cyclostome species have enlarged zooids - gonozooids - for brooding larvae, and some species also possess non-feeding zooids - kenozooids - with space-filling and structural roles. Modern cyclostomes exhibit polyembryony: fertilized ova divide to produce multiple, genetically identical larvae which are housed in the spacious gonozooid before being released, swimming for a short period before settling and undergoing metamorphosis to establish new clonal colonies. Gonozooids are also very important in the taxonomy of cyclostomes, particularly in the largest suborder the Tubuliporina. Unfortunately, not all colonies develop gonozooids and infertile colonies may be difficult to identify even to family-level. Differentiation A colony is founded by a larva which settles and metamorphoses into a zooid, the ancestrula. In Cyclostomata it may be of two types: holoancestrula and artroancenstrula (in crisiids) The ancestrula gives rise to the second generation of zooids, which in turn gives rise to a third, and so on, in a process called astogeny. Generational variation among zooids is called astogenetic differentiation. In all species, there is a primary zone of differentiation, which is limited to the first few generations and followed by a much longer zone of repetition of nearly identical zooids. In some species, however, there is a secondary differentiated zone, which can take various forms. In species in which the colony branches, new branches normally arise by the division of a distal growing tip of an existing branch. An adventitious branch, in contrast, arises from the side of an existing branch, beginning with a short series of differentiated zooids, a secondary zone. Subsequent generations of zooids along the branch then typically return to the normal colony budding pattern. Ecology At the present day cyclostome bryozoans are exclusively marine and stenohaline, with most species living subtidally on the continental shelf. UK government-sponsored scientific reports in connection with renewable energy in 2014 uncovered the first recordings of Escharoides bishopi and the non-native Fenestrulina delicia in British waters 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