Yagunova E.B. 2006. [Astogeny of Cribrilina annulata (Fabricius, 1780) (Bryozoa: Cheilostomata): the standard and the anomalies] // Invertebrate Zoology. Vol.2 (for 2005). No.2: 203–216 [in Russian, with English summary].

Department of Invertebrate Zoology, Biology and Soil Science Faculty, St.-Petersburg state university, Universitetskaya nab., 7/9, St.-Petersburg, 199034 Russia.

ABSTRACT: About 6000 young colonies of Cribrilina annulata (Fabricius, 1780) were collected from different substrates during consecutive summer seasons of 2000 – 2002s in the White and Barents seas. All colonies have been mapped. After analysing budding pattern, the theoretical morphospace of the structure of early astogenesis zone has been described. Then the number of theoretically possible types of structures has been determined. For the collected colonies the number of realized structures has been counted and, thus, the empirical morphospace of early astogenesis zone has been described as well. It has been demonstrated that only a small part of all theoretically possible colony structures are realized in nature, the proportion of the realized variants decreasing with the increase of the number of zooids in the colony. The frequencies of the discovered structure variants turned out to be considerably different. The astogenesis leading to the most common colony structure has been called the “modal astogenesis”.  The “ideal” astogenesis has been constructed on the assumption of “the perfect precision” of the budding process (synchronized development of all the possible buds). The “ideal” and the “modal” astogenesis have been shown to coincide. So, the diversity of colony structures can be interpreted as a result of fluctuations, accidental deviations from the “ideal” budding mode. This means that the observed plasticity of the colony formity in early development of C. annulata is not adaptive but random. Furthermore, the analysis of the structure variants in collected colonies suggests that the colonies most divergent from the “ideal” ones lack vitality and die.

KEY WORDS: modular construction, astogeny, Bryozoa, Cribrilina annulata.

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