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Zooplankton of Wellington Harbour, New Zealand

Hydrozoa

Hydrozoa

The most abundant medusa throughout the year is that of Obelia geniculata (L.) (Text-fig. 3, D). The hydroids are found in great numbers on the Macrocystis pyrifera colonies at Point Gordon, Kau Point and in Kau Bay. The hydroids start to liberate medusae in April, when small medusae measuring between 1.6mm and 2.5mm in diameter occur abundantly in the plankton. From May through to December both large and small medusae are very abundant. These are very common in January. Few medusae are recorded in February and March, when the majority of these are large and measure over 5mm in diameter (Text-fig. 7).

The medusae of Octophialucium funerarium (Quoy and Gaimard) (Text-fig. 3, E) and of Phialella quadrata (Forbes) (Text-fig 3, F) occur in significant numbers in the plankton. These are readily separated by the presence of eight radial canals in Octophialucium funerarium, and four radial canals in Phialella quadrata. The medusae of Octophialucium funerarium occur rarely in occasional August samples, and this infrequent occurrence continues from September into December. Few medusae are recorded in January, and they are rare in February and March. During the next four months occasional very large medusae were caught below six fathoms, but were absent from the surface samples. Phialella quadrata is both smaller in size and more common, and occurs throughout the year. This medusa is few in number in September, common in October through to December, very common in January, and rare for the remainder of the year (Text-fig. 7).