Deuterostomes

What are deuterostomes?

A major clade of bilaterian animals in which the blastopore typically becomes the anus (mouth forms second).

What major phyla are listed under deuterostomes?

Echinodermata, Hemichordata, and Chordata.

What are echinoderms?

Marine animals with spiny skin such as sea stars, brittle stars, sea urchins, sand dollars, and sea cucumbers.

Slow

Coelom

Endoskeleton

Water Vascular system

Tube feet

What is the typical body symmetry of adult echinoderms?

5- part “Radial” symmetry → Bilateral

How do echinoderm larvae differ from adults?

Larvae are bilaterally symmetric; adults show pentaradial (five-fold) symmetry in most groups.

What is the echinoderm endoskeleton made of?

Internal calcareous plates or ossicles.

What is the water vascular system?

A hydraulic system of canals unique to echinoderms that powers tube feet used for locomotion, feeding, and respiration.

What are tube feet?

Extensions of the water vascular system used for locomotion, feeding, adhesion, and gas exchange.

How does the water vascular system function?

Water enters through the madreporite, moves through canals into tube feet; hydraulic pressure extends/retracts tube feet.

What roles do tube feet play?

Movement, opening prey (e.g., bivalves), respiration, and sensory detection.

What is a sea star's feeding mechanism?

Sea stars can evert part of their stomach to externally digest prey and then retract it.

Can sea stars regenerate lost arms?

Yes—many sea stars can regenerate arms and sometimes entire body parts.

What are brittle stars known for?

Long, flexible arms used for rapid, snake-like movements and diverse feeding strategies.

Suspension, predators, scavengers

What characterizes echinoids (sea urchins & sand dollars)?

No arms, a rigid test (shell) of fused plates, and complex jaw-like structures (Aristotle's lantern) in sea urchins.

5 radially arranged groups of tube feet

Sea Urchin

Mouth on underside

Ringed by highly complex, jaw-like structures→Seaweed

Roughly spherical

What are sea cucumbers like?

Elongate echinoderms with reduced skeletons that often feed by deposit or suspension feeding.

San Dollar

Mostly flat

What is hemichordata?

A phylum of wormlike deuterostomes (acorn worms and pterobranchs) with some chordate-like features.

Half skin

What developmental trait distinguishes deuterostomes from protostomes?

The fate of the blastopore (anus first) and often radial, indeterminate cleavage.

What is radial, indeterminate cleavage?

A cleavage pattern in embryos where cells divide symmetrically and early cells can form complete embryos (regulative development).

What is the ecological importance of echinoderms?

They are key benthic grazers, predators, sediment recyclers, and ecosystem engineers.

How do sea stars open bivalve shells?

Tube feet and hydraulic pressure slowly pry shells open, then extrude stomach to digest prey.

How do echinoderms respire?

Via tube feet, papulae (skin gills), or through modified structures depending on the group.

Why is the deuterostome developmental mode significant evolutionarily?

It underlies the body plans of vertebrates and related groups and correlates with indeterminate development and complex body plans.

What is the role of tube feet in feeding for sea cucumbers?

They use modified tube feet to capture food particles or to deposit-feed along sediments.

How does the echinoderm endoskeleton benefit the animal?

It provides internal support and sites for muscle attachment while allowing growth via plate addition.

What are some basic ecological roles of deuterostomes as a group?

Predation, grazing, sediment turnover, and as keystone species in marine ecosystems.