Nannotax3 - ntax_Farinacci - Chrysochromulina mactra

Original descriptions of taxa. For coccolithophores, and many calcispheres, these are pages from the Farinacci & Howe Catalog of Calcareous Nannofossils. In other cases (e.g. non-calcifying haptophytes) the data is directly compiled on this site. The "Catalogue of Calcareous Nannofossils" was originally compiled by Prof A. Farinacci 1969-1989, since 2000 it has been updated and extended by Richard Howe - see The Farinacci and Howe Catalog - an Introduction.
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Citation: Chrysochromulina mactra Manton 1972

Type sample (& lithostrat): Culture No. 222 in the Plymouth collection

Standardised type level: 160_HOLOCENE

Type locality: August 9, 1959 from the sea near Plymouth, England,

Farinacci catalog page (& compiler): n/a

Current citation: Chrysochromulina mactra Manton 1972

Cells 15-20 µm in length and breadth. Two equal flagella, 20--40 µm long. Haptonema 30-40 µm long when fully extended, coiled into a helix of about 12 gyres when retracted. Two gulden-brown plastids, bifid posteriorly; each with a large bulging pyrenoid attached near the base of the cleft. Scales large, rimless, very thin and of two kinds: the outermost tub-shaped, the innermost platelike. Plate scales usually 2 x 1.6 µm though with a few much smaller ones, all with a pattern of ridges radiating from a quadrangular plain centre visible on both surfaces, the ridges extending to the edge on the proximal surface but covered with a thin finely striated band peripherally on the distal surface. Tub-shaped scales with straight sides, up to 1.5 µm high, slightly diverging, transversely striated, and a flat base 1 x 1-3 µm wide, marked by a pattern of radiating ridges.

DISTRIBUTION
Isolated from Plymouth, subsequently found once at Bergen, Norway, and Hirtshals, Denmark, in summer.

EXTERNALS OF THE CELL AS A WHOLE
When first isolated (M. Parke, personal communication) the cell size of this species was 15-20 µm and its shape 'rather like that of a squat strawberry'. The flagella were twice the body length and the external scales were described as 'resembling ice cream tubs'.

The haptonema was best studied in whole mounts since it tended to become discarded under the conditions of light microscopy. When fully extended it was more or less equal to the flagella in length or slightly longer (Figs. 1, 2). When retracted, it was commonly coiled into a helix of about 12 gyres, best seen in a detached specimen such as that of Fig. 4.

THE SCALES
The most distinctive and, in the present context, important attributes of this species are the scales. These are of two kinds, namely, flat apparently rimless plates and deep cup- or tub-shaped scales. Both sorts are large enough to be seen individually with the light microscope although the plate scales are only detectable in this way in edge view being completely transparent otherwise.In spite of their large size the scales of both types are exceptionally thin in texture. This means that in dried preparations well spread plates scales, commonly present in large numbers, are clearly displayed after shadowing though they would otherwise be almost invisible, being little more opaque than the supporting film. Tub scales on the other hand are invariably collapsed and though their surface markings can be studied in this way their true shape can be seen directly only in sections. Since they readily become separated from the subtending cells, which appear naked when sectioned, such detached scales, often still associated together in sheets, are the main source of morphological information whether studied with the light microscope on fresh liquid mounts or with an electron microscope on shadowcast dried preparations or after embedding. Examples of all these modes of viewing will be found in Figs. 11-20.

The tub scales when seen in section (Fig. 16) are flat bottomed and straight sided. The junction of the sides with the base is marked by a slight keel-like thickening and the sides themselves diverge slightly. When viewed end-on a tub appears approximately circular or slightly oval in optical section (Fig. 19); the base plates (Figs. 14, 15, 17) are similar unless their shape is masked by folds or tearing. The patterning of the base plate is that usual on the proximal face of scales in this genus, being built up of radiating ridges arranged in quadrants from a cruciform plain centre. The patterning on the sides is more difficult to see but when favourably placed with respect to the angle of shadowing it appears as a system of delicate more or less parallel lines running transversely relative to the long axis of the tub (Fig. 14, bottom left); the inner face of the sides is patternless. Dimensions are somewhat variable but an average size in the cultured material was 1 × 1.3 µm at the base and slightly more distally, the average height being 1.5 µm. In the wild material (Fig. 15) dimensions are similar though the height is perhaps slightly less (for further details see Fig. 20).

The plate scales are less individually distinctive than the tub scales since there are fairly close parallels in other species, notably C.pringsheimii Parke et Manton (Parke & Manton, 1962), C. brevifilum Parke et Manton (Parke, Manton & Clarke, 1955; Manton unpub.), etc. However, the dimensions of plate scales in C. mactra are unusually large, an average size (Figs. 11, 12) being 1.6 × 2 µm though there is a considerable range of smaller sizes present concurrently (Fig. 14). The patterning recalls that on the bases of tubs, being composed of radiating ridges arranged in quadrants round a cruciform plain centre visible on both faces (Figs. 11, 12). The two surfaces are nevertheless easily distinguished (see Fig. 13) by the fact that the ridges extend without interruption to the plate edge on one face, known from other evidence to be the proximal face, while the peri- pheral ends of the ridges on the distal face are overlaid by a band of differently striated material. The striations of this peripheral band (Fig. 12) are approximately parallel to the plate edge and recall those on the sides of tubs (Fig. 14).

Sections of plate scales add one further piece of information which could not have been ascertained otherwise. In Figs. 12 and 13 the peripheral band of con- centrically striated material on the distal scale-face is pressed so closely against the underlying radially striated material after the scale has dried that it could not be known by simple inspection whether or not these two layers are bonded together. When seen in section, however (Fig. 18), there is no doubt that they are completely free from one another except at the edge where they join. Some further comment on this feature will be found below.

References:

Manton, I. (1972). Preliminary observations on Chrysochromulina mactra sp. nov. British Phycological Journal. 7: 21-35. gs

CATALOG - Chrysochromulina mactra

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