LOWER CARBONIFEROUS BRYOZOA 
Table 33 Abundance and diversity of the fauna at Carrick Lough and 
Sillees River. 
Element Number of genera* Number of species* 
Bryozoans 30 69 
Brachiopods 47 56 
Arthropods 
Trilobites 6 7 
Ostracods 1 1 
Echinoderms 
Crinoids 2+ 2+ 
Blastoids 1 1 
Molluscs 
Gastropods 4 4/5 
Bivalves 2 22 
Sponges ? 210 
Corals 3 24 
Annelids 1 ! 
*Modified from Brunton (1987) 
Although the fauna from County Fermanagh is very well-known, 
its palaeoecology has been a matter of some debate. The succession 
at Carrick Lough consists of thin alternating beds of dark argillaceous 
muddy limestones and paler grey to yellowish bioclastic limestones, 
while at Sillees River the fauna was etched from biomicritic lime- 
Stones. The lithology of the bryozoan-bearing strata is that of a distal 
reef or off-reef deeper water facies. 
__ Extensive reef development occurred in the Asbian of north west 
Ireland (George et al. 1976); one such reef lay just south of the 
DINANTIAN 
[GR [CH [AR [HO|AS [ER [PE_ 
ORDER 
Hexites paradoxus 
Nematopora hibernica 
Pseudonematopora planatus 
Rhabdomeson progracile 
Rhabdomeson rhombiferum 
Rhombopora cylindrica 
Rhombopora hexagona 
Cryptostomata 
Streblotrypa pectinata 
Clausotrypa ramosa 
Baculopora megastoma 
Diploporaria marginalis 
Diploporaria tenella 
Ichthyorachis newenhami 
|s 
1& 
\2 
| 
Thamniscus colei 
Rhombocladia dichotoma 
Leioclema indentata 
Dyscritella miliaria 
Tabulipora urii 
Tabulipora howsii 
Tabulipora minima 
Trepostomata 
Stenophragmidium sp. 
Fistulipora incrustans 
Sulcoretepora parallela 
Goniocladia cellulifera 
Cystoporata 
lAbbreviations: SIL: Silesian; CR: Courceyan; CH: Chadian; AR: Arundian; 
HO: Holkerian; AS: Asbian; BR: Brigantian; PE: Pendleian. 
Fig. 104 Range chart of bryozoans described in this study. 
| 
163 
collecting localities which are in proximal reef or off-reef facies 
(Tavener-Smith 1973). 
Bryozoans favour clean sediment-free water in which suitable 
substrates are available (Schopf 1969, Cuffey 1970).The depositional 
environment at Carrick Lough and Sillees River did not favour 
extensive bryozoan colonisation because the water was too muddy, 
as was the substrate. Fistulipora incrustans and Tabulipora howsii 
colonised substrates such as brachiopod shells, spines and other 
bryozoans. They developed small button-like zoaria, which were 
size-controlled because the adjacent muddy sediment could not be 
extensively encrusted by bryozoans. Similar evidence for the soft 
nature of the substrate is suggested by brachiopod attachment styles. 
The 56 brachiopod species discussed by Brunton, 1987) are more or 
less equally divided into those that are pedicle supported, quasi- 
infaunal, and spine supported. Only 3 species were found to be 
permanently cemented, probably to other brachiopod shells. It is 
suggested that bryozoans found permanent points of attachment to 
small shelly substrates from which erect or adnate colonies devel- 
oped, and that they were not attached directly to any lithic substrate. 
Bryozoans are abundant at Carrick Lough and Sillees River, and 
calcified, decalcified and silicified zoaria have been obtained. 
Silicification seems to have occurred in the pale limestones and not 
in the argillaceous and muddy limestones. It is impossible to quan- 
tify the abundance of bryozoan colonies in pure numerical values. 
This is due to the very fragmented nature of the zoaria. Almost 
without exception all colonies are broken or disarticulated but not 
heavily abraded nor shredded into fine hash. Bryozoan colonies are 
found lying on bedding planes and are stacked one upon another. 
The fauna comprised bryozoans of four of the five stenolaemate 
orders (cyclostomes were absent), with a numerical and taxonomic 
weighting towards the fenestrates. The cryptostome taxa all formed 
small delicate erect expansions and were quite abundant. In contrast, 
while the trepostomes are taxonomically moderately diverse they 
occurred in small numbers. The cystoporates which comprised three 
taxa were reasonably abundant. 
The bryozoan community was dominated by large erect planar 
and conical fenestrate zoaria, which exploited the seawater up to 20 
cm above the substrate. Between Fenestella s.l. zoaria grew the 
smaller fenestellids such as Baculopora, Diploporaria, Ichthyorachis, 
Penniretepora and Thamniscus, as well as the delicate cryptostomes, 
two Tabulipora species and the cystoporates Sulcoretepora and 
Goniocladia. Colonising the sea floor were Rhombocladia, 
Tabulipora, Stenophragmidium and Fistulipora. In addition 
Stenophragmidium grew epiphytically ona soft cylindrically shaped 
substrate (possibly algae), and Tabulipora and Fistulipora encrusted 
brachiopod spines and crinoid ossicles. 
Few holdfasts were recovered from this fauna, which is in keeping 
with other fenestrate-rich faunas (F.K. McKinney pers. comm.). Of 
those that were found, the majority belong to the cystoporates 
Goniocladia cellulifera and Sulcoretepora parallela, with a single 
holdfast of Thamniscus colei being present in the sample. 
The attitude and prevalence of fenestellid fronds on bedding 
planes, the limited abrasion, and lack of holdfasts indicates that the 
fauna has been translocated. This movement has taken place 
downslope off reef slopes into deeper water. However, the move- 
ment distance cannot have been great as fragemnts display little 
abraision of fine surface skeletal detail, such as carinal nodes and the 
superstructure of Hemitrypa hibernica. 
If, as Brunton (1987) postulates, the Carrick Lough and Sillees 
River fauna is an in situ assemblage then bryozoans preserved in 
growth position would be expected. As outlined above they are not 
thus preserved. Tavener-Smith (1973) considers that the Carrick 
Lough fauna is an accumulated assemblage, that is it has not been 
