Deuterostomes

Deuterostomes: Echinodermata​

* “spiny” “skin”​
* Sea stars, sea urchins, sand dollars​
* Sessile or slow-moving animals​
* Secondary radial symmetry​
* Larvae are bilateral​
* 7,000 marine species​

Echinoderm characteristics​

* Endoskeleton of hard calcareous plates​
* Water vascular system​
* Tube feet that function in locomotion, feeding, and gas exchange​
* 7,000 species​
* Include sea daisies, sea cucumbers, brittle stars, sea urchins, sand dollars, sea feathers, sea biscuits​

Basic overview of key concepts

Sponges are basal animals that lack true tissues

Cnidarians are an ancient phylum of eumetazoans

Lophotrochozoans, a clade identified by molecular data, have the widest range of animal body forms

Ecdysozoans are the most species rich animal group

Echinoderms and chordates are deuterostomes

Overview of invertebrate life

Invertebrates are lacking a backbone

They account for 95% of known animal species

They occupy almost every habitat on earth

They are morphologically diverse

Chordates

* Phylum Chordata - two subphyla of invertebrates as well as the hagfishes (Craniata) and vertebrates​
* Chordates are bilaterally symmetrical coelomates with segmented bodies​

Deuterostomes:​ \n Phylum Chordata​ \n (Chapter 34)​

* 57,000 species of chordates​
* 34,000 species of fish!​
* Echinoderms and chordates ​
* have evolved independently for over 500 million years​
* are closely related​
* ​

Chordate Characteristics

1. Notochord​
2. Dorsal, hollow nerve cord​
3. Pharyngeal slits​
4. Muscular, postanal tail​

Phylum chordata

* 2 invertebrate subphyla:​
* Urochordates and Cephalochordates​

\
* Chordata Includes 7 major clades​
* Craniates – notochord, brain case​
* Vertebrates – vertebral column​
* Gnathostomes – jawed mouths​
* Osteichthyes – bony fishes​
* Sarcopterygii – Lobe-finned fishes ​
* Tetrapods – “four” “legs”​
* Amniotes – amniotic egg​

Chordates without backbones​ \n Subphylum Urochordata​

* Tunicates (sea squirts)​
* Sessile marine animals​
* Filter feeders​
* Adults __do not__ resemble chordates​

\-But larvae do​

Chordates without backbones​ \n Subphylum Cephalochordata​

* Lancelets​
* Marine filter feeders​
* Closely resemble the idealized chordate​
* Also display swimming mechanism of early fishes (S-shaped)​

How did vertebrates evolve from lancelet-like ancestors?​

* 530 m.y. old fossils from China​
* Provide “missing links”​
* *Haikouella* – brain but no cranium​
* *Haikouichthys* – has a cranium​
* may be the earliest fossil with ALL vertebrate characteristics ​
* (textbook features *Myllokunmingia fengjiaoa*)​

**Neural crest** ​

**Neural crest – feature unique to craniates**

**A group of embryonic cells found only in craniates**​

​

**Role? Develop into bones, cartilage, CNS**​​

**Clade Myxini: hagfishes**​

* the most basal group of craniates​
* 30 species, all marine​
* Bottom dwelling scavengers​
* Lack a backbone of vertebrae ​

– retain notochord throughout life​

* Lack jaws​
* Secrete water-absorbing slime as defense mechanism​

**Vertebrates**​

* Retained primitive chordate and craniate characteristics​
* Have additional specializations​


1. Pronounced cephalization​
2. Vertebral column​
3. Closed circulatory system​

High Degree of Cephalization​

* Cranium and brain​
* Eyes, ears, nose​

Vertebral column​

* Surrounds and protects the nerve cord​
* Is a part of the vertebrate **axial skeleton**​
* (support, large body size, fast movement)​
* ​
* Most vertebrates have an ​appendicular skeleton (bones of ​the limbs, thoracic, and pelvic ​girdles)​

Closed circulatory system​

* Ventral, chambered heart​
* Blood → arteries → capillaries​
* Blood is oxygenated as it passes through capillaries in gills or lungs​

**Clade Petromyzontida: Lampreys**​

* Most basal group of vertebrates​
* 35 species​
* Marine & fresh water​
* No jaws​
* Cartilaginous skeleton​
* No paired appendages​