"?, Data uncertain

Central area comparatively small. Separating lines obscurely bent and sometimes equipped with small branches in the middle. Extension of narrow hyaline ray inside central area conspicuous in shape being semicircular at the top, then contracted, and widely expanded. Areolated sectors moderately wide (six or seven areolae between two hyaline rays) and truncated toward valve center.


A. arachne, A. elegans, and A. roperianus—warm water region (Simonsen, 1974).

A. heptactis—temperate [Davis Strait—Cape of Good Hope (Hendey, 1964)].

A. hookeri, A. hyalinus, and A. parvulus—southern cold water region (Hustedt, 1958a).

How to identify: Examinations of cells in valve view, whole cells, or single valves are required for identification purposes. Water mounts may be sufficient in some cases; permanent mounts of cleaned material are recommended.

Remarks: Special distributional as well as taxonomic problems connected with the three species classified as Antarctic (southern cold water region) should be noted. Asteromphalus hookeri has been reported as common in north temperate waters (Hendey, 1964), and our own observations indicate that the species described by Karsten (1905) as A. hyalinus may be present in the Norwegian and the Barents Seas as well as in the North Pacific. Examination of Antarctic material showed that A. parvulus and larger specimens of A. hyalinus are not readily distinguished, and a comparison with Ehrenberg's (1844c) illustrations of A. darwinii and A. rossii indicates a possible conspecificity between these four species. Hernandez-Becerril (1991a, 1992a) provided detailed information on the valve structure seen with SEM and on the taxonomy and biogeography of the genus (information that has not been included in this chapter). It should be noted, however, that A. sarcophagus was placed in the subgenus Liriogramma (Kolbe) Hernandez-Becerril, and that reinstatement of the genus Spatangidium Brebisson with S. arachne as the type was suggested.

Family Heliopeltaceae H. L. Smith 1872

Glezer et al. (1988) and Simonsen (1979) regarded Actinoptychus as well as Aulacodiscus as members of this family. Round et al. (1990) put Aulacodiscus Ehrenberg in the family Aulacodiscaceae (Schtitt) Lemmermann and retained Actinoptychus Ehrenberg in Heliopeltaceae. The two genera are primarily benthic. Two species are often recorded from plankton and are included here.

Actinoptychus senarius (Ehrenberg) Ehrenberg (Plate 22) Basionym: Actinocyclus senarius Ehrenberg. Synonym: Actinoptychus undulatus (Bailey) Ralfs in Pritchard. References: Ehrenberg, 1838, p. 172, Plate 21, Fig. 6; Ehrenberg, 1843, p. 400, Plate 1,1, Fig. 27, Plate 1,3, Fig. 21; Pritchard, 1861, p. 839, Plate 5, Fig. 88; Hustedt, 1930, p. 475, Fig. 264; Cupp, 1943, p. 67, Fig. 29, Plate 5, Fig. 1; Hendey, 1964, p. 95, Plate 23, Figs. 1 and 2; Takano, 1990, pp. 258-259. Cells disc shaped with valves divided into sectors, usually six, alternately raised and depressed. A central nonareolated area, hexagonal in outline. Each of the raised sectors with a labiate process with an external tube. Areolation coarse and irregular. Chloroplasts large and numerous. Morphometric data: Diameter, 20-150 ¿im; areolae, four to seven in 10 ¡jum.

Distribution: Cosmopolitan?

Aulacodiscus argus (Ehrenberg) A. Schmidt Basionym: Tripodiscus argus Ehrenberg.

References: Ehrenberg, 1844a, p. 73; Schmidt, 1886, Plate 107, Fig. 4; Hustedt, 1930, p. 503, Fig. 281. Cells box shaped with flat or slightly convex valves. Valve structure complex and dense consisting of one layer with angular areolae overlying a layer with finer pores. Three to six marginal labiate processes with prominent pear-shaped extensions raised above valve surface. Chloroplasts fairly large and roundish.

Morphometric data: Diameter, 80-260 /xm; areolae, four to six in 10 /xm.

Distribution: Cosmopolitan?

How to identify: The species may be identified in valve view in water mounts or, in critical cases, as valves cleaned of organic matter and mounted in a medium not necessarily of a high refractive index.

Suborder Rhizosoleniineae

Family Rhizosoleniaceae Petit 1888

Dactyliosolen, Guinardia, and Rhizosolenia are the recent, marine, planktonic genera of this family as circumscribed by Simonsen (1979) and Glezer et al. (1988); Round et al. (1990) included the more recently described genera Proboscia, Pseudosolenia, and Urosolenia. In the latter classification Rhizosoleniaceae was placed in the order Rhizosoleniales P. Silva in the new subclass Rhizosoleniophycidae Round 8c Crawford.

Sundstrom (1986) stressed the necessity of splitting Rhizosoleniaceae and establishing new families since he found that his circumscription of Rhizosolenia, the type of the family, comprised species that differed considerably from those in Guinardia and Dactyliosolen. He suggested that Rhizosoleniaceae should be confined to Rhizosolenia Brightwell, Pseudosolenia Sundstrom, and possibly Proboscia Sundstrom. However, no new families were described.

For a lack of better alternatives this chapter will deal with the heterogeneous family Rhizosoleniaceae sertsu lato comprising Proboscia, Pseudosolenia, Rhizosolenia sensu lato, Guinardia, and Dactyliosolen. Most of the data and information on Rhizosolenia sensu stricto, Pseudosolenia, and Proboscia are from Sundstrom (1986). Rhizosolenia and Proboscia species present in polar regions are dealt with specifically by Priddle et al. (1990).

Characters of Rhizosoleniaceae sensu lato: Cells in chains. Cells cylindrical.

A single process with internal labiate, sometimes more tubular structure. Unipolar valve symmetry. Numerous small chloroplasts. Resting spores seldom.

Terminology specific to Rhizosoleniaceae (mainly after Sundstrom, 1986) (Fig. 15):

Contiguous area—part of the ventral side of the valve contiguous with the adjacent valve of linked cells, usually delimited by low marginal ridges.

Claspers—pair of membranous structures usually continuous with marginal ridges of contiguous area clasping otaria of the adjacent valve of linked cells. In Proboscia the structures clasping the distal part of the proboscis of linked cells.

Otarium—one of the pair of membranous costae that occur opposite each other at or near the base of the external process, previously called a wing.

Proboscis—elongated part of the valve with truncate tip; the distal part fits into a groove on the adjacent valve of linked cells. Segment—band—copula—single element of the girdle.

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