Zoo 110 lec final: Other deuterostomes

Echinoderms & Chordates

Phylogenetic relationships of Echinodermata + Hemichordata within Ambulacraria

1. Ambulacraria includes Echinodermata (starfish, sea urchins) and Hemichordata (acorn worms, pterobranchs).

   1. share a common ancestor within Ambulacraria

2. Molecular and morphological studies suggest that Hemichordata are more closely related to Chordata than to Echinodermata

3. share certain features, like the water vascular system

Characteristics of Deuterostomia

1. Coelom develops by enterocoely

2. Blastopore = anus

3. Gill slits in the pharynx

4. Radial cleavage

5. Regulative development

First 3 synapomorphies of Phylum Echinodermata

1. Endoskeleton

   1. soft tissue of large plates or small scattered ossicles

2. Water-vascular system

3. Tube feet (pedicellariae)

Last 4 synapomorphies of Phylum Echinodermata

1. Dermal branchiae

   1. Gills on their skin

2. No brain

   1. simple sense organs

3. Limited open circulatory system

4. No respiratory/excretory systems besides skin gills

What are the five classes within Echinodermata

1. Crinoidea

2. Asteroidea

3. Ophiuroidea

4. Echinoidea

5. Holothuroidea

Class Crinoidea animals

Sea lilies & feather stars

Class Crinoidea features

1. Sessile adults

   1. stalk + holdfast (anchor mechanism) 

   2. Some have a really large stock covered in skeletal plates

   3. Inside calyx is the mouth that have arms around them to filter feed

2. Marine, mostly deep water

3. Arms with pinnules for filter feeding, Ambulacral groove transports food

   1. ambulatory-> ability to walk

4. Excellent fossil record

Class Asteroidea animals

Sea stars

Class Asteroidea features

1. 1500 species, living on rocky, sandy, or muddy substrates

2. Predators

   1. particularly of bivalves

3. Morphology:

   1. At least 5 arms (can have more)

   2. Oral (belly side with mouth) + aboral (we see this side) surfaces

   3. Tube feet in ambulacral grooves

   4. Water Vascular System

Class Ophiuroidea animals

Brittle stars and basket/serpent stars

Class Ophiuroidea features

1. Five arms, no pedicellariae, respiration using gills

2. Closed ambulacral grooves

   1. By shields formed by skeletal series of plates

3. Tube feet without suckers, 

   1. move by muscular action(contraction) of arms

   2. Snaking around to move their body

   3. Alien like***

4. Generally feed on small particles

Class Echinoidea animals

Urchins & sand dollars

Class Echinoidea features

1. Closed ambulacral grooves; ambulacral areas extend up sides of body

2. Spines present, often used for locomotion, no arms present

   1. Sand dollars spines are really tiny

3. Tube feet and pedicellariae well developed

4. Test

5. Complex mouthpart

   1. Aristotle’s lantern

6. Generally herbivores, but some species may be carnivores

Class Holothuroidea animals

Sea cucumbers

Class Holothuroidea features

1. Elongated oral-aboral axis

   1. Oral end —--body—- aboral end

2. Reduced ossicles

3. Lie on side

   1. tube feet typically developed on bottom side only to inch along the seafloor

4. Series of oral tentacles around mouth

5. Feed on small particles

Sea star water vascular system

Madreporite allows water in→ stone canal→ ring canal→ radial canals→ lateral canals→ ampullae→ tube feet

Sea star water vascular system function

1. locomotion

2. circulation

   1. water, nutrients, and gases throughout the body

General soft tissue anatomy of the sea star

1. Epidermis

   1. spines, pedicellariae, and dermal branchiae

2. Coelom: 

   1. Internal body cavity filled with coelomic fluid

3. Digestive System: 

   1. Mouth, stomach, intestine, and anus

4. Reproductive System

   1. Gonads in the arms, external fertilization

How do Sea cucumber breathe

1. Breathe through anus

   1. Respiratory tree off of cloaca

      1. Site for diffusion of gasses from the sea water

      2. Bringing it in by opening and closing their anus

How do Sea cucumber defend against predators

1. Can eject guts as defense mechanism

   1. Can regenerate their entire gut after ejecting them

What phylum represents our closest invertebrate relatives?

1. Hemichordates (acorn worms)

   1. Pharyngeal Slits

   2. Notochord-like structure

   3. Dorsal Nerve Cord

2. considered to be a sister group

Why are Hemichordates our closest invertebrate relatives

1. Pharyngeal Slits

2. Notochord-like structure

3. Dorsal Nerve Cord

4. considered to be a sister group

What larvae type does class Crinoids have?

1. Doliolaria

   1. Has cilia on its body

What larvae type does class Asteroids have?

1. Bipinnaria + Brachiolaria

   1. Two larval stages

What larvae type does class Opiuroids have?

Ophiopluteus

What larvae type does class Echinoids have?

Echinopluteus

What larvae type does class Holothuroids have?

Auricularia

What type of symmetry do larval echinoderms have?

bilateral symmetry

What type of symmetry do adult echinoderms have

pentaradial symmetry

What type of nervous system is present in echinoderms?

1. simple nervous system

   1. decentralized and lacks a true brain

   2. Nerve ring around the mouth

      1. Branches out into radial nerves that extend along each arm

   3. Radial nerves control the movement of the tube feet and coordinate other motor functions

What type of circulatory system is present in echinoderms

1. Open circulatory system

   1. rely on the coelomic fluid and water vascular system to transport nutrients, gases, and waste products

What do different echinoderms feed on?

Many carnivorous, feeding on molluscs, crustaceans, polychaetes, echinoderms, fishes, etc. 

How do class asteroidea feed?

1. Can evert their cardiac stomach through their mouth into the shells of their prey to engulf them

   1. Evert stomach between valves of bivalve shell

How do class Ophiuroidea feed?

1. Omnivorous

   1. use their tube feet to capture prey

2. ~  suspension feeders

How do class Echinoidea feed?

Use Aristotle’s lantern to eat algae

How do class Holothuroidea feed?

Detritivores and Filter Feeders via tentacles

How do sea urchins impact California’s kelp forests?

1. By creating Urchin barrens

   1. Allows them to take over fields of kelp

What are the five synapomorphies of Phylum Chordata

1. Notochord

   1. As you get bigger this will go away-> is reduced down and replaced

   2. Only fully found in lamprey and hagfish

2. Dorsal hollow nerve cord

   1. Dorsal to digestive tract & forms a tube

   2. This can become reduced in some species

3. Pharyngeal (gill) slits

   1. Highly vascularized 

   2. Lead to gills in aquatic species

4. Endostyle

   1. Takes food to the gut easily via mucous it secretes

   2. Becomes your thyroid gland

5. Postanal tail

   1. tail for swimming purposes

   2. Gets reduced the further out of the water species go

First 6 characteristics of chordates

1. Bilateral symmetry

2. segmented but with frequently inconspicuous segmentation

3. Triploblastic + eucoelomate 

   1. (with well-developed coelom)

4. Epidermis present, 

   1. dermis present in vertebrates

5. Complete digestive system

6. Smooth, skeletal, and cardiac muscle

Last 6 characteristics of chordates

1. Vertebrates with a three-lobed brain

2. Photoreceptors + statocysts 

   1. (simple in protochordates, more developed in vertebrates)

3. Sexes usually separate except for in sea squirts + some fishes

4. Vertebrates with paired glomerular kidneys

5. Respiration by gills, lungs, and skin

6. Closed circulatory system, vertebrates with chambered hearts + RBCs

What are the 3 Subphylum of phylum Chordata

1. Urochordata

2. Cephalochordata

3. Vertebrata

First 4 features of Subphylum Cephalochordata (Amphioxus/Branchiostoma)

1. Lancelets 

2. ~All they do is bury themselves in sand and eat***

   1. Generate a water current by beating cilia

      1. Wheal organ in mouth

      2. Endostyle that will secret mucus in pharyngeal slits to trap food particles to then pass down to the gut

3. Notochord extends to tip of head (cephalo- + chord)

4. Marine, fishlike filter feeders in sandy environments

Last 4 features of Subphylum Cephalochordata (Amphioxus/Branchiostoma)

1. Possess all five chordate synapomorphies

2. Segmented muscles (myomeres)

3. Circulatory system similar to vertebrates, but no heart

   1. Contraction of muscles to move blood

4. No gills, kidneys, liver (do have a cecum tho), or brain

What are the 9 synapomorphies of subphylum Vertebrata?

1. Vertebrata have vertebrae!

2. Endoskeleton of bone or cartilage

3. Muscularized pharynx

   1. We don’t need a ciliated current to pump water

4. Gills (lost in tetrapods)

5. Chambered heart

6. Tripartite brain

7. Well-developed, paired sense organs (nose, eyes, ears)

8. Liver & pancreas

9. Glomerular kidney

What is the one extinct Agnathans we learned?

Ostracoderms

What are some basic features of Ostracoderms

1. Armored with a bony dermis

   1. Fossilizes well

2. Most had no paired fins, and those that did formed fins from their dermal bone (not the endoskeleton)

   1. Weren’t true fins

3. Pulled water into pharynx by muscular pumping

   1. To filter out sediment 

4. Probably filtered food from sediment, but may have been predators of soft-bodied animals

5. Extinct at the end of the Devonian

What is one extinct Gnathostomes we learned?

Placoderms

What are some basic features of Placoderms

1. Earliest group to have paired fins (appendages) + jaws ***

2. Huge morphological diversity

3. Silurian – Devonian

   1. extinct at end of Devonian

4. Armor extended back to pectoral girdle (shoulders) 

5. Origin of internal fertilization***

6. Origin of viviparity

How are placoderms different from ostracoderms?

1. Jaws

2. Armor Structure

   1. Placoderms had true bony armor 

      1. on head & thorax

      2. Fused boney-plates

   2. Ostracoderms were armored fish 

      1. covered most or all of their body.

      2. made of non-fused bony plates or scales

3. Significance

   1. Placoderms were one of the first major lineages of jawed vertebrates

   2. Ostracoderms primitive jawless vertebrates, early evolutionary stage

Are any groups of chordates non-monophyletic? If so, which ones?

1. Yes

   1. Agnatha

   2. Amphibia

   3. Reptilia

   4. Fish

Which chordate group is sister to Subphylum Vertebrata?

1. Urochordata (tunicates)

   1. presence of a notochord, dorsal nerve cord, pharyngeal slits, and a post-anal tail

Are chordates monoecious or dioecious? Are there any exceptions to this rule?

1. Majority of species are dioecious

2. Exceptions

   1. Some fish species

   2. Cephalochordata-> Amphioxus (Lancelets)

   3. Urochordata-> Tunicates

Why is it challenging to reconstruct the origins of Chordata?

1. Incomplete Fossil Record

   1. Earliest chordates were probably soft-bodied=> Didn’t fossilize well

2. Lack of Clear Transitional Forms

3. Molecular vs. Morphological Data Discrepancies

4. Evolutionary Radiation

   1. underwent rapid diversification early in their history

   2. makes it challenging to reconstruct the exact sequence of evolutionary events that led to the emergence of the phylum

Are representatives of Subphylum Urochordata sessile or pelagic? Any exceptions?

1. Adults are sessile (some pelagic)

2. larva is pelagic

Why was Garstang’s Hypothesis of Larval Evolution rejected?

1. Lack of fossil support showing vertebrates evolving from larval forms.

2. Adult features appear to have evolved directly in early vertebrates, not through a larval form.

3. Neoteny is not a dominant evolutionary mechanism in the origin of vertebrates.

4. Modern developmental genetics and evolutionary biology support different pathways of chordate evolution

Why are larval lampreys (ammocoetes) a good model for the ancestral vertebrate?

1. Exhibit several primitive features that resemble the early characteristics of vertebrates

2. Anatomy gives us a clue to what the early vertebrate looked like

   1. simple body plan, lack of jaws, and primitive circulatory and nervous systems

What “firsts” are present in “Class” Placodermi? (think about feeding & reproduction!)

1. Origin of internal fertilization***

2. Origin of viviparity

3. Earliest group to have paired fins (appendages) + jaws