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They also have eyes usually on stalks, a primitive ventral nerve cord and "brain" ganglia near the antennae , a digestive system which is a straight tube for grinding food and a pair of digestive glands. Gills are used for respiration and they have a pair of green glands to excrete wastes found near the base of the antennae. Their bodies are composed of three body segments - the head , the thorax and the abdomen.
In some species the head and thorax are fused together to form a cephalothorax which is covered by a single large carapace. Each or body segment can have a pair of appendages. For example, the Malacostra have a head with 5 segments,a thorax with 8 segments and the abdomen has 6 segments.
On the segments of the head, these include two pairs of sensory antennae, one pair of mandibles for chewing food , and two pairs of maxillae to help the mandibles in positioning the food.
The thorax has legs, which may be specialised for use in walking or feeding. The abdomen has legs usually used for swimming swimmerets and ends in a fan-shaped tail telson. Larva of a crab.
Most Crustaceans are either male or female and reproduce sexually. A small number, including barnacles, are hermaphrodites. In other species, viable eggs are produced by a female without needing to be fertilised by a male. In many decapods, the first one or two pairs of swimmerets are specialised for sperm transfer by the males and the females hold the eggs until they hatch into free-swimming larvae. In many species the fertilised eggs are just released into the water or attached to objects in the water.
Most Crustaceans are motile able to move about independently and can be herbivores, carnivores or detritvores. Some are parasites and live attached to their hosts e. Crayfish Virtual Dissection. Castellucci Navigation. Use the diagram below to locate and identify the organs of the circulatory system.
The heart is dorsally located and has several arteries. The crayfish has an open circulatory system in which the blood flows from arteries into sinuses , or spaces, in tissues. The blood flows over the gills before returning to the heart. Label the heart and color it along with the arteries red.
Use the diagram below to locate and identify the organs of the digestive system. Locate the maxillae that pass the pieces of food into the mouth. The food travels down the short esophagus into the stomach. A digestive gland produces digestive substances to facilitate the absorption of nutrients. The stomach is attached to the intestine which will lead to the anus.
Label the mouth, stomach and intestine. Color the mouth, stomach and intestine yellow. Use the same diagram above to locate and identify the organs of the excretory system.
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