Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
CHAPTER 20 Crustaceans 20-1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Probably most abundant animals in the world are members of the copepod genus Calanus Divided into 5 classes 20-3 Current molecular phylogenies do not support the monophyly of all classes Former members of phylum Pentastomida placed in class Maxillopoda, subclass Pentastomida 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. Overview Pentastomids 20-5 Also called tongue worms Parasites of vertebrates, living in lungs or nasal cavities Closely related to fish lice 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 20-6 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 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 20-7 Head has 5 fused somites Thorax has 8 Abdomen has 6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 20-9 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 Dorsal tergum and ventral sternum are plates on each somite lacking a carapace Telson is not a somite 20-10 Joints are soft and thin, allowing flexibility 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 20-12 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. 20-13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Internal Features 20-16 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Muscular System 20-17 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Respiratory System 20-19 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Circulatory Open circulatory system Dorsal heart 20-21 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 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 Contains ameboid cells that may help prevent clotting Hemocyanin and/or hemoglobin are respiratory pigments Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Excretory System 20-22 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea 20-24 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 ClMarine crustaceans have urine that is isosmotic with blood Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 20-25 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea 20-26 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-27 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Reproduction, Life Cycles, and Endocrine Function 20-28 Diversity of Reproduction Barnacles are monoecious but generally crossfertilize 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 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 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 20-29 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-30 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Ecdysis 20-31 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 lipidimpregnated protein Most of the cuticle is composed of several layers of the procuticle Exocuticle, beneath the epicuticle, contains protein, calcium salts, and chitin Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-32 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea 20-33 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea 20-34 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-35 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Hormonal Control of Ecdysis 20-36 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Subphylum Crustacea Other Endocrine Functions 20-37 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 20-38 Gastric mill grinds up food in 1st compartment Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-39 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 20-40 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-41 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 20-42 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 Notostraca, includes tadpole shrimp Enclosed by a bivalved carapace Order Cladocera, includes water fleas 20-43 Carapace forms a large dorsal shield Order Conchostraca, includes clam shrimp Lack a carapace Carapace encloses the body but not the head Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-44 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 20-45 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Fertilized eggs highly resistant to cold Critical for winter survival of population Cladocerans: Development mostly direct Other branchiopods: Gradual metamorphosis 20-46 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 20-47 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-48 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 20-49 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 20-50 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Subclass Copepoda Third in numbers of species Lack a carapace and retain simple, median, nauplius eye in the adult Single pair of uniramous maxillipeds and four pairs of flattened, biramous, thoracic swimming appendages A major articulation separates the posterior from the anterior, appendage-bearing portion of the body Antennules often longer than other appendages 20-51 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Parasitic forms highly modified and reduced Often unrecognizable as arthropods Free-living copepods may be the dominant consumer Marine copepod Calanus is most abundant organism in zooplankton by biomass Cyclops and Diaptomus important elements of freshwater plankton Some free-living copepods are intermediate hosts of human parasitic tapeworms and nematodes 20-52 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Development is indirect Some highly modified parasites have unusual metamorphoses 20-53 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Subclass Tantulocarida Only recently described Approximately 12 species Tiny copepod-like ectoparasites of deep-sea benthic crustaceans No head appendages beyond one pair of antennae in sexual females Likely alternate between a parthenogenetic cycle and a bisexual cycle with fertilization Tantalus larvae penetrate cuticle of host by mouth tube Abdomen and all thoracic limbs are lost during metamorphosis to an adult 20-54 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-55 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Subclass Branchiura Lack gills Most are ectoparasites of marine and freshwater fish 5–10 mm long Broad, shield-like carapace, compound eyes, four biramous thoracic swimming appendages, and a short unsegmented abdomen Second maxillae are modified as suction cups to attach to host fish Development is direct 20-56 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-57 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Subclass Pentastomida Tongue worms Consist of about 90 species of parasites of vertebrate respiratory systems Most infect reptile lungs, a few infect air sacs of birds or mammals More common in tropical regions extending out to North America, Europe, and Australia Range from 1 to 13 cm in length Chitinous cuticle regularly molted 20-58 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-59 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Five protuberances on the anterior end provide the phylum name Four of the protuberances bear claws Fifth contains the mouth and two pairs of hooks Simple straight digestive system Nervous system has paired ganglia along the ventral nerve cord Lack any circulatory, excretory, or respiratory organs Sexes are separate 20-60 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Females larger than males Larvae hatch out as oval, tailed creatures with four stumpy legs Most life cycles require an intermediate vertebrate host, usually a fish or reptile After ingestion by an intermediate host Produces millions of eggs that pass up the host trachea, are swallowed and leave host with feces Larva penetrates intestine and migrates until it changes to a nymph Nymph becomes encapsulated and remains dormant until eaten When eaten, juvenile migrates to lung, feeds on blood and tissue, and matures 20-61 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-62 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Subclass Cirripedia Includes barnacles in order Thoracica 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, and thoracic legs are long with hairlike setae Jointed cirri bear setae and extend from the plates to feed on small particles In barnacles in intertidal zones, plates close to protect against dessication 20-63 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-64 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Most non-parasitic barnacles are hermaphroditic and undergo metamorphosis during development 20-65 Most hatch as nauplii and become cyprid larvae with a bivalve carapace and compound eyes Attach to substrate by first antennae and adhesive glands Secrete calcareous plates, lose eyes, and transformation of swimming appendages to filtering cirri Parasitic forms may have a kentrogon stage that injects cells into the hemocoel of host Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-66 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 20-67 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans 1st pair of thoracic limbs are maxillipeds Remaining thoracic limbs lack exopods Abdominal appendages bear gills, except for uropods Common land forms include sow bugs and pill bugs Cuticle lacks protection of insect cuticle Must live in moist habitats Some isopods are highly modified as parasites of fishes or crustaceans Development typically direct but may be metamorphic in parasitic forms 20-68 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-69 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-70 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Order Amphipoda Amphipods resemble isopods Lack a carapace, have sessile compound eyes, and one pair of maxillipeds However, they are compressed laterally, and gills are in the thoracic region Abdominal and thoracic limbs are grouped for jumping and swimming Many are marine, others are beach-dwelling, freshwater, or parasitic Development is direct 20-71 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-72 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-73 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 Carapace does not completely enclose gills Lack maxillipeds and all limbs have exopods Most are bioluminescent with a lightproducing organ called a photophore Form a major component of the diet of baleen whales and of many fishes Eggs hatch as nauplii Development is direct 20-74 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-75 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brief Survey of Crustaceans Order Decapoda 5 pairs of walking legs and 3 pairs of maxillipeds In crabs, first pair of walking legs form pincers Range from a few millimeters to the Japanese crab with a 4 m leg-span Approximately 18,000 species Includes crayfishes, lobsters, crabs, and true shrimp Crabs have a broader cephalothorax and reduced abdomen, compared to crayfish or lobsters 20-76 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-77 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-78 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylogeny and Adaptive Diversification Phylogeny Remipedia appear to be the most primitive of Crustacea Fossils of an arthropod in the Mississippian are likely the sister group to remipedians One theory is that each modern somite represents two ancestral somites that fused together, forming the biramous appendage The pentastomids were placed in Ecdysozoa because of the similarities in larvae, molting of the cuticle, and sperm morphology Phylogenies based on rRNA genes and affirmed in sequences of mitochondrial DNA indicate that pentastomids are crustaceans 20-79 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylogeny and Adaptive Diversification Adaptive Diversification Crustaceans are unquestionably the dominant arthropod in marine environments They also share dominance in freshwater environments with the insects The class Malacostraca is most diverse and members of Copepoda are most abundant Copepods are particularly successful as parasites of both vertebrates and invertebrates 20-80 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylogeny and Adaptive Diversification Classification Class Remipedia Class Cephalocarida Class Branchiopoda Order Anostraca Order Notostraca Order Cladocera Order Conchostraca 20-81 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylogeny and Adaptive Diversification Class Ostracoda Subclass Maxillopoda Subclass Mystacocarida Subclass Copepoda Subclass Tantulocarida Subclass Branchiura Subclass Pentastomida Subclass Cirripedia 20-82 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylogeny and Adaptive Diversification Class Malacostraca Order Isopoda Order Amphipoda Order Euphausiacea Order Decapoda 20-83