Hagfish and Lampreys

1
Hagfish and Lampreys
Myxini
Petromyzontida
jawed fishes
Gnathostomata jaws paired fins 3 semi-circular
canals
Vertebrata vertebrae 2 semi-circular canals
Craniata Cranium 3-part brain gill pouches
2
Class Myxini

• slime hags
• myzin slime
• ca. 530 MYA
• 1 order, 1 family
• Diagnostic features
• 3 pairs of barbels around mouth
• 4 rows of teeth on tongue
• Other characters
• 1-14 gill openings
• 4 hearts
• no lateral line
• knotting behavior

Myxiniformes Myxinidae
3
Class Petromyzontida

• lampreys
• 1 order, 3 families
• Diagnostic features
• teeth on oral disc and tongue
• 7 pairs of gill openings
• single medial nostril
• ammocoete larvae
• Other characters
• some anadromous
• some parasitic micropredators
• paired-species

Petromyzontiformes Petromyzontidae
4
Lamprey as micropredator
5
Class Chondrichthyes

• sharks, rays chimaera
• Diagnostic features
• pelvic claspers
• prismatic calcification
• Other characters
• cartilaginous skeleton
• ceratotrichia
• no lungs or swimbladder
• protrusible upper jaw
• overhanging snout with single nostrils

6
Basic Adaptations

• Buoyancy
• Respiration
• two-pump
• ram ventilation
• Placoid scales
• reduce turbulence
• teeth
• spines
• Senses
• odor low frequency sounds
• vision
• electroreception
• Osmoregulation
• Internal fertilization

7
Chondrichthyes Phylogeny
Class Chondrichthyes divided into two subclasses
Holocephali and Elasmobranchii
8
Subclass Holocephali

• chimaeras
• 1 order, 3 families
• Diagnostic features
• 4 gills openings under one cover
• no spiracle
• large plate-like teeth
• Other characters
• autostylic
• modern forms lack placoid scales
• deep-sea, noctural

9
Subclass Elasmobranchii

• sharks and rays
• Diagnostic features
• 5-7 gill openings
• spiracle
• placoid scales
• numerous teeth rapidly replaced
• Other characters
• amphistylic / hyostylic

10
Elasmobranchii Phylogeny
Subclass Elasmobranchii separated into two
subdivisions Selachii (sharks) and Batoidea
(rays) 13 orders and 51 families
11
Osteichthyes Phylogeny
Distinctive features of Osteichthyes
include skeleton with bony elements lepidotrichia