|Decapoda (yabbies plus)
| Major Group: Crustacea
Minor Group: Malacostraca
Decapoda literally means “ten legs”. The name indicates the five pairs of pereiopods. Decapoda is a diverse order, containing almost all of the best known, edible and commercially important crustacean species; shrimps (Atyidae), prawns (Palaemonidae), yabbies (Parastacidae), crayfish (Parastacidae) and crabs (Parathelphusidae). Macrobrachium (Palaemonidae) is cultured extensively in Asia. The yabby, Cherax (Parastacidae), is popular in Australian aquaculture. All these decapods quickly mature to an edible size in 2 years. However, the larger crayfish, Euastacus and Astacopsis (Parastacidae), have a harder exoskeleton, are slower growing and therefore more vulnerable to overfishing and habitat degradation. Many Parastacidae species are now protected as their numbers are in serious decline.
| Ecology: Instream habitat: Decapoda species are primarily marine, but also occur in estuarine and fresh surface waters in mountain and desert habitats as well as underground waters. Surface aquatic habitats encompass lentic and lotic waters, permanent and ephemeral waterbodies and areas subject to seasonal torrential flow. Such habitats include; lakes, swamps, lagoons, billabongs and pools; creeks and streams flowing through open grassland and forested areas. Underground aquatic habitats tend to be limestone caves but also include freshwater bores and wells. Decapod crustaceans in surface waters are found in sheltered littoral areas particularly amongst vegetation, in packs of leaf litter, under stones, rocks or under rotting logs and also in interstitial waters. Burrowing species prefer the softer sand and clay substrata whilst other species are found on gravel and rocky substrata.
Feeding ecology: Decapod crustaceans are often the largest invertebrates in a stream and so play an important role in the food chain. Many are opportunistic feeders upon detritus and dead animal matter, some are filter feeders and others are predators upon smaller invertebrates and fish.
Habit: Most Decapoda species crawl along the substratum or burrow into it. Some species such as Paratya australiensis (Atyidae) and Macrobrachium australiense (Palaemonidae) are active swimmers. They swim forwards by pulling with the modified swimming legs or dart backwards by flicking the tail. Burrowing decapods create either short burrows forming a catacomb of holes in soft stream banks, or long narrow and meandering burrows extending twenty to thirty centimetres into the bank. The burrows are connected to open waters or the watertable. If the water body dries out, the burrows are sealed with a mud chimney. Decapoda species may be migratory, gregarious, cryptic, diurnal, nocturnal or noctidiurnal. They maintain their balance when swimming and crawling by means of a sand grain structure called a statolith inside a sensory organ called a statocyst at the base of 1st antennae. When the animal is horizontal the statolith sits squarely on a set of hairs in the base of the statocyst. As the animal moves around so does the statolith, helping the animal to know which way is really up. When decapod crustaceans shed their exoskeleton they loose their statoliths. New ones are gained by either rubbing their antennal bases in the sand while the new exoskeleton is soft or by carefully putting sand grains into the pores with their smaller pincer legs.
Life history: Females of the families Atyidae, Kakaducarididae and Palaemonidae attach eggs to their pleopods. Freshwater species do not have long planktonic juvenile stages as do the marine species. The young start life as smaller versions of the parents with claws and strong legs.
|Information Sources: Short et al. 2013, Davie 2002, Davie 2002a, Gooderham & Tsyrlin 2002, Ingram et al 1997
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