The Bryozoan Skeletal Index (BSI) is a measure of the relative proportion of skeleton to open space in stenolaemate bryozoans. Here the measure is calculated for the Families of the Suborder Rhabdomesina of the Order Cryptostomata and in the Order Trepostomata. Patterns show that in the former, the members of the Family Arthrostylidae yield lower BSI values than members of other cryptostome families, while in general the BSI values in the trepostomes are higher than those of the cryptostomes. A number of taxa are evaluated with respect to BSI as their ordinal or familial placement has varied according to different authors; these include Coelotubulipora and Tebitopora. For both, BSI values are low, suggesting that placement in the Cryptostomata is correct. However, other morphological characters indicate that the former is a trepostome and the latter a cryptostome. The genera Nematotrypa and Cyclophaenopora that had been placed in either the Arthrostylide or the Nematotrypidae are considered and shown to likely belong in the latter family rather than the former. BSI is a measure that can be utilized with some value in systematic placement but only alongside salient and characteristic morphological data.

Wyse Jackson, Patrick N., Marcus M. Key, Jr., and Catherine M. Reid. Skeletonisation in the Stenolaemate Bryozoan Orders Cryptostomata (Suborder Rhabdomesina) and Trepostomata: the Role of the Bryozoan Skeletal Index (BSI) as a Taxonomic Character. In Bryozoan Studies 2022: Proceedings of the Nineteenth International Bryozoology Association Conference (Dublin, Ireland, 22-26 August 2022), edited by Marcus M. Key, Joanne S. Porter, and Patrick N. Wyse Jackson., 169-181. Boca Raton: CRC Press, 2023.

Marcus Key is the Joseph Priestley Professor of Natural Philosophy at Dickinson College.

For more information on the published version, visit Taylor and Francis's Website. https://www.taylorfrancis.com/books/edit/10.1201/9781003454915/bryozoan-studies-2022-marcus-key-joanne-porter-patrick-wyse-jackson

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