Family MILNESIIDAE Ramazzotti, 1962

Milnesiidae: Milnesium sp., habitus, bucco-pharyngeal apparatus, first leg of female, first leg of male

© Copyright S. Claxton, Camden, NSW

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Introduction

The buccal tube is rigid with stylet supports and stylet sheaths and the pharynx is without apophyses and placoids. Each leg has two claws but the branches of the claws are separate. The main branch of each claw has two accessory points; the secondary branch, attached to a basal part, is short and has two or three branches. An operculate buccal tube and six oral papillae distinguish Milnesium from Limmenius, the only other genus in the family, and found in New Zealand and New England National Park, New South Wales.

Milnesium tardigradum is a large, cosmopolitan species distinguished by its size, its rapid movements and its short, very wide buccal tube. Colour is very variable, ranging from colourless to orange, brown or red particularly in larger specimens. Many specimens have been recovered with rotifers, nematodes or other tardigrades in their mouths and rotifer trophi or tardigrade buccal apparati can often be seen in the intestines of slide-mounted specimens. Males are often found and are generally smaller than females; they have a modified claw on the first pair of legs. Eggs are large and smooth, and up to 20 have been found laid in the exuvium. The species is extremely common in all types of environments and particularly in dry lichens, both in Australia and overseas.

A new species of Milnesium has been recovered from mosses from Tasmania and from New England National Park, New South Wales. This species has a buccal tube about two to three times longer than that of M. tardigradum; it has long, very fine stylets which lie close to the sides of the buccal tube, and in these features, appears to be intermediate between M. tardigradum and Limmenius porcellus. The mouth is terminal as in M. tardigradum but unlike that species the oral cavity is elongate and the front part of the head containing the oral cavity is retractable, forming a protrusible ‘nose’. A number of slide-mounted specimens have rotifer trophi in the intestines indicating that the species is carnivorous.

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