Discussion

Of the previous descriptions of the species published, only two (Lutken, 1873; Sars, 1895) are full descriptions, and Lutken's is in Danish. Barnard (1932) described P. erraticus in some detail, and stated that P. boopis differed only in the ventral tubercles. Since this is the first paper of a series towards a revision of the New Zealand Amphipodan fauna, a detailed description of the New Zealand specimens is given. The species itself is very constant in form.

There are five species in the genus, P. boopis, P. erraticus, P nodosus, P. Physeteris, and P. gracilis; and what Stephenson (1942) calls “a rather uncertain variety,” P. boopis var. physeteris. P. physeteris has the gills tufted, whereas in the other four species they are not tufted but elongate-cylindrical. P. nodosus may be distinguished in turn by the rugged dorsal surface. In P. erraticus, P. gracilis, and P. boopis the dorsal surface is smooth, and in P. gracilis the ventral surface lacks the characteristic pointed tubercles of P. erraticus and P. boopis. The female of P. erraticus has one pair of tubercles on each of segments 5 and 7, and two pairs on segment 6; and the male has one pair on each of segments 5, 6, and 7. On the other hand, P. boopis has one pair of tubercles on segments 5, 6 and 7 in the female. and one pair on only segments 6 and 7 in the male.

Otherwise P. erraticus and P. boopis are similar Although both species have been recorded elsewhere from Megaptera nodosa, I have not as yet seen P. erraticus collected from New Zealand.

Short references to the occurrence of P. boopis on whales are made in whaling papers by Lillie (1915) and Matthews (1937, pp. 47, 48).

The maxilliped palp in the young of the genus Paracyamus is easily distinguished under a high power microscope, and the constancy of the size-degeneration ratio makes it an eminently satisfactory characteristic for distinguishing the genus from Cyamus.

The growth stages of the palp (Text-figs.) in P. boopis closely parallel those figured by Chevreux (1913, fig. 62) for P. erraticus. Up to a size of about 3·5 mm. the palp is well developed; above this the maxilliped shows the degeneration characteristic of the genus. This agrees with Chevreux's findings for P. erraticus:

“… ce palpe était encore complètement développé chez les exemplaires de 3 millimètres de longueur. In commence à s'atrophier et ne possède plus que deux articles chez un spécimen long de 4 millimêtres, pour en arriver à être très court et uniarticulé chez les adultes.”

The following list of Cetaceans occurring in New Zealand waters (Oliver, 1922) and their Cyamid parasites as found elsewhere (cf. Barnard, 1932, and Stephensen, 1942) suggests that further examination of these animals will add a number of species of Cyamidae to the New Zealand fauna.