Quarterly Journal of Microscopical Science, Vol s3-90, 221-233, Copyright © 1949 by Company of Biologists

Observations on the Branchial Crown of the Serpulidae (Annelida, Polychaeta)

¹ Department of Zoology, Bedford College, University of London

1. This paper records various observations supplementing, and in some cases correcting previous accounts of the internal structure of the branchial crown in Pomatoceros triqueter, Serpula vermicularis, Hydroides norvegica, Vermiliopsis infundibulum, Salmacina incrustans, Protula intestinum, Spirorbis corrugatus, and Spirorbis militaris.

2. The muscles in the opercular peduncle of Pomatoceros are longitudinal.

3. A single layer of small longitudinal muscle-fibres, of unknown function, has been found on the abfrontal face of the internal branchial and internal peduncular nerves of most of these serpulids.

4. External branchial muscles are well developed in Pomatoceros, reduced in Serpula, Hydroides, Vermiliopsis, and Spirorbis militaris, and apparently absent in Protula and Spirorbis corrugatus.

5. The pinnules of Pomatoceros and Hydroides, like filaments and opercular peduncles, have a double innervation.

6. The internal skeleton of the serpulid crown consists of sheets and strands of connective tissue-fibres and, in the opercula, of a cartilage-like tissue with a ground substance giving the staining reactions of collagen. The serpulid branchial skeleton is compared with that of sabellids, and the chemical nature of these skeletons is discussed.

7. Extensions of the prostomial and peristomial cavities accompany the branchial blood-vessels into the base of the crown, but have no connexion with the cavities in the branches of the crown. The arrangement of the latter is described. The nature of all these cavities, whether coelomic or blastocoelic, is obscure.

8. The ‘palps’ of Pomatoceros, Serpula, Hydroides, and Vermiliopsis closely resemble pinnules. The blood-vessel and nerve of the ‘palp’ of Pomatoceros are branches of those in the adjacent filament. It is suggested that the serpulid ‘palp’ is a modified pinnule.