Week 7: Deuterostomes

Echinoderms- sea stars and sea urchins Four phyla: Echinoderms- sea stars and sea urchins Hemichordata- “acorn worms” burrow in marine sands or muds Xenoturbellida- one genus, only two species- worm-like Chordata- include the vertebrates (have backbones)- fish, sharks, amphibians, mammals, and reptiles Focus on echinoderms and chordates 2

Review: Protostomes vs. Deuterostomes Similarities: Bilaterally symmetric Triploblastic Coelomates Differences: Initial pore development (anus first in deuterostomes) Process of coelom formation in embryonic stages When the embryo is developing, there are three tissue layers- ectoderm (skin, nervous system, teeth, hair, nails, linings of mucous membranes), mesoderm (muscles, red blood cells), and endoderm (GI tract, respiratory tract, urinary system, auditory system, endocrine glands, endocrine organs) Human abdominal cavity- surrounds digestive tract, vital organs– important for protection, movement, etc. 3

Scientific Method: Important Questions What are the big patterns? What processes led to that pattern? Physiological mechanisms Developmental processes Understanding evolutionary history Adaptive significance Why should we care?

Echinoderms- sea stars and sea urchins Four phyla: Echinoderms- sea stars and sea urchins Hemichordata- “acorn worms” burrow in marine sands or muds Xenoturbellida- one genus, only two species- worm-like Chordata- include the vertebrates (have backbones)- fish, sharks, amphibians, mammals, and reptiles Focus on echinoderms and chordates 5

Echinoderms (“spiny skin”) Sea stars, sea urchins, sea cucumbers 7,000 species, found at any depth in the ocean; very abundant, especially deep in the ocean Able to regenerate lost tissues- like limbs Actually radially symmetric 6

Echinoderms Bilaterians (larvae are bilaterally symmetric, but adults have five-sided radial symmetry) Endoskeletons = hard structures made from CaCO3 inside epidermal tissue, protection and support Three major synapomorphies to be familiar with. 7

Echinoderms Water vascular system= branching, fluid-filled tubes Controls the tube feet (movement and feeding) 8

Echinoderms- sea stars and sea urchins Four phyla: Echinoderms- sea stars and sea urchins Hemichordata- “acorn worms” burrow in marine sands or muds Xenoturbellida- one genus, only two species- worm-like Chordata- include the vertebrates (have backbones)- fish, sharks, amphibians, mammals, and reptiles Focus on echinoderms and chordates 9

Hemichordata “Acorn worms” Sister to the echinoderms Marine animals, some are called “acorn worms”, usually live in burrows 10

Echinoderms- sea stars and sea urchins Four phyla: Echinoderms- sea stars and sea urchins Hemichordata- “acorn worms” burrow in marine sands or muds Xenoturbellida- one genus, only two species- worm-like Chordata- include the vertebrates (have backbones)- fish, sharks, amphibians, mammals, and reptiles Focus on echinoderms and chordates 11

Xenoturbellida Marine, worm-like Only one genus, two species 12

Echinoderms- sea stars and sea urchins Four phyla: Echinoderms- sea stars and sea urchins Hemichordata- “acorn worms” burrow in marine sands or muds Xenoturbellida- one genus, only two species- worm-like Chordata- include the vertebrates (have backbones)- fish, sharks, amphibians, mammals, and reptiles Focus on echinoderms and chordates 13

Chordata Sea squirt >65,000 species, most diverse of the deuterostomes Includes vertebrates but also cephalochordates and urochordates 14

Chordate Synapomorphies Pharyngeal gill slits Dorsal hollow nerve cord Notochord Muscular, post-anal tail Pharyngeal gill slits- slits that open into the throat, found in developing human embryo (in vertebrates they’re pharyngeal pouches– can develop into gills in marine fish) 15

Chordate Synapomorphies Pharyngeal gill slits Dorsal hollow nerve cord Notochord Muscular, post-anal tail Pharyngeal gill slits- slits that open into the throat, found in developing human embryo Dorsal hollow nerve cord- runs the length of the body, composed of projections from neurons; a hollow tube; in humans (and all vertebrates) it was modified into the brain and spinal cord Notochord- stiff, supportive, flexible rod that runs the length of the body (ventral to the nerve cord), support for the body and movement, but in vertebrates it disappears after embryo development- it still helps organize the body plan during embryo development Like our tailbone 16

Cephalochordates (lancelets) “Fish-like,” burrow in sand, suspension feed Muscle contractions on either side of notochord help with movement 18

Urochordates (sea squirts) Pharyngeal gill slits help with feeding and gas exchange Nerve cord, notochord, and tail help with swimming

Vertebrates Brain and spinal cord (the dorsal hollow nerve cord)– nerve cells that run from brain to posterior of body Pharyngeal pouches in embryos Notochord only in embryos, replaced with vertebrae (important segmentation)

Chordates: Vertebrates Pharyngeal gill slits Dorsal hollow nerve cord Notochord Muscular, post-anal tail Vertebrates: Pharyngeal pouches, not slits Spinal cord, not dorsal hollow nerve cord *Vertebrae, not notochord Pharyngeal gill slits- slits that open into the throat, found in developing human embryo (in vertebrates they’re pharyngeal pouches– can develop into gills in marine fish) 25

Vertebrates: Major Synapomorphies Vertebrae (column of cartilaginous or bony structures; protects spinal cord) Cranium (bony, cartilaginous, or fibrous case enclosing the brain; protects brain and eyes)

Key innovations 480 mya: Bony exoskeleton 440 mya: Jaws 420 mya: Bony endoskeleton 365 mya: Limbs for moving on land (tetrapods) 340 mya: Amniotic egg Jaws- important for being able to actually bite food Tetrapods- include mammals, reptiles, and amphibians Amniotic egg- egg that has membranes surrounding a food supply, water supply, and waste repository– in the mammals and reptiles 27

Question 1 What synapomorphy distinguishes animals as a monophyletic group, distinct from choanoflagellates? Multicellularity Movement via hydrostatic skeleton Growth by molting Ingestive feeding

Question 1 What synapomorphy distinguishes animals as a monophyletic group, distinct from choanoflagellates? Multicellularity Movement via hydrostatic skeleton Growth by molting Ingestive feeding

Question 2 Which of the following patterns in animal evolution is correct? All tripoblasts have a coelom All tripoblasts evolved from a common ancestor that had a coelom Sponges have epithelial tissues that line an enclosed fluid-filled cavity Bilateral symmetry and cephalization evolved once

Question 2 Which of the following patterns in animal evolution is correct? All tripoblasts have a coelom All tripoblasts evolved from a common ancestor that had a coelom Sponges have epithelial tissues that line an enclosed fluid-filled cavity Bilateral symmetry and cephalization evolved once

Question 3 Which of the following patterns in animal evolution is correct? Segmentation evolved once Coelom was lost or reduced in many lineages Sponges lack true tissue and are asymmetrical Radial symmetry evolved once

Question 3 Which of the following patterns in animal evolution is correct? Segmentation evolved once Coelom was lost or reduced in many lineages Sponges lack true tissue and are asymmetrical Radial symmetry evolved once

Question 4 In a “tube within a tube” what is the interior tube? Ectoderm Mesoderm The coelom The gut

Question 4 In a “tube within a tube” what is the interior tube? Ectoderm Mesoderm The coelom The gut

Question 5 What is the diagnostic trait(s) of vertebrates? Vertebrae and cranium Jaws and spinal cord Endoskeleton constructed of bone Endoskeleton of reinforced cartilage

Question 5 What is the diagnostic trait(s) of vertebrates? Vertebrae and cranium Jaws and spinal cord Endoskeleton constructed of bone Endoskeleton of reinforced cartilage

Question 6 Which lineages make up the living amniota? Reptiles and mammals Viviparous fishes Frogs, toads, salamanders, and caecilians Hagfish, lampreys, and cartilaginous fishes

Question 6 Which lineages make up the living amniota? Reptiles and mammals Viviparous fishes Frogs, toads, salamanders, and caecilians Hagfish, lampreys, and cartilaginous fishes

Question 7 True or false? Vertebrates were able to harvest food by biting before jaws evolved. The hypothesis that tetrapod limbs evolved from fish fins has been supported by molecular evidence.

Question 7 True or false? Vertebrates were able to harvest food by biting before jaws evolved. False The hypothesis that tetrapod limbs evolved from fish fins has been supported by molecular evidence. True