invertebrate zoology lecture 17: phylum arthropoda, part 1
TRANSCRIPT
Invertebrate Zoology
Lecture 17: Phylum Arthropoda, Part 1
Lecture outline Phylum Arthropoda
Diversity/ClassificationPhylogenyBauplan BasicsFocus: Arthropod exoskeletonFeeding/digestionCirculation/gas exchangeOsmoregulation/excretionNervous system/sensoryReproduction
Diversity/Classification Subphylum
Trilobitomorpha Two longitudinal
furrows divide body into three sections
Marine; Paleozoic Extinct (end of
Permian)
Diversity/Classification Subphylum Crustacea: Lobsters,
crabs, barnacles, copepods, etc…
Antarctic krillEuphausia superba
Subphylum Hexapoda: Insects
Dennis Kunkel
Brusca & Brusca
Subphylum Myriapoda: Centipedes and Millipedes
Subphylum CheliceriformesSpiders, mites, horseshoe crabs,
scorpions, sea spiders et al…
PhylogenyBased on body plan & development
Hypothesis 1:
Bauplan basics Features shared with Phylum Annelida
Classic protostome development Segmentation; segments added posteriorly Nervous system architecture
Derived characters (differ from Annelida) Rigid cuticle: contains chitin; forms
exoskeleton Open circulatory system; hemocoel Reduced coelom
Key hypothesis: loss of functionality (i.e. peristalsis)
Where are coelom “remnants” located?
Intermediate phylaWhy considered intermediate?
Phylum Onychophora
Phylum Tardigrada
Bauplan basics Other features
Tagmatization
Paired jointed appendages “Primitive condition”: appendages associated
with each segment, Lack motile cilia, except for some sperm
Why? Which other group has non-motile cilia?
Focus: cuticle Epidermis
Secretes cuticleDermal glands
Variety of secretionsSensory structures
ProcuticleChitinCalcium carbonate
CrustaceaSclerotizationJoints
EpicuticleCement layerWax layer
Molting
Feeding/digestion
Different modes of feeding Variety of mouthparts Complete digestive system
Note digestive cecum
Circulation/gas exchange Open circulatory system; ostiate heart
Hemocoel: space bounded by basement membrane of epidermis
Re-entry of hemolymph into heart?
Circulation/gas exchange
Respiration: Subphylum Crustacea Gills; body surface (small forms)
Circulation/gas exchange
Respiration: Hexapoda & Myriapoda Tracheal system (openings = spiracles)
Circulation/gas exchange
Respiration: Cheliceriformes book lungs; book gills
Crustacea: Gills (ammonia release only Antennal (green) gland
Entry via hemocoel channels & active transport Selective secretion and uptake along tubule
Osmoregulation & ammonia excretion
Hexapoda, Myriapoda, Chelicerata: Malpighian tubules
Closed distally: hemocoelActive ion transport
fluid uptake Open into hindgut
Adaptive value?
Osmoregulation & ammonia excretion
Organization Brain (=cerebral ganglia) Subesophogeal (subenteric)
ganglion Ventral nerve cord (paired,
fused partly or completely) Ganglia: one per segment
or fewer (consolidated)
Nervous system
Crab: Note consolidated thoracic ganglia
Nervous system
Sensory systems: Compound eye
Compound eyes comprised of multiple ommatidia Interommatidial hairs in some…
Sensory systems: Compound eye
Key structuresCorneaCrystalline
cone/stalkIris (=corneal
pigment cells)Retinular cell
w/rhabdome
Sensory systems: Compound eye Light-adapted vs. dark-adapted eye
Shift in pigment position (within iris)Alteration in light pathwayConsequences for sensitivity and acuity
Sensory systems: Compound eye Mosaic theory of insect vision
Each ommatidium views piece of visual field Adaptive advantages of compound eye Acuity varies with
Ommatidia concentrationSizeFlatness
Key: angular distance
Sensory systems: Sensillae Mechanosensory & chemosensory
Reproduction: Overview
Sexual reproduction Usually gonochoristicSome hermaphrodites
Example: Barnacles
Parthenogenesis in some groupsPart of aphid life cycleSome crustaceans living in temporary ponds
Egg production often food limited. Why?Example: Antarctic krill
Reproduction: Male system Testes Vas deferens Seminal vesicle Accessory glands
Types of secretions?
Ejaculatory duct Gonopore
Spermatophores (in some)
Penis or modified appendages for copulation
Damselfly penis Barnacle penis
Spider pedipalps
Reproduction: female system Ovaries
Ovariole structureEgg batches
Oviduct Accessory glands
Types of secretions?
Copulatory bursa Spermathecae
Function? Bees and lobsters…
Reproduction & molting Mate guarding
Adaptive value for male?Adaptive value for female?
Reproduction & cannibalism Hexapoda & Cheliceriformes (i.e. spiders)
Adaptive value for male?Adaptive value for female?