Echinoderms Overview

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Questions and Answers

What is a characteristic feature of echinoderms?

They have endoskeletons made from rigid calcium carbonate plates. (correct)

They possess an external skeleton made of chitin.

They have a segmented body plan similar to arthropods.

They are primarily freshwater organisms.

Which class includes organisms commonly referred to as starfish?

Ophiuroidea

Asteroidea (correct)

Echinoidea

Holothuroidea

How many species approximately belong to the class Ophiuroidea?

Roughly 5,000 species.

Approximately 2,000 species. (correct)

Around 1,000 species.

About 10,000 species.

What distinguishes brittle stars from sea stars?

Brittle stars have extremely flexible limbs, while sea stars have more rigid arms. Signup and view all the answers

What are tiny sea daisies classified as?

A type of sessile organism in the class Asteroidea. Signup and view all the answers

What characteristic of brittle stars allows them to escape from predators?

Their limbs can easily regenerate Signup and view all the answers

Which of the following is true regarding crinoids?

They are mostly sessile as adults Signup and view all the answers

How do sand dollars and sea urchins differ in terms of physical characteristics?

Sea urchins have a hard outer shell called a test Signup and view all the answers

What is a significant feature of the water vascular system in echinoderms?

It allows for locomotion and feeding Signup and view all the answers

Which type of symmetry do adult echinoderms display?

Pentaradial symmetry Signup and view all the answers

Which statement regarding the reproductive strategies of echinoderms is accurate?

Some are hermaphrodites and produce both eggs and sperm Signup and view all the answers

What unique ability do sea cucumbers possess for self-defense?

They eject their internal organs Signup and view all the answers

How do echinoderms primarily extract oxygen from water?

Using their tube feet Signup and view all the answers

Which of the following echinoderm classes contains species known for having a hard outer shell?

Class Echinoidea Signup and view all the answers

What common characteristic is shared among all echinoderms during their larval stage?

They exhibit bilateral symmetry Signup and view all the answers

Study Notes

Echinoderms

Marine invertebrates with endoskeletons made of calcium carbonate plates
About 7,000 species
Found in benthic ecosystems, including intertidal zones, coral reefs, and deep ocean trenches
Live in tropical, temperate, and colder waters
Classified into five classes: Asteroidea, Ophiuroidea, Crinoidea, Echinoidea, and Holothuroidea

Class Asteroidea

Includes sea stars (starfish)
About 2,000 species
Most species have five arms extending from a central disc
Examples include: common starfish, purple sunstars, and sand stars
Three species of tiny sea daisies are also in this class
Sessile, resemble flowers or small sea anemones
Live on submerged wood

Class Ophiuroidea

Includes brittle stars
About 2,000 species
Have five arms radiating from a central disc
Very flexible limbs
Move by twisting motion of two arms
Drop damaged or trapped arms
Limbs regenerate quickly
Examples: common brittle star, ruby brittle star, and great basket star
Basket stars are a type of brittle star with branching arms

Class Crinoidea

Includes crinoids (feather stars and sea lilies)
Were abundant during the Mississippian Subperiod
Only a few hundred species exist today
Sessile echinoderms with feathery appendages that emerge from stalks
Feather stars have up to 150 arms
Can crawl or swim near the seafloor
Many crinoids are sessile as adults

Class Echinoidea

Includes sea urchins and sand dollars
Over 900 species
Have a hard outer shell called a test
Sand dollars have short spines, sea urchins have longer, sharper spines
Live at all depths in oceans
Examples: long-spined urchin and keyhole urchin

Class Holothuroidea

Includes sea cucumbers
Roughly 1,200 species
Range in size from less than one inch to over 6 feet in length
Tapered, cylindrical bodies
Have toxic internal organs they eject at predators
Can regenerate their internal organs
Can project hook-like structures from their skin

Echinoderm Movement

Slow-moving (sea urchins, sea stars) or sessile (sea lilies, sea daisies)
Use a water vascular system to move: water through canals and into tube feet
Tube feet excrete sticky chemicals to adhere to surfaces and prey
Brittle stars move quickly due to serpentine motion of limbs
Start their lives as free-swimming larvae
Some can swim as adults (sea cucumbers, feather stars )

Echinoderm Skin & Organs

Thin layer of skin called an epidermis
Spiny texture from bumps and ridges in the endoskeleton
Sand dollars and sea urchins have true spines
Sea cucumbers do not have plates, have tiny spicules embedded in their skin
Loosely organized nervous system with a neural net
Nerve ring encircles the mouth connected to radial nerves in the arms of sea stars and brittle stars
No brains or eyes, can sense light and movement through eyespots
Open circulatory systems
Most lack organized respiratory systems: use tube feet to extract oxygen from water and tiny skin gills to bring in oxygen and release carbon dioxide
Digestive systems vary: most have complete systems, sea stars excrete most waste through tube feet

Echinoderm Symmetry and Limbs

Larvae exhibit bilateral symmetry
Adult echinoderms exhibit pentaradial symmetry: five projections extending from a central point
Arms extending from a central disc (sea stars)
Feathery feeding tentacles (sea cucumbers)
Tube feet also arranged in fives

Echinoderm Reproduction & Regeneration

Reproduce sexually by producing eggs and sperm
Some are hermaphrodites
Some brood their eggs
Other echinoderms produce free-floating or swimming larvae
Brittle stars and sea stars regenerate limbs
Can create entire organisms through fission
Develop whole organisms if divided through their central discs
Sea urchins and sea cucumbers also reproduce if divided in two

Echinoderm Diet

Sea urchins are grazers
Sea lilies and sea cucumbers use feeding tentacles
Brittle stars collect small pieces of algae and animal matter with tube feet
Sea stars are active predators: pursue sessile or slow-moving prey
Attach to prey with tube feet
Can pry open bivalve shells
Turn their stomach inside out and insert it into the shell
Excrete enzymes to digest prey
Pull the stomach back into its body

Role of Echinoderms in Ecology

Keystone species in many ecosystems
Sand dollars and sea cucumbers oxygenate the seafloor
Brittle stars, sea stars, and sea urchins are food sources
Sea urchins keep algae growth in check
Sea stars clean the seafloor by consuming dead animals
Overpopulation can be problematic
Overpopulation of purple sea urchins has decimated sea kelp beds
Crown-of-thorns sea stars are voracious coral predators

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Description

Explore the fascinating world of echinoderms, marine invertebrates with unique features such as endoskeletons made of calcium carbonate. This quiz covers various classes including Asteroidea and Ophiuroidea, highlighting their characteristics and habitats. Test your knowledge of these diverse species found in different marine ecosystems.