Lecture 6: BILE 1263 - Living Organisms

Overview

• Focus on Echinodermata and Arthropoda
• Comparison of evolutionary traits and adaptions

Echinodermata

• Characteristics:
  • Marine environments
  • Specialized water vascular system with tube feet and pedicellaria
  • Pentamerous radial symmetry
• Classes:
  • Urchins (Sea urchins)
  • Holothuroidea (Sea cucumbers)
  • Asteroidea (Starfish)
  • Ophiuroidea (Brittle stars)

Water Vascular System

• Water enters through madreporite
• Controls locomotion and feeding through tube feet

Anatomy

• Organs in each arm (e.g., digestive glands, gonads)
• Hard calcified plates; known as a test

Notable Features

• Aristotle’s Lantern: A feeding apparatus in some echinoderms
• Transition from bilateral to radial symmetry in adulthood

Arthropoda

• Characteristics:
  • Jointed exoskeleton and appendages
  • Bilateral symmetry
  • Tagmosis: Fusion and specialization of body segments
  • Open circulatory system with hemolymph
  • Growth through ecdysis (molting)

Segmentation and Growth

• Ancestral forms with biramous appendages
• Growth through molting due to non-growing exoskeleton

Adaptive Features

• Eyes: Compound and simple
• Sensory Organs: Antennae, setae
  • Diverse functions, from sensory reception to communication

Example Classes and Orders

Crustacea

• Malacostraca: Crabs, lobsters, shrimp
• Branchiopoda: Brine shrimp, water fleas
• Maxillopoda: Barnacles

Decapoda

• Examples: Caribbean spiny lobster, blue land crab
• Economically important; specialized appendages for feeding and defense

Isopoda

• Terrestrial and marine species (e.g., woodlice)

Barnacles

• Sessile adults with feeding appendages
• Ecological and economic implications (e.g., fouling on ships)

Evolutionary Context

• Convergence with mollusks despite distinct evolutionary paths
• Evidence from fossil record (e.g., Burgess Shale)

Cultural and Economic Importance

• Various species have ecological, economic, and cultural significance

Notable Adaptations

• Velvet Worms: Possible arthropod ancestors; flexible cuticle
• Hemocyanin: Respiratory pigment in arthropods and mollusks

Conclusion

• Echinodermata and Arthropoda exhibit diverse and complex adaptive strategies
• Both phyla play crucial roles in marine ecosystems and have significant evolutionary histories

This lecture provided insights into the anatomy, evolutionary traits, and ecological roles of key marine taxa.