Skeletal Ultrastructure in Some Articulate Cyclostome Bryozoans

Abstract

Wtwlorr. M. J . & 7tidnr, P. D. 1998. Skeletal ultrastructure in some articulate cyclostome hryozoans.-Acw Zoolo,yic.tr (Stockholm) 79: 133-148.The ultrastructure of the calcareous skeleton is dcscrihcd in I I species of articulate cyclostome hryoioans with elastic joints. Ten species have interior walls comprising semi-nacreous and pseudofoliated lahrics without a precursory granular layer. Exterior walls consist o f outer. finely granular and planar sphcrulitic layers. succeeded by semi-nacreous and pseudofoliated fahrics like those of interior walls. Outer lahrics are calcitied as longitudinal strips. each corresponding to a planar spherulitic unit. Articulation surfaces comprise ring diaphragms o f very line granular fahric with concentric laminations. The semi-nacre of walls adjacent to ring diaphragms contains minute holes. C'ri,sitliporcr oc.c.iclrrrrtr1i.s is unique in having interior walls of transverse lihres succeeded hy pseudofoliated fahric. articulation surfaces festooned with deep pits hut lacking well-differentiated ring diaphragms. and pseudopores containing sieve-like closure plates. The ultrastructure of most articulates resemhles tuhuliporine cyclostomes with dominantly semi-nacreous walls. although the lack of precursory granular fahric in the interior walls and the presence of suhcircular tahlets of seminacre (without six-fold sectoring) may he peculiar to articulates. In contrast. Crisuliportr is more similar to other tuhuliporines with transverse lihrcs. evidence which. together with other skeletal characters. suggests that Cri.sir/ipirtr evolved jointing indcpcndently of the rest of the articulate cycloslomcs. 0 I99X The Royal Swedish Acadcmy of Sciences. Puhlishcd hy Elscvicr Science Lid. All rights reserved Mic~lrctrl J. Wwc/orr. I k I x r r~r t w i~ r!/ P t r l t /~~o / i / i~l i~g \ .

Skeletal Ultrastructure of the Early Astogenetic Stages of Some Cyclostome Bryozoans

“…The shared skeletal fabric suite in the protoecia of all taxa, may be regarded as the primitive condition in cyclostomes. Such a fabric is distinct from the fabric suites expressed in the adult (post-protoecial) skeletons of most species , 1997, 1998. However, the protoecial fabric suite resembles closely that found in the exterior walls of some plagioeciid tubuliporine species (such as Plagioecia patina, Weedon & Taylor 1997).…”

“…1992; Taylor & Jones 1993; Taylor et af. 1995; ; , 1997, 1998. These studies have primarily employed scanning electron microscopy (SEM) to observe directly the growing surfaces of the skeletal walls in order to assess the pattern and direction of growth of the constituent calcite crystallites.…”

“…The calcitic skeletal ultrastructure of all five suborders of the bryozoan order Cyclostomata (class Stenolaemata) have recently been described and reviewed (Boardman er , 1997, 1998. These studies have primarily employed scanning electron microscopy (SEM) to observe directly the growing surfaces of the skeletal walls in order to assess the pattern and direction of growth of the constituent calcite crystallites.…”

Skeletal resorption in bryozoans: occurrence, function and recognition

“… References: 1, Borg (1926); 2, Weedon & Taylor (1998); 3, Harmer (1891); 4, Jenkins & Taylor (2014); 5, Borg (1944); 6, P.B. Batson et al .…”

“…Morphology of skeletal resorption zones. (A) Deeply pitted, smooth stereom‐like resorption zone at the abscission surface of Crisulipora occidentalis (from Weedon & Taylor, 1998). (B–H) Hornera sp.…”