Abas R.Ross & P.A.Sims, 1980
Holotype species: Abas wittii (Grunow) R.Ross & P.A.Sims
Original publication and holotype designation: Ross, R. & Sims, P.A. (1980). Syringidium Ehrenb., Dextradonator Ross & Sims, nov. gen. and Abas Ross & Sims, nov. gen. Bacillaria 3: 115-127.
Fossil: This is a genus of fossil species, or a genus with a fossil type species, or a genus the type species of which was originally described as a fossil.
Description: Cells united by long processes to form curving filaments. A fossil genus previously classified amongst the diatom spore forms under the name Syringidium, some of which must remain as spores (cf. Cerataulina). Abas is known from Eocene to Oligocene strata of tropical sites. Valves circular with radiating areolae closed by cribra. Valve mantle shallow and vertical with scattered areolae and a slight spinose rim between the mantle and valve face. The mantle edge is as wide as the porous part and has an internal flange. Two massive cylindrical elevations arise from the valve rim and fuse completely with those from the adjacent frustule. The elevations bend and (almost) touch centrally between the frustules - here there are a few pores in the elevations on the inner (i.e. adjacent) side. Also arising from the valve rim equidistant from the elevations is a spear-like projection with an apical barb near the tip. This is the exit tube of a rimoportula. A group of small spines also occur on the centre of the valve (reported in Ross & Sims but not seen by us). Valvocopula with a curved flange (pars interior) fitting inside the flange on the inside of the valve mantle. The valvocopula is deep with undulating rows of areolae and a plain abvolvar rim. Ross & Sims also record a further copula and one hyaline pleura. All are complete.
The most recent alteration to this page was made on 2017-08-14 by M.D. Guiry.Taxonomic status: This name is of an entity that is currently accepted taxonomically.
Most recent taxonomic treatment adopted: Fourtanier, E. & Kociolek, J.P. (1999). Catalogue of the diatom genera. Diatom Research 14(1): 1-190.
Comments: Ross & Sims (1980) discuss this genus in detail and comment on its systematic position. They tentatively suggest a place in the Hemiauloideae and reinforce this by comparison of its girdle structure with that of Dextradonator. It is a very unusual diatom in that the two elevations are completely fused. We know of only one other group in which a fusion occurs but this fusion is lateral and the setae then separate again distally (i.e. some species of the Chaetoceraceae). A fusion such as in Abas raises interesting points from a morphogenetic standpoint since the separate silicalemmas would need to fuse.
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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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Citing AlgaeBase
Cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 14 August 2017. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 18 April 2024
