Class BRANCHIOPODA Latreille, 1817

Notostraca

Museums

Museum list

Regional Maps

Class BRANCHIOPODA Latreille, 1817

Compiler and date details

June 2012-January 2013 - ABRS

31 December 2010 - updated by Gary C. B. Poore

6 May 2006 - Brian V. Timms

Introduction

Branchiopod crustaceans exhibit considerable morphological diversity, so that it is difficult to cite defining characteristics. Most are small, freshwater animals with numerous, similar, flat and leaf-like (phyllopodous) limbs; most have numerous body somites, though many exhibit fusion of these and tagmatization. Generally, there is a head with two pairs of antennae, paired eyes, various mouthparts, and then a thorax with numerous phyllopodous limbs, followed by an abdomen often limbless. Many forms have a carapace, often bivalved.

For convenience branchipods are often divided into the large and small branchiopods. The large ones include the fairy shrimps (Anostraca), the clam shrimps (once called the Conchostraca, but now recognised as three suborders and five families in the Diplostraca) and the shield or tadpole shrimps (Notostraca). The small branchipods, the cladocerans, comprise a fourth suborder of the Diplostraca. This is the widely accepted classification of Martin and Davis (2001), but many other classifications exist (e.g. Fryer 1987; Dumont & Negrea 2002). Most studies (op. cit.; Braband et al. 2002; Weekers et al. 2002) point to a monophyletic origin for the Branchiopoda, despite their diversity and the various classification schemes. Stenderup et al. (2006) offered a molecular phylogeny.

Almost all large branchiopods inhabit temporary pools of fresh water, though a few live in inland saline waters, particular in Australia. Among the Anostraca, the endemic genus Parartemia lives in waters just as saline as those occupied by the famous brine shrimp Artemia; moreover, Parartemia speciated within Australia far more than Artemia has across the world. The other dominant genus, Branchinella, mainly inhabits fresh waters but has a few representatives in saline waters. The only clam shrimp to penetrate saline waters is found in Australia (Eocyzicus parooensis Richter & Timms, 2005). The shield shrimp Triops is often found in saline waters in Western Australia (see Timms et al., in press). In a sense these are special cases, for branchipods generally live in a vast array of temporary fresh waters, including particularly claypans, seasonal swamps of various kinds (e.g. blackbox swamps), temporary lakes, clear water pools (e.g. gilgai), and rock pools (gnammas).

All branchiopods produce cysts (embryos in an arrested state of development and enclosed in tough case) which are resistant to desiccation and hence are an important survival mechanism in temporary waters. Ornamentation on these cysts tends to be species specific (Timms et al. 2004, on Australian anostracans), but is not always (Dumont et al. 2002). Dispersal tends to be by passive movement of cysts, either by wind or with waterbirds.

Diversity of large branchiopods in Australia is low at the family and generic level, with only five genera of anostracans, seven of clam shrimps, and two notostracans (Brendonck et al. 2008). However, two of the fairy shrimp genera (Parartemia and Branchinella) have radiated so that species richness is high at about 50 species of anostracans, with more being described almost every year. There are about 26 species of clam shrimp and two of shield shrimps, though both of these figures are likely to change with further study.

Timms (2006) examined the large branchiopods of gnammas (rock holes) in Australia, finding the highest species diversity in Western Australia.