Abas R.& 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.
Taxonomic status: currently recognized as a distinct genus.
Most recent taxonomic treatment adopted: Fourtanier, E. & Kociolek, J.P. (1999). Catalogue of the diatom genera. Diatom Research 14(1): 1-190.
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 14 Aug 2017 by M.D. Guiry.
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.
Numbers of names and species: There is only one species or infraspecific name in the database at present, which has been flagged as accepted taxonomically on the basis of the listed literature under the species name. In some instances, opinions on taxonomic validity differ from author to author and users are encouraged to form their own opinion. AlgaeBase is a work in progress and should not be regarded as a definitive source only as a guide to the literature..
Names: ('C' indicates a name that is accepted taxonomically; 'S' a homotypic or heterotypic synonym; 'U' indicates a name of uncertain taxonomic status, but which has been subjected to some verification nomenclaturally; 'P' indicates a preliminary AlgaeBase entry that has not been subjected to any kind of verification. For more information on a species click on it to activate a link to the Species database):
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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.
Created: 16 September 2003 by M.D. Guiry
Verified by: 14 August 2017 by M.D. Guiry
Linking to this page: http://www.algaebase.org/search/genus/detail/?genus_id=46626
Please cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 2020. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 30 November 2020.