and the margin, and by the lack of isolated rows of areolae typical for A. actinochilus.
Actinocyclus vestigulus T. P. Watkins in Watkins & Fryxell (Table 26) Reference: Watkins & Fryxell, 1986, p. 296, Figs. 9-16. Sometimes with a not very distinct, more or less central annulus with the smaller areolae almost linearly arranged. Position of labiate processes in relation to the irregular fascicles obscure. Pseudonodulus difficult to see with LM.
A. spiritus—southern cold water region A. vestigulus—warm water region? How to identify: The Actinocyclus species presented here can hardly be identified as whole cells in water mounts since, as far as known, they all have numerous small chloroplasts lying against the cell wall and more or less the same cell shape. Actinocyclus spp. may easily be confused with Coscinodiscus spp. and Azpeitia spp. when seen in water mounts, and examination of cleaned material mounted in a medium of a high refractive index is necessary to ensure correct identification.
Remarks: The pseudonodulus was not mentioned in the original description of the genus, but was first noted by Smith (1853) according to Simonsen (1975), and is now regarded as typical for the genus. In some species the pseudonodulus is similar to a valve areola in size and structure, and/or it is positioned in the bend between valve face and mantle. This explains why it has so often been overlooked (Simonsen, 1982). The morphology of the pseudonodulus varies considerably within the genus as well as within one species. Andersen et al. (1986) showed that each labiate process of the Actinocyclus sp. that they examined contained material which they proposed is related to movement noted in this centric diatom. Their investigation thus throws light upon the long-speculated function of the labiate process.
Genus Azpeitia M. Peragallo in Tempère & Peragallo Type: Azpeitia temperi M. Peragallo.
Correct name: Azpeitia antiqua (Pantocseck) Sims (vide Fryxell et al., 1986b, p. 6).
References: Fryxell et al., 1986b; Sims et al., 1989. The genus was described from fossil material and encompasses living marine planktonic species as well. The living ones are better known as Coscinodiscus spp. and were transferred to Azpeitia by Fryxell et al. (1986b).
Marked difference in the areola patterns on valve face and mantle.
Valves generally flat.
Valve center generally with an annulus.
Large nearly central labiate process on the edge of the annulus.
A ring of large labiate processes, similar in shape, at the edge of valve mantle.
Characters showing differences between species: Valve face areolation: pattern and areola size. Position and shape of annulus. Size of labiate processes.
Shape and structure of bordering zone between valve face and mantle (hyaline, marginal ridge).
Azpeitia africana (Janisch ex A. Schmidt) G. Fryxell 8c T. P. Watkins in Fryxell et al. (Plate 20, Table 27)
Basionym: Coscinodiscus africanus Janisch ex A. Schmidt. References: Schmidt, 1878, Plate 59, Figs. 24 and 25; Hustedt, 1930, p. 428, Fig. 231; Fryxell et al. 1986b, p. 22, Figs. 22, 23, 32-1, and 32-2. Valves circular, sometimes slightly elliptical. Distinct external marginal slits leading into labiate processes. Central labiate process on edge of an eccentric circle of linearly arranged areolae. Areola rows radiating from the annulus and, in larger specimens, in spiraling rows.
Azpeitia barronii G. Fryxell 8c T. P. Watkins in Fryxell et al. (Plate 20, Table 27)
Reference: Fryxell et al. 1986b, p. 20, Figs. 18-3, 18-5, 19-21, and 31. Sublinear areolation. Areolae of same size over most of the valve. Curved marginal ridge; some rounding between valve mantle and face. Central labiate process large, noticeable with LM. Central annulus possibly missing.
Azpeitia neocrenulata (VanLandingham) G. Fryxell 8c T. P. Watkins in
Fryxell et al. (Plate 20, Table 27)
Basionym: Coscinodiscus neocrenulatus VanLandingham.
Synonym: Coscinodiscus crenulatus Grunow non C. crenulatus Castracane.
References: Grunow, 1884, p. 83, Plate 4, Fig. 17; Hustedt, 1930, p. 411,
Fig. 219; VanLandingham, 1968, p. 930; Fryxell et al. 1986b, p. 18, Figs.
Areolation fasciculated with radial rows of areolae usually parallel to an edge row. Marginal labiate process and a depression on the mantle at the
PLATE 20 Azpeitia africana, A. neocrenuiata, A. tabularis, and A. barronii. Valves with areola-tion. Scale bar =10 (im.
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