DESMIDS OF SOME SELECTED AREAS OF BANGLADESH. 3. DOCIDIUM, PLEUROTAENIUM, TRIPLASTRUM AND TRIPLOCERAS

23 taxa belonging to Pleurotaenium, 2 under Triploceras and 1 each under Docidium and Triplastrum have been recorded in this paper from some selected areas of Bangladesh. Of these, 11 are new records for the country. Introduction This is the third paper in a series under the above title. The first and second papers with the same title have already been published in this journal (Islam and Akter 2004 and Islam and Begum 2004). The present paper includes the species belonging to Docidium, Pleurotaenium, Triplastrum and Triploceras from the same selected areas as mentioned in the above papers. The illustrated descriptions of these taxa are given below. For materials and methods, dates and places of collections and other information see Islam and Akter (2004). Taxonomy Class: Chlorophyceae; Order Desmidiales; Family: Desmidiaceae A total of 27 taxa (Docidium 1, Pleurotaenium 23, Triplastrum 1 and Triploceras 2) have been described with diagrams and photomicrographs. Of these, 11 taxa are new records for the country (marked by *). Genus: Docidium de Brebisson 1844 em. Lundell 1871 Cells straight, cylindrical, smooth, or with undulate margins, 8-26 times longer than broad; circular in cross section, slightly constricted in the midregion, with an open sinus; apex usually truncate, rounded, sometimes dilated, smooth or rarely with a few intramarginal granules; base of semicell inflated, with 6-9 visible folds (plications) at the isthmus, the folds usually subtended by granules; cell wall smooth or faintly punctulate; chloroplast axial with irregular longitudinal ridges and 6-14 axial pyrenoids; zygospore unknown. 1. Docidium baculum de Bréb. var. baculum (Pl. 1, Figs. 4-5) (Prescott et al. 1975, 102, Pl. 37, Figs. 1-4). Cells straight, cylindrical or very slightly tapering; apex smooth, rounded-truncate, not dilated; base of semicell with single inflation, with several folds; cell length 207210.2 μm; mid-diam. 11-14.20 μm; isthmus 8.5 μm; apex 7-10 μm.


Introduction
This is the third paper in a series under the above title.The first and second papers with the same title have already been published in this journal (Islam andAkter 2004 andIslam andBegum 2004).The present paper includes the species belonging to Docidium, Pleurotaenium, Triplastrum and Triploceras from the same selected areas as mentioned in the above papers.The illustrated descriptions of these taxa are given below.
For materials and methods, dates and places of collections and other information see Islam and Akter (2004).

Genus: Docidium de Brebisson 1844 em. Lundell 1871
Cells straight, cylindrical, smooth, or with undulate margins, 8-26 times longer than broad; circular in cross section, slightly constricted in the midregion, with an open sinus; apex usually truncate, rounded, sometimes dilated, smooth or rarely with a few intramarginal granules; base of semicell inflated, with 6-9 visible folds (plications) at the isthmus, the folds usually subtended by granules; cell wall smooth or faintly punctulate; chloroplast axial with irregular longitudinal ridges and 6-14 axial pyrenoids; zygospore unknown.
Note: Our specimen is smaller than the typical form with thick wall and irregular shallow undulations.
Specimens studied: Collected from a pond near Uttara Shopping Centre near the Zia Int.Airport on 6 Sept. 1989 and from a ditch near Kaliganj Railway Station, Kaliganj, Gazipur on 14 Aug. 1989; fairly common in both the collections.6. Pl. ehrenbergii var.undulatum Schaar.
Cells cylindrical with distinct median constriction; each semicell broader at the base, gradually and slightly tapering toward the apex; marginal wall undulate up to the base of apex and with 5-ring-like whorls of spiny outgrowths present from the base of semicell up to below the apex; apex slightly flat, truncate with a ring of 10-12 spines, more or less horizontally spreading; cell length 270-329 µm; mid-diam.without spines 45-51.6 µm, with spines 61-76 µm; isthmus 29-32.3µm; apex without spines 25-32.3µm; with spines 38-51.6 µm.
Note: Our form differs from the typical by its broader apex and the apical spines are more or less horizontal instead of slightly vertical.
In our form apical dentations are not pointed and the semicells are gradually narrowed from base to apex.
Specimen studied: Collected from a pond opposite Uttara Shopping Centre near Zia Int.Airport, Dhaka on 6 Sept. 1989; common.
Specimen studied: Collected from Khilkhet beel near the Zia Int.Airport, Dhaka on 6 January 1990.
Note: This rare species was reported earlier from Narayanganj district by Islam (1980) which was little bigger in size than the present one, otherwise there is no difference between these two collections.
Specimens studied: Same as the above one and also from a rice-field at Manikganj on 1 April 1989 and from a rice-field at Kaliganj, Gazipur on 14 Aug. 1989;common.
Specimen studied: Collected from a ditch near Kaliganj Railway Station, Gazipur on 12 Sept. 1989.