Echinoderms and Chordates

Figure 32.11

ANCESTRALPROTIST

Porifera

Ctenophora

Cnidaria

Acoela

True Tissues

Metazoa

Eumetazoa

Bilateria

Hemichordata

Echinodermata

Chordata

Platyhelminthes

Rotifera

Ectoprocta

Brachiopoda

Mollusca

Annelida

Nematoda

Arthropoda

Deuterostom

ia

LophotrochozoaEcdysozoa

Single common animal ancestor

Only phylum containing vertebrates

prot

osto

mes

inve

rteb

rate

s

Bilateral & 3 germ layers

Deuterostomes

• Radial cleavage• Blastopore = anus• Mesoderm from distal end of archenteron

(Mesodermal endoskeleton)

Echinodermata

Feather star

Echinoderms• Pentamerous radial symmetry at full development

– (bilateral as larvae)• Water vascular system• Endoskeleton (CaCO3) covered by thin epidermis (skin)

– Ossicles• No brain or central nerve cord• No separate respiratory and circulatory system• No Excretory and osmoregulatory organs• Complete digestive tract• Typically dioeciously w/ external fertilization

– Larval state

5 Classes

• Asteroidea• Ophiuroidea• Echinoidea• Crinoidea• Holothuroidea

Asteroidea

Asteroidea• Arms radiating from central disc• Tube feet, – Chemical adhesive

• Seastars = Predators• Sea daisies (suspension feeders that use sticky

membrane)• Everts stomach • Can regenerate lost arms

Ophiuroidea (brittle stars)• long slender arms• That can grip• Tube feet (no adhesive)• Mouth on underside• Filter feeders, scavenger, and predators

Feather star

Echinoidea (urchins and sand dollars)• No arms• Retain 5 rows of feet• Elongated spines w/ attached muscles to move them• Grazers and filter feeders• Ossicles fused into a solid/rigid test• Mouth down

Crinoidea (sea lilies and feather stars)• Mouth up• Feather like arms that radiate upward• Filter feed with tubefeet• Sea lilies

– attached to substrate by a stalk• Sea feathers

– crawl on substrate with long featherlike arms

Feather star

Holothuroidea (sea cucumbers)• elongated on short axis• No arms• “no skeleton”• widespread ossicles• No spines• 5 rows of tube feet those around mouth developed

into feeding tentacles

Chordates• Deuterostomes, Bilaterally symmetric bodies w/ coelum• Segmented/metamerism (somites)

Chordate characteristics1. Dorsal Hollow nerve cord:2. Notochord (phylum’s namesake)

3. Pharyngeal slits or clefts (not gill)4. Muscular post-anal tail

Dorsal Hollow Nerve Cord

Cephalachordata (lancelets)• Filter feeding larvae filter feeding “fish-like”

– adults up to 6 cm long• And retain all major chordate characteristics in maturity• Gas exchange occurs across the body surface (not with gills)• Myotomes + notochord swimming • Closed circulatory system• Protonephridia• Dioecious w/ External fert.

Urochordata (tunicates/sea squirts)• Sessile filter feeders, or drifting pelagic filter• Has chordate characteristics in larval stage

– pharyngeal slits only in adult• Incurrent siphon gill slits/pharyngeal basket atrium excurrent siphon• Waste/anus empties into atrium and out the excurrent siphon• Gas exchange across surface• Open circulatory system• Hermaphroditic w/External fertilization• Rapid development with larval stage often lasting only a single day• Bilaterally symmetrical