Pegmatothylakos, McLoughlin, Bomfleur, Mörs & Reguero, 2016

McLoughlin, Stephen, Bomfleur, Benjamin, Mörs, Thomas & Reguero, Marcelo, 2016, Fossil clitellate annelid cocoons and their microbiological inclusions from the Eocene of Seymour Island, Antarctica, Palaeontologia Electronica 11 (1), pp. 1-27 : 10-12

Genus PEGMATOTHYLAKOS gen. nov.

zoobank.org/ 339BAEBC-42C6-46E3-B480-61B6E3E8CA4D

Type Species. Pegmatothylakos manumii sp. nov., by monotypy.

Etymology. Greek: pegma – a scaffold or framework; thylakos – sac. Gender: neuter.

Diagnosis. Fossil cocoons lacking an obvious sheet-like alytine. Inner layer of cocoon consisting of irregular slender-threaded, mesh-like hapsine. Outer layer of cocoon (= pegmatine) representing a shell of rigid girders interconnected to form a semi-regular reticulate framework enclosing rounded-polygonal lumina.

Remarks. This is the fourth genus established for fossil clitellate annelid cocoons. The genus is unique in lacking any obvious sheet-like alytine layer and in possessing a robust, rigid, reticulate framework layer (pegmatine) external to the felt-like hapsine ( Figure 1.4 ). The pegmatine also differs from the outermost (hapsine) layer of other fossil clitellate cocoons in being dark brown to black rather than yellow to red in reflected light, thus suggesting some difference in its chemistry. The hapsine of Pegmatothylakos is otherwise similar to the equivalent layer in Burejospermum and Dictyothylakos species, but less dense than that in Pilothylakos .

Figures

FIGURE 1. Diagrammatic sections through the walls of fossil clitellate annelid cocoons showing the general structure and representation of layers. 1, Burejospermum. 2, Pilothylakos. 3, Dictyothylakos. 4, Pegmatothylakos.