BIS2C: Lecture 31: Deuterosomes I: Echinoderms & Hemichordates

Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016

Lecture 31:

Deuterosomes I: Echinoderms & Hemichordates

BIS 002C Biodiversity & the Tree of Life

Spring 2016

Prof. Jonathan Eisen1

• SLIDES AVAILABLE AT http://tinyurl.com/BIS2CL31

Where we are going and where we have been…

•Previous lecture: •30: Triploblasts: Protostomes:

Ecdysozoans II I

•Current Lecture: •31: Deuterosomes I: Echinoderms &

Hemichordates

•Next Lecture: •31: Deuterosomes II: Chordates

Topics ..

• Deuterostome innovations and uses of these innovations

• Major Groups of Deuterostome

• Focus on Echinoderms

• Innovations

• Symmetry

• Tube feet

• Chordate Introduction

Animals - AKA Metazoans

Metazoans

Clicker

What evidence supports the assertion that the common ancestor of metazoans at least colonial, if not multicellular?

A. Comparisons of modern metazoans

B. Comparisons of metazoans to choanoflagellates

C. Neither A nor B

D. Both A and B

!6Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016

Clicker

What evidence supports the assertion that the common ancestor of metazoans at least colonial, if not multicellular?

A. Comparisons of modern metazoans

B. Comparisons of metazoans to choanoflagellates

C. Neither A nor B

D. Both A and B

Clicker

What is the best evidence that sponges are the deepest branching group within the metazoa?

A. They are the most primitive animals

B. They have cells similar to those seen in choanoflagellates

C. All other animals are more complex

D. Sponges are not bilaterally symmetric

E. Branching patterns in molecular phylogenies

Clicker

What is the best evidence that sponges are the deepest branching group within the metazoa?

A. They are the most primitive animals

B. They have cells similar to those seen in choanoflagellates

C. All other animals are more complex

D. Sponges are not bilaterally symmetric

E. Branching patterns in molecular phylogenies

Figure 31.1 A Phylogenetic Tree of the Animals

Notochord

Hemichordates

DEUTEROSTOMES (Chapter 33)

Chordates

EchinodermsRadial symmetry

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

PROTOSTOMES (Chapter 32)

Centopheres

Sponges (Chapter 33)

Diploblasticanimals(Chapter 31)

Bilaterains(triploblastic)

etazoans

Notochord

Hemichordates

Chordates

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

Centopheres

etazoans

Common ancestor

Notochord

Hemichordates

Chordates

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

Centopheres

etazoans

Common ancestor

•Colonial •Cell adhesion systems

Notochord

Hemichordates

Chordates

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

Centopheres

etazoans

Common ancestor

Notochord

Hemichordates

Chordates

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

Centopheres

etazoans

Unique cell junctions; collagen and proteoglycans in extracellular matrix

Common ancestor

Notochord

Hemichordates

Chordates

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

Centopheres

etazoans

Multicellularity, Blastula

Common ancestor

Notochord

Hemichordates

Chordates

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

Centopheres

etazoans

Common ancestor

Monoblasts (Sponges)

Silicaceous spicules

Choanocytes; spicules

Notochord

Hemichordates

Chordates

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

Centopheres

etazoans

Common ancestor

Notochord

Hemichordates

Chordates

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

Centopheres

etazoans

Common ancestor

Eumetazoans

Notochord

Hemichordates

Chordates

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

Centopheres

etazoans

Two embryonic cell layers; nervous system

Common ancestor

Eumetazoans

Notochord

Hemichordates

Chordates

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

Centopheres

etazoans

Common ancestor

Notochord

Hemichordates

Chordates

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

Centopheres

etazoans

Common ancestor

Diploblasts

Notochord

Hemichordates

Chordates

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

Centopheres

etazoans

Common ancestor

Diploblasts

Triploblasts (Bilaterians)

Simplification; loss of nervous system

Notochord

Hemichordates

Chordates

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

Centopheres

etazoans

Common ancestor

Diploblasts

Notochord

Bilateral symmetry along an anterior-posterior axis; three embryonic cell layers

Hemichordates

Chordates

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

Centopheres

etazoans

Common ancestor

Diploblasts

Notochord

Hemichordates

Chordates

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

Blastopore develops into mouth

Centopheres

etazoans

Common ancestor

Diploblasts

Notochord

Hemichordates

Chordates

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

Exoskeleton molting Blastopore develops into mouth

Centopheres

etazoans

Common ancestor

Diploblasts

Notochord

Blastopore develops into anus

Hemichordates

Chordates

Placozoans

Cnidarians

Arrow worms

Lophotrochozoans

Calcareous sponges

Demosponges

Glass sponges

Ecdysozoans

Exoskeleton molting Blastopore develops into mouth

Centopheres

etazoans

Common ancestor

Diploblasts

Animal Diversity

Protostomes

Deuterostomes

Figure 33.1 Phylogeny of the Deuterostomes

General/Common Features of Deuterostomes Common Ancestor

• Development !Radial cleavage !Blastopore becomes the anus

and mouth forms on opposite side

!Coelom develops from mesodermal pockets that bud off from the gastrula cavity

!Triploblastic, coelomate animals with internal skeletons

!Complete gut.

• There are far fewer species of deuterostomes than protostomes.

Three Main Clades

Echinoderms

Hemichordates

Chordates

Ambulacrarians

Chordates

Common ancestor (bilaterally symmetrical, pharyngeal slits present)

Echinoderms

Hemichordates

Lancelets

Tunicates

VertebratesVertebral column, anterior skull, large brain, ventral heart

Notochord, dorsal hollow nerve cord, post-anal tail

bulacrarians

• Two main groups: echinoderms and hemichordates

• Have ciliated, bilaterally symmetrical larvae

• Adult hemichordates are also bilaterally symmetrical.

Ambulacrarians

Chordates

Echinoderms

Hemichordates

Lancelets

Tunicates

Ciliated larvae

bulacrarians

Ambulacrarians

Chordates

Echinoderms

Hemichordates

Lancelets

Tunicates

Radial symmetry as adults, calcified internal plates, loss of pharyngeal slits

Ciliated larvae

bulacrarians

Ambulacrarians - Others - Xenoturbellids

Xenoturbellids

Xenoturbellids (two species): wormlike organisms that feed on or parasitize mollusks in the north Atlantic.

Xenoturbella in the news

• VIDEOS

Ambulacrarians

Xenoturbellids

Ambulacrarians

Xenoturbellids

Acoels

Acoels: also wormlike, live as plankton, between grains of sediment, or on other organisms such as corals.

Ambulacrarians

Xenoturbellids

Acoels

s Not clear exactly where acoels branch in the tree

Figure 33.4 Highly Reduced Acoels Are Probably Relatives of the Ambulacrarians

• See http://www.nature.com/news/2011/110209/full/470161a.html for discussion of acoels

• http://www.latimes.com/science/sciencenow/la-sci-sn-churro-sea-worm-bilateria-20160205-story.html

• http://www.nature.com/nature/journal/v530/n7588/abs/nature16545.html

Clicker

Which of the following topics would studies of Xenoturbellid evolution be most useful for?

A. Origin of diploblasty

B. Origin of radial symmetry

C. Origin of bilateral symmetry

D. Origin of segmentation

E. Origin of blastulas

Clicker

Which of the following topics would studies of Xenoturbellid evolution be most useful for?

A. Origin of diploblasty

B. Origin of radial symmetry

C. Origin of bilateral symmetry

D. Origin of segmentation

E. Origin of blastulas

Protostomes

Xenoturbellids

Ambulacrarians

Xenoturbellids

Acoels

sFocus on Two Main Lineages of Ambulocrarians

Hemichordates

Xenoturbellids

Acoels

s Focus on Hemichordates

Hemichordates

Hemichordates Body Plan

Saccoglossus kowalevskii

ProboscisCollarTrunk

Proboscis

Proboscis used for feeding and locomotion and sometimes protection

Collar

Collar contains a stomochord similar to the notochord of chordates

Trunk contains pharynx and pharyngeal gill slits

For Your Personal Enjoyment

Group 1: Acorn worms

• Up to 2 m long, burrow in soft marine sediments

• Digestive tract is a mouth, pharynx, and intestine

• The pharynx opens to the outside via pharyngeal slits.

• Vascularized tissue around the slits is a gas exchange surface.

• Prey is captured with the large proboscis, which is covered in sticky mucus.

Acorn Worms

Slides by Jonathan Eisen for BIS2C at UC Davis Spring 2016 43

Group 2: Pterobranchs

• Sedentary marine animals that live in tubes secreted by the proboscis.

• Some are solitary, others form colonies.

• The collar has one to nine pairs of arms with tentacles for prey capture and gas exchange.

Ambulacrarians

Chordates

Echinoderms

Hemichordates

Lancelets

Tunicates

Ciliated larvae

bulacrarians

Focus on Echinoderms

Ambulacrarians

Chordates

Echinoderms

Hemichordates

Lancelets

Tunicates

Ciliated larvae

bulacrarians

Focus on Echinoderms

Echinoderms

Diversity

~7,500 species

Symmetry

Larvae are

bilateral

Echinoderm Symmetry

Body Plan

Aboral (top)

Oral (bottom)

No head or brain

Water Vascular System

Water enters through pores known as madreporites

Circulates through canals that lead to tube feet

Hydraulic system used for locomotion, feeding, waste transport, respiration

Echinoderm Video

Endoskeleton

• Endoskeleton derived from mesoderm • The endoskeleton is covered in epidermis • The skeletal plates are connected by collagen which can be

stiff or flexible which controls body tone without muscle

Echinoderm Endoskeleton

For your personal enjoyment

Crinoidea- Sea Lily’s and Feather Stars

• 600 described extant species, many more in the fossil record • Both shallow water and deep trenches • Oral surface in dorsal, aboral surface is ventral • Sea Lily’s are attached to the surface by a stalk

Fossil Sea Lily’s, 330 mya

Feather Star

Asteroidea- Sea stars

• 1500 described species, both shallow and deep habitats • Mostly predaceous with an evertable stomach • Remarkable capacity for regeneration

Pycnopodia- sunflower star

Asteroidea- Evertable stomach

• When feeding, sea stars can extend their stomach pushing it through very small openings • The water vascular system is used to slowly pull muscles apart along with specialized ‘catch collagen’

Asteroidea- Crown of Thorns

• Among the largest sea stars, spines have neurotoxins • Voracious predator of coral (Great Barrier Reef) • Introduced species that is difficult to control

Ophiuroidea- Brittle stars and basket stars

• 1,900 described species • Long, slender arms often with spines; fast moving • Secretive predators, some are bioluminescent

Brittle Star Basket Star Basket Star

Echinoidea- Sea Urchins and Sand Dollars

• 950 described species • Slow moving, grazers on algae (Aristrotle’s lantern) • Protected by spines (urchins) and a calcareous test

StrongylocentrotusAristotle’s lantern

Echinoidea- Sea Urchins and California Kelp

• Urchins feed on kelp (brown algae) • Kelp forests in California harbor a great diversity of species • If unchecked, urchins can create ‘urchin barrens’ • Sea otters prey on urchins (using tools) keeping populations in check; they are a keystone species

Kelp forest, Monterey Bay

Holothuroidea- Sea Cucumbers

• 1,200 described species, scavengers and filter feeders • Soft-bodied, secondary bilateral symmetry* • Catch collagen allows them squeeze into tight places • Unique defense (evisceration), some are toxic

Chordates

Echinoderms

Hemichordates

Lancelets

Tunicates

Ciliated larvae

bulacrarians

Focus on Chordates

Deuterostomes

Chordate Derived Traits Most Apparent in Juveniles

Notochord

• Notochord is a dorsal supporting rod. • Core of large cells with fluid-filled vacuoles, making it rigid but

flexible. • In tunicates it is lost during metamorphosis to the adult stage. • In vertebrates it is replaced by skeletal structures.

Dorsal hollow nerve cord

• Formed by an embryonic folding of the ectoderm • Develops to form the central nervous system in vertebrates

Post Anal Tail

• Extension of the body past the anal opening • In some species (e.g., humans) most visible in embryos • The combination of postanal tail, notochord, and muscles

provides propulsion

Pharyngeal Slits

• The pharynx is a muscular organ that brings water in through the mouth (via cilia) which then passes through a series of openings to the outside (slits).

• Ancestral pharyngeal slits present at some developmental stage; often lost or modified in adults.

• Supported by pharyngeal arches.

Clicker

Why are pharyngeal slits NOT considered a synapomorphy of chordates?

A. They occur in other deuterostomes B. They are lost in some chordates C. They are modified into gills in vertebrates D. They only occur in the embryo of some chordates

Clicker

Why are pharyngeal slits NOT considered a synapomorphy of chordates?

A. They occur in other deuterostomes B. They are lost in some chordates C. They are modified into gills in vertebrates D. They only occur in the embryo of some chordates

Figure 33.1 Phylogeny of the Deuterostomes

Chordates

Echinoderms

Hemichordates

Lancelets

Tunicates

Ciliated larvae

bulacrarians

Focus on Chordates

Chordates

Echinoderms

Hemichordates

Lancelets

Tunicates

Ciliated larvae

bulacrarians

Three Major Groups *Lancelets *Tunicates *Vertebrates

Lancelets (aka Cephalochordates)

Chordates

Echinoderms

Hemichordates

Lancelets

Tunicates

Ciliated larvae

bulacrarians

Focus on Lancelets

Branchiostoma lanceolatum

TailAnusDorsal hollow nerve cord

NotochordPharyngeal slits

Lancelet Has Key Chordate Features

Branchiostoma lanceolatum

TailAnusDorsal hollow nerve cord

NotochordPharyngeal slits

Lancelet Features

• Lancelets (aka amphioxus) are very small, less than 5 cm.

• Notochord is retained throughout life.

• Burrow in sand with head protruding; also swim.

• Pharynx is enlarged to form a pharyngeal basket for filtering prey from the water.

• Fertilization takes place in the water.

• Segmented body muscles

Lancelet development

Tunicates

Chordates

Echinoderms

Hemichordates

Lancelets

Tunicates

Ciliated larvae

bulacrarians

Focus on Tunicates

Adult Tunicates

• Tunicates (sea squirts or ascidians, thaliaceans, and larvaceans):

• Sea squirts form colonies by budding from a single founder. Colonies may be meters across.

• Adult body is baglike and enclosed in a “tunic” of proteins and complex polysaccharides secreted by the epidermis.

Adult Tunicates

• Solitary tunicates seem to lack all of the synapomorphies of chordates?

• No dorsal hollow nerve cord, no notochord, no postanal tail

Adult Tunicates

• Solitary tunicates seem to lack all of the synapomorphies of chordates?

• No dorsal hollow nerve cord, no notochord, no postanal tail

HOW ARE THESE CHORDATES?

Juvenile Tunicates

Ascidian tunicate larva

• Sea squirt larvae have pharyngeal slits, a hollow nerve cord, and notochord in the tail region.

• The swimming, tadpolelike larvae suggest a relationship between tunicates and vertebrates.

• Larvacean tunicates do not undergo the metamorphosis and retain all of the chordate features.

Larvacean tunicates

Vertebrates

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