Hagfishes There are 45 living species. Possess integumentary glands that secrete mucus for protection. (Gives them the common name “Slime Hags”.) Similar to amphioxus, tunicates, and echinoderms because they lack jaws, paired appendages, and bone. Lack vertebrae.*
Hagfishes, Cont. Remain Isosmotic with sea water. Are Serially Hermaphroditic (are male when newly matured but become female). [Other organisms may start as female and become male.] Oviparous reproduction.
Lampreys There are approximately 40 living species. Feed by attaching the buccal funnel with keratinized “teeth” to prey and secreting an anticoagulant onto the tissue. Most species are Anadromous. (Reside in the ocean as adults and return to rivers to spawn).
Lampreys, Cont. Some species remain in fresh water their entire lives. Adults die after spawning. Eggs hatch into Ammocoete larvae. Larvae are filter feeders that trap food in a mucus-like secretion which comes from the subpharyngeal gland.
Extinct Jawless Vertebrates There are many groups of extinct jawless vertebrates according to fossil records. Many of these species possessed body scales, shields, or plates. Also, many species possessed “acellular” bone, which differs from typical vertebrate bone by lacking enclosed cells.
Gnathostomes Gnathostomata = All of the jawed vertebrates. Also possess: - Paired Nostrils - Five Gill Slits - Articulated Gill Arches - Two Sets of Paired Appendages - Three Semicircular Ducts in the Ears
Gnathosomtes, Cont. Considered the dominant vertebrates. Include: - Placoderms (plate; skin) (heavily armored) [Extinct.] - Chondrichthyes (cartilaginous fishes) - Etc. (every other vertebrate group)[Group of Placoderms and Chondrichthyestogether is called Elasmobranchiomorphi.]
Chondrichthyes Chondrichthyes = The cartilaginous fishes, including the sharks, skates, rays, and chimaeras. - Elasmobranchii includes the sharks, skates, and rays. - Holocephili includes the chimaeras.
Chondrichthyes, Cont. Chimaera (Ghost Shark) *From Wikipedia
Chondrichthyes, Cont. There are approximately 800 living species. Lack true bone and dermal plates although the cartilage is calcified. Possess Placoid Scales that may be remnants of body armor. May be Oviparous, Ovoviparous, or Viviparous.
Chondrichthyes, Cont. Fertilization of eggs is internal and males possess Claspers to facilitate copulation. Lack swim bladders, but produce lipids in the liver to increase bouyancy. Possess electroreceptors called Ampullae of Lorenzini to locate prey.
Chondrichthyes, Cont. Differences in Holocephali: - Scales are mostly absent. - Upper jaw is firmly attached to the cranium. - Gills are covered by a flap called an Operculum.