Key to Australian Freshwater and Terrestrial Invertebrates

Phylum Arthropoda
Subphylum Crustacea
Class Malacostraca
Order Anaspidacea

Common names: anaspid shrimps, cave shrimps

Overview

Anaspidacea is a small order of slender, aquatic crustaceans. Anaspids lack a true carapace and their compound eyes (when present) may be sessile or stalked. The first pair thoracic appendages are modified as maxillipeds that are used for feeding. Thoracic limbs (pereopods) 2-8 have the endopod developed into full walking legs. On these appendages are epipods which function as flattened gills and paddle-like exopods that allow for movement in the water. Sometimes the exopods are not present and in cave-dwelling species the abdominal legs (pleopods) are often reduced or absent. In the Anaspididae, the telson and uropods form a tail fan, but in other families, the uropods are elongate and the telson short. Anaspids may be up to 50 mm in length, but are typically less than 10 mm and are usually dull brown.

Distribution and diversity

Anaspids are Gondwanan in distribution, occurring in cool creeks, lakes, swamps and caves. Approximately 70 species from 11 genera in 4 families have been described from southern South America, New Zealand and southern Australia. Around 21 species are known from Australia. The families Psammaspididae and Stygocarididae are restricted to caves and only Stygocarididae occurs outside Australia (in New Zealand and South America), with the greatest diversity in Tasmania and a few locations in southern mainland Australia. Anaspididae are found only in Tasmania and range from being strict stygobionts (only living underground) to species living in lakes, streams and pools. Koonungidae is found in Tasmania and the south-eastern part of the Australian mainland, where they are found in caves or in the burrows made by crayfish (Decapoda).

Life cycle

Little is known about the mating strategies of anaspid shrimps. Eggs are laid on vegetation or in crevices on the surface of other submerged objects such as stones and are not guarded or cared for. They may take 35-60 weeks to hatch. The eggs of some species are also known to enter a phase of dormancy during winter.

Feeding

Little is known about the feeding habits of most anaspid shrimps and they are generally considered to be generalist omnivores, eating organic detritus from the substratum. However, the morphology of the maxillipeds of some anaspids suggests filter feeding and/or raptorial feeding strategies.

Ecology

All anaspids are aquatic, being found in cool creeks, lakes and swamps and there are both epigean and subterranean species. Lake species live in mats of algae growing on the bottom. Smaller species live among sand grains in underground springs. Both Allanaspides and Micraspides are known to inhabit the burrows of freshwater crayfish. The most terrestrial forms (Micraspides) live in the burrows of crayfish (Decapoda) in grassy, waterlogged swamps. Anaspidaceans are not strong swimmers, instead they mostly walk over the substrate. The exopods of the thoracic legs are in nearly constant motion to circulate fresh, oxygen-bearing water past the flattened epipods. When startled, anaspidaceans are capable of jumping upwards. Much of the information about this order comes from the single species Anaspides tasmaniae, a large anaspid from south-eastern Australia. Several members of this order are blind, cave-dwelling species and their biology is not well-known. Four species of Australian anaspidaceans are listed by the World Conservation Union (IUCN) as Vulnerable, or facing a high rate of extinction in the wild, largely due to their restricted distribution and the introduction of trout into the rivers and streams.