Fishes - Postcranial Morphology

Precaudal vertebrae

vertebral column

anterior vertebrae from the skull to the end of the body cavity

Caudal vertebrae

vertebral column

posterior vertebrae from the end of the body cavity to the end of the body

Features of both Precaudal and Caudal Vertebra

Centrum

• disc-shaped central part of vertebra

Neural Spine

• dorsal projection from centrum with a neural arch at the base which houses the spinal cord

Differences between Caudal and Precaudal Vertebra

Plural ribs

• paired ventral projections from precaudal vertebra which project the body cavity

Haemal Spine

• single ventral projection from caudal vertebra

• haemal arch at base contains the caudal artery

Urostyle

caudal fin complex

posterior vertebral element often made of fused vertebrae

Epurals

caudal fin complex

modified neural spines

Hypurals

caudal fin complex

flattened haemal spines associated with the urostyle

Principal caudal fin rays

caudal fin complex

fin rays that reach the posterior margin of the caudal fin

Procurrent fin rays

caudal fin complex

small fin rays that end short of posterior margin of caudal fin

Protocercal

caudal fin types

• ‘primitive’ undifferentiated fin

• rays continuous with dorsal and anal fin rays

• found in lampreys and larvae of modern fishes

Heterocercal

caudal fin types

• unequally lobed (larger top lobe)

• vertebral column extends into dorsal lobe of tail

• found in chondrichthyes and early diverging bony fishes

Homocercal

caudal fin types

• equal lobed

• fin rays arranged symmetrically

• common in modern bony fishes

Posttemporal

pectoral girdle and fin

usually has two processes that articulate with bones of skull

Supracleithrum

pectoral girdle and fin

forms joint with posttemporal for cranial rotation during feeding

Cleithrum

pectoral girdle and fin

largest bone in pectoral girdle

Radials

pectoral girdle and fin

support fin rays

fin rays

pectoral girdle and fin

flexible supports for pectoral fins

Basipterygium

pectoral girdle and fin

• paired, internal pelvic bones

• attach to radials, which then attach to fin rays

• in modern fishes, basipterygia and radials become fused or lost

Dorsal and Anal fin

median fins

• can have spines, soft rays, or a combination

• there can be 1, 2, or many dorsal fins

Pterygiophores

• internal supports of dorsal and anal fins

Lepidotrichia

• bony elements of fin rays in bony fishes

• called ‘ceratotrichia’ when cartilage

Adipose fin

small fin behind the dorsal fin

supported by cartilaginous ceratotrichia

Myomeres

Muscles

W-shapes postcranial skeletal muscle

each myomere is activated at once, different myomeres are activated sequentially from anterior to posterior

Epaxial muscles

myomeres

located dorsally

Hypaxial muscles

myomeres

located ventrally

Placoid scales

present in most sharks and their relatives

do not increase in size with growth

Cosmoid scales

in fossil coelacanths and lungfishes

Ganoid scales

rigid, armor-like

Present in sturgeons, paddlefishes, gars, and bichirs

Leptoid scales

most common

made completely of thin, bony material

four main types