SKELETAL ULTRASTRUCTURE IN SOME ARTICULATE CYCLOSTOME BRYOZOANS

Citation
Mj. Weedon et Pd. Taylor, SKELETAL ULTRASTRUCTURE IN SOME ARTICULATE CYCLOSTOME BRYOZOANS, Acta Zoologica, 79(2), 1998, pp. 133-148
Citations number
27
Categorie Soggetti
Zoology
Journal title
ISSN journal
00017272
Volume
79
Issue
2
Year of publication
1998
Pages
133 - 148
Database
ISI
SICI code
0001-7272(1998)79:2<133:SUISAC>2.0.ZU;2-E
Abstract
The ultrastructure of the calcareous skeleton is described in Il speci es of articulate cyclostome bryozoans with elastic joints. Ten species have interior walls comprising semi-nacreous and pseudofoliated fabri cs without a precursory granular layer. Exterior walls consist of oute r, finely granular and planar spherulitic layers, succeeded by semi-na creous and pseudofoliated fabrics like those of interior walls. Outer fabrics are calcified as longitudinal strips, each corresponding to a planar spherulitic unit. Articulation surfaces comprise ring diaphragm s of very fine granular fabric with concentric laminations. The semi-n acre of walls adjacent to ring diaphragms contains minute holes. Crisu lipora occidentalis is unique in having interior walls of transverse f ibres succeeded by pseudofoliated fabric, articulation surfaces festoo ned with deep pits but lacking well-differentiated ring diaphragms, an d pseudopores containing sieve-like closure plates. The ultrastructure of most articulates resembles tubuliporine cyclostomes with dominantl y semi-nacreous walls, although the lack of precursory granular fabric in the interior walls and the presence of subcircular tablets of semi nacre (without six-fold sectoring) may be peculiar to articulates. In contrast, Crisulipora is more similar to other tubuliporines with tran sverse fibres, evidence which, together with other skeletal characters , suggests that Crisulipora evolved jointing independently of the rest of the articulate cyclostomes. (C) 1998 The Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd. All rights reserved.