Ch 34: Hemichordates and Chordates

Deuterostomes part 2 - Echinoderms, Hemichordates, Chordates

Phyla Hemichordata

Acorn worms

deposit feeders

bilateral symmetry

2 of 4 chordate characteristics:

• pharyngeal gill slits

  • allow water to leave and filter nutrients (we had them as embryos)

• dorsal hollow nerve cords

marine worms that live in mud, sand, and under rocks

Tornaria larva: very similar to bipinnaria echinoderm larva

3 main body parts: proboscus (before the mouth, sand burrowing) — collar — trunk

• mouth between proboscus and collar

class Enteropneusta: gut breathing — reference to gill slits (acorn worms)

Hemichordata Class Pterobranchia (body plan)

“wing gills”

deep oceans

secrete a tube that they live within

have a U-shaped digestive tube

• complete with diverticuliti

planula-like larva

closed circulatory system (blood lacks cellular elements and color)

filter feeders

gill slits

excretory: diffusion across body wall

Decentralized NS

diecious (external fertilization)

Phylum Chordata (“cord”)

Small phyla

5% are invertebrates: Two invertebrate groups

• Urochordates (sea squirts/tunicates, make up 90% of invertebrate chordates) and cephalochordates (lancelets)

Diverged from common ancestor shared with echinoderms

• Because of egg yolk

3 subphylum:

• Cephalochordates (lancelets)

• Urochordates (tunicates)

• Vertebrates

  • Myxini (hagfish) and Petromyzontida (lamprey)

4 characteristics

• Notochord

• Dorsal hollow nerve cord

• Pharyngeal slits or clefts

• Post-anal tail

closed circulatory system (ventral heart)

complete digestive system

Lecithal & microlecithal

• latin for yolk

• little amount of yolk (humans and echinoderms)

• megalecithal = large amount of yolk (chicken)

• telolecithal = yolks at one end of the egg — yolk is not evenly distributed between eggs

• homolecithal = yolk is evenly distributed between eggs

endostyle and thyroid

1) gland found in pharynx of basal chordates

• more of a feeding gland that secretes mucus

2) developed into the thyroid gland

• produces T3 and T4

• Important for metabolism, energy production, growth, neurological development

Both require iodine

goiter

hypothyroidism (low iodine)

pharyngeal slits

completely perforate into the pharynx

• can be used for jaw structures, respiration, or feeding

dorsal hollow nerve cord

anterior end forms brain

fluid with cerebrospinal fluid that we are constantly producing

notochord

humans absorb it and can be in spine

flexible rod

pharynx

connects respiratory system and digestive system

• slits:

  • simple: filter nutrients or for respiration

  • evolved: become the jaw, glands, or ear bones

Meckel’s cartilage

only ossified part of the skeleton in Chondrichthyes

Cyclostome (jawless vertrebrates)

Class Myxini: Hagfish

Class Petromyzontida: lampreys

swim bladder

buoyancy device (gas or fat bladder); lung derivative

lobe fins

fleshy, muscular fins

Subphylum Cephalochordata (Lancelets)

named for blade-like shape

used to be named Amphioxus, genus is now Branchiostomata

marine suspension feeders/planktonic; retain notochord in the head

Tapered at both ends, laterally flattened

Subphylum Urochordata (Tunicates or sea squirts)

marine, sessile, or planktonic suspension filter feeders

Tail and developed NS in tunicate larva

• adult: absorbs tail, becomes sessile, NS degenerates

have an outer protective coat called a tunic

draw in water through an incurrent siphon that filters food particles

do not parasitize but can be very invasive

Fewer HOX genes:

• have 9 instead of 13 (less specialization)

monoecious (cross fertilize)

Major transitions in Chrodate history

increase specialization and # of HOX genes as time goes on

Craniates (vertebrates)

Chordates w/head and vertebrate

cranium encasing the brain

significant muscle formation aroung the gut

• smooth muscle: gut muscles that causes peristalsis

Heart on the ventral side

All have cranium (skull), brain, eyes, and other sensory organs

two HOX genes clusters pharyngeal slits, muscles, heart, neural crest cells

• they can dislodge and form structures or form facial defects

what is the significance of the development of heads in chordates?

allows for a new way of feeding in active predation and avoiding predators

neural crest cell formation

become many kinds of important cells and form many important structures

Subphyla Vertebrata

backbone — more efficient at capturing food, moving, and avoiding predation

Hagfish: basal vertebrates

more complex skeletal and nervous systems

• disparity: limbs of different functions, sizes, etc.

expansion of Dlx and HOX genes (second gene duplication)

• Dlx: transcription factors (turn genes on)

• provide opportunity for more complexity

Have

• Vertebral columns: replaces notochord

• Dlx gene duplication: homoeotic

• Elaboration of the skull: becomes thicker, holds sensory organs

• more efficient gills (due to higher metabolic demand) and fins stiffened by bones (fin rays) in aquatic vertebrates

Class Myxini (Cyclostomes)

Hagfishes and Slime Eels

• Slime eels: make slime through slime glands

• Slime gets in gills of predator and greatly expands to suffocate the predator

Cartilaginous skull

no jaws, vertebrate remnants

very small

retain notochord, move like snakes

marine, scavengers,

Family Petromyzontida (Cyclostomes)

lampreys (latch onto rocks)

ectoparasitic to fish

retain notochord

Non cartilaginous vertebral column (not bone either)

marine and freshwater

jawless, raspy tongues

mineralization

originated in vertebrate mouthparts (first seen in Chondrichthyes jaws)

advantages of having a jaw

1) eating/capturing prey/ tearing

2) defense

3) vocalization

4) move/build/grasping things

Clade Gnathostomes

bones (jaws)

expansion of HOX genes

• basal chordates: 1 cluster

• basal vertebrates: 2 clusters

• gnathostomes: 4 clusters

enlarged forebrain

lateral line system forms along with paired fins

Class Chondrichthyes

sharks, rays, etc

cartilaginous skeleton, fusiform body that helps reduce drag

• swim quickly, cannot maneuver well

two chambered hearts

gills: ventilate due to higher metabolic demand

• Ram ventilation: open mouth and swim through water

• buccal pumping: put water in mouth, close jaw, and use muscles to push water over the gills

cloaca: chambered end of the body where the reproductive, digestive, and excretory tracts merge

Reproductive strategies

ovuliparous: laying unfertilized eggs (sharks do not do this)

oviparous: laying fertilized eggs, hatching occurs externally

• horn shark

oviviparous: embryo matures inside female, hatches internally, and is born alive BUT they receive nourishment form the yolk ONLY

viviparous: same as oviviparous but embryo receives nourishment from mother

• oophagy: nourishment from eggs

• embryophagy: embryo eats another embryo

• hemotrophic: nourishment by blood (placenta)

animals with gas glands?

Actinopterygii, Actinistia, dipnoii, amphibia, Reptilia, Mammalia

lungs

invagination of endoderm

gills

evagination of the ectoderm

Clade/Superclass Osteichthyes

bony fishes and tetrapods

Class Actinopterygii (ray finned fish)

skin glands that secrete mucus to reduce water resistance

thin, flat, bony scales

swim bladder for buoyancy

lateral line system to detect vibration (how they hear)

operculum - bony flap protecting the gills

2-chambered heart: atria and ventricle

mainly ovuliparous, external fertilization

ossified endoskeleton of CaPO4 which hardens cartilage

Class Sarcopterygii

lobed fins and paired functional lungs

includes coelacanths, lungfishes

rod shaped bones with muscle in pelvic and pectoral fins

“large fin”

Subclass Actinistia

Coelacanths

though to have gone extinct

lobe fins move opposite of each to each like human limbs (cross stepping)

live in deep ocean caves

• can’t see bc they live in darkness

Subclass Dipnoii

paired functional lungs

• have both lungs and gills

“two ways to breathe”

freshwater

estivate: burrow into the mud and secrete a mucous casing over themselves when over is scarce or ceases, slows metabolism

tetrapods

four limbs

Amphibia, Reptilia, Mammalia

Gnathostomes with four limbs

Adaptations:

• 4 limbs, feet with digits: supports weight, generation of force, mobility

• Pharyngeal clefts: parts of ears, glands, and hyoid (loss of gills)

• Ears

• Neck: advantageous to sensory adaptations

• Pelvic girdle fused to vertebrate: generates force, allows mobility

• variable limb function

Tiktaalik

“Fishapod”

estimated transition from fish to amphibians

Class Amphibia

amphibians

basal tetrapods

both ways of life

• freshwater and terrestrial

Legs, ears, eyelids, voice (larynx)

pulmocutaneous respiration (?)

lungs - simple, buccal pumping

3-chambered heart; pulmonary veins

increased brain size

Urodela, Anura, Apoda

Order Urodela

Salamanders (amphibs)

have tails

Order Anura

Frogs and toads (amphibs)

lack tails

Order Apoda

Caecilians (amphibs)

legless and resemble worms