Although it is debatable whether hagfish are vertebratescurrent classification places the hagfish within the SubphylumVertebrata. Hagfish and Lampreys are placed in differentclasses of the Superclass Agnatha.

Phylum Chordata

Subphylum Vertebrata

Superclass Agnatha

Class Myxini - hagfishes

Class Cephalaspidomorphi - lampreys

Although they aresuperficially similar theydiffer in many ways

Characteristic Lampreys HagfishesDorsal fin 1 or 2 NonePreanal fin Present PresentEyes Well developed RudimentaryOral disk Present AbsentLateral line system Well developed AbsentBarbels Absent 3 pairsSpiral valve intestine Present AbsentNostril location On top of head On snoutExternal gill openings 7 1-14Cranium Well developed RudimentaryVertebrae Present AbsentPronephric kidney Present AbsentOsmoregulation Hyper- or hypoosmotic isomoticEggs Small, no hooks Large, with hooksEmbryonic cleavage Holoblastic Meroblastic

Hagfishes - 43 spp. - worldwide - marine in cool waters - inshore athigh latitudes - osmoconformers - 30-80 mm in length

Live in association with the bottom, in burrows, in colonies,scavengers on carrion, life history poorly known, commercially impt.

Produce large hookedeggs 2-3 cm in length

Lampreys - 40 spp. - in cool waters of northern and southernhemispheres - either anadromous, or entirely freshwater

Two different lifestyles - parasitic and nonparasitic (brook lampreys)

Parasitic forms feed on large prey, mostly fishes, feeding on blood ortissue fluids, or muscle

Have oral disk with keratinized teeth, action of the tongue raspshole and tears flesh

Respiration with gill pouches - allows respiration while attachedto host.

Parasitic forms are anadromous - they spawn in clear flowingstreams in gravel

Like salmon - theyare semelparous -they invest heavilyin reproduction anddie after spawning

Produce small eggs (1 mm) - one female may produce 250,000 eggs

Lamprey larvae and juvenilesare called ammocoetes - theylive in gravel and filter feed -parasitic forms theymetamorphose as they migratedownstream and adopt aparasitic lifestyle

Nonparasitic lampreys are called brook lampreys - retain thejuvenile form, filter feed, and mature - mature earlier and spawnfewer eggs.

There are many species pairs of brook and parasitic lampreys -with the brook lamprey apparently derived from the parasitic formby loss of the parasitic phase

Neoteny - retention of juvenile characteristics in the adult -reproductive maturation while in the juvenile body form

Grade Telostomi - bony vertebrates (formerly C. Osteichthyes)Class Acanthodii - spiny sharksClass Sarcopterygii - lobe-finned fishes

Subclass Dipnoi - lungfishes Subclass Coelocanthomorpha - coelacanths

Subclass Osteolipimorpha - “rhipidistians”- extinct Subclass "Tetrapoda”-(amphibians, reptiles, mammals, birds)

Class Actinopterygii - ray-finned fishes Subclass Chondrostei - sturgeons, paddlefish, birchirs

Subclass Neopterygii - "modern" ray-finned fishes - the most primitive neopterygians are gars and the bowfin

Lungfishes, coelacanths, sturgeons, paddlefishes, birchirs, gars, andbowfin are remnants of early fish groups. Many of the ancestralgroups were widespread. Today, the few species remaining areoften distributed among different continents (relictual distributions)and many have lost characteristics commonly seen in fossil species.

All non-tetrapod Teleostomes have lungs (or swimbladders), bone,bony scales or scutes, bony gill covers, bony fin rays (lepidotrichia)Lungs likely originated in species living in oxygen poor waters.A bony skeleton has been nearly lost in some living Chondrosteansand Dipnoans.

Subclass Dipnoi - lungfishes - 6 spp. - 1 in Australia, 1 in SouthAmerica, and 4 in Africa - a “relictual” distribution

Australian

South American

African

The Australian lungfishis most similar to earlylungfishes

Characteristics: lobed paired fins, upper jaw fused to cranium,internal nostrils, cloaca, dermal tooth plates (blade-like in modernforms), ventral connection to one or two dorsal lungs, spiralvalve intestine

In their evolution, lungfishes have lost or reduced manycharacteristics seen in the earliest forms:

loss of bone, reduction in thickness of scales, loss ofseparation between dorsal, anal, and caudal fins, loss ofrays on paired fins, and reduction of lobes to filaments

Neoceratodus forsteri - found in Australia - omnivorousheavy scales and large lobed fins with rays

2m in length - heavy bodied, lives only in permanent bodies ofwater, incapable of aestivation, gills used for respiration

Lepidosiren paradoxa - found in South American - omnivorouslung is primary respiratory organcan live in mud burrow during dry periods

Protoperus (4 species) found in Africa - predators lung primary respiratory organ undergoes true aestivation with reduction in metabolic rate

Protopterus spp. and Lepidosiren some haveexternal gills in larvae (like amphibians)

All lungfish lay eggs.

Mud burrow of Protopterus sp.lined with a mucous cocoonwhere they can live for months oryears.

The last gill arch oflungfishes has no gillfilaments or capillarybeds. The blood flowsdirectly through the gillarch to the lungs.

Blood returns to theheart from the lungswell oxygenated.

Oxygenated bloodpartially mixes withdeoxygenated bloodand is then pumpedback through gill archesand on to the body.

Subclass Coelacanthamorpha - “fringe-finned” fishesearly forms originated in and diversified in freshwaterhave sculptured enamel on teeth, upper jaw fused to skull, no cloaca,fossil forms had cosmine layer on scales )but this is not seen in theliving species), spiral valve intestine, hollow dorsal spines,

lobed fins - bothpaired andunpaired, and ajointed skull,

Latimeria has anonfunctional lung - filledwith fat - for buoyancyLike elasmobranchs itosmoregulates using urea toraise tonicity

It is livebearing with a 9 cmegg

one living species - Latimeria chalumnae- lives in relatively deep water in theIndian Ocean off the coast ofMadagascar - discovered in 1938 -recently discovered in Indonesia also

Lives over rocky bottoms -slow moving - “lie-in-wait”predator

Class Actinopterygii - ray-finned fishes originated in Devonian - 325 million years ago and were rare

until about 200 million years ago today the dominant fishes in freshwater and the sea fins lack fleshy lobes and are supported by lepidotrichia have branchiostegal rays early and primitive forms have ganoid scales no external gills in larvae (with one problematic exception) dorsal lung or swimbladder (usually with a dorsal connection) external nostrils

The Class Actinopterygii is divided into two subclasses - theSubclass Chondrostei - sturgeons, paddlefish, bichirs

Subclass Neopterygii - gars, bowfin, teleosts

Chondrosteans - originated in lower Devonian (325 mya) - becamedominant group, most died out in Mesozoic (100 mya)survived today by two orders -

O. Acipenseriformes- sturgeons (23 spp.) and paddlefish (2 spp.) O. Polypteriformes - 11 spp.- bichirs and reedfish

Chondrosteans usually have a spiracle, heterocercal tail, no premaxilla, upper jaw (maxilla) united with skull, spiral valve intestine, reduction in bone, usually lack vertebral

centra, well developed notochord, one or no branchiostegal rays

Order Acipensiformes - with 2 very different families F. Acipenseridae - sturgeons (26 spp.) - all northern hemisphere - anadromous and with some entirely freshwater - five rows of bony scutes on body, four barbels, - inferior and protrusible mouth, no teeth in adults - includes largest freshwater fishes - beluga sturgeon, over 1 ton

- feed on invertebrates andsmaller fish

- sluggish swimmers- source of caviar, and

edible flesh- require clear fast flowing

water over gravel forspawning

- several species threatenedwith extinction becausedamming and siltation

F. Polyodontidae - paddlefishes - 2 spp. - one in Mississippi drainage - 2m, non-protrusible mouth one in Yangtze drainage - 3m, protrusible mouth both have paddlelike snout that is an electrical sense organ with ampullary organs, and with minute barbels very long gill covers American species is a plankton feeder with 100s of gill rakers Asian species is a piscivore

O. Polypteriformes - bichirs and reedfishes11 spp. only in Africa, predators, relatively common appear relatively late in fossil record but have many primitivecharacteristics

similar to Sarcopterygians - lobed pectoral fins, ventrallyconnected lungs, larvae have external gills (like lungfishes)

Lobes do not have a skeleton similar toSarcopterygians and tetrapods.

Similar to Actinopterygians in possession of ganoid scales (like gars)unique in possession of 5 to 18 dorsal finlets - each with a single spine, and rays attached to the spine

lungs used in low oxygensituations, and some speciesrequire access to air at thesurface

Common in the aquariumtrade - often sold as ropefishor congo eels.

Within the Subclass Neopterygii historically there have been twoDivisions with a variety of names 1. Holostei (gars and bowfin) and Teleostei or 2. Ginglymodi (gars) and Halecostomi - bowfin and teleosts the second classification reflects greater evolutionary

similarity of bowfins to the teleosts each has a maxilla that is more moveable

Division Ginglymodi,Order Semionotiformes,

Family Lepisosteidae - gars - 2 genera, 7 species. most primitive of the Subclass Neopterygii finned fishes good fossil record - back to permian-triassic-jurassic (200

to 150 mya) fossil forms known throughout N. Hemisphere

Modern Gars fresh to brackish water alligator gar (to 3 m) sometimes found in sea water all in North and Central America - Costa Rica and Cuba

elongate jaws and body,modified heteroceral tail (dorsal lobe extension)heavy ganoid scales, 3 branchiostegals,swimbladder highly vascularized - can be used as lungunique opisthocoelous vertebrae (anterior convex, posterior concave) classic lie-in-wait predators attack from the side with lateral movement of head eggs and larvae are toxic

Division Halecostomi, Subdivision Halecomorphi, Order Amiiformes Family Amiidae - 1 sp. - Amia calva - bowfin freshwater throughout eastern North America fossil relatives known worldwide in Mesozoic - 150 - 300 mya

more advanced than gars10-13 branchiostegals,round relatively thincycloid scales,very long dorsal fin

exhibit some primitive characteristicstail appears homocercal - modified heteroceral with upturned

vertebral column and larger dorsal lobe modified spiral valve intestine highly vascularized swimbladder that can serve as lung used as lung in warm water, and can live through dry spells in

burrows

The most primitive fish with sexually dimorphic coloration - onlymales have a spot at the base of the caudal finextensive male parental care, with aggressive guarding of youngA relatively intelligent fish, can be easily trained for hand feeding.