Echinoderms and chordates are fascinating marine creatures with unique features. Echinoderms, like sea stars, have pentaradial symmetry and a water vascular system. Chordates, including humans, have a notochord and pharyngeal slits during development.

Both groups are deuterostomes, differing from protostomes in key developmental aspects. Their embryonic development involves three germ layers and distinct patterns of cleavage and coelom formation. These traits set them apart in the animal kingdom.

Echinoderms and Chordates

Characteristics of echinoderms

• Exclusively marine animals live in ocean habitats (sea stars, sea urchins, sea cucumbers)
• Exhibit pentaradial symmetry in adult body plan with five or multiples of five arms or rows of structures
• Possess a unique water vascular system hydraulic network of fluid-filled canals and tube feet used for locomotion, feeding, and gas exchange
  • Madreporite porous plate allows water to enter the system
  • Ring canal encircles the mouth and connects to radial canals
  • Radial canals extend along each arm or ambulacral area
  • Tube feet muscular, fluid-filled extensions used for movement and feeding
• Have an endoskeleton composed of calcium carbonate ossicles provides structure and support for the body
• Display remarkable regenerative abilities can regenerate lost body parts
• Undergo metamorphosis from a bilateral larval stage to a radially symmetric adult form

Deuterostomes vs protostomes in development

• Blastopore fate differs between the two groups
  • Deuterostomes blastopore becomes the anus, mouth forms secondarily at opposite end of embryo
  • Protostomes blastopore becomes the mouth, anus forms secondarily at opposite end of embryo
• Coelom formation occurs through different processes
  • Deuterostomes enterocoelous coelom formation, coelom forms by outpocketing of archenteron (primitive gut), mesoderm buds off from endoderm
  • Protostomes schizocoelous coelom formation, coelom forms by splitting of mesoderm, mesoderm develops as solid mass then splits to form coelom
• Cleavage patterns are distinct
  • Deuterostomes exhibit radial and indeterminate cleavage, blastomeres can develop into any part of embryo
  • Protostomes display spiral and determinate cleavage, fate of each blastomere is determined early in development

Distinguishing traits of chordates

• Possess a notochord flexible, rod-like structure runs along dorsal side of body, provides support and aids in muscle attachment, present at some stage of development in all chordates
  • May be replaced by vertebral column in vertebrates
• Have pharyngeal slits series of openings in pharynx (throat region) that connect to outside environment, present at some stage of development in all chordates
  • Function in filter feeding and gas exchange in aquatic chordates
  • Develop into other structures in terrestrial chordates (Eustachian tubes, tonsils)
• Develop a dorsal hollow nerve cord from plate of ectoderm that rolls up and forms a tube, located above notochord
  • Anterior portion develops into brain, posterior portion becomes spinal cord in vertebrates
• Exhibit a post-anal tail muscular extension of body posterior to anus, present at some stage of development in all chordates, used for locomotion in aquatic species
• Have a segmented muscular system with blocks of muscle (myomeres) arranged along notochord, enables efficient swimming motion in aquatic chordates

Embryonic development in deuterostomes

• Three primary germ layers form during gastrulation:
  • Endoderm: gives rise to digestive tract lining and associated organs
  • Mesoderm: develops into muscles, skeleton, and circulatory system
  • Ectoderm: forms nervous system and outer skin layer
• Early embryos display bilateral symmetry, which is maintained in most chordates throughout development