1 / 83

CHAPTER 20

CHAPTER 20. Crustaceans. Overview. Over 67,000 living species Insects and crustacea compose over 80% of all named animal species Probably most abundant animals in the world are members of the copepod genus Calanus Divided into 5 classes

Download Presentation

CHAPTER 20

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. CHAPTER 20 Crustaceans

  2. Overview • Over 67,000 living species • Insects and crustacea compose over 80% of all named animal species • Probably most abundant animals in the world are members of the copepod genus Calanus • Divided into 5 classes • Current molecular phylogenies do not support the monophyly of all classes • Former members of phylum Pentastomida placed in class Maxillopoda, subclass Pentastomida

  3. Overview • Pentastomids • Also called tongue worms • Parasites of vertebrates, living in lungs or nasal cavities • Closely related to fish lice

  4. 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 • Some segments may lack appendages • All appendages, except perhaps first antennae, are biramous

  5. Subphylum Crustacea • Primitive crustaceans may have up to 60 segments; derived crustaceans have fewer • Tagmata are usually head, thorax, and abdomen • Not homologous across taxa • In most one or more thoracic segments are fused with the head as a cephalothorax • Arrangement of tagmata in Malacostraca is the ancestral plan • Head has 5 fused somites • Thorax has 8 • Abdomen has 6

  6. Subphylum Crustacea • Anterior end is a non-segmented rostrum • Telson, with the last abdominal somite and uropods, forms a tail • Dorsal covering is the carapace • May cover most of body or just cephalothorax

  7. Subphylum Crustacea Form and Function • External Features • Secreted cuticle is made of chitin, protein, and calcareous material • Heavy plates have more calcareous deposits • Joints are soft and thin, allowing flexibility • Dorsal tergum and ventral sternum are plates on each somite lacking a carapace • Telson is not a somite • Bears anus and may be homologous to the pygidium • In some species, telson may bear a pair of processes, the caudal furca • Gonopores may be at base of appendages, at the tail, or on somites without legs

  8. Subphylum Crustacea • Appendages • Members of Malacostraca and Remipedia have appendages on each somite • Other classes may not bear appendages on abdominal somites • Specialization of appendages based on the basic biramous plan • Maxilliped has a basal protopod, a lateral exopod, and a medial endopod • Endites are medial processes, exites are lateral processes and epipod is an exite on the protopod • Appendages represent serial homology • Have evolved a wide variety of walking legs, mouthparts, swimmerets, etc. from modification of the basic biramous appendage

  9. Subphylum Crustacea • Internal Features • Muscular and nervous systems and segmentation exhibit metamerism of annelid-like ancestors • Hemocoel • Persistent blastocoel that becomes filled with blood • Coelomic compartments remain as end sacs of excretory organs and gonads • Coelomates only in technical sense of the term

  10. 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 • Strong muscles located on each side of stomach control the mandibles

  11. Subphylum Crustacea • Respiratory System • Smaller crustaceans may exchange gases across thinner areas of cuticle • Larger crustaceans use featherlike gills for gas exchange • Decapod carapace overlaps the gill cavity, leaving anterior and posterior openings • “Bailer” of 2nd maxilla draws water over gill filaments • Gills may project from pleural wall, the articulation of thoracic legs, or thoracic coxae

  12. Subphylum Crustacea • Circulatory • 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 of hemolymph • Hemolymph conducted to gills, if present, for oxygen and carbon dioxide exchange • Hemolymph may be colorless, reddish, or bluish • Contains ameboid cells that may help prevent clotting • Hemocyanin and/or hemoglobin are respiratory pigments

  13. Subphylum Crustacea • Excretory System • Antennal or maxillary glands • Called green glands in decapods • End sac of antennal 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 • 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

  14. Subphylum Crustacea • Nitrogenous wastes 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

  15. Subphylum Crustacea • Nervous and Sensory Systems • More fused ganglia than in other arthropods • 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 • Eyes and statocysts are largest sensory organs • 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

  16. Subphylum Crustacea • Statocyst opens at base of first antenna in crayfish • Statocyst lined with sensory hairs that detect position of grains of sand • Compound eyes, made of many units called ommatidia • Cornea focuses light down the columnar ommatidium • Distal retinal, proximal retinal, and reflecting pigment cells form a sleeve around each ommatidium • Each ommatidium detects a restricted area of objects, a mosaic, in bright light • In dim light, the distal and proximal pigments separate and produce a continuous image

  17. Subphylum Crustacea • Reproduction, Life Cycles, and Endocrine Function • Diversity of Reproduction • Barnacles are monoecious but generally cross-fertilize • In some ostracods, males are scarce and reproduction is by parthenogenesis • 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

  18. Subphylum Crustacea • Most crustaceans have a larva unlike the adult in form, and undergo metamorphosis • 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 larva with a bivalve carapace and finally to a sessile adult with plates

  19. Subphylum Crustacea • Ecdysis • 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 is made of a very thin lipid-impregnated protein • Most of the cuticle is composed of several layers of the procuticle • Exocuticle, beneath the epicuticle, contains protein, calcium salts, and chitin

  20. Subphylum Crustacea • Endocuticle has a heavily calcified principal layer and an uncalcified membranous layer • 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 • Epidermal cells enlarge before ecdysis

  21. Subphylum Crustacea • Secrete a new epicuticle and then begin secreting a new exocuticle • Enzymes released into the area above new epicuticle dissolve the old endocuticle • When only the old exocuticle and epicuticle remain, the animal swallows water to expand and burst the old cuticle • Soft new cuticle stretches and then hardens with the deposition of inorganic salts • Molting occurs often in young animals and may cease in adults

  22. Subphylum Crustacea • Hormonal Control of Ecdysis • Temperature, day length, or other stimuli trigger central nervous system to begin ecdysis • Central nervous system decreases production of molt-inhibiting hormone by the X-organ • Promotes release of molting hormone from the Y-organs which promotes ecdysis

  23. Subphylum Crustacea • Other Endocrine Functions • Removing eyestalks accelerates molting and prevents color changes to match background • Hormones from neurosecretory cells in eyestalk control dispersal of cell pigment • Neurosecretions from pericardial organs stimulate increase in heartbeat • Androgenic glands in male amphipods stimulate expression of male characteristics

  24. Subphylum Crustacea • Feeding Habits • Same fundamental mouthparts 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 • Crayfishes have a two-part stomach • Gastric mill grinds up food in 1st compartment

  25. Brief Survey of Crustaceans Class Remipedia • Only 10 described species • All found in caves connected to the sea • Primitive features include 25–38 segments with similar, paired, biramous, swimming appendages • Antennules also biramous • Maxillae and maxillipeds are prehensile and specialized for feeding • Swimming legs are directed laterally rather than ventrally as is found in copepods and cephalocarids

  26. Brief Survey of Crustaceans Class Cephalocarida • Only 9 species described • Live in coastal bottom sediments from intertidal zones to 300 meters depth • Thoracic limbs and 2nd maxillae are very similar • Lack eyes, a carapace, and abdominal appendages • True hermaphrodites and unique in discharging eggs and sperm through same duct

  27. Brief Survey of Crustaceans Class Branchiopoda • Over 10,000 species, 4 orders • Order Anostraca, includes fairy shrimp and brine shrimp • Lack a carapace • Order Notostraca, includes tadpole shrimp • Carapace forms a large dorsal shield • Order Conchostraca, includes clam shrimp • Enclosed by a bivalved carapace • Order Cladocera, includes water fleas • Carapace encloses the body but not the head

  28. Brief Survey of Crustaceans • In all flattened, leaf-like legs serve as respiratory organs, assist in suspension feeding, and, (except for cladocerans), 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

  29. Brief Survey of Crustaceans • Fertilized eggs highly resistant to cold • Critical for winter survival of population • Cladocerans: Development mostly direct • Other branchiopods: Gradual metamorphosis

  30. Brief Survey of Crustaceans Class Ostracoda • 6,000 known species • Most are dioecious • Enclosed in a bivalve carapace • 0.25–8.0 mm long • Fusion of trunk somites • Thoracic appendages are reduced to two or one • Most are benthic or climb onto plants, but some are planktonic, parasitic, or burrowing • Widespread in both marine and freshwater habitats • Development by gradual metamorphosis

  31. Brief Survey of Crustaceans Class Maxillopoda • General body plan • Five cephalic, six thoracic and four abdominal somites plus a telson • No appendages on abdomen • When present, the eye is unique in structure and called a maxillopodan eye

  32. Brief Survey of Crustaceans Subclass Mystacocarida • Less than 0.5 mm long • Live in interstitial water between sand grains • 10 species have been described from around the world • Primitive in several characteristics

More Related