14-2 Deuterostomes

Deuterostomes

Include two diverse phyla: Phylum Echinodermata and Phylum Chordata. Animals in these phyla share molecular and embryological developmental similarities.

Ossicles

Calcium carbonate endoskeleton of echinoderms

Aboral surface

Top of the body of the echinoderm

Oral surface

mouth side of the echinoderm

Water Vascular system

in echinoderms, network of fluid filled hydraulic canals that operate tube feet. For locomotion & feeding.

Madreporite

Intake valve located on the aboral surface in echinoderms part of water vascular system- where water enters.

Aristotle’s lantern

Feeding structure in echinoderms: made of five large tooth-like ossicles

Vertebrates

chordates that have a backbone made of cartilage, or calcified bone

Cranium

In vertebrates, a skull that contains a brain

Gnathostomes

Vertebrates that have hinged jaws, mineralized skeletons, and a large forebrain

Tetrapod’s

Vertebrates that have hinged jaws and paired limbs that can support their weight on land.

Amniotes

Vertebrates that can complete their life cycle on land; terrestrially- adapted

Ectotherm

Animal that cannot regulate its body temperature

endotherm

animal that maintains a constant body temperature

Lateral Line

A series of canals along the side of a fish or larval amphibian, that functions in the detection of vibrations changes in water pressure. and movement.

Deuterostome characteristics

Deuterostome phyla share embryological traits: they have deuterostome development where the blastopore becomes the anus, and the mouth forms later. These animals are triploblastic, exhibit bilateral symmetry at some stage, have a complete digestive tract, a central nervous system, and a true coelom. Segmentation, development type (direct/indirect), and habitat can vary among species within the phyla.

Phylum Echinodermata(sea stars, sea cucumbers, sea urchins, brittle stars, and sand dollars)

Echinoderms are marine invertebrates with a CaCO3 endoskeleton and water vascular system. They exhibit deuterostome development, have a complete digestive tract, and lack segmentation. While they lack respiratory and circulatory systems, their well-developed true coelom helps with these functions. The coelom of females often fills with eggs during spawning. Echinoderms use broadcast spawning for gamete dispersal and have indirect development.

Show bilateral symmetry, but only as larvae.

Unlike the larvae adult echinoderms have pentamerous symmetry (a type of radial symmetry) in multiples of 5s (examples 5 or 10 arms in sea stars, 5 rows of tube feet in sea urchins)

They have an internal skeleton or endoskeleton composed of CaCO3 ossicles or plates. Wehn the animal dies the endoskeleton remains and is called a test.

Echnoderm water vascular system

Echinoderm Water Vascular System (WVS) - Notes (Shortened):

• Unique hydraulic system used for locomotion and feeding via tube feet.

• Water enters through madreporite, travels to ring canal, then into arms and ampullae.

• Ampullae muscles contract, pushing water into tube feet, forming suction for gripping surfaces or prey.

• When muscles relax, tube feet retract.

Echnoderm diversity

• Ophiuroidea (Brittle & Basket Stars):

  • Brittlestars: distinct central disc, move by thrashing arms.

  • Basketstars: filter feeders.

• Asteroidea (Sea Stars):

  • Pentamerous symmetry; madreporite on aboral surface.

  • Use tube feet to pry open bivalves, evert one stomach to externally digest prey.

• Echinoidea (Sea Urchins, Sea Biscuits, Sand Dollars):

  • Sea Urchins: long spines for movement & defense; feed using Aristotle’s Lantern.

  • Sea Biscuits/Sand Dollars: benthic, often buried; holes in test help anchor in surf.

• Holothuroidea (Sea Cucumbers):

  • 5 rows of tube feet; may have tentacles.

  • Expel organs to deter predators.

Phylum Chordata

Chordates are segmented deuterostomes with a complete digestive tract and true coelom. They are triploblastic, bilaterally symmetrical at some life stage, and can have direct or indirect development. Includes non-vertebrate chordates and vertebrates (fish, amphibians, reptiles, mammals – including humans).

Four chordate characteristics

All chordates have these traits at some life stage:

• Notochord – flexible dorsal support rod (becomes backbone in vertebrates)

• Dorsal hollow nerve cord – forms spinal cord

• Pharyngeal gill slits – become gills in aquatic species or jaw/ear structures in land animals

• Post-anal tail – tissue extending beyond the anus

Some species show these only in larval or embryonic stages.

Subphylum Urochordata (tunicates or sea squirts)

Larvae have all 4 chordate traits; adults do not.
Adults are sac-like blobs, with incurrent/excurrent siphons.
They filter feed using gills and often live in colonies.

Subphylum Cephalochordata (Lancelets)

Adult lancelets retain all 4 chordate characteristics.
They have clearly segmented muscles and use gills to filter feed.
Found buried in sand in estuarine and marine habitats.

Subphylum Vertebrata

• Vertebrates have a vertebral column (cartilage or bone) and a cranium (skull).

• Key features: segmentation, true coelom, bilateral symmetry, triploblastic, complete digestive tract.

• Focus on synapomorphies and how form relates to function across clades.

Jawless Fishes (Hagfish & Lamprey)

• Cartilaginous backbone and cranium.

• Hagfish: marine, benthic scavengers; secrete slime.

• Lamprey: ectoparasitic on bony fish; use oral disc to feed; harmful to Great Lakes fisheries.

Gnathostomes (Jawed Vertebrates)

• Traits: hinged jaws, large forebrain, mineralized skeleton.

• Evolution of jaws enabled consumption of more varied, mobile prey.

Fishes (Cartilaginous, Ray-Finned, Lobe-Finned)

• Traits: paired fins, scales, complex sensory systems, ectothermic.

• Reproduction: internal or external fertilization; egg-laying or live birth.

Cartilaginous Fishes (Sharks & Rays)

• Cartilage skeleton, electrosensory systems.

• Adaptations: stingrays are flattened for sand-burial; shark teeth specialized by diet (e.g., plate-like for crushing mollusks, saw-like for slicing sea turtles).

Vertebrates

Ray-Finned & Lobe-Finned Fishes (Bony Fishes)

• Ray-finned Fishes: Bony internal skeleton, bony scales, and operculum (protects gills). Most are marine; ~40% are freshwater. High freshwater diversity due to geographic isolation and adaptive radiation.

• Lobe-finned Fishes: Includes Coelacanth, once thought extinct until rediscovered in 1938. Important in the evolution of tetrapods (land vertebrates), supported by fossils and anatomy.

Tetrapods (Terrestrial Vertebrates)

• Evolved from lobe-finned fishes; capable of supporting body weight out of water.

• Key adaptations for land: prevention of desiccation, air breathing, reproduction without water.

Amphibians (Frogs, Toads, Salamanders, Newts)

• Earliest tetrapods, but not fully adapted to land.

• Require water for reproduction and larval development. Vulnerable to dehydration (no scales).

• Ectothermic with lungs (some also use skin for respiration).

• Metamorphosis (e.g., frogs from tadpoles to adults).

Amniotes (Reptiles, Birds, Mammals)

• Fully adapted to life on land, can complete life cycle without water.

• Evolution of the amniotic egg (or placenta) enables terrestrial adaptation.

Reptiles (Turtles, Lizards, Snakes, Crocodilians, Birds)

• Keratin scales or modified scales (feathers) provide protection against desiccation.

• Most are ectothermic, but birds are endothermic (can regulate body temperature).

• Adapted to various habitats (dry, aquatic, tropical, temperate).

• Specialized features for different lifestyles.

Mammals (Monotremes, Marsupials, Eutherians)

• Keratin hair/fur and mammary glands (milk production).

• Fur: insulation, skin protection, sensory (whiskers), and courtship (e.g., lion's mane).

• Endothermic, highly advanced sensory systems, and differentiated teeth (for varied diet).

• Diverse group with varying diets and habitats.