Shield shrimps, tadpole shrimps

Code OE019999

Crustacean order Notostraca. The order Notostraca comprises a single extant family, Triopsidae, with two Australian species, Triops australiensis and Lepidurus apus. The Notostraca are placed with the orders Conchostraca, Anostraca and Cladocera in class Branchiopoda.

Notostraca are distinguished by a broad, shield-like carapace which, although attached only at the head, covers the head, thorax and much of the abdomen. The compound eyes are on the anterior carapace. The antennules are single-branched and unsegmented. The second antennae become reduced during development and are small or vestigial in adults. The body posterior to the head is relatively undifferentiated, composed of very many ring-like segments. The first 11 of these comprise the thorax, a variable number comprise the abdomen. Thoracic and anterior abdominal segments carry branched appendages with plate-like gills. Posterior abdominal segments are without appendages. The final segment bears a pair of long, multisegmented caudal filaments.

The two species are readily distinguishable. L. apus has a prominent supra-anal plate. T. australiensis has no plate.

Triopsidaeoccur in water bodies ranging from permanent farm dams, ditches etc., to very impermanent rain-filled pools. Salinities vary from oligotrophic to modestly saline. T. australiensis is distributed throughout a wide area of inland Australia, L. apus has a broad distribution through the south-east and south-west. The distributions overlap in northern Victoria and much of NSW.

Reference:

Williams, W.D. (1980) Australian Freshwater Life: The Invertebrates of Australian Inland Waters. The Macmillan Company of Australia, Melbourne.