ASIM'S WEBWORLD View: Main School Main AP Biology Chapter Guides RELATED LINKS Review Questions and Answers		AP BIOLOGY: Chapter Forty-One Outline INTRODUCTION Development of Jointed Appendages First accomplished by the arthropods Necessary adaptation with advent of rigid exoskeleton Success of the Arthropods Includes nearly two-thirds of all named species on earth May include 30 million species of insects alone Are abundant in all habitats, but dominate terrestrial regions Economic Importance Cause extensive damage to food crops Are important human food source Pollinate crops, control insects and weeds Produce products like silk and honey Critical importance in recycling organic matter GENERAL CHARACTERISTICS OF ARTHROPODS Possess Characteristic Jointed Appendages Phylum name means "jointed feet" Appendages modified into antennae, mouthparts and legs Other External Characteristics Bodies are segmented Some members have large numbers of segments In others the segments are fused into functional units: tagma fig 41.1 Process called tagmatization Segmentation may be more obvious during development of larvae Head and thorax may be fused into a cephalothorax Have rigid external skeleton: exoskeleton Immature forms may not resemble adult form May change characteristics in metamorphosis from egg to adult Members are generally small in size MAJOR GROUPS OF ARTHROPODS Primarily Categorized by Modifications of Anterior Appendages fig 41.2 Mandibulates have modified mandibles Anterior, but not the most anterior appendages Include crustaceans, insects, centipedes, millipedes Most anterior appendages are sensory antennae Chelicerates lack mandibles and instead possess chelicerae Include spiders, mites, scorpions Evolved from very most anterior appendages May appear as pincers or fangs Secondarily Categorized Anatomy of All Appendages Aquatic mandibulates Appendages are biramous (two-branched) fig 41.3 Typical of crustaceans Possess nauplius larva fig 41.4 Terrestrial mandibulates Appendages are uniramous (one-branched) Typical of insects, centipedes, millipedes Also characteristic of phylum Onychophora Mandibles evolved independently in terrestrial and aquatic mandibulates Mandibulates and chelicerates evolved independently, neither gave rise to other Second chelicerate appendages are pincer or feelerlike, followed by legs Chelicerae resemble other chelicerate appendages more closely than mandible resemble other mandibulate appendages EXTERNAL FEATURES Exoskeleton All arthropods covered by hardened skeleton or cuticle Tough outer covering is secreted by and fused with epidermis Varies in toughness and thickness Crustaceans add calcium carbonate, making it less flexible Functions of exoskeleton Prevents excessive water loss Protects from predators, parasites and injury Growth requires periodic ecdysis New exoskeleton grown beneath old one Controlled by hormones Separated by a fluid that dissolves components of old skeleton Old skeleton cracks open and is shed New skeleton is initially quite soft and must be expanded to full size Hardens with exposure to air or water Compound Eye fig 41.5 Composed of many ommatidia: independent visual units Each covered with a lens Linked to eight retinula cells and central light-sensitive rhabdom Apposition eyes Example: bee Each ommatidium acts in isolation Surrounded by pigment cells An image inverted on each ommatidium retina Individual images formed in brain Superposition eyes Example: moth Images from ommatidia are combined on cornea at rear of eye Not associated with pigment cells Single right-side-up image is formed Ocelli are simple eyes with single lenses fig 41.5b Sometimes occur together with compound eyes Function in distinguishing light and darkness May also serve as horizon detectors in locusts and dragonflies INTERNAL FEATURES fig 41.6 Reduction of Coelom Through the Course of Evolution Consists of cavities housing reproductive organs and some glands Arthropods completely lack cilia Have tubular gut that extends from mouth to anus Circulatory System fig 41.6b Open system, no closed blood vessels Longitudinal heart along dorsal thorax and abdomen With contraction, blood flows into head When heart relaxes blood returns it Series of one-way valves in posterior of heart allows blood to flow inward only Blood from anterior end flows through spaces to posterior end Flow is more rapid with greater activity Blood delivers nutrients, transports wastes Respiratory System Functions to transport oxygen directly to tissues All parts of body must be near air passage limiting body size Possess no single respiratory organ, but a system of branched tracheae fig 41.7 Become smaller tracheoles that are in contact with individual cells Air passage controlled through external spiracles Closing spiracles conserves water Air flow assisted by muscular movements in larger organisms Many chelicerates have book lungs or book gills A series of leaflike plates within a chamber Air drawn in and out by muscular contractions These respiratory systems unique to arthropods and Onychophora Crustaceans have typical gills Excretory System Several forms of excretory systems Principal components of the land mandibulate are Malpighian tubules fig 41.6b Slender projections of the digestive tract Located at the junction of the midgut and hindgut Fluid of blood passes through walls of tubules Nitrogenous wastes are precipitated as fluid passes toward hindgut Waste emptied into hindgut and eliminated Most water and salts reabsorbed by hindgut and returned to body Nervous System fig 41.6b Predominant double chain of ganglia runs along ventral surface Anterior end possess three fused pairs of dorsal ganglia: the brain Much control of activities regulated by ventral ganglia Many activities continued with brain removed Brain appears to be inhibitor, not stimulator as in vertebrates SUBPHYLUM CHELICERATA: THE CHELICERATES Class Arachnida: The Arachnids Largest class of chelicerates Possess a pair of chelicerae, pair of pedipalps, four pair of legs Chelicerae: frontmost appendages, fangs with poison glands Pedipalps: next set of appendages, like legs but one less segment Have specialized functions: copulatory organs, sensory organs Other general characteristics Most are carnivorous, mites are herbivorous Most ingest only preliquified foods, thus digestion is external Are generally terrestrial, evolved direct transfer of sperm Breathe by trachea, book lungs or both Include 11 orders Order Scorpiones: the scorpions fig 41.1;8 Pedipalps are modified into pincers Use pincers to handle and tear food apart Have venomous stingers on terminal segment Distinctive jointed abdomens Extremely ancient group of terrestrial arthropods Respiration via book lungs Males deposit spermatophores, picked up by females Order Araneae: the spiders fig 41.9 Hunt prey or catch it in webs fig 3.14d Silk formed from fluid protein, forced out spinnerets fig 41.10 Modified appendages May be up to six pairs Many forms are active hunters fig 41.9b Have poison glands leading through chelicerae Some are poisonous to man and large mammals Examples: black widow and brown recluse fig 41.11 Reproduction Males produce sperm web, add drop of sperm, pick up with pedipalps May involve elaborate courtship Male fits pedipalps into special plate on female's abdomen Female may eat male once fertilization is complete Eggs enclosed in silken egg sac Young resemble adults, go through several molts Order Acari: the mites fig 41.12 Most diverse in terms of numbers and species Generally very small in size Cephalothorax and abdomen fused into an ovoid body Respiration occurs through trachea or directly through exoskeleton Development occurs on many complex successive stages Various juvenile stages have become reproductive Called paedomorphosis Many live on humans, some transmit diseases fig 41.13 Ticks are blood-feeding ectoparasites, transmit various diseases fig 41.12c Cause extensive plant damage Some are valuable biological controls Order Opiliones: the daddy longlegs fig 41.14 Possess compact, oval bodies with extremely long, slender legs Respire by a single pair of trachea Engage in direct copulation, unusual among arachnids Males possess penis Females use ovipositor to deposit eggs Most are predators, some are scavengers or feed on plant juices Class Merostomata: The Horseshoe Crabs fig 41.15 Example: Limulus, common on North Atlantic coasts Evolution Ancient group, fossils identical to 220 million years old Limulus May be derived from trilobites Reproduction Live in deep water, migrate to shallow coastal waters to mate fig 41.16 External fertilization, larvae resemble trilobites General biology Feed at night on mollusks and annelids Swim on backs by moving abdominal plates Possess five pairs of walking legs Protective shell ends in tail spine, the telson Breathe via five pairs of book gills Class Pycnogonida: The Sea Spiders fig 41.17 Common, but rarely observed because of small size Adults are generally parasites or predators on other animals General biology Have sucking proboscis with terminal mouth Body consists mostly of cephalothorax, no well-defined head Possess four to six pairs of legs Males exhibit parental care of young, carry eggs on legs Lack excretory and respiratory systems, exchange by diffusion Not closely related to other two classes SUBPHYLUM CRUSTACEA: CRUSTACEANS Arrangement and Nature of Appendages Two pairs of antennae, three pairs of chewing appendages Number of legs varies with the species All are biramous Excluding first pair of antennae Single-branched appendages previously biramous, one branch lost in evolution Evolution of crustaceans All descended from common ancestor as evidenced by nauplius larvae fig 41.4 Some groups lack larvae and undergo direct development into adult General Biology Have legs on abdomen and thorax like millipedes and centipedes (unlike insects) Only arthropods with two pair of antennae Mandibles evolved from limbs that developed a chewing function Many have compound eyes and tactile hairs over whole body Have feathery gills near base of legs Excretion of nitrogen wastes occurs mostly across surface of cuticle Osmotic composition of blood regulated by labyrinth or green gland Diversity of Crustaceans Decapods ("ten-footed") include lobsters, shrimp and crabs fig 41.18 Exoskeleton reinforced with calcium carbonate Body segments fused into cephalothorax, covered by carapace Crushing pincers common, used to obtain food Abdominal swimmerettes used in reproduction and locomotion fig 41.19 Snapping of telson and uropods causes forceful, rapid movements Crabs have larger broader carapace than lobsters fig 41.18c Shrimps have smaller carapace than crabs or lobsters fig 41.18b Terrestrial crustaceans Pillbugs and sowbugs, terrestrial isopods, order Isopoda fig 41.20a Sand and beach fleas, order Amphipoda Planktonic crustaceans Copepods, order Copepoda fig 41.20b Water fleas, order Cladocera fig 41.21 Ostracods, order Ostracoda Fairy shrimp and brine shrimp, order Anostracoda Barnacles, order Cirripedia fig 41.22,24.11 Are sessile as adults, but have free-swimming larvae Head attached to submerged object, food swept into mouth by feathery legs Protected by calcareous plates attached to substrate Are hermaphroditic which is unusual for crustaceans SUBPHYLUM UNIRAMIA General Characteristics Evolved from annelids similar to oligochaetes, related to Onychophora Respire via trachea Filter waste products through Malpighian tubules Classes Diplopoda and Chilopoda: The Millipedes and Centipedes fig 41.23 Both possess head region followed by numerous segments Share similar reproductive strategies Fertilization is internal, direct transfer of sperm Sexes separate, all species lay eggs General appearance of young is similar to adult Centipedes Have one pair of legs per segment Are carnivorous, eat mainly insects Appendages of first trunk segment modified into poison fangs Millipedes Have two pairs of legs per segment Each segment derived from two fused segments Most are herbivorous Can roll bodies into a flat coil May secrete defensive fluids and cyanide gas Class Insecta: The Insects Largest group of organisms on earth Especially numerous in the tropics Enormous diversity fig 41.24,25 External features fig 41.6 Primarily terrestrial organisms, small in size Have three body segments: head, thorax, abdomen Have three pairs of legs, all attached to thorax Have one pair of antennae May have one or two pairs of wings Most possess compound eyes, many have ocelli Elaborate mouthparts, widely variable fig 41.26 Characterized by unsegmented mandibles Segmented maxillae comprise secondary pair of mouth parts Labium forms the lower lip Labrum forms the upper lip Chewing insects have a tonguelike hypopharynx Orders classified by structure of mouthparts, feeding habits Chewing or mandibulate mouthparts fig 41.26 Coleoptera = beetles Hymenoptera = bees, wasps and ants Isoptera = termites Orthoptera = grasshoppers and crickets Elongate, stylet-like mouthparts Diptera = horseflies, blackflies, mosquitos have fused stylets fig 41.27a Advanced flies have piercing or lobe-like labium fig 41.27c Lepidoptera = moths, butterflies have coiled proboscis Thorax consists of three fused segments (tagmata) Each has a pair of legs Legs may be absent in some larvae Example: bees fig 34.9 Example: flies fig 41.28,30 Structure of insect wings If two pairs, attach to middle and posterior segments If one pair, attach to middle segment Arise as saclike outgrowths, are solid excluding veins Are not homologous to other appendages Two pairs are the basic construction for winged insects fig 41.25a One pair lost in the evolution of groups like flies fig 41.25b Most wings folded at rest, except for outstretched dragonfly wings Forewings may be hard and tough, form covering for hindwings Example: beetles fig 41.25d Example: grasshoppers and crickets fig 41.6,24c May possess detachable scales, like butterflies and moths fig 41.29 Some groups like springtails never evolved wings Other insects are derived from winged ancestors Fleas fig 41.25e Lice fig 41.25f Internal organization fig 41.6 Tubular, somewhat coiled digestive tract Greater coiling associated with sucking mouthparts Dilute digestive enzymes less effective on liquids than solids Anterior and posterior digestive regions lined with cuticle Digestion occurs within stomach or midgut Excretion through Malpighian tubules Trachea extend throughout body, may form air sacs fig 41.7 Spiracles are permanently closed in some aquatic, parasitic forms Fat body is food-storage organ or is similar to vertebrate liver Sense receptors Possess wide variety of sensors in addition to eyes Sensory hairs located all over bodies Sense of taste located on mouthparts Sense of smell located on antennae Sound detected by tympanum, associated with tracheal air sacs fig 41.6a Sensory hairs may also detect sound waves Insect communication Produce sounds which are mostly inaudible to humans Produce chemicals called pheromones Life histories Most insects hatch from eggs outside of the mother`s body Young insects undergo regular ecdysis, stages called instars Simple metamorphosis fig 41.30 Wings develop during juvenile stages Immature stages generally called nymphs Complete metamorphosis fig 41.30 Wings appear only during resting stage just prior to final molt Resting stage called a pupa or chrysalis fig 41.31 Pupa does not normally move, except mosquitos Juveniles and adults live in distinct habitats Development is indirect, larvae are wormlike Larva do not have compound eyes Larvae may or may not have legs fig 41.28,30,31 Generally have chewing mouthparts Pupa generally are usually inactive and do not feed Juvenile hormone controls ecdysis and molting via ecdysone fig 41.32 DEUTEROSTOMES Embryological Feature Shared by Four Phyla Echinodermata, Chordata and two smaller groups Four phyla share common ancestry Characteristics Blastopore becomes anus, mouth develops at other end Have radial cleavage Daughter cells are identical for a brief period of time Produce whole individual if separated Individuals are identical in genetic makeup Whole groups of cells move during embryonic development Coelom produced by evagination of archenteron Archenteron becomes gut cavity PHYLUM ECHINODERMATA: THE ECHINODERMS General Ecology of Echinoderms Ancient group of marine animals, well-represented in fossil record Name means "spiny skin" fig 41.33 Examples: sea stars, brittle stars, sea urchins, sand dollars, sea cucumbers Basic Features of Echinoderms Have epidermis stretched over an internal skeleton Endoskeleton composed of ossicles: movable or fixed calcium plates Plates enclosed within living tissue when first formed Bear spines as indicated by phylum`s name Have perforations through which tube feet extend Have a five-part body plan Adults have no head or brain Nervous system composed of circular nerve ring and its branches Capable of complex response patterns, but lack centralized functions Possess a water vascular system Five radial canals extend from a ring canal around the esophagus Radial canals determine basic five-part symmetry fig 41.34a Water enters through madreporite, a sievelike plate Flows to ring canal through the tubular stone canal Radial canals extend out into hollow tube feet fig 41.34b Some echinoderms have suckers at end of tube feet, others do not Each tube foot has a muscular fluid-filled ampulla at its base Feeding strategies of echinoderms Sea cucumbers: tube feet around mouth are modified for feeding fig 41.33b Sea lilies: tube feet arise from branched arms, filter food Brittle stars: tube feet pointed and specialized for feeding fig 41.33d Development of the coelom Large coelom interconnected with complicated system of tubes Helps provide for circulation and respiration Respiration and waste removal occur through skin gills Digestive system is simple but complete: mouth, gut and anus Capable of extensive regeneration Some animals may drop parts when attacked May reproduce asexually by splitting into parts Sexual reproduction and fertilization is external Sexes are separate, but difficult to distinguish externally Develop into free-swimming, bilaterally symmetrical larvae fig 41.35 Significantly different from annelid/mollusk trochophore larvae Larvae possess bands of cilia, used for locomotion Diversity of Echinoderms Class Crinoidea: the sea lilies and feather stars fig 41.33c,36 Mouth and anus located on upper surface in an open disk Simple excretory and reproductive systems Extensive water vascular system Large numbers of highly branched arms located around central disk Filter feeders, food collected by mucus from tube feet on pinnules Sea lilies are attached to a substrate by a stalk Feather stars detach from stalks early in development, attach to substrate by claw-like structures Sexes separate, external fertilization Females may brood young Crinoids resemble early fossil echinoderms Class Asteroidea: the sea stars Most familiar echinoderms, the "starfish" fig 41.33a,34 Active, important marine predators Arms prominent and set off from the disk, generally five in number Mouth located in center of the lower surface Often feed on bivalve mollusks fig 41.37 Sexes separate, external fertilization Females may brood young Class Ophiuroidea: the brittle stars fig 41.33d Slender arms more sharply set off from central disk than sea stars Move by active movement of their arms along the substrate Capture suspended particles with tube feet, long spines or arms Arms detach readily, helping protect animals from predators Class Echinoidea: the sea urchins and sand dollars fig 41.33e,f Lack distinct arms, but retain familiar five-part body plan Five rows of tube feet protrude through plates of the skeleton Skeletons are made up of fused calcareous plates Walk along substrate with tube feet or movement of spines Feed on algae, debris scraped off the surfaces by triangular teeth Reproduction similar to other echinoderms Larvae have long arms, unlike those of other classes Class Holothuroidea: the sea cucumbers fig 41.33b Soft, sluglike organisms with tough, leathery outer skin Most lie on sides at the bottom of the ocean Mouth is located on one end Surrounded by tube feet modified into tentacles Tentacles secrete mucus to trap food particles Calcareous skeleton reduced to widely separated, microscopic plates Have highly branched respiratory trees that originate from cloaca Water brought into and out of cloaca by muscular contractions Gas exchange occurs across the respiratory trees Have tube feet on body, may be restricted to five grooves Move by tube feet or wriggling of the entire body Some forms are hermaphroditic, unusual for echinoderms