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Bryozoa
Escharoides mamillata (Wood, 1844)
Nomenclature
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Family: ExochellidaeGenus: Escharoides
- lectotype: B.M.(N.H.) Palaeont. Dept. D6935
SUMMARY
Colonies are encrusting, multiserial and sheet-like. The ancestrula appears not to have been described but early astogenetic stages contain relatively small autozooids lacking avicularia (and ovicells).
Autozooids are rounded rhomboidal in outline shape and large, about 0.70-0.75 mm long by 0.60-0.70 mm wide (fide Lagaiij 1952, p. 88). The strongly convex cryptocystal frontal shield is covered by nodules aligned in radiating ridges converging on the mucro which is tall and blunt. Pseudopores are lacking. Areolar pores occur in one to two rows around the perimeter of the frontal shield. The orifice is suborbicular, indented by a stout, lyrula-like denticle on the proximal edge of the thick peristome. Oral spines usually number 4 but these are invisible in ovicellate zooids possessing avicularia. The distal edge of the orifice forms a shelf sloping into the zooid. The ovicell is globular with a cryptocystal ectooecium, resembling a frontal shield, covered by nodules aligned in radial ridges and imperforate except for a line of small peripheral pores. Zooidal basal walls are complete, i.e. without an uncalcified window.
Adventitious avicularia are small, located in pairs on either side of the orifice, invariably present in ovicellate zooids but typically lacking in non-ovicellate zooids, and directed distally. The rostrum is triangular and sometimes curved inwards towards the midline of the autozooid. Although calcified, the pivotal bar is seldom preserved in fossils. Occasional smaller avicularia are associated with areolae around the borders of the autozooids.