Lecture 20 Key Concepts/Terms

what makes a deuterostome?

blastopore develops into the anus first (rather than the mouth like in protostomes)

homalozoans

ancestral deuterostomes that have similar traits of both echinoderms and chordates, suggesting they are in fact an ancestral group

echinoderms

first deuterostome

echinoderms - pentaradial symmetry

five axes of symmetry (even though they are bilaterians)

echinoderms - skeletons

technically internal skeletons because there is a very thin layer of skin on top, although they act as more of a shell

echinoderm larvae

have bilateral symmetry (become pentaradial in adulthood)

water vasculature system

aids in gas exchange and locomotion; tube feet (water filled canals)

tube feet

Extensions of an echinoderm's water vascular system that stick out from the body and function in movement and obtaining food.

madreporite

sievelike structure through which the water vascular system of an echinoderm opens to the outside

oral and aboral surface

starfish attach to surfaces with their oral surface, aboral surface is the "top"

sexual reproduction in echinoderms

involves separate male and female individuals that release their gametes into the water

asexual reproduction in echinoderms

regeneration (same way as sponges)

extinct echinoderms

20 extinct classes

what are the three extant groups of echinoderms?

crinoids, echinozoans and asterzoans

crinoids

sea lilies and feather stars
can be sedentary or mobile

echinozoans

sea urchins, sand dollars, sea cucumbers
lack arms

sea urchins

echinozoans
hemispherical body form
ball and socket joins on spines

sand dollars

echinozoans
flattened body form
clearest visual pentaradial symmetry in the echinozoans

sea cucumbers

echinozoans
elongated body form
previously thought to be distantly related to urchins and sand dollars

asterozoans

sea stars and brittle stars

sea stars

asterozoans
predatory
live in a range of marina habitats
vary in size

brittle stars

asterozoans
flexible arms that allow for free swimming
arms can't adhere to surfaces (only used for feeding and movement)
nocturnal

acorn worms

hemichordates
sister taxa to echinoderms

dorsal hollow nerve cord

nerve cord found in all chordates that forms the spinal cord and brain

notochord

A flexible rod that supports a chordate's back

pharyngeal gill slits

all chordates share this, appear in the pharynx at some stage in their development, evolved to aid in respiration and filter feeding

post-anal tail

a tail that extends beyond the anus; exhibited by all chordates at some stage of development

chordate segmentation

all chordates are segmented; most of them have their segmentation internally

what are the two groups of non-vertebral chordates?

lancelets and tunicates

chordate traits are easily seen in the _____ form of tunicates

larval

do lancelets show chordate traits?

yes

what are tunicates also sometimes called?

sea squirts

You take Dr. Smith's advice and go to the aquarium. You see a tank labelled Sea Stars. Thanks to BIO200, you know that the sign is incorrect. You know you are looking at brittle starts because the organisms in the tank...

A) ... are pentaradially symmetric
B) ... have a water vascular system
C) ... are anchored to the glass with their tube feet
D) ... are brightly colored
E) ... are swimming freely, using their jointed arms

E) ... are swimming freely, using their jointed arms