Pyrosomatida
Taxonomy and identification

Neumann (1913a), in his excellent work on the pyrosomes recorded by the Deutsche Tiefsee Expedition, established the basis of classification of the order Pyrosomatida. He acknowledged the existence of two distinct groups of species, called sections, included in the single genus then recognized: Pyrosoma Péron, 1804. Neumann´s sections were: Pyrosomata fixata (for the species Pyrosoma agassizi Ritter and Byxbee, 1905 and Pyrosoma spinosum Herdman, 1888) and Pyrosomata ambulata (including all the other species known to that time). Metcalf and Hopkins (1919) considered these sections subgenera, but retained their plural names, which were incompatible with the rules of Zoological Nomenclature. The latter authors described new species and subspecies, as well as hybrid forms, in a very imprecise way, thus creating confusion in the systematics of the group. Garstang (1929) replaced the plural subgeneric names with the generic names Pyrostremma (for the section Pyrosomata fixata) and Pyrosoma s.s. (for the section Pyrosomata ambulata). Ivanova-Kazas (1956, 1960, 1961, 1962) described important reproductive differences between these two groups. Based on these observations, Van Soest (1979) subdivided the order into two subfamilies and added the new genus Pyrosomella, for the species Pyrosoma verticillatum Neumann, 1909c and P. operculatum Neumann, 1908. Van Soest subsequently (1981) published a monograph on the order Pyrosomatida, on which the following synopsis is based.

A total of only 8 species is recognized, 5 of which have been recorded from the South Atlantic Ocean. The present work includes succinct information for the identification of these latter taxa. Pyrosomella verticillata, a species that is very likely present in the area, is also included.

A key for the identification of pyrosomes is not available. The most commonly used diagnostic characteristics are the general morphology of the colony and the appearance of the colonial wall, the presence/absence of a diaphragm in the opening of the colony, and the general morphology of the zooids, mainly the size of siphons in relation to the size of the branchial basket. The general morphology of pyrosomes is schematized in Figs. longitudinal section, detail of an ascidiozooid, Cyathozooid of P. verticillata, to identify structures in the remaining figures.