Main Content
< Top page

The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Pyramimonas

  1. Pyramimonas cirolanae Pennick (ref. ID; 3724)
  2. Pyramimonas disomata Butcher (ref. ID; 3724)
  3. Pyramimonas gorlestonae (Pennick & S. Cann, 1982) (ref. ID; 3724)
  4. Pyramimonas grossii Parke (ref. ID; 3724)
  5. Pyramimonas obovata N. Carter (ref. ID; 3724)
  6. Pyramimonas occidentalis Pennick, 1982 (ref. ID; 3724 original paper)
  7. Pyramimonas orientalis Butcher (ref. ID; 3724)

Pyramimonas occidentalis Pennick, 1982 (ref. ID; 3724 original paper)

Diagnosis

Motile cells 5.5-7.0x4.5-5.5 um, obovoid. 4 flagella 1.5-2 times the length of the cell body, with anterior flagella pit. Flagella covered with 2 layers of scales, visible only with the electron microscopes: an inner layer of small pentagonal scales 60 nm across, and an outer layer of flat, unchannelled, spine-tipped scales 325x200 nm. Pyrenoid single, posterior, surrounded by a large starch deposit. Cells covered with numerous scales of 3 types, visible only under the electron microscope. A layer of small square or pentagonal scales 55-60 nm across lying in the flagellar pit and on the anterior of the cell next to the plasmalemma: a middle layer of square scales with sides 245 nm, bearing a raised cross at the centre of the field, lying above the small square scales in the flagellar pit and on the anterior of the cell, but next to the plasmalemma on the rest of the cell body; and an outer layer of openwork scales 200 nm in height and 325 nm across the square base, which bears 12 downward-pointing spine. 4 uprights arise from the periphery of the base, each bearing typically 4 spines. Uprights arch towards the centre to connect with an upright linked to cross-shaped struts at the base. (ref. ID; 3724)

Descriptions

Cells of P. occidentalis appear obovoid under the light microscope. Their size varies from 5.5-7.0x4.5-5.5 um, and in general form they resemble P. orientalis Butcher. The internal structure of P. occidentalis generally resembles that of other small species of the genus. No trichocysts are present. The large basal pyrenoid is rather diffuse and invested in a large starch grain. Thylakoids do not penetrate the pyrenoid. Large vesicles are present between the pyrenoid and the flagellar roots. Vesicles containing individual scales and scale reservoirs also occur in this region. The 4 flagella, which arise in an anterior pit, are 1.5-2 times the cell body length. The cell body bears 2 superimposed layers of scales with correspond morphologically with the middle and outer layer scales of other species of Pyramimonas and the Pyramimonas-like motile stage of Halosphaera russellii Parke. On the flagella are three types of appendage; inner and outer layer scales and flagellar hairscales. Their arrangement is identical with that found on other scale-bearing Pyramimonas species. Inner layer body scales are small box-like structures. They occur only in the flagellar pit and on the anterior of the cell. Each side measures 55 nm, thickening towards the middle. The centre of each scale is in the form of a cross. Middle layer scales are 245 nm square with 70 nm high unperforated rims. The central field of these scales is distinguished by a raised cross. There is no central boss. Outer layer scales are openwork structures 200 nm in height and 325 nm across the base. The base of each scale is roughly square bearing 12 downward-pointing spines. From this base arise inverted Y-shaped uprights bearing long spines, typically 4 apiece. These uprights curve to meet a central upright coming from the junction of 4 Y-shaped horizontal bars in the plane of the base. These horizontal bars join the base at the points of origin of the 4 outer arched uprights. The whole scale has a very characteristic spiny appearance. Inner layer flagellar scales are pentagonal, 60 nm across, arranged in close spiral rows. Occasionally these scales also occur among the square scales on the anterior of the cell body. Above this layer is an imbricated layer of outer scales. These scales are asymmetrical, 325 nm long by 200 nm wide, bearing a prominent spine that runs the length of the scale, protruding from the lamina towards the distal end of the flagellum. The unchannelled lamina is perforated by a single aperture next to the spine in the proximal third of the lamina. The lamina bears two faintly-discernable diagonal markings. (ref. ID; 3724)

Comments

The structure of P. occidentalis most closely resembles that of P. orientalis Butcher. It is distinguished from this taxon by its much longer flagella, its slightly larger size and its scales. The outer layer flagellar scales are unchannelled, as opposed to the longitudinal striations in P. orientalis sensu Moestrup and Thomsen. The middle layer body scales of P. occidentalis bear a prominent cross readily visible in shadowcast preparations; P. orientalis has scales with longitudinal strait. The outer layer scales of P. occidentalis have thickened, spine-bearing arches arising from the centre of each side of the square base, unlike P. orientalis which has a finer, rounded, structure devoid of spines. The internal structure of P. occidentalis differs from P. orientalis in that the pyrenoid is not penetrated by thylakoid lamellae, and the starch grain is very large. (ref. ID; 3724)

Type locality

Pyramimonas occidentalis was isolated by Purkiss from the English Channel in 1971. (ref. ID; 3724)