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Lecture Crustacea Ecdysis Molting animals grow in the intermolt phases, or instars. Soft tissue increases in size until there is no space within the cuticle. When body fills the cuticle, animal is in the premolt phase. Molting occurs often in young animals and may cease in adults. Arthropods Chapter 20 Chelicerata – Arachnids, horseshoe crabs, sea spiders. Myriapoda – Centipedes, millipedes. Crustacea – Crabs, lobsters, shrimp, copepods, ostracods, barnacles, pill bugs, brine shrimp, water fleas, remipedes, ect. Hexapoda – Insects, silverfish, springtails. Chelicerata, unlike insects, have only two body segments instead of three: a fused head and thorax (cephalothorax) and an abdomen Chelicerata species have eight legs (four pairs) whereas insects have six (three pairs). The Chelicerae are pointed appendages to grasp food, and are found in place of the chewing mandibles most other arthropods have. Types of chelicerae: (A) jackknife, (B) scissor, and (C) 3-segmented chelate HORSESHOE crab • Use hemocyanin (protein) to carry oxygen. The copper present in hemocyanin make their blood blue. • Blood contains amebocytes, which play a role similar to white blood cells of vertebrates in defending the organism against pathogens. • Amebocytes from the blood of L. polyphemus are used to make Limulus amebocyte lysate, which is used for the detection of bacterial endotoxins in medical applications. Crustaceans (Lobsters,Crabs, and Shrimp) Just the Facts…. Crustaceans belong to the Phylum Arthropoda (jointed feet). a segmented body that is bilaterally symmetrical All Arthropods have jointed appendages. All Arthropods have an exoskeleton (carapace). • 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. • They also have eyes usually on stalks The Exoskeleton Is made of a tough fibrous material called chitin. This gives the skeleton strength and flexibility. There are several pairs (5 or more) of jointed appendages (movable arms and legs). Subphylum Crustacea Crustaceans, subphylum Crustacea typically have biramous, branched, appendages that are extensively specialized for feeding and locomotion. Crustaceans On the segments of the head, two pairs of sensory antennae, one pair of mandibles (lower jaw for chewing food) two pairs of maxillae (to help the mandibles in positioning the food). Two pairs of maxilliped: pair of appendages for holding prey. 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). Crustaceans are the only arthropods that have two pairs of antennae. They also have a pair of mandibles (jaw-like appendages) and two pairs of maxillae on the head. Muscular System • Extensor muscles extends the tail of the crayfish. • Flexor muscle bends the tail of the crayfish. Crustacea - Muscular System Most muscles arranged as antagonistic groups. Flexors draw a limb toward the body and extensors straighten a limb out. Antagonistic pairs of muscles are muscle where one move the bone in one direction and the other moves it back the other way in transmission of nerve impulses to the muscles. It is impossible to fully stimulate the contraction of two antagonistic muscles at the same time • Encephalon: site of the mental functions of a crayfish. • Digestive gland: glandular organ that produces digestive enzymes. • Ganglion of ventral nerve cord: budge related to a collection of nerves of the abdomen of a crayfish. • Ventral nerve cord: collection of nerves in the abdomen of a crayfish. Crustacea - Respiratory System Smaller crustaceans may exchange gases across thinner areas of cuticle. Larger crustaceans use featherlike gills for gas exchange. 2nd maxilla draws water over gill filaments. Haemolymph, is a fluid, analogous to the blood in higher phyla, that circulates in the interior of the arthropod body remaining in direct contact with the animal's tissues. The open circulatory system is a system in which a fluid in a cavity called the hemocoel bathes the organs directly with oxygen and nutrients and there is no distinction between blood and interstitial fluid; this combined fluid is called hemolymph or haemolymph. Circulatory system • Hemolymph conducted to gills, if present, for oxygen and carbon dioxide exchange. • Hemolymph may be colorless, reddish, or bluish. Hemocyanin (blue) and/or hemoglobin (red) are respiratory pigments. • Hemolymph fills all of the interior hemocoel of the body and surrounds all cells. Hemolymph is composed of water, inorganic salts (mostly Na+, Cl−, K+, Mg2+, and Ca2+), and organic compounds (mostly carbohydrates, proteins, and lipids). The primary oxygen transporter molecule is hemocyanin. • There are free-floating cells, the hemocytes, within the hemolymph. They play a role in the arthropod immune system. Ameboid cells may help prevent clotting. Excretory System Antennal or maxillary glands are called green glands in decapods. End sac of antennal gland has a small vesicle and a spongy labyrinth. Resorption of salts and amino acids occurs as the filtrate passes the excretory tubule and bladder. Mainly regulates the ionic and osmotic composition of body fluids. Crustacea - Excretory System Nitrogenous wastes are excreted across thin areas of cuticle in the gills. Freshwater crustaceans constantly threatened by over-dilution with water. Gills must actively absorb Na+ and Cl-. Marine crustaceans have urine that is isosmotic with blood. Nervous System Pair of supra-esophageal ganglia connects to eyes and two pairs of antennae. Neuron connectives join this brain to the subesophageal ganglion. Supplies nerves to mouth, appendages, esophagus, and antennal glands. Double ventral nerve cord has a pair of ganglia for each somite to control appendages. Eye System Compound eyes are made of many units called ommatidia. Cornea focuses light down the columnar ommatidium. Ommatidium of a krill. Compound eye : Very good at detecting movement (except Copepod) reduces spatial resolution but increases sensitivity to dim light. Dark adaptation in the compound eye of Aleochara bilineata. the electroretinogram (ERG) techniqueuses electrodes to measure electrical activity in the insect eye in response to pulses of light. Reproduction • Most Crustaceans are either male or female and reproduce sexually. A small number, including barnacles, are hermaphrodites (monoecious), but they generally cross fertilize. In other species, viable eggs are produced by a female without needing to be fertilised by a male (Parthenogenesis, Ostracods). • 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. The larvae metamorphose through a number of stages before they become adults. Class Branchiopoda Water fleas produce females parthenogenetically in summer. Males are produced when unfavorable conditions arise overwintering fertilized eggs are produced that are resistant to cold and desiccation. Diversity of Reproduction Most crustaceans brood eggs in brood chambers, in brood sacs attached to the abdomen, or attached to abdominal appendages. Crayfishes develop directly without a larval form. Diversity of Reproduction Most crustaceans have a larva unlike the adult in form, and undergo metamorphosis. - Gulf shrimp Diversity of Reproduction The nauplius is a common larval form with uniramous first antennae, and biramous second antennae and mandibles that all aid in swimming. Appendages and somites are added in a series of molts. Metamorphosis of a barnacle proceeds from a free-swimming nauplius to a cypris larva with a bivalve carapace and finally to a sessile adult with plates. Feeding Habits Same fundamental mouthparts in various crustaceans are adapted to a wide array of feeding habits. Suspension feeders generate water currents in order to feed on plankton, detritus ,and bacteria. Predators consume larvae, worms, crustaceans, snails, and fishes. Scavengers eat dead animal and plant matter. Feeding Habits Crayfishes have a two-part stomach. Gastric mill grinds up food in 1st compartment. http://shapeoflife.org/video/marine-arthropodssuccessful-design