Chordata: Lancelets & Tunicates

Chordata

Humans and all vertebrates are in the Phylum _______

Cambrian Period (~ 518 MYA)

The first vertebrates evolved in the _______

Late Precambrian Period (650+ MYA)

The first invertebrates evolved in the _________

The notochord

1. _______: A flexible rod-like structure that runs from head to tail in the embryo (and in adult Lancelets)

vacuolated cells

Structure of the notochord in embryos:

Made up of _______ (fluid filled)

Surrounded by a sheath of connective tissue

This makes it flexible but rigid, acting as a hydrostatic skeleton

midline

The notochord during embryonic development:

• Serves as a _____ during embryonic development and influences development of surrounding tissues

spinal cord and brain

The notochord during embryonic development:

• In vertebrates, the notochord signals development of the ________, but is largely lost in the adult

hydrostatic skeleton

Functions of the notochord in invertebrate chordates:

• Provides structural support

• Point for muscle attachment

• Functions as a _________ to allow locomotion

lateral undulation

The notochord in locomotion:

Allows for________

Muscles contract on one side of the body at a time, creating S-like waves (Moving like a snake or fish)

embryonic development

The notochord in adult vertebrates:

The notochord is largely lost during development in vertebrates

It signals development of the brain and spinal cord during _______

(Becomes parts of the vertebral column and discs)

Tunicates

The notochord in adult invertebrates:

Lost in _____ and Present in adult Lancelets

The dorsal nerve chord

2. ___________: Becomes the central nervous system in vertebrates (spinal cord and brain)

hollow and dorsal

The dorsal nerve chord:

Most of the invertebrates we’ve talked about have had a solid ventral nerve chord

In chordates, the nerve chord is ___________

hollow tube

Structure of the dorsal nerve cord:

Dorsal to the notochord

Forms when ectoderm rolls into a _______

Creates a fluid filled cavity

notochord

The _____ triggers development of the nerve cord into the CNS

Lancelets

The dorsal nerve cord in adult invertebrates:

______- remains intact, but does not develop into a complex CNS like in vertebrates

Tunicates

The dorsal nerve cord in adult invertebrates:

______: greatly reduced in adults

The endostyle

3. _______: A small, ciliated, glandular structure running along the ventral side of the pharynx

Secretes mucous

Structure and function of the endostyle in invertebrates:

Used for filter feeding

________ that can trap food particles in the water

Cilia move trapped food to the digestive system

thyroid gland

The endostyle in vertebrate chordates:

Gives rise to the _______, which regulates metabolism

Pharyngeal slits

4. _______: A series of openings along the pharynx that allow water to flow through the pharynx for filter feeding

pharynx

Structure and function of the pharyngeal slits:

Water flows in through the mouth into the ______

Food particles are trapped by mucus secreted by the endostyle

Water flows out through the pharyngeal slits

respiratory structures

Pharyngeal slits in vertebrate development:

Present in early vertebrate embryos

Develop into _______ in many aquatic vertebrates

In humans they become parts of the throat, jaw, and middle ear

embryonic stages

5. The post anal tail:

meaning it extends backwards past the anus

• In some vertebrates (like humans) it is only present during _______

lost

The post anal tail in invertebrates

Lancelets: used for swimming

Tunicates: _______

Phylum Chordata

________:

Consists of 3 subphyla: Cephalochordata, Urochordata, and Vertebrata

Cephalochordata

_______: lancelets

Urochordata

________: tunicates

Vertebrata

_______: vertebrates

Fish-like chordate

Subphylum Cephalochordata The lancelets:

________ invertebrates found in marine habitats

Very small (2.5-8 cm)

Used as a model organism to study early vertebrate evolution

burrowed into sediment

Subphylum Cephalochordata The lancelets:

Most species live ________ on the sea floor as adults, but can swim by lateral undulation

Feed by filter feeding

No Respiratory System (rely on diffusion)

green fluorescent proteins (GFPs)

Subphylum Cephalochordata The lancelets:

Produce _________, creating bioluminescence

Simple open circulatory system

Subphylum Cephalochordata Anatomy:

• No respiratory system (rely on diffusion)

• __________ -blood is pumped by a dorsal blood vessel (no heart)

The Notochord

Subphylum Cephalochordata Anatomy:

________- Present and hollow, but reinforced with collagen for more rigidity (functions similarly to a spine), extends into the head (hence the name, cephalochordata)

The Nerve Cord

Subphylum Cephalochordata Anatomy:

______ • Dorsal and Hollow

• Contains ganglia for simple processing of sensory information

• Extends into the head forming a rudimentary brain

muscles and sensory structures

Subphylum Cephalochordata Anatomy

The Nerve Cord:

Peripheral nerves innervate the _________

Nervous system is simple, but more complex than a nerve net

single frontal eye

Subphylum Cephalochordata Anatomy:

Vision

Lancelets have a _______ that can detect light and motion

Contains photoreceptors but is not image forming

Dioecious

Subphylum Cephalochordata Reproduction and Development:

• _______

• Reproduce by spawning

• Free swimming larvae

Lateral undulation

Because they share many features of vertebrate anatomy, and are likely similar to the common ancestor of vertebrates, lancelets can be used to study vertebrate

evolution

• The notochord ——> spinal column

• ______ ————> early vertebrate-like locomotion

• The pharyngeal ———> slits fish gills

• Nerve cord early ———> vertebrate brain evolution

Filter feeders

Subphylum Urochordata Tunicates

• May be solitary or colonial

• All are marine

• ________

• Simple anatomy- Adult form has lost many of the chordate features

cerebral ganglion

Subphylum Urochordata Tunicate Development:

During development into the adult form

• the _______ becomes simpler

• sensory organs are lost (including eyes and statocyst)

• notochord is lost

• Post anal tail is lost

Tunic

Subphylum Urochordata Tunicate Anatomy:

The ______ : An outer covering that may be tough like cartilage or thin and gelatinous

tunicin

Subphylum Urochordata Tunicate Anatomy:

The Tunic contains _____, which is a variety of cellulose

They are the only animal that produces a form of cellulose!

endostyle

Subphylum Urochordata Tunicate Anatomy:

The Pharynx

(the whole blue area) • Composes the majority of the tunicate’s body

• Covered in pharyngeal slits

• Contains the ______ a ciliated groove that secretes mucous for trapping food particles

Buccal Siphon

Subphylum Urochordata Tunicate Anatomy:

The ______ (also known as the oral siphon)

• The inflow for water into the pharynx

Water flows into the pharynx and passes through the pharyngeal slits into the atrium

Atrial Siphon

Subphylum Urochordata Tunicate Anatomy:

The ________

• Food is trapped in the pharynx in mucus produced by the endostyle

• Water leaves the atrium through the _______

pharynx

Subphylum Urochordata Tunicate Anatomy:

Digestive System

• Food particles caught in mucous lining the ______ are moved to the stomach for digestion

• The intestine carries food waste to the anus near the atrial siphon

open circulatory system

Subphylum Urochordata Tunicate Anatomy:

Circulatory System

• Have an ___________, but blood is contained in vessels in many parts of the body

• Heart stops every few minutes, and changes the direction of blood flow

Direct diffusion

Subphylum Urochordata Tunicate Anatomy:

Respiration

• ________ from water passing through the body

Dorsal nerve cord (CNS)

Subphylum Urochordata Tunicate Anatomy:

Nervous System

• Simple, but does have a central nervous system and peripheral system

• ___________ is reduced to a cluster of ganglia near the pharynx that regulate water flow and feeding

Peripheral Nervous System

Subphylum Urochordata Tunicate Anatomy:

Nervous System

• __________ extends nerves to other parts of the body, primarily the siphons

• Some sensory cells are present on the body

Hermaphroditic

Subphylum Urochordata Tunicate Reproduction:

________ with a single ovary and testis

Sperm are released into the water and taken in by another tunicate through the buccal siphon

Fertilization then happens internally

pelagic

But not all tunicates are sessile, some are ______

Salps are one group where adults live suspended in open water

shared tunic

Colonial tunicates:

• Many zooids (individuals) live together with a _______

• Zooids have their own digestive and reproductive systems

• Colony can also reproduce asexually by splitting off or budding

tunicate beds

Colonial tunicates

Some colonial species form “________” that can serve as habitat for other invertebrates and small fish (similar to corals or sponges)