POLYCHAETOUS ANNELIDS Part VII. Capitellidae (Plates 43-58, 1 Chart) By Olga Hartman This constitutes one of the oldest known groups of polychaetous anne-lids; it was already known in the late seventeen hundreds through the species Capitella capitata (Fabricius). The affinities of the group with other polychaetous annelids, however, were not clarified until detailed anatomical studies of organ systems had verified and proved their true relations. They had been variously considered as oligochaetes, repre-sentatives of Maldanidae, Arenicolidae, and Serpuliformia even as late as 1865 (see Eisig, 1887, pp. 1-10, for detailed history). The family name was first erected as the Capitellacea by Grube (1862) when Notomastus, Dasybranchus, and Capitella were correctly grouped together. A year later the family name, Halelminthea Carus, was proposed for Capitella, but this author considered it in the Oligo-chaeta together with an opheliid, Polyophthalmus; the name Halelmin-thea now has only historical interest. Today the various genera and species of Capitellidae (see below) are indisputably considered distinct, forming a closely related family; their affinities are with other sedentary chaetopods. Externally and grossly considered, many capitellids resemble ter-restrial oligochaetes because of their plain, unadorned exterior. In details, however, the body is seen to consist of a distinct prostomial lobe, a thorax with a limited number, and an abdomen with a variable number of segments. The thorax and abdomen, though distinct from each other, are sometimes indivisible in external view or are separate from each other by transitional segments (pi. 58, fig. 1). The prostomium is a plain, short, rounded (pi. 55, fig. 1) or elongated (pi. 47, fig. 4) lobe, without eyes (pi. 50, fig. 4) or with a pair of pigmented areas (pi. 47, fig. 4) at the sides. A pair of eversible nuchal organs or ciliated mounds, homo-logous with the lateral organs farther back, is more or less conspicuous at the posterior margin of the prostomium, or may be reduced nearly to dis-[391]
BioStor
