Chordates

Symplesiomorphies of Phylum Chordata

Key characteristics: pharynx, notochord, dorsal hollow nerve cord, segmented post anal tail, endostyle (homologous to the thyroid).

Subphylum Urochordata (Tunicates)

All are marine filter feeders. Larvae look like tadpoles and all are free swimming. Most adults are sedentary.

Subphylum Cephalochordata (Amphioxus/lancelets)

All are marine filter feeders that typically burrow in mud. Adults have chordate traits but differ from vertebrates in using gill slits for filtering (not respiration).

Subphylum Vertebrata Characteristics

vertebral column, cranium, dorsal hollow nerve chord, pharyngeal gill slits

Superclass Cyclostomi

Classes Myxini and Petromyzontida

Order Myxiniformes

Hagfish, elongate, scaleless with reduced eyes and no vertebrae

petromyzontiformes

Lamprey

Class Chondrichthyes

sharks, rays, and skates (Elasmobranchii) chimaeras (Holocephali). Non-calcified to semi-calcified endoskeletons; placoid scales (dermal denticles = tooth like);

Order Lamniformes

Two dorsal fins, an anal fin, five gill slits, eyes without a nictitating membrane,mouth extends behind the eyes.

Superclass Osteichthyes

largest vertebrate group, comprising over 28,000 species. All have a bony endoskeleton with a two chambered heart.

class sarcopterygii

lobe finned fishes (lungfish and coelocanths)

Class Anctinopterygii

ray finned fishes, 50% of all vertebrae

Order Salmoniformes

are migratory, spawning in freshwater.

Order Esociformes

long & streamlined. Pike, Mudminnows and pickerel.

Order Perciformes

fin spines on dorsal, anal and pelvic fins. 4 gill arches.

Order Gadiformes

cod, hakes, pollack, haddock. fins are spineless

Order pleuronectiformes

flatfish, flounder, halibut, sole

Order Anguilliformes

Eels. Elongated fish, lack pelvic fins and some lack pectoral fins. Dorsal and Anal fins are flushed with caudal.

order lophiiformes

angler fish

Synapomorphies of Vertebrata

vertebral column, cranium, cartilaginous/bony endoskeleton, tripartite brain, muscularized pharynx

Class Amphibia

mucosal glands in skin, water permeable

Order Urodela

Salamanders, body segmented with costal grooves, simplified skull, no middle ear cavity

Order Anura

Frogs and Toads, skulls have reduced bones, tails short or absent, vary by lifestage, hind limbs elongated, caudal vertebrae are fused into urostyle

Order Gymnophonia 

Caecilians, limbless, serpentine bodies. Tail reduced, eyes reduced, dense, ossified skulls. 

Amphibia families that occur in Maine

Ambystomatidae, Plethodontidae, Proteidae, Salamandridae, Bufonidae, Hylidae, Ranidae

Ambystomatidae

mole salamanders, no nasolabial grooves, have lungs, ambystoma laterale

Plethodontidae

lungless salamanders, have nasolabial grooves. plethodon cinereus

Bufonidae

true toads, teeth absent in upper and lower jaws, skin ossified to skull, shortened limbs, parotoid glands. Bufo americanus

Hylidae

Tree frogs, horizontal pupils, enlarged finger pads, hyla versicolor and pseudacris crucifer

Class Reptilia

all sauropsids, orders: Squamata, Testudines, Crocodilia

Order Squamata

scaly, snakes and lizards, cranial kinesis, paired hemipenes and pleurodont dentition

Family Viperidae

loreal pit, triangle shaped head and keeled scales

Family Colubridae

11 spp in Maine. liochlorophis vernalis

Order Testudines

turtles, terrapins and torises, modified ribs form the carapace, skull fused, beak with no teeth

Family Chelydridae

snapping turtles, limbs cannot be fully retracted into the shell, upper jaw hooked. Snapping turtle Chelydra serpentina

Family Emydidae

lack inframarginal scutes and have convex eighth cervical vertebrae, Clemmys guttata/insculpta