Chapter 14: Echinoderms and Hemichordates Flashcards
Libbie Hyman described echinoderms as “a noble group especially designed to puzzle the zoologist.” Why is this an accurate description?
They have many different characteristics, forms, and behaviors that vary between species. Unique combination of characteristics
Who are the closest extant relatives of echinoderms?
Hemichordates and Chordates
List and describe the classes that comprise phylum Echinodermata.
Class Asteroidea- 1500 extant species, Sea stars
Class Ophiuroidea- bittle stars and basket stars
Class Echinoidea- Sea urchins, sand dollars, and heart urchins; 2 shapes (irregular and regular); wide distribution; test
Class Holothuroidea- sea cucumbers; 1150 extant species
Class Crinoidea- sea lilies and feather stars; attached to substrate for most of life; 625 extant species.
Describe the functions of pedicellariae
Used for protection; contain venomous glands.
Explain catch collagen. Why is it advantageous to sea stars?
Connective tissue that can quickly change from a liquid to solid; allow echinoderms to hold posture without muscles.
How does gas exchange and excretion occur in sea stars?
The coelom allows for an exchange of gases and excretion of wastes via diffusion. Wastes exit through tube feet.
Describe feeding in sea stars.
Mouth contains a 2-part stomach in the central disc. The cardiac stomach can be everted through the mouth during feeding.
Describe reproduction in sea stars.
External fertilization
Regeneration- can regenerate even when all arms are lost; only requires central disc
Describe regeneration and autotomy in sea stars.
Regeneration- able to replicate new sea stars as long as central disc is present.
Autonomy- detachment of a body part voluntarily if injured; takes month to regenerate
Describe the ways that brittle stars differ from sea stars.
Arms are slender, no peridellariae, ambulacral grooves are closed and covered in ossicles, tube doesn’t have suckers, arms are jointed,no anus, leathery skin
Do brittle stars share any similarities with sea stars? If so, what are those similarities?
Yes, they both contain a nervous system and Water Vascular system.
What sets a basket star apart from a brittle star?
Contain branching tendrils and much larger
How many sets of branching legs do basket stars typically have?
5 sets or more
Can basket stars regenerate their limbs like sea stars do?
Yes
Describe the distribution of basket stars.
Found in all of the world’s oceans, and live at depths of a few feet to over 4000 feet.
Basket stars eat a variety of foods. What are they?
Plankton, jellyfish, Fish Larvae, and Crustaceans
Describe the way that basket stars catch prey.
Their branches contain hooks that snag food from the water. The branching tendrils then travel to their jaws where food is deposited.
Basket stars are nocturnal. What is the advantage to hunting at night?
Predators are less likely to spot them at night
Does the life cycle of all basket stars include a larval stage?
No, some do not have a larval stage and appear as adults
Describe asexual reproduction in basket stars.
Splitting, a piece of one individual can become separated and form into a clone
Describe the two shapes of echinoids.
Regular- spherical shape; radial symmetry Ex. Most urchins
Irregular-secondarily bilateral; short spines Ex. Sand dollar & heart urchins
Example of Regular Shaped Echinoid
Most Urchins
Example of Irregular Shaped Echinoid
Sand dollar and heart urchin
Describe the distribution of echinoids.
Found in all seas (intertidal to deep oceans);
What are the habitat preferences of regular urchins?
Rocky or hard substrate
What are the habitat preferences of sand dollars and heart urchins?
Burrowing into sand
Describe the anatomy of the test and pedicellariae of echinoids.
Test- compact skeleton containing 10 double rows of plates with stiff moveable spines
Pedicellariae- 3 jaws and mounted on long stalks; have venom glands to paralyze prey
Describe digestive system of Echinoids
Coiled inside of the Test
What is Aristotle’s Lantern
Complex Chewing apparatus in Echinoids
Describe reproduction in echinoids.
Separate sexes; external fertilization; start as Echinopluteus Larvae for several months
What do Echinoids start as?
Echinopluteus Larvae
Describe the anatomy of sea cucumbers.
Greatly enlongated; reduced ossicles; leathery body wall; no cephalization
Class Holoturoidea=?
Sea cucumbers
Does the life cycle of all sea cucumbers include a larval stage?
Most do, there are exceptions however; one species broods young inside of themselves
List and describe 3 adaptations for swimming that some species of sea cucumbers have.
Some have skirts, sails, aural tentacles to pull themselves along
Describe sea cucumber tentacles.
Highly modified tube feet powered by water pressure; covered in mucus substance that traps food.
What do sea cucumbers eat?
Dead decaying flesh, the sea floor, algae, waste
Explain nutrient cycling.
Processing waste and excreting it in a form that other organisms can eat.
Describe the functions of the sea cucumber’s cloaca.
Respiration (attached to respiratory tree), Nutrient Retrieval, Lifting Off of Ground
Describe the defense mechanisms that sea cucumbers have to avoid predation.
Contain toxins that make it unappetizing, May have tubules attached to breathing apparatus that forces water out as well as the tubules that become sticky and tangle up predators
When threatened, sea cucumbers can undergo a process called evisceration. Explain that process.
Special collagen will go soft in certain places and allow them to rupture and expel intestines/organs out of their bodies; giving predators something to eat. Also allows for them to clean out themselves.
List and describe the members of class Crinoidea.
Sea Lilies- attach to substrate for most of life; flower shaped body at tip of stalk
Feather Stars- many long, branched arms, free moving, use cirri to crawl
What do feather stars use to crawl?
Cirri
What do feather stars use to swim?
Sweeping motion of long feathery arms
Describe two infestors that live on feather stars. What adaptations do they have to facilitate this lifestyle?
White Shrimp with Black Stripes are able to blend into some feather stars and hide from predators
Brown and White Clingfish has no find and wiggles its way around the feather star arms
Explain “individual fidelity” that’s seen in some infestors.
When an organism returns to the same host within hours
What anatomical features found in other echinoderms are absent in crinoids?
Lack a Madreporite, Spines, Pedicellariae
Describe the characteristics of hemichordates.
Marine animals (worm-like, bottom dwellers) solitary and colonial; have 3-part coelom.
Describe the anatomy of an acorn worm.
Mucus-covered body, long trunk, short collar, contain proboscis for feeding
Describe feeding and digestion in acorn worms.
Deposit feeders- extract organic components from sediments.
Suspension feeders- capture plankton and detritus.
Describe reproduction in acorn worms.
External Fertilization (Dioecious)
