The Arthropods PDF

Lesson 10 THE ARTHROPODS Introduction In terms of number and diversity, Phylum Arthropoda trumps all other animal taxa. Approximately 85% of all animal species described to date (including both extant and fossil) belong to this prodigious phylum. Bugs, flies, ticks, grasshoppers, ants, spi...

Lesson 10 THE ARTHROPODS Introduction In terms of number and diversity, Phylum Arthropoda trumps all other animal taxa. Approximately 85% of all animal species described to date (including both extant and fossil) belong to this prodigious phylum. Bugs, flies, ticks, grasshoppers, ants, spiders, scorpions, centipedes, crabs, lobsters, shrimps, and barnacles are all arthropods. Despite the extensive and conspicuous variations in these animals’ body plan and ecological niche, they all incredibly belong to a single phylum. Arthropoda comes from the Greek words arthron, “joint” and podos, “foot”. Roughly translated, the name arthropoda refers to “those with jointed feet”. This etymology reflects the overarching characteristic of these animals: they all have segmented and jointed skeletal covering, with intrinsic musculature between individual joints of appendages. Although there are literally million species of arthropods, recognize that their body plans are just variations of the arthropod theme. Defining Characteristics Epidermis produces a segmented, jointed, and hardened (sclerotized) chitinous exoskeleton, with intrinsic musculature between individual joints of appendages Complete loss of motile cilia in adult and larval stages General Characteristics Largest phylum in the animal kingdom Comprises nearly 85% of all described animal species Several types live in aquatic environments, and others reside in terrestrial ones; some groups are even adapted for flight Appendages are characteristically segmental and jointed In primitive condition, each segment has pair of appendages Segmentation Metameric segmentation more pronounced in larval forms and “primitive” forms Adult stages of more advanced forms have fused segments o tagmatization— fusion and modification of different regions of the body into a functional morphological unit called tagma o Two of the major arthropod groups (Insecta and Crustacea) have three distinct tagmata: head, thorax, and abdomen o Some arthropods have a fused head and thorax (cephalothorax) Cephalization Development of anterior tagma (head, cephalon or cephalothorax) Associated with the development of central nervous system and specialized sensory systems in the anterior tagma o Compound eyes ▪ Composed of many individual, repeating visual units called ommatidia ▪ found in insects and crustaceans ▪ confer broad field of vision Z.G. Baoanan and J.R.R. Pagaduan. (2020). Invertebrate Zoology Course Pack. Department of Biology, College of Science, University of the Philippines, Baguio City. All Rights Reserved.  o Antennae ▪ Also called “feelers” ▪ Paired appendage for sensing ▪ Tactile, and olfactory receptors (sometimes even auditory) ▪ Could also detect changes in humidity Setae chitinous projections of the exoskeleton secreted by trichogen cell maybe branched, plumose or in the form of spines structurally different from annelid setae Cuticle Epicuticle o made up of proteins, lipoproteins, wax, and lipid o Endocuticle o composed largely by polysaccharide chitin in association with a number of proteins o hardened by sclerotization/tanning (insects) or by mineralization (crustaceans) Sclerotization or tanning – cross-linkages between proteins Mineralization – deposition of calcium carbonate in some procuticle layer LESSON CORRELATES— Commercial Uses of Chitin Chitin produced by arthropods is durable, non-allergenic and biodegradable. Because of these key properties, chitin is used in several commercial applications: 1. Solubilized and reformed into fibers used in making fabrics and surgical sutures 2. Biodegradable capsule for therapeutic drugs 3. Possible substitute for plastic wrap 4. Base material for products that may reduce caloric and cholesterol uptake, owing to its non-digestibility and binding affinity to organic and inorganic compounds) 5. Candidate for removing toxic organic and inorganic compounds from drinking water and sewage treatment Z.G. Baoanan and J.R.R. Pagaduan. (2020). Invertebrate Zoology Course Pack. Department of Biology, College of Science, University of the Philippines, Baguio City. All Rights Reserved. Locomotion Hardened exoskeleton poses limitations on locomotion which necessitates morphological adaptations. Exoskeleton is not a continuous covering. Cuticle is divided into separate plates known as sclerites connected by articular membranes Antagonistic contraction of flexor and extensor muscles aids locomotion Some arthropods have a substance called resilin or “animal rubber” in wing joints and jumping legs. Resilin has the capacity to store energy upon compression and release it efficiently Hemocoel also plays as hydrostatic skeleton. This allows arthropods to extend their legs/ appendages by increasing the blood pressure Molting process of shedding old chitinous and cuticular covering to make way for new growth takes place on the exoskeleton and lining of the guts new cuticle is secreted before old one is shed Old cuticle is split by uptake of water or air or increased blood pressure Both under neural and hormonal control Nervous System single muscle fiber may be innervated by as many as 5 different types of neurons strength of contraction depends upon the rate at which nerve impulses are delivered to the fibers some of the neurons are inhibitory Muscular System Differs significantly from that of other invertebrate groups Arthropod muscle is entirely striated, whereas most other invertebrates possess primarily (or entirely) smooth muscle Striated muscle can contract far more quickly than smooth muscle Without striated muscle, arthropods would never have achieved flight Circulatory System Circulatory system is of Open Type o Hemolymph (blood equivalent) leaves the heart through closed vessels but enters the heart directly from the hemocoel through perforations called ostia o oxygenated blood moving through a series of sinuses and finally being drawn back into the heart through the ostia as the heart expands Components o ostia, heart, arteries, sinuses, hemolymph; some with capillaries Excretory System Aquatic arthropods o Series of metabolic reactions o Nitrogenous waste in the form of ammonia Terrestrial arthropods o Malpighian tubules—branching tubules of the digestive tract that absorbs solutes, water, and wastes from the surrounding hemolymph o Nitrogenous waste: uric acid, feces, urine Z.G. Baoanan and J.R.R. Pagaduan. (2020). Invertebrate Zoology Course Pack. Department of Biology, College of Science, University of the Philippines, Baguio City. All Rights Reserved. Respiratory System (Arthropod Structure and Function, 2020) several adaptations depending on the subgroup and habitat. Aquatic arthropods respire using gills that absorb oxygen from water. Some terrestrial arthropods (spiders and scorpions) have book lungs–stacks of folded tissue that have a large surface area for absorbing oxygen Most terrestrial arthropods have evolved an elaborate system of trachea (respiratory tube) that take in air and deliver it throughout many regions of the body Taxonomy and Diversity A. Subphylum Trilobitomorpha Two anterior-posterior furrows divide the body into three regions Fossil group of extinct marine arthropods that form the class Trilobita Carapace E.g. Trilobites B. Subphylum Chelicerata G: claw Defining Characteristics o No antennae o Body divided into prosoma (cephalothorax) and opisthosoma (abdomen) o First pair of appendages are adapted for feeding (called chelicerae) 0-4 pairs of eyes Spiders, mites, ticks, pseudoscorpions, daddy long legs and scorpions Prosoma and opisthosoma joined by a pedicel Have spinnerets (one individual may contain > 7 different silk glands) Respiration in more primitive arachnid is by internalized book lungs connected to the outside of abdomen by spiracles More advanced forms have spiracles (which can be closed in between “breaths”) that lead to systems of tubules called tracheae Class Merostomata o Composed primarily of extinct species o Only 4 are extant species including the Horseshoe crab (Limulus polyphemus) o All marine with limited distributions in eastern North America, Southeast Asia, and Indonesia o Cephalothorax- covered by carapace o Abdomen has telson— terminal appendage/ last segment of some arthropods; “tail” Class Arachnida o Have a cephalothorax and abdomen o No antenna o Lack mandibles o Spinnerets in spiders make webs o Order Scorpiones- true scorpions o Order Uropygi- whip scorpions o Order Amblipygi- tail-less scorpions o Order Acari- ticks, mites o Order Opiliones- daddy long legs Z.G. Baoanan and J.R.R. Pagaduan. (2020). Invertebrate Zoology Course Pack. Department of Biology, College of Science, University of the Philippines, Baguio City. All Rights Reserved.  o Order Araneae- spiders LESSON CORRELATES— Uses of silk proteins created by spiders 1. Egg sacs that protect developing embryos 2. Fine threads for aerial dispersal of newly emerged young 3. Air-tapping diving bells for underwater foraging 4. Webs for trapping preys, building homes or mating 5. Used by humans as crosshairs in optical equipment 6. Safety lines during climbing Class Pycnogonida o Body not divided into distinct regions (tagmata) o Unique proboscis at the anterior end, with an opening at its tip o Variable numbers of walking legs among species o E.g. Sea spiders C. Subphylum Madibulata Bauplan o Appendages on the third head segment are modified as mandibles, for chewing or grinding food o Retinula of compound eyes contains 8 cells Superclass Myriapoda o Orders were classes before o Order Chilopoda ▪ Centipedes (predators) ▪ Name means "100 legs" ▪ Flattened body ▪ Have 1 pair of legs per body segment ▪ Pincers can inject venom o Order Diplopoda ▪ Millipedes ▪ Name means "1000 legs" ▪ Have 2 pairs of legs per body segment ▪ Rounded body ▪ Scavengers or herbivores Superclass Hexapoda o Class Insecta ▪ 3 pairs of legs ▪ 3 body parts - head, thorax, abdomen ▪ Wings in most insects ▪ All appendages attached to the thorax Z.G. Baoanan and J.R.R. Pagaduan. (2020). Invertebrate Zoology Course Pack. Department of Biology, College of Science, University of the Philippines, Baguio City. All Rights Reserved.  ▪ 9-11 segments in abdomen ▪ Mandibles for chewing ▪ Order Mantaphasmatodea- CN: gladiators, cross bn stick insect, mantid, and grasshopper ▪ Order Ephemeroptera- mayflies; adults are nonfeeding Subclass ▪ Order Odonata- damselflies, dragonflies Pterogyta ▪ Blattaria- cockroaches ▪ Mantodea- praying mantis ▪ Isoptera- white ants/termites ▪ Order Grylloblattaria ▪ Orthoptera- Grass hopper ▪ Phasmida- walking sticks (Carausius sp.); leaf insect (Phyllium sp.) ▪ Order Diptera- true flies (horseflies, mosquitoes) Superorder ▪ Order Lepidoptera- butterflies Holometabola ▪ Order Hymenoptera- ants, bees, wasps Metamorphosis Change from larval to adult form. Occurs in animals that have indirect development in which young differ drastically (in form or life style) from adult G: meta – “beyond”, morphe- “form” describing the series of changes through which an insect passes in its growth from the egg through the immature stages (nymph or larva and pupa) to the adult. A change of form, used to describe the post embryonic changes in insects as they progress to adulthood. Types of Metamorphosis Anamorphosis— typical of chilopods and diplopods and most crustaceans; additional segments added with each molt; indefinite growth. Ametabolous— no metamorphosis. Little or no change between the immature and adult form except in size and development of the sexual organs. Hemimetabolous (Incomplete) Metamorphosis o immature forms are often called nymphs o Partial change in wing and external genitalia development with each molt. o Most adults and nymphs have the same habits and live in the same environment. o Life Cycle: Egg → nymphal instars → adult Holometabolous (Complete) Metamorphosis o Immature forms are called larvae o Larvae are very different in form from the adult. o The pupal stage is a transition stage, when the larva is transformed to the adult. o Pupa does not feed and movement is very restricted. o Great metabolic changes occur. o Pupa molts to the adult form. o Life Cycle: Egg → larval instars → pupa → adult Z.G. Baoanan and J.R.R. Pagaduan. (2020). Invertebrate Zoology Course Pack. Department of Biology, College of Science, University of the Philippines, Baguio City. All Rights Reserved.  Superclass Crustacea o Bauplan ▪ Head bears 5 pairs of appendages, including 2 pairs of antennae ▪ Development includes a triangular larvae called nauplius bearing 3 pairs of appendages and medial eye o Marine members include shrimp, lobster, barnacles, & crabs o Terrestrial crustaceans called isopods (pillbugs or rollypollys) o Freshwater members include crayfish and daphnia o All have mandibles for chewing or tearing o Have cephalothorax & abdomen o Barnacles are sessile o Lobsters and large crustaceans are called Decapods 10 legs o Diversity ▪ Class Malacostraca ▪ Class Isopoda Woodlice Sea slaters ▪ Class Amphipoda ▪ Class Euphausiacea Krill ▪ Class Decapoda Crabs, shrimps, lobsters ▪ Class Copepoda copepods ▪ Class Branchiura fish lice ▪ Class Thecostraca Barnacles Z.G. Baoanan and J.R.R. Pagaduan. (2020). Invertebrate Zoology Course Pack. Department of Biology, College of Science, University of the Philippines, Baguio City. All Rights Reserved. References Arthropod Structure and Function. (2020). Retrieved from CK-12 Foundation: https://www.ck12.org/book/ck-12-biology-advanced-concepts/section/15.30/ Encyclopedia Brittanica. (2020). Retrieved from Encyclopedia Britannica: https://www.britannica.com/science/spiracle#:~:text=Spiracle%2C%20in%20arthropods%2C %20the%20small,certain%20thoracic%20and%20abdominal%20segments. Pechenik, J. A. (2015). Biology of Invertebrates. New York: McGraw-Hill Education, Inc. Z.G. Baoanan and J.R.R. Pagaduan. (2020). Invertebrate Zoology Course Pack. Department of Biology, College of Science, University of the Philippines, Baguio City. All Rights Reserved.