Chapter 13: Echinodermata

Phylum Echinodermata: 4 main classes we covered

• Asteroida: sea stars

• Echinoidea: sea urchins /dollars

• Holothuroidea: sea slugs

• Ophiuroidea: brittle stars

Phylum Echinodermata: 4 main classes we covered

• Asteroida: sea stars

• Echinoidea: sea urchins /dollars

• Holothuroidea: sea slugs

• Ophiuroidea: brittle stars

Main characteristics of echinodermata

•“Spiny Skin”

•No distinct brain (circumoral ring and radial nerves)

•Complete digestive system

•No circulatory system, uses coelom

•Gas exchange via dermal branchiae or other specialized systems

•Endoskeleton made of calcium carbonate ossicles

•Bilateral symmetry in larvae but pentaradial in adulthood

•Exclusively marine

4 different classes

know identifying characteristics of each

Class Asteroida: sea stars

• tube feet for locomotion and prey

• Penetration symmetry

• Regeneration

• Madreporite (and anus) on aboral surface . Water vascular system

• Pedicellaria on a aboral surface used for defense and cleaning, act like claws

• Spines for support and protection

• Dermal Branchiae: skin gills

• Carnivores. Eat bivalves by ejecting stomach

• Ampullae and tube feet involved in water vascular system. Ampullae extend and contract to have feet shorten or extend

Class Asteroidea: Sea star external anatomy

Be able to identify each side

Different types of Asteroidea

Identify the external anatomy on aboral surface
■ Central disk
■ Arms
■ Madreporite plate
■ Spines
■pedicellariae

Class asteroids sea stars External anatomy oral side

Identify structures on the oral side

• mouth

• Ambulacral grooves lined with tube feet

• Ambulacral spines

Sea star internal anatomy

identify the following internal anatomy

• Cardiac stomach
  ■ Pyloric stomach
  ■ Pyloric ceca
  ■ Gonads
  ■ Ambulacral ridge
  ■ Ring canal
  ■ Ampullae

Sea star cross section

Sea star internal anatomy

Class Ophiuroidea: brittle stars

• Be able to recognize a brittle star and identify the mouth, arms, central disk,
  distinguish between oral/aboral surface

• Be able to compare and contrast brittle stars and sea stars

• long, skinny arms distinct from central disk

• Deposit or suspension feeders

• Crawl with arms instead of with tube feet

• Reported on ORAL surface instead of aboral

• Tube feet without suckers

Class Echinoidea: sea urchins (Regular) and sand dollars (irregular)

• rigid shell called a “test” formed by skeletal ossicles. Provide structural support

• Sea urchins have pedicellariae (like class asteroidea) that clean the epidermis and release poison. 3-jawed variety on long stalks most common

• Test has plates with moveable, stiff spines

• Tube feet extend along 5 ambulacral rows

• Spines articulate on ball and socket joints

• Compact body

• Lack arms but have ambulacral areas that reflect pentaramous symmetry

Regular Echinoidea: Sea Urchins

• spherical or disk shaped body with no arms

• Ossicles fused to form rigid shell like test

• Madreporite on ABORAL surface

• Long, well developed moveable spines

• Radial symmetry

• Spherical shape

• Tube feet and spines used for locomotion

• Aristotles lantern and peristome used for feeding

• Skin gills for gas exchange

Sea urchin anatomy: external

Identify the following;

• spines

• Test

• Tube feet

• Peristome

• Tooth

• Mouth

Know structures function

Sea urchin anatomy: internal

Identify the following

• aristotles lantern

• Digestive system

• Gonad

Know the function of each structure too

Sea urchin: Practice identifying internal anatomy

Class Holothuroidea: Sea cucumbers

• ring of tentacles around mouth for deposit feeding

• No arms, spines, or pedicellariae

• Ossicles are highly reduced to microscopic elements

• Soft, elongated body

• Rely on water vascular system for locomotion

• Internal madreporite

Sea cucumber dissection