Actinopterygii

Chondrostei

Paleonisciformes

Neopterygii

Teleostei

Cephalachordata

Hagfishes

Lampreys

• scales - reduction in heaviness
• branchiostegal rays - developed from bones in the floor of the mouth
• swimbladder - trend toward use primarily as a hydrostatic organ
• jaws - separation of premaxilla and maxilla, sliding of maxilla - suction feeding

• Scale fragments found (with ganoine) in late Silurian (ca. 400 MYA) suggests early Actinopterygiins co-occurred with placoderms and early elasmobranchs
• Complete fossils found in the mid- to late Devonian, freshwater and marine habitats
• Actinopterygiin radiation (late Paleozoic) coincided with extinction of ostracoderms, placoderms, acanthodians
• Evolution of jaw over Actinopterygiin evolution led to diversified feeding habits
• Scales were reduced from heavy interlocking units to thinner, lighter cycloid structures
• Extinct by middle Mesozoic (Jurassic)
• Extant fishes, i.e. sturgeons (Acipenseridae), paddlefishes (Polydontidae)have been suggested to be chondrosteans, although hotly debated

• arose late Permian, early Triassic
• Extant Neopterygiins are intermediate between paleoniscids and teleosts
• gars retain ganoid scales, bowfins retain gular plate; both have heterocercal tail elements

• Arose in mid- late Triassic (200 MYA)
• 4 major lineages; one thought have given rise to modern Teleosts

References for your enjoyment:

Mallatt, J. and J. Sullivan. 1998. 28s and 18s sequences support the monophyly of lampreys and hagfishes. Mol. Biol. Evol. 15: 1706-1718.

Delarbre et al. 1998. The complete sequence of the mitochondrial DNA of the dogfish, Scyliorhinus canicula. Genetics 150: 331-344.

• Invertebrate chordate like Urochordata (Tunicates)
• accepted as sister group to Craniata (supported by molecular data)
• lack cranium, brain, heart, RBCs, gills
• have 25 pairs of gonads--segmented features
• "Amphioxus" larvae of a species of Branchiostoma
• commercial food value

• Small, up to 3 cm in length
• Taxonomy based on myomere counts and number of dorsal chambers

• Two families: Epigonichthyidae, Branchiostomatidae: 22 species
• Distributed in marine environments both tropical and temperate

• Spawning occurs in early summer, larvae metamorphose after 2-5 months Adults live 1-4 years
• Filter feeders, bury in the bottom or occur in pelagic zone as adults, larvae are planktonic
• Ciliated pharyngeal cavity, endostyle (pharyngeal organ) secretes mucous

Order Myxiniformes-Hagfishes

• Relationships to Vertebrates highly controversial
• Morphological data indicates monophyly of hagfishes; sister relationship of Lampreys and Anaspida
• Mallatt and Sullivan argue for monophyly of Hagfishes and Lampreys based on:

0. Vertically biting tounge apparatus
1. Elongated oral region with respiratory flap called the velum (not seen in Ostracoderms
2. 18S ribosomal DNA data (nuclear gene)
3. 28S and 18S rDNA sequences combined

• commercial value -- eelskin

• Elongate, eel-like, round buccal cavity with rasping teeth and tounge
• Possess a single gonad, rather than paired gonads like gnathostomes
• Possess four hearts, (1) posterior to gills, and (3) just behind the mouth
• Respiration at gills, and cutaneous
• Lack complete eyes, possess barbels, slime glands and pores (up to 200)
• Taxonomy based on number of efferent gill ducts, number of slime pores
• Fossil hagfish (300 MYA) possessed functional eyes

• Almost world-wide distribution; marine, restricted to cold waters (tropical species caught at 2700 m)
• Few species occur shallower than 30 m, limited by salinity and temperature
• One (possibly two) families Myxinidae with 43 species

• Females produce few (ca. 30), large eggs (1.5 - 2.5 cm), direct development
• Probably iteroparous
• Ages of maturity, reproductive lifespan, spawning times and places unknown for most species
• Scavenger feeders

 Subphylum Vertebrata

• Superficially resemble hagfishes, lack jaws, paired fins
• Have parasitic and non-parasitic species (brook lampreys)
• Produce ammocoete larva (6mm on hatching) similar to Branchiostoma larvae; but differ in feeding mechanism

• Elongate, eel-like, round buccal cavity with rasping teeth and tounge
• Possess a single gonad, rather than paired gonads like gnathostomes
• Possess a single heart
• Respiration at gills, branchial sacs
• Parasitic forms have complete eyes, sight feeders
• Non parasitic forms have greatly reduced eyes
• Largest diploid chromosome number (140-170 chromosomes in some species!)

• Almost world-wide distribution but seldom below 30^o latitude in either hemisphere; two species occur at high elevations in Mexico
• Non-parasitic forms entirely freshwater, parasitic forms fresh or anadromous
• One (possibly three) families Petromyzontidae with 41 species

• Females produce many (1000-100,000), small eggs (order of magnitude smaller than hagfishes)
• Semelparous
• Ages of maturity, reproductive life-span, spawning times well documented for parasitic and non-parasitic forms
• Feeding varies among species, all start as filter feeding larvae (ammocoetes) and then either do not feed upon maturity, or are parasitic