Lower Vertebrates (Deuterostomes) - Key characteristics of the vertebrates (Phylum Chordata) include: Notochord replaced by spinal chord, internal skeleton (cartilage or bone), metameric segmental organization, dorsal nerve chord, appendages with opposing muscle, complete digestive system with specilizations, heart 2 - 4 chambered, paired aortic arches, 5 lobed brain, coelom divided into thoracic, abdominal, 2 paired appendages.

Nonvertebrate (invertebrate) deuterostomes have some but not all of these characteristics and yet appear to be ancestrally related to the chordates.

Phylum Echinodermata - starfish, brittle stars, sand dollars, sea cucumbers, sea feathers, sea urchins, sea lilies

Key Characteristics - unsegmented, radial symmetry, pentamerous, endoskeleton with dermal calcareous spines and oscicles. Water vascular system to control tube feet, Closed blood vascular system with amoebacytes, Eversible stomach, digestive glands, Respiratory dermal branchiae, Nerve ring with radial nerves down each arm, nerve net also. some sessil.

 

Class Asteroidea - Sea stars and starfish

Second Image Key

1. Ambulacral ridge

7. Pyloric caecum (digestive gland)

8. Gonad (under digestive gland)

10. Pyloric stomach

11. Spines
Class Echinoidea - Sea urchins, sea biscuits, sand dollars
Gonads on top (2), intestine (3) with calcareous teeth (7) and stomach (8)

Class Holothuroidea - sea cucumber, sea mouse

Tentacles (1), Gonads (3), Respiratory tree (5), Intestine (6), Tube feet (7)

Class Ophiuroidea - Brittle Stars - 5 arms more distinctly marked off from central disk

Class Echinoidea - sand dollar

 
Class Crinoidea - Sea feathers (image 1) and Sea lilies (Image 2)

Lophophorates - all have a curved ridge with cilliated tentacles attached for filter feeding (Phoronids, Ectoprocts, Brachiopods)

Phylum Phoronida - tubed lophophores

 

Phylum Ectoprocta - bryozoams - form large encrusted colonies on rocks in the intertidal zone

Phylum Brachiopoda - shelled lophophorates that superficially look like scallops of the mollusk group but the shell forms a top and bottom, not sides of animal

Phylum Ectoprocta -2nd image
Phylum Chaetonatha - arrow worms

Phylum Pogonophora - Bearc worms.

Key Characteristics - body tripartite, elongate (protostome, mesosome, metasome) body enclosed in secreted sand shell, faint segmentation. small tentacles with adhesive glands, no digestive system, closed circulatory system. Respiration and digestion through tentacle

Phylum Hemichordata - Acorn worms

Phylum Hemichordata - acorn worm

has some chordate characteristics such as;

3 body parts, gill slits, dorsal nerve

Larvae is similar to echioderm larva, a few developmental gene differences may give rise to the worm instead of the starfish.

Phylum Urochordata - tunicates

Marine sessil animal with heart that pumps in both directions, around a pharyngeal basket of hundreds of gill slits to filter feed.

Larvae is free swimming with several vertebrate characteristics including; notochord, gill slits, dorsal nerve cord post anal tail
Tunicate adult
Tunicate larvae

Phylum Cephalochordata - lancets

Oral tentacles (lophophore-like), dorsal nerve cord, notochord, lateral segmetal muscles, postanal tail, 60 gill slits, heart

2. dorsal nerve cord

5-6 gill slits, gill bars

11. Wheel organ

12. Oral tentacles (cirri)

Phylum Agnatha - hagfish, lamprey

Image 1. Hagfish

Image 2. Lamprey mouth with horny teeth
lamprey has 7-17 gill slits, dorsal-caudal tail

Phylum Chondrichthes - sharks, rays, skates, chimeras, ratfish

Order Elasmobranchii - Sharks, rays

Order Rajiformes - Skates & Sawfish

Order Chimaeriformes - Chimeras

 
Key Characteristics - dorsoventrally flattened, heterocercal tail, dorsal, pectoral, pelvic fins, placoid scales & teeth, lateral line divides epaxial & hyaxial muscles, jaws, intestine with spiral valve, 5-7 gill slits, no swim bladder

Image 1. Skate

Image 2. Ratfish

Phylum Actinopterygii - primitive boney fish

order Acipenseriformes - sturgeons, paddlefish

Order Seminotiformes - gar

Order Amiformes - Bowfin

Image = paddle fish

Key Characteristics - dorsoventral flattened, heterocercal tail, dorsal, pectoral, pelvic fins, placoid teeth, jaws and spiral valve all like sharks. Freshwater, airbladder with pwneumatic tube, nostrils, 3-5 gill slits are more like modern boney fish

Image 1 Sturgeon

Phylum Sarcopterigyii - lungfish, Key characteristics, Broad crushing teeth, spiral valve intestine, bilobed airbladder/lung with pneumatic tube to pharynx and tube from pharynx to nostrils, lobe fins with musculature for walking
Gar
Bowfin

Phylum Osteichthyes - modern boney fish

Key characteristics - 1-3 dorsal fins with spines, pectoral, pelvic, & anal fins, operculum protects gills, allows water movement over gills without swimming, lateral line for hearing, gill raker teeth, ganoid scales, elongated intestine

Order Perciformes - perch

Order Siluriformes - Catfish

for other orders see notes
Dragon fish