Deuterostomes

What fossil clade is thought to represent the earliest deuterostomes with bilateral symmetry?

Carpoids

What key feature suggests carpoids were bilateral?

Their symmetrical fossil body plans

What does the fossil record suggest about echinoderm ancestry?

Echinoderms evolved from bilaterally symmetric ancestors

What evidence links echinoderms with hemichordates?

Similar larval forms

What is the larval form of echinoderms called?

Bipinnaria larva

What is the larval form of hemichordates called?

Tornaria larva

Why is larval similarity important in phylogeny?

It indicates shared ancestry

What evidence links echinoderms to chordates?

Fossil carpoids may have had gill slits

What skeletal structure supports fossil echinoderm identity?

Stereom (porous calcite skeleton)

What modern technique revealed gill slits in fossils?

X-ray micro-tomography

What is the common ancestor of protostomes and deuterostomes?

The Urbilaterian

Which living group may resemble the Urbilaterian?

Xenacoelomorpha (“the purple sock”)

What defines deuterostome development?

The blastopore becomes the anus

Which three phyla are deuterostomes?

Echinodermata, Hemichordata, Chordata

What is the water vascular system?

A hydraulic system unique to echinoderms

What are the main components of the water vascular system?

Madreporite, ring canal, radial canals, tube feet

What function do tube feet serve?

Locomotion, feeding, and gas exchange

How do starfish eat bivalves?

By prying shells open and everting the stomach

What is stomach eversion?

The stomach is pushed outside the body to digest prey

Why is external digestion advantageous?

It allows consumption of large prey

What type of circulatory fluid do starfish have?

Coelomic fluid

Why is starfish blood considered primitive?

It lacks respiratory pigments

What is a hemichordate?

A marine deuterostome related to echinoderms and chordates

What is the body plan of a hemichordate?

Proboscis, collar, and trunk

What structure in hemichordates resembles chordate gills?

Pharyngeal gill slits

What is a cephalochordate?

A chordate that retains chordate traits as an adult

What is a common example of a cephalochordate?

Amphioxus (lancelet)

What structure runs the length of Amphioxus?

The notochord

What is a urochordate?

A chordate whose chordate traits are mostly in the larval stage

What is another name for urochordates?

Tunicates

What are the two siphons of tunicates called?

Oral siphon and atrial siphon

What structure produces mucus for feeding in tunicates?

Endostyle

What is the function of the pharyngeal basket?

Filter feeding

What class of urochordates includes sea squirts?

Ascidiacea

What class of urochordates includes salps?

Thaliacea

What class of urochordates retains a larval body plan?

Larvacea

What extraordinary feature do larvaceans possess?

A secreted mucus “house” for filter feeding

What is neoteny?

Persistence of juvenile traits into adulthood

What is another term for neoteny?

Paedomorphism

How is neoteny important in chordate evolution?

It may explain retention of larval traits

Which chordate group shows neoteny?

Urochordates

What is a notochord?

The most primitive axial skeleton

What function does the notochord serve in cephalochordates?

Structural support for swimming

What function does the notochord serve in vertebrate embryos?

Signals ectoderm to form the CNS

What remnant of the notochord persists in adult humans?

Intervertebral discs

What synapomorphy is shared by all chordates?

A notochord

What additional synapomorphies appear later in chordate evolution?

Vertebrae, jaws, bones, limbs, fur/milk

Which animals are considered craniates?

Chordates with a skull

What distinguishes hagfish skulls?

Cartilaginous bars with a persistent notochord

What distinguishes lamprey skulls?

More complete braincase and branchial basket

What evolutionary trend defines vertebrates?

Replacement of notochord with vertebrae

What major evolutionary transition allowed life on land?

Tetrapod locomotion

What synapomorphy allowed reproduction on land?

Eggshell

What synapomorphy defines mammals?

Fur and milk