Family OREELLIDAE Puglia, 1959

Oreellidae: Oreella sp. female, habitus ventral

© Copyright Dr S. Claxton, Camden, NSW

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Introduction

Oreellids are unplated, terrestrial Echiniscoidea with eight indistinct body segmental folds and a short median caudal projection. They exhibit some plesiomorphic features found otherwise only in the marine Arthrotardigrada and not in the terrestrial Echiniscoidea. These include a telescopic leg and the presence of two lateral seminal receptacles consisting of invaginations of the cuticle which open directly to the exterior without a duct on each side of the female gonopore. The primary clava and cirrus A are located more anteriorly than in Echiniscidae and in some species (Oreella mollis) the two structures share a common base. The primary and secondary clavae are papillar or club-shaped and the primary clava is longer in males than in females. Paired internal and external cephalic cirri are present and are similar to those found in the Echiniscidae. Sense organs are present on the first and fourth pair of legs. Larvae have only two claws per leg and lack gonopore and anus; juveniles have four claws and an anus, and adults have four claws, anus and gonopore as in the Echiniscidae. Unlike other heterotardigrades, oreellids lay free eggs which bear processes which are remarkably similar to those of some species of the eutardigrade genus Minibiotus.

The family consists only of the genus Oreella Murray, 1910; the type locality is the Blue Mountains, Australia. Four species are known from Australia, South America, New Zealand, South Africa and Antarctica (with a single questionable citation from Germany). No type material has survived and efforts to recollect the species in the Blue Mountains have not been successful. However, a species of Oreella has been recovered from mosses at Cambewarra Mountain and New England National Park, New South Wales and from Tasmania (Claxton unpubl. data). This species has characteristics of the type species, O. mollis (secondary clavae reduced to hemispherical papillae, slender primary clava in both males and females, primary clava and cirrus A arising from common base) as well as O. minor (spurs on the internal claws, dimensions of cirri and clavae). In the original description of the latter species, Ramazzotti stated that the secondary clava was so difficult to see that he did not describe its morphology. This structure is also very difficult to see in Australian specimens appearing to be papillate but covered by a thin layer of cuticle which prevents it from rising above the line of the head. This species has been designated as O. cf. mollis until material can be recollected at the type locality. The two Australian species, O. cf. mollis and Oreella sp. nov., have the same indistinct secondary clava but the latter species does not have papillae covering the body. The bucco-pharyngeal apparatus in both species has calcium carbonate encrusted stylets, stylet supports and placoids. In both species, the females have short ovoid primary clavae while those of males are long and slender (as recorded for O. minor by Ramazzotti 1964).

Oreella has been collected in all Southern Hemisphere countries and appears to be rare on all continents, except in rainforest or other high rainfall habitats (Binda & Kristensen 1986). In Australia, it has been found in rainforest remnants in New South Wales and in Tasmania.

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