Published online by Cambridge University Press: 11 May 2009
The gross anatomy of the heart-body of the lugworm Arenicola grubii Clap, was described by Gamble & Ashworth (1900) and Ashworth (1904) who noted that it was also well developed in A. ecaudata Johnston (Ashworth, 1904) but was absent in A. claparedii Levinsen and A. cristata Stimpson. These authors noticed that there was no trace of a heart-body in young specimens of A. marina (L.) but that it was recognisable in worms measuring 65 mm or more in length. In such worms the heart-body tissue was described as consisting of two simple layers. In larger worms the layers are invaded by tissue resembling the wall of the heart and are probably invaginations of it. Dissection does suggest that the heart-body which lies only within the ventricle, is indeed formed by invaginations from the wall of the heart.