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Biology 320 Invertebrate Zoology Fall 2005 Presentation Transcript

Slide 1 - Biology 320Invertebrate ZoologyFall 2005 Chapter 16 – Introduction to Phylum Arthropoda
Slide 2 - Phylum Arthropoda Horseshoe crabs, crustaceans, arachnids, insects, and millipedes One million described species 80% of all known animals Another 30 million undescribed species of insects, estimated Only birds, bats, and insects have the ability to fly Amazing adaptive diversity
Slide 3 - Thought to be closely related to annelids Recently thought to be more closely related to nematodes Two major extant taxa Chelicerata – horseshoe crabs and arachnids Mandibulata Crustacea – crabs, barnacles, and water fleas Tracheata – insects and centipedes
Slide 4 - Segmentation Metamerism is the technical term for segmentation Individual segments are termed somites Certain body regions of arthropods display a fusion of several segments Arthropods display tagmosis (tagmatization) Segments are organized into regions called tagma (tagmata) Insects posses a head, thorax, and abdomen Arachnids and crustaceans (typically) possess a cephalothorax and abdomen
Slide 5 - ppt slide no 5 content not found
Slide 6 - Cephalization Highest degree of cephalization of any phylum we have discussed to this point Head possesses Concentration of ganglia (brain) Concentration of sensory structures Eyes and antennae Mouth, feeding appendages, and legs (in those with a cephalothorax)
Slide 7 - Appendages Segmented with articulations Specialized for specific functions Some posses more than 10 types Enormous variety May be simple, or have multiple branches
Slide 8 - Body Wall Cuticle (exoskeleton) is most superficial layer Made of chitin and protein Provides strength and protection Epidermis Monolayered Secretes cuticle Thin connective tissue layer Specialized individual muscles, rather than sheets
Slide 9 - Exoskeleton Cuticle has hard areas and soft areas Allows for movement at articulations Some areas are sclerotized Proteins crosslink causing cuticle to harden and darken Typical of arachnids and insects Some areas are mineralized Calcium salts are added to cuticle Crustaceans supplement sclerotization with mineralization
Slide 10 - Two main layers of exoskeleton Epicuticle – thin outer layer that is water / gas resistant Waterproofed by different types of lipids Useful in dry environments Important for osmoregulation in FW environments Procuticle – thick portion
Slide 11 - Must be periodically molted in order for growth to occur Rigid exoskeleton cannot stretch Process known as ecdysis Regulated by the steroid hormone ecdysone Even the lining of the foregut, hindgut, tracheae, etc. are shed
Slide 12 - Has been thoroughly studied in decapods When animal prepares to molt Old cuticle begins to detach New cuticle begins to form Layer of molting fluid (containing proteases and chitinases) forms between the two cuticles Epicuticle of new cuticle protects it from enzymes Calcium from old cuticle is reclaimed During ecdysis Animal is very vulnerable Usually molts inside burrow, shelter, etc. Molting related complications / deaths are common Ecdysis
Slide 13 - After molting Animal takes up water or air, and swells as a result May ingest old cuticle to reclaim calcium Sclerotization and mineralization (crustaceans) occur Excess water or air is eliminated Animal now has room for growth Some molt periodically Others have a fixed number of instars (life stages) separated by molts
Slide 14 - Musculature Lack sheets of muscles Small individual muscles that are specialized Flexors Extensors Often arranged antagonistically Control one articulation or one sclerite Striated, for rapid contraction
Slide 15 - Locomotion Arthropods posses a large variety of appendages, that serve different purposes Walking legs Paddles – swimming Wings - flight
Slide 16 - Coelom Arthropods have an exoskeleton, and therefore do not rely heavily on a hydrostat Coelom is reduced compared to that of the annelids Hemocoel is the functional body cavity No segmental divisions
Slide 17 - Hemal System Transports nutrients, hormones, wastes, and gasses (in some) Open system in most System consists of: Large dorsal heart Tubular and contractile Possesses ostia Arteries that branch off of heart Sinuses are separated by perforated diaphragms Pericardial – dorsal Perivisceral – middle Perineural (in some) - ventral Blood Crustaceans and chelicerates have hemocyanin Hemocoel Muscles and organs are housed here
Slide 18 - Generalized blood flow Oxygenated blood leaves heart via arteries Travels to sinuses and hemocoel where tissues and organs are bathed in blood Deoxygenated / waste laden blood travels to respiratory structures (in all but tracheates) and gas exchange occurs Blood enters heart via ostia
Slide 19 - Excretion Two main excretory structures Saccate nephridia Malpighian tubules Saccate nephridia Mainly found in aquatic species Not actually used for excretion, as wastes (ammonia) diffuse across gills Maintain ion balance and fluid volume Go by many name, such as “green glands” in crayfish Consists of a tube and an end sac which is bathed in blood
Slide 20 - Malpighian tubules Primary excretory organ of terrestrial species Stringy tubules located at the junction of the midgut and hindgut Create uric acid and guanine and transfer to the gut lumen Wastes form a precipitate in this low pH environment Nitrogenous wastes are removed with feces Adaptation to terrestrial existence
Slide 21 - Gas Exchange Small arthropods conduct gas exchange across body surfaces Larger varieties make use of specialized structures that must be moist Interestingly, the epicuticle of respiratory structures is not water / gas proof Many types of respiratory structures Particular structures are mainly dependent on the type of habitat the animal inhabits
Slide 22 - Aquatic invertebrates Gills Already discussed Book gills Flat sheets on ventral surface Possessed by horseshoe crabs Terrestrial species Tracheae Tubular invaginations that branch and lead directly to cells, not to the hemal system Spiracle diameter regulated by a sphincter Opening / closing of spiracles is useful for ventilation and reducing water loss Book lungs Common in arachnids Invagination of exoskeleton which contains many smaller invaginations (large SA) Exchange occurs between surfaces of book lungs and blood
Slide 23 - Digestive System Complex, but somewhat similar to annelid system Epithelium at junction of foregut-midgut secretes a thin peritrophic membrane around bolus Protects delicate walls of midgut from abrasion Gut lumen reabsorbs water
Slide 24 - Nervous System Similar to that of annelids CNS Brain Ventral nerve cord PNS Segmental nerves connecting to muscle and sensory organs Numerous types of sensory structures Exoskeleton is modified to accommodate sensory receptors
Slide 25 - Mechanoreceptors Setae Hollow extensions of cuticle w/ sensory neurons inside Trichobothria Sensitive “hairs” that detect weak air currents Chemoreceptors Sensilla Similar to setae Equilibrium Statocysts Possessed by some Ocelli Most use light as a point of reference for orientation
Slide 26 - Sound detection Tympanic membrane Responds to air vibrations Can also produce sound in some Useful for locating / attracting mates Moths use to hear bat echolocation Temperature – humidity detectors Thermo-hygroreceptive sensillia Usually found on antennae of insects
Slide 27 - Eyes Most have ocelli Many also have compound eyes Composed of many subunits called ommatidia 15 – thousands per eye Each unit has own lens and own field of vision Fields of vision of adjacent ommatidia overlap Composite image formed, similar to vertebrate eyes Are usually motion detectors that have a range of about 20cm Many have eyestalks Some have color vision and respond to colored flowers
Slide 28 - Reproduction Mostly gonochoric Fertilization is primarily internal in terrestrial species Can be internal or external in aquatic species Most copulate and there is often selectivity on the part of the female Females often store sperm in a seminal receptacle Sperm transfer is direct in some Penis may deliver sperm directly, or serve as an intromittant organ Spermatophores are frequently used for indirect transfer Many brood and display parental care