Deuterostomes: Echinoderms and Chordates
Deuterostomes: Echinoderms and Introduction to Chordates
Overview of Deuterostomes
- Deuterostomes are a major group of animals.
- Includes Echinoderms and Chordates.
- Bilateria: Characterized by Bilateral symmetry.
- Eumetazoa have tissues.
- Position of Deuterostomes in the animal phylogeny: Sponges, Cnidarians, Flatworms, Molluscs, Annelids (Lophotrochozoa), Nematodes, Arthropods (Ecdysozoa), Echinoderms, and Chordates.
- Approximate evolutionary timeline:
Embryological Development: Protostomes vs. Deuterostomes
- Gut formation pattern differentiates animal categories.
- Protostome development: the mouth develops first.
- Deuterostome development: the anus develops first.
- Key features:
- Mesoderm
- Future mouth, digestive tract, and anus development
- Spiral cleavage in protostomes
- Radial cleavage in deuterostomes.
Phylogeny of Deuterostomes
- Includes:
- Xenoturbellida
- Echinodermata (Echinoderms)
- Crinoidea
- Asteroidea
- Ophiuroidea
- Holothuroidea
- Echinoidea
- Hemichordata (Hemichordates)
- Pterobranchia
- Harrimaniidae
- Ptychoderidae
- Chordata (Chordates)
- Tunicata
- Phlebobranchia
- Thaliacea
- Aplousobranchia
- Appendicularia
- Stolidobranchia
- Molgulidae
- Vertebrata
Major Deuterostome Groups
- Echinodermata: Approximately 7,000 species.
- Hemichordata: Approximately 85 species.
- Chordata: Approximately 60,000 species.
Echinoderms
- Characterized by spiny skin.
- All marine species.
- Slow-moving or sessile organisms.
- Thin epidermis covering calcareous plates.
- Use a hydrovascular system for movement via tube feet.
- Echinoderms are Deuterostomes!
General Echinoderm Anatomy
- Key features:
- Central disk
- Digestive tract (stomach, anus, digestive glands)
- Ring canal
- Gonads
- Ampulla
- Podium (tube feet)
- Radial canal
- Spine
- Gills
- Madreporite
- Radial nerve
Major Classes of Echinoderms
- Asteroida: Sea stars.
- Ophioroida: Brittle stars.
- Echinoida: Sea urchins.
- Crinoida: Sea Lilies/feather stars.
- Holothuroida: Sea Cucumbers.
Echinoderm Life Processes
- Gas exchange
- Nutrient acquisition
- Material distribution
- Osmotic stress management
- Waste expulsion
- Reproduction
Hemichordates
- Body plan:
- Prosome/proboscis
- Mesosome/collar
- Metasome
- Features:
- Mouth
- Prebranchial nerve ring
- Dorsal nerve cord
- Gill slits
- Pharynx/gut
- Ventral nerve cord
- Anus
- Apical organ
- Protocoel, mesocoel, and metacoel
- Stomochord
- Dorsal cord
- Ciliated band
- Ventral, post-anal tail
Chordates
- Key characteristics:
- Notochord
- Dorsal, hollow nerve cord
- Post-anal tail
- Pharyngeal slits or clefts
- Muscle segments
Chordate Evolution
- Evolved during the Cambrian explosion, approximately 530 million years ago.
- Bilaterian deuterostomes with about 65,000 extant species, including approximately 57,000 vertebrates.
- Examples of early chordates: Myllokunmingia, Haikouella, and Tully monster.
Chordate Phylogeny
- ANCESTRAL DEUTEROSTOME
- Notochord.
- Common ancestor of chordates
- Echinodermata
- Chordates
- Urochordata
- Cephalochordata
- Myxini
- Petromyzontida
- Vertebrates
- Gnathostomes
- Jaws, mineralized skeleton
- Chondrichthyes
- Osteichthyans
- Lungs or lung derivatives
- Actinopterygii
- Lobe-fins
- Lobed fins
- Actinistia
- Dipnoi
- Tetrapods
- Limbs with digits
- Amphibia
- Amniotes
- Mammalia
Urochordates: Tunicates
- Key features:
- Notochord
- Dorsal, hollow nerve cord
- Tail
- Muscle segments
- Incurrent and excurrent siphons
- Pharynx with numerous slits
- Intestine, anus, stomach, esophagus, and atrium
- Larval form has chordate characteristics which are lost during the metamorphic transition to the adult form.
Vertebrates
- Chordates and vertebrates are not the same things.