Coscinodiscus marginatus

Overview

Coscinodiscus marginatus is a diatom that forms a round siliceous shell. Under a microscope, intricate patterns spread within its coin-like outline. Its long fossil record can be explored alongside its distribution in today’s seas.^[1][3]

Key facts

A round outline alone makes it difficult to distinguish similar diatoms. Two large processes at the margin are important features of this species. A small structure can provide the clue that distinguishes the names of microscopic organisms.^[1]

Time and place

Its fossil occurrence record extends from Eocene strata approximately 48 million years old to recent deposits. It also appears in current marine catalogs. Distribution has been reported along several Australian coasts and in Antarctica, among other places.^[2][3]

The time range describes source context, not the complete duration of this species.

Size, form and skeleton

The round valve face is flat or slightly depressed at the center. A steep side wall descends from the margin, and the surface has polygonal structures and small processes. Comparing the circle seen face-on with the valve’s thickness from the side reveals a three-dimensional shell.^[1]

Specimen 1967-17 presented by the United States Geological Survey has a disc-shaped shell 115 µm in diameter.^[4]

Habitat and reproduction

It is a marine diatom. An Australian marine diatom catalog records occurrences in Moreton Bay, Cape Byron, and Gulf St Vincent, among other places. Small shells allow comparison of organisms from widely separated seas.^[3]

Fossil discovery

A name established in the nineteenth century continues into catalogs of living marine organisms and fossil research. Sancetta’s 1987 description was also compared in a 1993 United States Geological Survey publication. As microscopic observation developed, the shell’s detailed features became easier to read.^[1][3]

References

1. USGS1993 — Sancetta’s diatom descriptions and comparisons
2. Paleobiology Database — Fossil occurrence records for Coscinodiscus
3. Australian Biological Resources Study — Coscinodiscus marginatus
4. US Geological Survey Professional Paper 196 — Description of diatom specimens
5. 2019 original description — Fossil diatoms from an Eocene lake in Canada

Research questions

Can the whole shell be understood from a single valve viewed face-on? Diatom shells are compared through their two valves and the girdle connecting them. Marginal processes and the valve’s side walls help researchers distinguish similar species.^[1]

Observation

Move your gaze from the center of the round valve toward its margin. After locating surface patterns and large processes, picture the side wall to begin seeing the three-dimensional structure within a flat circle.^[1]