Invertebrate Zoology Lecture 17 Phylum Arthropoda Part 1

Invertebrate Zoology Lecture 17: Phylum Arthropoda, Part 1

Lecture outline § Phylum Arthropoda «Diversity/Classification «Phylogeny «Bauplan Basics «Focus: Arthropod exoskeleton «Feeding/digestion «Circulation/gas exchange «Osmoregulation/excretion «Nervous system/sensory «Reproduction

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 krill Euphausia superba

Subphylum Hexapoda: Insects Brusca & Brusca Dennis Kunkel

Subphylum Myriapoda: Centipedes and Millipedes

Subphylum Cheliceriformes Spiders, mites, horseshoe crabs, scorpions, sea spiders et al…

Phylogeny Based 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 phyla Why 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 cuticle «Dermal glands § Variety of secretions «Sensory structures § Procuticle «Chitin «Calcium carbonate § Crustacea «Sclerotization «Joints § Epicuticle «Cement layer «Wax 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

Osmoregulation & ammonia excretion § 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: hemocoel «Active ion transport fluid uptake § Open into hindgut «Adaptive value?

Nervous system § 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

Sensory systems: Compound eye § Compound eyes comprised of multiple ommatidia § Interommatidial hairs in some…

Sensory systems: Compound eye § Key structures «Cornea «Crystalline cone/stalk «Iris (=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 pathway «Consequences 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 concentration «Size «Flatness § Key: angular distance

Sensory systems: Sensillae § Mechanosensory & chemosensory

Reproduction: Overview § Sexual reproduction «Usually gonochoristic «Some hermaphrodites § Example: Barnacles § Parthenogenesis in some groups «Part of aphid life cycle «Some 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 structure «Egg batches § Oviduct § Accessory glands «Types of secretions? § Copulatory bursa § Spermathecae «Function? «Bees and lobsters…