studying and identifying bryozoans.

Stenolaemata zooids are characteristically elongated and cylindrical. Each zooid sits in a chamber called a "zoecium," encased in a calcified cystid for protection. Zooids within a single colony may differ considerably in form and function (polymorphism). Most numerous are the feeding zooids, or autozooids, each of which has a coelom, or inner body cavity, formed from the mesoderm, as well as a digestive tract, nervous system, and muscles. Although an autozooid feeds independently, it connects and communicates with the entire colony. Non-feeding zooids, or heterozooids, in Stenolaemata include gonozooids (reproductive) and kenozooids, which lack an internal organ system and serve as extra support for the colonial skeleton.

To feed, an autozooid extends an organ called a lophophore, consisting of a tentacle sheath and a ball of rolled-up, hollow tentacles. The tentacles open up into a graceful, flowerlike, bell-shaped structure. Cilia studding the tentacles draw currents of water into the mouth, to the center of the lophophore, and into the digestive tract and gut, with a caecum that grinds up food particles with peristaltic motions. The tract communicates directly, via pores, with another tract running the length of the supporting skeletal tube, allowing ingested food to be shared throughout the colony. A zooid passes its wastes through an anus, on the tentacle sheath below the tentacle ring.

Distribution

Stenolaemate bryozoans, like marine bryozoans in general, are found from the equator well into the arctic and Antarctic Ocean regions, but their greatest diversity occurs in the cool waters of the temperate latitudes and the cold waters of the near-polar regions.

Habitat

Stenolaemate bryozoans live from shallow, near-shore waters to abyssal depths, but prefer shallow waters. A colony, depending on species, may attach or root itself in its formative stages to nearly any sort of substrate, including rocks, seashells, seaweed, and wooden piers.

Behavior

Stenolaemate bryozoans live passive, stationary lifestyles, similar to corals.

Feeding ecology and diet

Stenolaemata feed themselves via their zooids, which draw water, by the action of their ciliated lophopores, through their bodies, snagging microscopic algae, animals, and organic detritus. A tiny stomach churns up the ingested food with peristaltic contractions, digests it, then absorbs some and passes some on to the rest of the colony.

Reproductive biology

Stenolaemata, like bryozoans in general, reproduce both sexually and asexually. Sexually, most stenolaemata are hermaphroditic. Different species may be simultaneous hermaphrodites, producing sperm and eggs at the same time, or protandric hermaphrodites, producing eggs and sperm at different times. Ovaries and testes form from modified autozooids. Most stenolaemata species temporarily keep their fertilized eggs within brood chambers modified from the coela of feeding zooids. Free-swimming sperm are snatched from open water by the autozooids and passed on to the eggs for fertilization.

The fertilized eggs undergo cleavage and become free-swimming larvae that force their way out of the brood chamber and become independent, free-swimming organisms. In a few days, they settle down on a growth-friendly substrate, each larva changing into a rootlike form, the ancestrula, which commences to grow asexually into an entire colony, building the skeleton and budding the zooids; the colony continues to grow in this fashion. If a piece of a colony is broken off from the rest, it can settle and build itself into a new, complete colony.

Conservation status

No species are listed by the IUCN.

Significance to humans

Stenolaemata are of no special significance to humans. In time, they may, since research is being done on bryozoans to find possible biochemicals within them that may have medical benefits.

Species accounts

Resources

Boardman, Richard S. Reflections on the Morphology, Anatomy, Evolution, and Classification of the Class Stenolaemata (Bryozoa). Smithsonian Contributions to Palaeobiology 86. Washington, DC: Smithsonian Institution Press, 1998.

Hayward, P. J., and J. S. Ryland. Cyclostome Bryozoans: Keys and Notes for the Identification of the Species. Leiden, The Netherlands: The Linnean Society of London, 1985.

McKinney, F. K, and J. B. C. Jackson. Bryozoan Evolution. Boston: Unwin Hyman, 1989.

Woollacott, R. M., and R. L. Zimmer, eds. Bryozoans. New York: Academic Press, Inc., 1977.

Faurie, A. S., E. R. Dempster, and M. R. Perrin. "Physiology and Ecology of Marine Bryozoans." Advances in Marine Biology no. 14 (1976): 285–443.

McKinney, F. K. "Feeding and Associated Colonial Morphology in Marine Bryozoans." Reviews in Aquatic Sciences no. 2 (1989): 255–280.

Ostrovsky, A. N. "Rejuvenation in Colonies of Some Antarctic Tubuliporids (Bryozoa: Stenolaemata)." Ophelia 46, no. 3 (1997): 175–185.

International Bryozoology Association. E-mail: msj@nhm.ac.uk Web site:

"Bryozoa Home Page." July 3, 2003 [July 30, 2003]. . "Bryozoa Information and Links." August 6, 2001 [July 30, 2003]. .

[Article by: Kevin F. Fitzgerald, BS]

An exclusively marine class of Bryozoa. The Stenolaemata include several thousand species distributed among five orders: Cystoporata, Trepostomata, Cryptostomata, Fenestrata, and Cyclostomata. First appearing late in the Early Ordovician, stenolaemates expanded quickly to dominate bryozoan assemblages until the mid-Cretaceous. See also Bryozoa; Cryptostomata; Cyclostomata (Bryozoa); Cystoporata; Trepostomata.

Stenolaemate colonies vary greatly in size and shape. Many Paleozoic through mid-Mesozoic forms were large and massive, but more recent representatives are commonly small and delicate. Colonies are encrusting, erect, or free-living. Some erect forms have single or regularly spaced, flexible cuticular joints; segments between joints and all other entire colonies are rigidly calcified and enclosed within a thin cuticular membrane. Living stenolaemate colonies are made up of individual feeding units called zooids with lophophores (rings of tentacles) that are circular in basal outline. Zooidal body cavities are enclosed within tubular or prismatic zooecia (skeletons of individual zooids), gradually expanding from their proximal ends. Zooecia typically are relatively thin-walled in colony interiors (endozone) and relatively thick-walled in outer regions (exozone).

Individual colonies are hermaphroditic. Colonies grow by asexual budding.

This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (May 2008)

Stenolaemata
Scientific classification
Kingdom: Animalia Phylum: Bryozoa Class: Stenolaemata
Orders
Cyclostomatida Hederellida (?) Trepostomatida Cystoporida Cryptostomida Fenestrida

Stenolaemata are a class of marine bryozoans with tubular zooids with strongly calcified walls. They are characterized by a lophophore which is protruded by the action of annular muscles. Most forms lack an operculum. The Batostoma genus (member of order Trepostomatida) existed in monticular colonies. Stenolaemata were the predominant bryozoan group during the Paleozoic. Some grew as lacy or fan-like colonies that became important reef builders and in some regions form an abundant component of limestones. Their numbers were greatly reduced during the terminal Permian extinction event.

This bryozoan-related article is a stub. You can help Wikipedia by expanding it.

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)