Aulacoseira Thwaites, 1848

Holotype species: Melosira crenulata (Ehrenberg) Kützing

Currently accepted name for the type species: Aulacoseira crenulata (Ehrenberg) Thwaites

Original publication and holotype designation: Thwaites, G.H.K. (1848). Further observations on the Diatomaceae with descriptions of new genera and species. Annals and Magazine of Natural History, Series 2 1: 161-172, pls XI, XII.

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Description: Cells linked tightly to form long straight, curved or even coiled filaments. Plastids discoid. A common freshwater, planktonic genus previously placed in Melosira. Valves circular. Valve face plain or with scattered poroids, which are often restricted to its periphery. Valve mantle deep, making a right angle to the planar valve face from which it is sharply differentiated; with vertical or curved rows of areolae. Mantle edge plain. Valve face/mantle junction provided with spines, which are expanded at their apices and fit with the spines of adjacent cells to form a linkage breakable only by damaging the spines. In some species the spines have two 'roots' that straddle a row of pores on the mantle, others have a single 'root' that runs between pore rows. Separation cells occur at intervals in A. granulata, the spines on these being lanceolate and of variable length; the areolae of separation valves are often in straight rows, those on other valves spiralling away from the sibling junction in opposite directions. Inside the valve mantle, at the junction between the plain mantle edge and the areolate portion, there is a thickening (ringleiste), which is hollow in A. ambigua. Mantle areolae simple, round to rectangular, containing volate occlusions. Small rimoportulae occur inward of the ringleiste and open through it to the outside. The copulae are split rings with ligulae; they are finely areolate, with an advalvar pars media.

The most recent alteration to this page was made on 2022-06-12 by M.D. Guiry.

Taxonomic status: This name is of an entity that is currently accepted taxonomically.

Gender: This genus name is currently treated as feminine.

Most recent taxonomic treatment adopted: Greifenstein, J., Shea, R. & Kociolek, J.P. (2022). A new Aulacoseira Thwaites (Bacillariophyta) Species from Wyoming, USA. Taxonomy 2022(2): 236–243, 4 figs, 1 table.

Comments: Simonsen (1979) resurrected the long disused name Aulacosira (sic) and the common species italica, granulata, islandica, nyassensis and distans of the genus Melosira are placed here (see also Haworth, 1988). M. varians has a very different wall structure and remains in Melosira (see p. 154). Davey & Crawford (1986) showed that the frequency of separation valve formation in A. granulata controls filament length, which in turn (Davey, 1986, 1987) may influence the buoyancy of this diatom. Why some species, e.g. A. italica subsp. subarctica, only appear to have separation valves while others, e.g. A. ambigua, only have linking valves is unexplained.

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Some of the descriptions included in AlgaeBase were originally from the unpublished Encyclopedia of Algal Genera, organised in the 1990s by Dr Bruce Parker on behalf of the Phycological Society of America (PSA) and intended to be published in CD format. These AlgaeBase descriptions are now being continually updated, and each current contributor is identified above. The PSA and AlgaeBase warmly acknowledge the generosity of all past and present contributors and particularly the work of Dr Parker.

Descriptions of chrysophyte genera were subsequently published in J. Kristiansen & H.R. Preisig (eds.). 2001. Encyclopedia of Chrysophyte Genera. Bibliotheca Phycologica 110: 1-260.

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M.D. Guiry in Guiry, M.D. & Guiry, G.M. 12 June 2022. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 18 May 2024

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