Exam II Rescheduled

• Lecture Exam II will be given on Thursday, April 27, instead of Thursday, April 20.
• Format (types and approximate number of questions) will be the same as in Lecture Exam I.
• I will be available for questions or discussion in the sunny part of the Student Union (outside McDonald's) from 11:00-1:00 on Thursday, April 20.

Deuterostomes
Origins and relationships

Deuterostome Synapomorphies

• Enterocoely (coelom develops as outpockets of archenteron)
• Radial cleavage
• Indeterminate development
• Blastopore forms anus
• Tripartite coelom (mesoderm)
• protocoel
• mesocoel
• metacoel

Deuterostomes - Major Groups

• Lophophorates
• Phylum Bryozoa (Ectoprocts, "moss animals")
• Phylum Brachiopoda ("lamp shells")
• Phylum Echinodermata
• Phylum Hemichordata
• Phylum Chordata

The Origin and Diversity of the Echinodermata

Phylum Echinodermata

• Five living classes
• Crinoidea
  • Sea lilies, feather stars
  • Mouth dorsal
  • Sessile (well, somewhat..)
• Asteroidea
• Sea stars, starfish
• Ophiuroidea
  • Brittle stars, basket stars
• Echinoidea
  • Sea urchins, sand dollars, heart urchins
  • No arms
  • Ossicles fused as a "test"
  • Holothuroidea Sea cucumbers
  • Body elongate
  • Rests on side
  • Ossicles tiny

Living Echinodermata
Synapomorphies

• Calcareous endoskeletal plates
• Secondary pentaradial symmetry
• Ancestors probably bilaterally symmetrical
• Five ambulacral ("arm") grooves
• Unique water vascular system used in locomotion and feeding

Living Echinodermata
Synapomorphies

• Calcareous endoskeletal plates (derived from mesoderm) may be:
• Microscopic disconnected ossicles loose in tissue (e.g. holothuroids)
• Larger, semi-loose ossicles bound by connective tissue (e.g., asteroids)
• Still larger, articulating (adjoining) ossicles (e.g., ophiuroid arms)
• Fused into plates (e.g. echinoid test, crinoid calyx)
• Secondary penta-radial (5 part) symmetry
• Bilaterally symmetrical as larvae
• Various types of symmetry found in fossils
• Ancient ancestors probably were slow-moving, bilaterallly symmetrical benthic forms
• Five ambulacral ("arm") grooves
• Unique water vascular system
• System of hydrostatic canals and ampulla-like tube feet
• Used for locomotion
• Used for feeding

Water Vascular System - Components

• Madreporite
• Water entry
• Filtering
• Stone Canal
• Ciliated
• Tiedemann's bodies
• Phagocytes
• Ring, radial, lateral canals
• Distribute fluid
• Ampullae
• Tube Feet

Water Vascular System - Locomotion and Feeding

• Tube feet function:
• Forward extension
  • Ampullae contract
  • Lateral canal valve closes
• Adhesion
  • Chemical adhesion
  • Suction
• Power stroke
  • Retraction of podia
  • Bending

Other forms of Locomotion in echinoderms

• Movement of spines
• E.g., sea urchins, sand dollars, heart urchins
• Movement of entire limbs
• E.g., ophiuroids, crinoids
• Contribution of body wall muscles
• E.g., sea cucumbers

Phylum Echinodermata -
General Characteristics

• Very successful
• Benthic
• No brain
• No cephalization
• Slow moving predators, sediment or suspension feeders
• Loss of bilateral symmetry

Current Echinoderm Diversity

• Two subphyla
• Pelmatozoa - one class
  • Class Crinoidea
• Eleutherozoa - Four major classes
  • Class Asteroidea
  • Class Ophiuroidea
  • ClassEchinoidea
  • Class Holothuroidea

Current Echinoderm Diversity and Relationships

Subphylum Pelmatozoa, Class Crinoidea

• "Armored echinoderms, feather stars"
• Locomotion: May be attached, may crawl, may swim! (bioluminescent!)
• Suspension feed
• Oral surface up!
• Food caught with adhesive podia (tube feet) and mucous
• Transported to mouth via tube feet in open ambulacral groove
• The most primitive of the living echinoderms, sister group to all four other modern classes
• Stalked crinoids were one of dominant sessile epibenthic filter feeders of the early Paleozoic seas
• Stalked crinoids mostly became extinct at end of Paleozoic, possibly due in part to bioturbators
• Today stalked crinoids persist only in refuges (deep or cold waters)
• Mobile stalkless crinoids have radiated since the Mesozoic in shallow, tropical waters

Subphylum Eleutherozoa
Class Asteroidea

• "Sea stars, starfish"
• Mostly scavengers, predators
• Oral surface down
• Eversible stomach
• Locomotion
• Mostly via tube feet
• Respiration/gas exchange
• Papulae

Subphylum Eleutherozoa
Class Ophiuroidea

• "Brittle stars"
• Feeding highly variable
• Most are active predators
• A few, like this basket star, are mucous suspension feeders
• Locomotion
• Mostly via highly mobile arms
• Respiration/gas exchange
• Bursae

Subphylum Eleutherozoa
Class Echinoidea

• "Sea urchins, sand dollars, heart urchins"
• Feeding variable
• Most are scraping herbivores - "keystone species" in many marine environments
• Some are deposit feeders
  • A few starfish
  • Heart urchins, sand dollars
• Locomotion
• Podia, moveable spines
• Respiration/gas exchange
• Podia and modified podia ("gills") around mouth

Subphylum Eleutherozoa
Class Holothuroidea

• "Sea cucumbers"
• Feeding
• Suspension/deposit feeders using tentacles (modified tube feet)
• Oral surface to side
• Locomotion
• Tube feet
• Body wall
• Respiration/gas exchange
• Hindgut, respiratory tree
• Tube feet (tentacles)

Review of oral/aboral surfaces

Echinoderm Early Evolution -
Two Important Fossil Groups

• Carpoids (Homalozoa)
• Had ossicles
• One ambulacral groove
• Asymmetrical
• Helicoplacoids
• Three ambulacral grooves
• Mouth on side

Ideas on Echinoderm Evolution

• Motile, bilateral ancestor with tripartite coelom
• Water-vascular system and a filter-feeding lophophore-like structure arose as a feeding device from the mesocoel (embryological evidence); tube feet originally used in feeding
• Ancestor became attached or relatively sessile
• Developed radial symmetry, skeleton for protection
• Radial symmetry, skeleton are secondary adaptations to relatively sessile lifestyle
• One ancestral lineage led to Pelmatazoa (oral surface up, tube feet for feeding)
• In Eleutherozoa, switch to oral surface down, use of tube feet for locomotion

Deuterostome Synapomorphies

• Tripartite coelom ( from enterocoelous mesoderm)
• protocoel - anterior
• mesocoel - gives rise to water vascular system and a lophophore- like structure in larval echinoderms
• metacoel - posterior

Ideas on echinoderm evolution

• Motile, bilateral ancestor with tripartite coelom
• Water-vascular system and a filter-feeding lophophore-like structure arose as a feeding device from the mesocoel (embryological evidence), tube feet originally used in feeding
• Ancestor became attached or relatively sessile
• Developed radial symmetry, skeleton for protection
• Radial symmetry, skeleton are secondary adaptations to relatively sessile lifestyle
• One ancestral lineage led to Pelmatazoa (oral surface up, tube feet for feeding)
• In Eleutherozoa, switch to oral surface down, use of tube feet for locomotion