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CH33 Arthropods All.Pptx 10/15/14 Biosc 41 Announcements 10/15 Quick Platyhelminthes Review v What type of symmetry do animals in Phylum v Quiz today- Phyla Platyhelminthes and Mollusca Platyhelminthes have? v v Lecture- Phylum Arthropoda Digestive system: mouth only (protostomes) v How does gas exchange take place? v Lab- Phylum Arthropoda v What are protonephridia for? v What is the class of free-living flatworms? An v Mon’s lecture will finish any arthropod info we don’t get to example? today, have arthropod quiz, and do an exam review activity v What are the classes of parasitic flatworms? Example? v Mon’s lab will finish arthropod lab material (+ crayfish dissection) Quick Mollusca Review Quick Mollusca Review v Features and structures universal amongst molluscs: v Four major classes: § Mantle- secretes shell in shelled molluscs; sometimes § Class Polyplacophora- Chitons portions of mantle form siphon(s) § Class Gastropoda- snails, nudibranchs, slugs § Foot- contains sensory cells; adapted in various ways in § Life cycle includes trochophore & veliger larvae different classes § Veliger stage involves torsion § Visceral mass- internal organs consistent between classes, but arranged in different orientations § Class Bivalvia- clams, oysters, mussels § Life cycle includes trochophore & veliger larvae § Circulatory system includes heart and is open in all but cephalopods (which have a closed circulatory system) § Class Cephalopoda- squid, octopus, cuttlefish, nautilus § Nervous system includes nerve cords and centralized brain tissue § Mantle has been modified to include a siphon for locomotion § Digestive system includes radula, well-developed digestive gland, and “complete gut” § Foot has been modified into tentacles § Heart and kidneys function as excretory system § Closed circulation and complex brain Quick Mollusca Review Quiz 5 v What is a possible adverse effect of suspension feeding? 1. What is the class of free-living flatworms? And an example? v Molluscs are the animal group with the largest number of 2. What are the two classes of parasitic flatworms? And an recent extinctions example of each? v What features distinguish bivalves from brachiopods (Phylum 3. Identify 3 of the 4 major classes of Phylum Mollusca Brachiopoda)? 4. What are three features distinguishing bivalve molluscs from brachiopods (Phylum Brachiopoda)? 5. What is a possible adverse effect of suspension feeding? 1 10/15/14 More Relationships… An Introduction to the Invertebrates, Arthropods, Part One Reference: Chapter 33 "Don't accept the chauvinistic tradition that labels our era the age of mammals. This is the age of arthropods. They outnumber us by any criterion – by species, by individuals, by prospects for evolutionary continuation." Stephen Jay Gould, 1988 Arthropod = “jointed leg” Arthropod Origins v Eumetazoan protostome, bilateral symmetry, triploblastic, v The arthropod body plan consists of a segmented coelomate (mostly) body, hard exoskeleton, and jointed appendages v Defining characteristics v This body plan dates to the Cambrian explosion § Segmented body (535–525 million years ago) § Some segments are fused by tagmosis into tagmata v Early arthropods show little variation from segment § Exoskeleton made of chitin to segment § Secreted by epidermis § Molting (Ecdysis à Ecdysozoa) § Exoskeleton shed regularly during life or only during larval development § No cilia in larvae or adults v Most successful in terms of diversity and sheer numbers § >1,000,000 species! Phylum Arthropoda – general body plan Tagmosis allows for specialization & diversity v Body divided into segments (somites) v Diversity of body form possible because of specialization of § Regionally fused into specialized groups by tagmosis (i.e., segments, regions and appendages 5 segments form head) v Tagmosis = segments grouped together § Internal cavity à hemocoel (not coelom!) § Specialized for particular functions for greater efficiency v Head, thorax and abdomen are tagmata § No internal segmentation (no septa – contrast w/annelids) § Regions specialized for performing different tasks v Each body segment has a pair of jointed appendages 2 10/15/14 Exoskeleton Structure The Arthropod Cuticle 1 4 v Cuticle forms well-developed exoskeleton made up of plates (sclerites) § Growth by ecdysis (hormone-induced molting) v Epidermis is a single layer of epithelial cells that secrete the cuticle in layers § Outer layer = epicuticle, with water-repellant hydrophobic layers § Inner layer = procuticle, protein & chitin § Procuticle is hardened by 1. Sclerotization = cross-linking of proteins into 3D matrix 2. Mineralization (in crustaceans) = depositing calcium carbonate in procuticle (i.e., crab shell) Molting The pros and cons of the arthropod exoskeleton v Stages between molts are termed instars v Pros § This is when actual tissue growth occurs, although there’s no size 1. Provides protection; hard covering over muscles & viscera increase until after the molt 2. Facilitates osmoregulation in terrestrial environment (less § Usually applies to immature stages water loss through epidermis) v Frequency of molting is under hormonal control (ecdysone) 3. No need for hydrostatic skeleton, so body plan could v Cuticle is weakened enzymatically, then animal crawls out diversify v After molting, animal sucks in air/water to inflate new 4. Better leverage than endoskeleton (or no skeleton) for cuticle which then hardens moving muscles attached to limbs v Cons 1. Growth must proceed through a series of molts 2. Chitin exoskeleton is heavy – constraint on size Arthropod circulation Arthropod Respiration v Open circulatory system v Varies between groups but usually by gills in aquatic habitats § Hemolymph moves through hemocoel, and has and a tracheal system in terrestrial arthropods amebocytes, pigments, and sometimes clotting factors § The tracheal system is composed of tubes that distribute § Muscular heart required since rigid exoskeleton prevents air throughout the body body movements from moving hemolymph § Some arthropods have a specialized lung-like structure called a book lung or book gill § Special chamber with platelike structures § Enhanced surface area facilitates rapid exchange of CO2 and O2 § Diffusion of gases across thin areas of the cuticle also contributes to respiration 3 10/15/14 Arthropod Osmoregulation and Waste Excretion Arthropod Nervous System v Reuptake of salts and nutrients v “Brain” is 2-3 ganglia with v Antennal and maxillary glands in crustaceans specific functions § Produce urine; ammonia also excreted from gills v Ganglionated ventral nerve cord v Malpighian tubules in arachnids and insects v Sense organs (sensilla) protrude out of cuticle § Blind tubes extend into hemocoel and empty into gut v Membranous drums (“ears”) § Produce uric acid which is passed through the anus v § Solid matter may also be passed through the anus Chemoreceptors with thin cuticle Arthropod Vision Arthropod Digestive System v Complete, with regional specialization • Simple ocelli • Complex lensed ocelli § Foregut - food intake, transport, storage, mechanical • Compound eyes made of ommatidia digestion (jaws, pharynx, gizzard) § Midgut - extracellular digestion, nutrient uptake (cecae, digestive gland, hepatopancreas) § Hindgut - excretion of undigested material, water reabsorption Arthropod Locomotion Arthropod locomotion v Striated muscle v Jointed appendages (limbs) + specialized muscles to move the limb pieces (podites) § Exoskeleton used as attachment point for muscles § Extrinsic muscles connect to body wall v Muscles anchor on inside of cuticle § Intrinsic muscles are contained entirely inside the limb § Connect into the jointed appendages on each segment v Ancestral condition, found in crustaceans, is to have biramous limbs (each limb has 2 branches) Uniramous (1 branch) Biramous - insects - crustaceans 4 10/15/14 Diversity of Arthropod legs Arthropod Taxonomy Seven Subphyla: 1. Trilobites (extinct since Paleozoic) 2. Onychophora (velvet worms) 3. Tartigrada (water bears) 4. Crustacea (crabs, lobsters, shrimp) 5. Chelicerata (spiders, horseshoe crabs, pycnogonids) 6. Myriapoda (centipedes, millipedes) 7. Hexapoda (Insects) Subphylum Trilobitomorpha (Extinct) Subphylum Onychophora 2 8 v Onychophora – “nail bearers” or “velvet worms” § 1-3 cm Cephalon v Transitional group within the Ecdysozoa – possess some features not characteristic of arthropods Thorax § Pseudocoelomate § Soft cuticle – no exoskeleton! Pygidium § No jointed appendages § Legs are hollow – “stub legs” v Found in litter layer & decaying logs § Prey on small worms, arthropods Most common group of fossil arthropods - Once abundant in oceans - Disappeared by Paleozoic (345 million yr ago) Subphylum Tartigrada Subphylum Crustacea v Most occur in marine and freshwater environments v “Water bears” or “moss piglets” v External Features: § About 0.5 mm § Distinguishing feature: only arthropods with 2 pairs of § Terrestrial and aquatic habitats antennae v true extremophiles: can survive § Body of 3 tagmata: head, thorax, abdomen § Wide temperature extremes (-80C to >100C) § Cephalic shield or carapace present to protect dorsum § Ionizing radiation § Mandibles, modified limbs, act as jaws; 2 pairs of § Outer space! (for a while) antennae v Capable of anhydrobiosis § Limbs are biramous (2 forks) § Able to desiccate to <3% water and § “Gills” are actually legs modified for gas exchange stay that way for >10 years 5 10/15/14 Subphylum Crustacea Generalized Crustacean Body Plan Marine arthropods video (~10 min): http://shapeoflife.org/video/phyla/marine-arthropods-
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