Siliceous and Delicious

Decided to flee the heat of the office, and so decamped with Beau to Bloc 11 Café after our weekly DSA session at Darwin’s. The calendar called for diatom morphospace, but I thought I felt more like working on the E/O diversity project, so I started trying to download the Neptune database again—this time a full report including all four microfossil groups—in order to see what the qualitative preservation values looked like for the samples. Alas, the Chronos interface gave me the usual barrage of Apache server errors, and no matter how often I tried, denied me access to the database. Ah well. Back to the morphospace, then!

Started with Brunia (allegedly a synonym of Bruniopsis, which is in Neptune), described in the van Heurck book I downloaded the other day. Very hard to extract useful information from the verbal description given, on account of the rather different language used to describe the morphology. What on earth is meant by ‘a delicate cellular structure’ in the description of the frustule—surely the thing is unicellular! Perhaps this describes an areolate pore pattern? Or describes the funny lobed ornamentation at the valve edge? Anyhow, I did the best I could in translating the description of the taxon into the terms used in my character list, and moved on.

Next up was Ceratoneis, for which I’ll need to visit the Farlow. Cestodiscus was a bitch to track down. Though I eventually found a paper by Fenner (1984) describing two species of the genus, this did not help that much with a generic description. The official generic description is quoted on the Diatom Wiki—but is almost totally useless. It doesn’t really say anything specific other than that the frustule is circular or oval, and that it has ‘radiating granules or cellules’ (the latter of which I don’t understand), and a ‘submarginal circle of obtuse processes’, which I take to mean spines originating on the valve face inward of the margin.

Charcotia was next and needed a reference from Farlow. Chasea has a description in the original paper defining the genus, but the photographs are lousy and I don’t quite understand the description—it talks about the form resembling Chaetoceros, but with an ‘endocyst’: what on earth is that supposed to be? Some sort of resting stage/spore? Totally confusing. Well, as far as I can tell from the pictures and the description, other than the inner layer of silica forming some sort of central dome, it otherwise does look like Chaetoceros or some other bipolar form. Moving swiftly along…