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CHAPTER 20 Crustaceans 20-1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sally Lightfoot Crab, from the Galapagos 20-2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Overview Over 67,000 living species Insects and crustacea compose over 80% of all named animal species Divided into 5 classes We will study 3 classes, Branchiopoda and Malacostraca, Maxillopoda Branchiopoda = water fleas, brine shrimp Malacostaca = isopods, krill, crab, lobster, etc. Maxillopoda = barnacles 20-3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea General Nature of a Crustacean Main distinguishing characteristic of crustaceans Two pairs of antennae Head also has a pair of mandibles and 2 pairs of maxillae One pair of appendages on each of the additional segments 20-5 Some segments may lack appendages All appendages, except perhaps first antennae, are biramous Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Tagmata (segments) are usually head, thorax, and abdomen In most one or more thoracic segments are fused with the head as a cephalothorax Arrangement of tagmata in Malacostraca is the ancestral plan 20-6 Head has 5 fused somites Thorax has 8 Abdomen has 6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Anterior end is a non-segmented rostrum (covers eyes in some) Telson, with the last abdominal somite and uropods, forms a tail Dorsal covering is the carapace 20-8 May cover most of body or just cephalothorax Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Form and Function External Features Secreted cuticle is made of chitin, protein, and calcareous material Heavy plates have more calcareous deposits Telson is not a somite 20-9 Joints are soft and thin, allowing flexibility Bears anus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Appendages Most have appendages on each somite Appendages represent homology 20-11 Have evolved a wide variety of walking legs, mouthparts, swimmerets, etc. from modification of the basic biramous appendage Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Appendages of crayfish: 3 main parts to each appendage Protopod = brown Endopod = blue Exopod = yellow 20-12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Crawyfish Appendage and Function (Number if pairs) Appendage Function # of pairs Antenna Touch, taste, equilibrium 2 Mandible Crushing food 1 Maxilla Handling food, drawing water currents to gills 2 Maxilliped Touch, taste, handling food 3 Walking legs Offense, Defense, walking (cheliped is 1st, with pincer) 5 Swimmeret Transfer sperm, create water currents, carrying eggs and young 5 Uropod Swimming, egg protection in females 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Internal Features Coelomates - reduced Persistent blastocoel that becomes filled with blood Hemocoel Protostomes (mouth first) Complete Gut 20-15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Muscular System Striated muscles Make up a major portion of crustacean body Most muscles arranged as antagonistic groups Flexors draw a limb toward the body and extensors straighten a limb out Abdominal flexors of a crayfish allow it to swim backward 20-16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Green Gland = Kidney Internal Anatomy of the crayfish. 20-17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Respiratory System Smaller crustaceans may exchange gases across thinner areas of cuticle Larger crustaceans use featherlike gills for gas exchange Circulatory 20-18 Open circulatory system No system of veins to separate blood from interstitial fluid Hemolymph exits heart through arteries Passes to hemocoel to return to the heart via sinuses Dorsal heart Single-chambered sac of striated muscle Valves in the arteries prevent backflow Hemolymph conducted to gills, if present, for oxygen and carbon dioxide exchange Hemocyanin and/or hemoglobin are respiratory pigments Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hemolymph travel: Heart, Body, Sinus, Gills, Heart via Ostium (opening) 20-19 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Excretory System 20-20 Antennal or maxillary glands Called “green glands” End sac of green gland has a small vesicle and a spongy labyrinth Labyrinth connects by an excretory tubule to dorsal bladder that opens to exterior pore Hydrostatic pressure within a hemocoel provides a force for filtration of fluid into the end sac Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Nervous and Sensory Systems 20-22 More fused ganglia than in other arthropods Pair of ganglia connects to eyes and two pairs of antennae Nerves join this brain to the mouth, appendages, esophagus, and antennal glands Ventral nerve cord has a pair of ganglia for each somite to control appendages Tactile hairs occur on the body, especially on chelae, mouthparts and telson Chemical sensing of taste and smell occurs in hairs on antennae and mouth Compound eye migrates pigments for day or night vision Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Compound eyes work differently during day and night. Pigment cells will expand or constrict to allow different amounts of light to hit the photoreceptor cells 20-23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Reproduction, Life Cycles, and Endocrine Function 20-24 Diversity of Reproduction Most crustaceans group eggs in brood chambers, in brood sacs attached to the abdomen, or attached to abdominal appendages Crayfishes develop directly without a larval form Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Most crustaceans have a larva unlike the adult in form, and undergo metamorphosis The nauplius is a common larval form Appendages and somites are added in a series of molts Metamorphosis of a barnacle proceeds from a free-swimming nauplius to a larva with a bivalve carapace and finally to a sessile adult with plates 20-25 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Life cycle of a Gulf Shrimp Metamorphosis 20-26 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Ecdysis 20-27 Necessary for a crustacean to increase in size the Exoskeleton does not grow Physiology of molting affects reproduction, behavior, and many metabolic processes Underlying epidermis secretes cuticle Outermost epicuticle and 2 layer procuticle dissolve and are discarded. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pre-molt Stage: Protocuticle sperates from epidermis. Epidermis secretes new epicuticle. Pre-molt Continued: Molting fluid dissolves endocuticle, and Solutions are rebsorbed. New exocuticle develops Ecdysis Stage: Old epicuticle and exocuticle are discarded. Post-ecdysis: New cuticle is stretched and hardens. Endocuticle is secreted. 20-28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lobster Molt A. Membrane between carapace and abdomen ruptures (2 hours) B. Head Thorax and Abdomen withdraw (15 minutes) C. Lobster continues rapid absorption of water to increase length by 20% and weight by 50%. Tissue water will be replaced by protein later. (weeks) 20-29 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Hormonal Control of Ecdysis 20-30 Temperature, day length, or other stimuli trigger central nervous system to begin ecdysis Central nervous system decreases production of molt-inhibiting hormone by the medulla region of the brain Promotes release of molting hormone from the glands near mandible which promotes ecdysis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea 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 Crayfishes have a two-part stomach 20-31 Gastric mill grinds up food in 1st compartment Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Diplopoda have a 2 part stomach: Cardiac and Pyloric Contain teeth for mastication and setae for straining 20-32 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Class Branchiopoda Over 10,000 species, 4 orders Order Anostraca, includes fairy shrimp and brine shrimp Order Cladocera, includes water fleas (daphnia) 20-33 Lack a carapace Carapace encloses the body but not the head Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-34 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans In all, legs serve as respiratory organs, assist in suspension feeding, and locomotion Most are freshwater Important component of freshwater zooplankton May reproduce by parthenogenesis to rapidly boost summer populations and then by sexual reproduction with the onset of unfavorable conditions Fertilized eggs highly resistant to cold 20-35 Critical for winter survival of population Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Class Maxillopoda General body plan No appendages on abdomen Subclass Cirripedia - barnacles 20-36 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Subclass Cirripedia Includes barnacles and three orders of burrowing or parasitic forms Adults are sessile and attach directly (acorn barnacles) or by a stalk (goose barnacles) Carapace surrounds body and secretes a set of calcareous plates Head is reduced, abdomen is absent Jointed feeding legs bear setae and extend from the plates to feed on small particles 20-37 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A. Acorn Barnacle 20-38 B. Gooseneck Barnacle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Barnacles on healthy grey whale Contains commensalistic barnacles And parasitic amphipods (arrows) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Life cycle of parasitic barnacle. Enters crab, root-like processes grow throughout body. Reproductive structure develops externally. 20-40 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Class Malacostraca Largest and most diverse class of Crustacea with over 20,000 species Contains three subclasses, 14 orders, and many suborders Order Isopoda Only truly terrestrial crustaceans Also have marine and freshwater forms Dorsoventrally flattened, lack a carapace, and have sessile compound eyes Common land forms include sow bugs and pill bugs Some isopods are highly modified as parasites of fishes or crustaceans 20-41 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A. Pill Bugs B. Freshwater Sow bug - aquatic isopod 20-42 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Isopod Parasite 20-43 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Order Euphausiacea Approximately 90 species Includes important ocean plankton called krill 20-44 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Order Decapoda 5 pairs of walking legs In crabs, first pair of walking legs form pincers (Chelipeds) Approximately 18,000 species Includes crayfishes, lobsters, crabs, and true shrimp (size of cephalothorax and abdomen vary) 20-45 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A. Tropical Rock Crab B. Hermit Crab C. Male Fiddler Crab D. Red Night Shrimp E. Spiny Lobster 20-46 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sponge Crab - masks itself with materials from environment, sponge 20-47