Cyclostomatida - Ecology

Ecology

At the present day cyclostome bryozoans are exclusively marine and stenohaline, with most species living subtidally on the continental shelf. Relative to cheilostomes, they appear to be less numerous and diverse in low latitudes - temperate and arctic environments host almost all of the large species. Although some cyclostomes encrust fleshy algae, the majority colonize hard substrates. Encrusting species can be especially numerous in cryptic habitats, for example, the concave interiors of bivalve shells. Cyclostomes are comparatively poor competitors for living space - they are routinely overgrown by larger animals such as sponges and ascidians, and also lose the majority of competitive encounters for space with cheilostome bryozoans. Tentacle size and number tend to be smaller in species of cyclostomes than cheilostomes. As a result cyclostomes create less powerful feeding currents. Colony size is small in many encrusting species, suggesting a "weedy", opportunistic life-style. These small encrusting colonies probably live for less than a year, whereas some of the larger encrusting and erect colonies are undoubtedly perennials. However, scant data exists on growth rates in cyclostomes.

Little is known about predation specifically on cyclostomes although it is likely that they are preyed upon by the nudibranchs (sea-slugs), pycnogonids (sea-spiders), echinoids and fishes which consume other marine bryozoans. Little is known about the reproductive ecology of cyclostomes. Sperm are known to be released from the tips of the tentacles, as in other bryozoans, but fertilization of eggs has never been observed. It is unclear if each gonozooid broods a single or multiple clutches of larvae, whether one or more clones of polyembryonous larvae are present per gonozooid, and what is the duration of the brooding period.