ORDOVICIAN BRYOZOA FROM THE LLANDEILO LIMESTONE 
Maesyrwyn 
vs 
500 metres 
rT 
Pantygwenin 
exploratory 
* trench 
Ir. 16h 
SLY Clog-y-fran 
Fig. 1 Locality map showing position of exploratory trench where the 
limestone blocks containing the fauna were collected. 
SYSTEMATIC PALAEONTOLOGY 
The terminology in all descriptions is that of Boardman et al. (1983). 
All genera are placed in families based on the following sources: 
Trepostomata —Astrova (1978); Cystoporata—Utgaard (in Boardman 
et al., 1983). Family level classification is generally unsatisfactory 
in Palaeozoic trepostomes and is currently being revised for the 
Treatise on Invertebrate Paleontology by R.S. Boardman. 
Biometric details for all trepostome species are tabulated (Table 
1). Each measurement was made up to seven times per specimen, 
and the means and ranges calculated for each parameter. Raw data 
can be found in an unpublished Ph.D. thesis (Buttler 1988). All 
specimens are represented by thin sections or acetate peels. Meas- 
urements given in the systematic descriptions are all mean values 
unless otherwise stated. All material is deposited in The Natural 
History Museum, London. 
Phylum BRYOZOA Ehrenberg, 1831 
Class STENOLOAEMATSA Borg, 1926 
Order TREPOSTOMATA Ulrich, 1882 
Suborder HALLOPOROIDEA Astrova, 1965 
Family HETEROTRYPIDAE Ulrich, 1890 
Genus DITTOPORA Dybowski, 1877 
Dittopora sanclerensis sp. nov. Figs 2-3 
HOLOTYPE. NHM PD 8338. 
PARATYPES. NHM PD 8333-8337, 8339-8341. 
NAME. The species is named after St. Clears (Sancler in Welsh), 
the nearest town to the type locality. 
DIAGNOSIS. Colony large, ramose. Autozooecia, with very thin, 
slightly wavy walls in endozone, which curve out from branch axis 
to intersect zoarial surface; polygonal in zoarial transverse section, 
rounded-circular in shallow zoarial tangential sections. Circular 
119 
mesozooecia present, originating in outer endozone/inner exozone. 
Partial and complete diaphragms in exozonal autozooecia; numer- 
ous diaphragms in mesozooecia. Acanthostyles large and abundant 
in exozone. 
DESCRIPTION. Zoaria erect with thick cylindrical branches, on 
average 5.8 mm in diameter. 
Autozooecia curve out gently from the branch axis in the endozone 
to meet the zoarial surface at 90°. Autozooecia within the endozone 
have very thin, slightly wavy walls. 
The exozone has an average diameter of 1.1 mm (although the 
range is large: 0.57—1.62 mm) and is recognised by a thickening of 
the zooecial walls. Autozooecia all originate in the endozone where 
they are polygonal in transverse section, becoming rounded-circu- 
lar in the exozone, as seen in tangential sections of branches. 
Autozooecial in the exozone contain abundant partial diaphragms 
and complete diaphragms (spaced on average 0.13 mm apart) 
which increase in thickness distally along the autozooecia. All 
diaphragms are basal and are deflected orally at their junctions with 
zooecial walls. Their laminae are continuous with the autozooecial 
linings. 
Mesozooecia are common and originate in the outer parts of the 
endozone and inner parts of the exozone. They are circular in 
shallow tangential sections and contain numerous thick, orally 
deflected basal diaphragms, spaced on average 0.83 mm apart and 
generally increasing in thickness distally along the mesozooecia. 
Acanthostyles are abundant and large, with an average diameter 
of 0.04 mm and density of four per mm?*. They originate deep 
within the exozone and can on rare occasions indent the zooecial 
apertures. A hyaline core is surrounded by steeply dipping conical 
laminae. 
Autozooecial wall thickness averages 0.08 mm in the exozone. 
Wall microstructure is composed of steeply inclined, U-shaped 
laminae. Zooecial boundaries are indistinct due to the presence of 
large acanthostyles which disrupt the wall structure. Frequently the 
autozooecia, and virtually all of the mesozooecia, are infilled with 
laminar calcite close to the zoarial surface. In longitudinal section 
this infilling consists of broad U-shaped laminae. Often large areas 
of adjacent zooecia are infilled. 
An intrazoarial overgrowth is recognised in one specimen (PD 
8334). It is continuous with the exozone and has endozonal and 
exozonal components. 
REMARKS. Dittopora sanclerensis sp. noy. is characterised by 
extremely thin endozonal walls which thicken markedly in the 
exozone. Partial and complete diaphragms are present in the exozonal 
autozooecia. Circular mesozooecia with numerous diaphragms are 
present. Acanthostyles are large and abundant in the exozone. 
Dittopora annulata (Eichwald, 1860), from the Orthoceras Lime- 
stone (Llanvirn) in Estonia and the Glauconite Limestone in Russia, 
is similar internally to Dittopora sanclerensis. However, D. annulata 
has alternating bands of autozooecia and mesozooecia, whereas in 
D. sanclerensis they are not arranged in bands. 
Modzalevskaya (1953) described two new species of Dittopora, 
D. sokolon and D. ramosa, from the western Russian Platform: D. 
sokolon has similar autozooecia, diaphragms and acanthostyles to 
D. sanclerensis but thicker endozonal walls; D. ramosa has similar 
diaphragms but smaller and more abundant acanthostyles. 
A common feature of D. sanclerensis is that zooecia close to the 
zoarial surface are filled with U-shaped laminar calcite (Fig. 2). This 
may be because the studied material consists mainly of the basal 
parts of colonies with ontogenetically older zooids. 
