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Crustaceans. Crustaceans: INTRODUCTION:. All arthropods are classified by the number of body segments they have and the structure of their appendages. There are approximately 25,000 species of crustaceans.
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Crustaceans: INTRODUCTION: • All arthropods are classified by the number of body segments they have and the structure of their appendages. • There are approximately 25,000 species of crustaceans. • This group includes crayfish, lobsters, water fleas, barnacles (all aquatic), and pill bugs ( terrestrial).
Crustaceans are very diverse, some are as small as a comma, and inhabit the upper layers of the water column. These are very important group. They make up the zooplankton and are the link between the photosynthetic phytoplankton in aquatic environment.
Migration: • When fall arrives the Atlantic waters off Florida gets cold. Spiny lobsters migrate toward warmer waters. As many as 100,000 lobsters travel day and night in chains of 50-60. They move in single file using their antennae to keep in contact with each other.
Crayfish: • These animals are similar to lobsters in both internal and external anatomy. • The body of crustaceans are covered with a secreted cuticle composed of chitin and proteins.
This animal has a body that is divided into two sections--- the cephalothorax and abdomen. • The cephalothorax consists of the fused head and thorax.
There are 13 segments covered by hard CARAPACE. This includes 5 fused segments (somites) of the head and eight somites of the thorax.
This carapace covers much if not all of the cephalothorax. • The abdomen is divided into 7 segments. • There is a nonsegmented ROSTRUM at the anterior end of the animal. Theseventh segment , called the TELSON, forms a flat triangularsection at the tail of the animals.
The opening of the gonadal pores are specific for each species. • In most crayfish they are on the median base of the fifth pair of walking legs. The oviducts are at the base of the third pair of walking legs.
APPENDAGES: • Crayfish have a pair of jointed appendages on each somite. • Each of the appendages are specialized and exhibit a biramous plan (two divisions).
There is a basal portion referred to as the PROTOPOD, and a lateral EXOPOD and a medial ENDOPOD. • The protopod is made up of two joints ( basis and coxa) and theexopod and endopod form one to several segments each. • The walking legs demonstrate UNIRAMOUS plan.
Internal Features : • Body Cavity: • The major body space in the arthropods is a blood filled coelum called a HEMOCOEL.
Muscular System: • Striated muscles make up a considerable part of the body of most Crustacean. • The muscles are usually arranged in groups. • FLEXORS which draw an appendage toward the body • and EXTENSORS which straighten the body part out.
The abdomen has powerful flexors, which are used when the animal swims backward. • Muscles on each side of the stomach controls the mandibles.
DIGESTION & EXCRETORY SYSTEMS • Crayfish trap food with their CHELIPEDS, and tear it with MAXILLAE & MAXILLIPEDS. • The Crayfish then chews with the mandibles.
The food passes through the esophagus to the stomach where teeth made of chitin grind it into fine paste that is mixed with digestive juices. • Digestive glands absorb the mixture and undigested particles pass through the intestines to the anus.
Excretion: Crayfish have an excretory organ called the GREEN GLAND. • This gland removes wastes from the blood while retaining the saltwhich is scarce in fresh water. This gland helps the crayfish control the amount of water entering the body.
RESPIRATORY SYSTEM: • Small crustaceans absorb oxygen over the thinner areas of the cuticle. • In larger crustaceans gills are used. • These organs are featherlike projections with very thin cuticle.
RESPIRATORY SYSTEM: • The gills are attached to each of the walking appendages in crayfish. As the crayfish walks, water moves across the gills where gas exchange takes place.
Nervous System: • The crayfish nervous system includes • a BRAIN, and VENTRAL NERVE CORD. • The brain is a pair of ganglia that supplies nerves to the eyes and antennae. • The nerve cord is divided to form two cords that have a pair of ganglia at each somite and gives off nerve cords to the appendages and muscles.
There is also a sympathetic nervous system associated with the digestive tract. • Sensory system consists of eyes, statocysts, and tactile organs. • The tactile organs are distributed over the body in the form of TACTILE HAIRS.
The statocysts are associated with the antenna of the crayfish. • The statocysts are pores that have sensory hairs associated with grains of sand. • When the animal changes its position the grains of sand shift and relay a stimulus to the brain through the sensory hairs.
The eyes are compound and made up of many photoreceptors called OMMATIDIA. • The eyes are set on short moveable stalks with 2000 light sensitive lenses.
REPRODUCTION: • Most crustaceans have separate sexes. DIOECIOUS- (Two Houses) Exception: • Barnacles on the other hand are MONOECIOUS (hermaphrodite).
Crayfish mate in thefall. The males use their first and second swimmerets to transfer sperm to the seminal receptacle of the female. • The sperm remains in the female until spring when it fertilizes the eggs as she lays them.
The female carries the sperm from fall to spring of the year. After the female lays the eggs they hatch after about six weeks . Eggs→
Cleaner Shrimp
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Gulf Shrimp reproduction: Shrimp found in the Gulf of Mexico go through several developmental stages. The eggs are laid in brackish water. The eggs hatch into larval stage called NAUPLIUS.
These young make up the zooplankton fauna. The young shrimp undergo three more developmental changes before reaching the adult shrimp stage.
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