Coelomate Ecdysozoans

Coelomate Ecdysozoans

Overview

• This section covers Chapter 14 and 15, focusing on coelomate ecdysozoans.
• Key groups include Protists, Basal Phyla, Spiralia, Animalia, Ecdysozoa, and Deuterostomia.

Shared Characteristics of Ecdysozoans

• Ecdysis: The process of molting the cuticle.
• Coelomate: Possessing a coelom.
• Protostome Development: Undergoing protostome development.
• Metamerism: Segmented body structure.
  • With tagmatization (specialization of body regions).
• Hemocoel: A body cavity containing blood.
• Open Circulatory System: Circulatory system where blood is not always confined to vessels.

Arthropoda

• Most diverse and successful animal group.
• Classification is continuously studied.
• Exoskeleton:
  • Chitinous and molted.
  • Jointed.
• Paired Appendages: Highly varied and specialized.
• Metamorphosis: Common, with distinct larval forms.
  • Hemimetabolous: Incomplete metamorphosis.
  • Holometabolous: Complete metamorphosis.
• Subphyla:
  • Trilobitomorpha: Extinct trilobites.
  • Chelicerata
  • Myriopoda
  • Pancrustacea
    • Crustacea
    • Hexopoda

Panarthropod Phylogeny

• Panarthropoda includes Arthropoda, Onychophora, and Tardigrada.
• Onychophora: Velvet worms.
  • Slime glands, oral papillae.
• Tardigrada: Water bears.
  • Cryptobiosis: a state of dormancy.
  • Stylets used in feeding.
• Arthropoda
  • Chelicerata
    • Euchelicerata
      • Pycnogonida: Sea spiders
      • Xiphosura: Horseshoe crabs
      • Opiliones: Harvestmen
      • Acarina: Ticks and mites
      • Scorpionida: Scorpions
      • Araneae: Spiders
  • Myriapoda
  • Mandibulata
    • Pancrustacea
• Hemocoel, metamerically arranged paired appendages, nonsclerotized cuticle shed by ecdysis are characteristics of Panarthropoda.
• Chelicerae are characteristic of Chelicerata.
• Compound eyes, sclerotized exoskeletal plates separated by nonsclerotized joint membranes, jointed legs are characteristics of Arthropoda.
• Mandibles are characteristic of Mandibulata.

Chelicerata

• Characteristics:
  • 2 tagmata (body sections):
    • Prosoma (Cephalothorax)
    • Opisthoma (Abdomen)
  • Chelicerae: First pair of appendages, often pincher-like.
  • Pedipalps: Second pair of appendages, often sensory, sometimes used in feeding or reproduction.
  • Dioecious: Having separate sexes.

Chelicerata: Merostomata

• Horseshoe Crabs (Xiphosura):
  • Now often considered within Arachnida.
  • 4 living species.
  • 2-part body: Prosoma & Opisthoma, with elongate telson.
  • Book gills.
• Eurypterids (extinct):
  • Some gigantic, “sea scorpions”.

Chelicerata: Pycnogonida

• Sea Spiders:
  • Short body, long legs.
  • Organs extend into legs.
  • Feed on cnidarians on the ocean floor.
  • May be a distinct Subphylum “Cheliceriformes”.

Chelicerata: Arachnida

• Book lungs; some with tracheae & spiracles.
• Eyes: Ocelli.
• Silk production in spiders.
• Pedipalp modifications.
• Orders:
  • Araneae: Spiders.
  • Scorpionida: Scorpions.
  • Opiliones: Harvestmen.
  • Acarina: Ticks & mites.
  • Solfugida: Sun spiders.

Cladogram of Chelicerata Relationships

• Euchelicerata
  • Pycnogonida
  • Xiphosura
  • Opiliones
  • Acarina
  • Scorpionida
  • Araneae
  • And more

Mandibulata Phylogeny

• Mouth appendages project from head, Malpighian tubules.
• Myriapoda:
  • Two tagmata, paired appendages on most segments
• Pancrustacea:
  • Appendages modified for crawling, swimming, feeding
• Hexapoda:
  • Three tagmata, three pairs of uniramous appendages, five pairs of head appendages
• Head and abdomen reduced, thoracic appendages used in filter feeding.
• Carapace absent, cephalothorax, four or five pairs of swimming legs.

Myriopoda

• All terrestrial.
• 2 tagmata: Head & trunk.
• Uniramous appendages (many).
• Many add legs and segments as they molt & grow.

Myriopoda: Diplopoda

• Diplopoda- Millipedes
  • 2 pair legs per “segment”.
  • Scavengers.
  • Repugnatorial glands.

Myriopoda: Chilopoda

• Chilopoda- Centipedes
  • 1 pair legs per segment.
  • Venomous predators.
• Pauropoda
  • Forest floor detritivores.
• Symphyla
  • Eyeless garden detritivores, some are pests.

Crustacea

• Characteristics
  • Biramous appendages
    • Exopodite/endopodite
  • 2 pair antennae
  • Compound eyes
  • Cephalothorax
  • Mandibles, maxillae, maxillipeds, Pereopods
  • Abdomen
    • Pleopods
    • Uropod & Telson

Crustacea: Malacostraca

• Malacostraca
  • Best known
    • Order Decapoda
      • Named for 10-legs (5 pairs of walking legs, starting with Cheliped
      • Lobsters, crayfish, crabs, shrimp, stomatopods
    • Order Isopoda
      • Dorsoventrally flattened, scavengers- pillbugs, etc.
    • Order Amphipoda
      • Laterally compressed sand fleas, etc.

Crustacea: Branchiopoda & Maxillopoda

• Branchiopoda
  • Mostly freshwater
  • “Gill-foot”- feathery appendages
  • Fairy shrimp & water fleas
• Maxillopoda
  • Diverse orders, 2 distinct subclasses:
    • Copepods- abundant, mostly planktonic. Swim with antennae
    • Barnacles- modified sessile adults, filter feed with legs

Hexapoda

• Characteristics
  • Distinct 3 tagmata structure
    • Head: compound eyes, 1 pair antennae, mouthparts
    • Thorax: 3 pair legs + wings
    • Abdomen: spiracles, genitals and ovipositors (females)
  • Flight- BIG DEAL!
    • Single greatest key to insect success
  • Development- Metamorphosis
  • Social behavior- eusociality
    • Bees, ants & wasps; termites

Hexapoda: Sample Orders

• Coleoptera- Beetles
  • Most diverse group
  • Forewings=elytra (hardened)
• Lepidoptera- butterflies & Moths
  • Important pollinators
  • Some store toxins from plants
• Diptera- flies
  • Single pair of wings
  • Fluid diets
  • Diverse, but many important to humans
• Hymenoptera- bees, ants, wasps
  • Many eusocial (basis of sociobiology)
  • Haplodiploidy
  • Important pollinators

Phylogeny of Hexapoda

• Covers the phylogeny of the 31 orders of Hexapoda.
• Includes orders such as Collembola, Protura, Diplura, etc.
• Highlights Holometabola, including Coleoptera, Lepidoptera, and Diptera.

Clade Panarthropoda

• Phyla Arthropoda and 2 others: Onychophora, Tardigrada.
• Onychophora
  • Velvet worms
  • Terrestrial, tropics
  • Spit sticky slime
• Tardigrada
  • Water bears
  • Microscopic
  • Cryptobiosis- stasis