Topic VertebratesVertebrata Fishes Phylum Chordata Subphylum Vertebrata craniata

Topic: Vertebrates/Vertebrata (Fishes) Phylum : Chordata Subphylum Vertebrata: (craniata) • Superclass: Agnatha (jawless fish) v Class: Cyclostomata (jawless vertebrates: lampreys and hagfishes) ü Order : Petromyzontia ü Order : Myxinoidea v Class: Ostracodermi (extinct) Ø Superclass: Gnathostomata (jawed vertebrates) v Class: Placodermi (armoured fishes, extinct) v Class: Chondrichthyes (cartilaginous fish) § Subclass: Elasmobranchii § Subclass: Holocephali v Class: Osteichthyes (bony fish)

The Classes of Vertebrates are often grouped into clades according to criteria of major evolutionary significance: A. jaws present or absent From most primitive to • agnatha = jawless most advanced: • gnathostomes = mouth with jaws • fishes B. fins versus walking legs • jawless fish 35 sp; >500 MY • pisces = paired fins for • sharks and rays 850 sp; swimming 420 MY • tetrapods = paired limbs for terrestrial locomotion • bony fish 21, 000 sp; 420 MY C. offspring develop within • amphibians 4300 sp; 360 MY fluid-filled sac of egg [sac • reptiles 7000 sp; 280 MY = amnion] • anamniotes = do not • birds 9700 sp; 150 MY develop within fluid filled sac; • mammals 4600 sp; eg fishes and amphibians • amniotes = do develop within a fluid filled sac; eg. reptiles, birds, mammals

Body Outline of Chordates

Subphylum: Vertebrata, is characterized by • Notochord is not present in adult; it is replaced by spine of cartilaginous or bony column /backbone. • A complex brain encased by a cranium, which protects and supports it. • Well developed head (cephalization) with advanced nervous and sensory structures. • Most have 2 pairs of appendages: 1 pair of pectoral and 1 pair of pelvic appendages. • • • Bony and/or cartilage endoskeleton for structural support and or locomotion. True body cavity – the coelom. Male and female are separate and distinct. Gill slits are few in number, when present. Variety of feeding strategies: herbivores, carnivores, omnivores, filter feeders, parasites. Well developed ventral heart with 2 -4 chambers. Closed circulatory system with hemoglobin pigment in the blood. Variety of habitats including fresh water, salt water, terrestrial. Specialized epidermal structures in the form of scales, feathers, hair, fur, spines. True kidneys. Efficient respiratory system of gills or lungs. Body is bilaterally symmetrical and of three parts –head (with internal skeleton the cranium), trunk and post-anal tail.

Morphometric characteristics of a generalized fish

Superclass: Agnatha. This includes the following two classes (i) Ostracodermi (ii) Cyclostomata Characteristics of Superclass Agnatha • Lack jaws hence the name agnatha (without jaw). • Vertebral spine is cartilaginous in nature. • Head with a cranium that encases a brain. • Mouth is generally round/circular. • No scales or exoskeleton. Characteristics of class Ostracoderms (i) They were first vertebrates, popularly called armoured fishes (ii) Originated about 500 million yrs ago, lived for about 200 million yrs and went into extinction about 300 million yrs ago. (iii) They were jawless and lived in freshwater. (iv) Paired fins were absent/present in some groups. (v) Median and caudal fins were present. (vi) The caudal fin was of heterocercal type ( a tail fin with unequal lobes in which the vertebral column turns upward into the larger lobe as in sharks) (vii) The head & thorax were covered by heavy amour of bones. (viii)Terminal mouth but mostly located ventrally & large no gill slits. (ix) Filter feeders & endoskeleton was either bony or cartilaginous.

Various ostracoderms of the class Osteostraci (bony shields)/paired fins

Characteristics of class Cyclostomata 1) Body is cylindrical, elongated and eel like 2) Skin is smooth, slimy & without scales 3) Mouth is circular, suctorial & without jaws 4) Respiratory organs are pouch/sac-like gills. 5) Gill slits 6 -14 pairs 6) A few horny teeth & a rasping tongue is present 7) Paired appendages are absent. 8) Skeleton is cartilaginous & notochord is persistent. 9) Single nasal aperture & a median olfactory organ is present. 10) Alimentary canal is straight. 11) Brain has very small cerebellum 12) They can be uni or bisexual Cyclostomata includes 2 orders 1. Order 1 : Petromyzontia (Lampreys) 2. Order 2: Myxinoidea (Hagfish) 1) 2) 3) 4) 5) 6) 7) 8) 9) Characteristics of Petromyzontia (Lampreys) They lack paired fins & scales. They are eel-like with lateral eyes & a single nostril on top of the head. Their body is soft , with ventral mouth which consists of horny teeth & a rasping tongue. Skeleton is cartilaginous & not well developed except for the skull & branchial region. Dorsal fins are absent. Adult has sucking mouth with which they parasite on other fishes. Lampreys live in seas but migrate to rivers for the purpose of spawning. 7 pairs of gill slits. All Lampreys has a life history that includes 2 distinct stages, the Ammocoete larva that lives buried in the mud for about 3 -7 yrs, and later become adult by metamorphosis

Lamprey attached to Lake Trout Head with cranium Gill slits Circular mouth Horny teeth

Characteristics of Myxinoidea (Hag Fishes) Ø They are exclusively marine & remains buried in the sand. Ø Usually attack the dying & dead fishes & enter inside their body (Scavengers) Ø Mouth is terminal & surrounded by soft lips. Ø 3 -4 pairs of tentacles are present around the edge of the mouth Ø Gill pouches joined to a common external opening on either side. Ø Nasal opening at the tip of the snout rather than on top of the head as in the lampreys. Ø Elongate (eel-like) & Scale less body. Ø Many mucous glands present for anti-predator defense. Ø Unsupported fin rays.

Osmoregulation Strategies Marine vertebrates are either osmotic conformers or osmotic regulators. A typical example of osmoconformers who are in osmotic and ionic equilibrium with seawater is the hagfish. Hagfish (cysclostomes) are the most primitive vertebrates. Osmoconforming (no strategy) Hagfish internal salt concentration = seawater. However, since they live IN the ocean. . no regualtion required!

Round mouth with Tentacles Gill Slits eel-like Body When the ugly predator encounters a carcass on the seafloor, it burrows into the body cavity of the dead or dying animal. There it eats, not only with its mouth, but also with its skin and gills.

Superclass: Gnathostomata (jaw bearing fishes) ü The most important advancement was the enlargement & the adaptation of the first gill arch to function as jaws. The second pair of gill arches became support structures for the jaws. ü The evolution of jaws permitted fishes & their descendants to utilize larger & harder food. This enabled them to become adapted to many new & diverse ways of living. ü Another advancement is the presence of paired appendages. Paired fins allow fish to balance & to maneuver well in water. this is an asset for predation

• • Gnathostomes are characterized by: A vertically biting device called jaws, and which is primitively made up by two endoskeletal elements, the palatoquadrate and Meckelian cartilage, and a number of dermal elements called teeth, sometimes attached to large dermal bones. Paired appendages (paired pectoral and pelvic fins) supported by an internal skeleton which supports more efficient locomotion. Gill arches which support/hold the gills lie internally to the gills and branchial blood vessels, unlike the gill arches of all jawless craniates, which are external to the gills and blood vessels. A horizontal 3 semicircular canal in the inner ear. Teeth - modified dermal scales More proficient predators than the jawless fish. • Class Placodermi (extinct) • The class Placodermi is regarded as the first set of fish with jaws but are now extinct. • The class are characterized by: • Well-developed fins and armour plating. Dermal armour consisting of head armour and thoracic armour. In the thoracic armour, the foremost dermal plates form a complete "ring" around the body and always include at least one median dorsal plate • Inhabit both freshwater and marine environment • Large size (up to 10 meters). • Bottom dwellers. • Lower jaw and teeth present. • Scavengers or predators. • Bottom dwellers.

Class Placodermi (extinct)

Characteristics of Class Chondrichthyes (cartilaginous fish) Osteichthyes (bony fish) Internal skeleton is composed of 1. cartilage rather than bone. 2. 2. Body scales are placoid (toothlike) in nature with a bony base. 3. Jaws suspended by two gill arches. 4. Swim bladder or lung absent; have 3. oil filled liver to provide neutral buoyancy. 5. Claspers (modified pelvic fins) 4. present in males for internal fertilization. 5. 6. Notochord present in the young and gradually replaced by a backbone of cartilage in adult. 7. Ventral mouth. 6. 8. Gills not cover by operculum. 7. 9. Fleshy pectoral and pelvic fins. 10. Cold blooded 8. (ectothermic/poikilothermic). 9. 11. Paired nasal openings 12. Two-chambered heart. 1. Bony endoskeleton Body covered by cycloid scales (thin and round bony scales) Paired pectoral and pelvic fins supported by bony rays. Bilaterally symmetrical tail fin. Visceral cleft as separate gill openings covered by a bony flap – the operculum. No external ear Eggs produced External fertilization. Poikilothermic (cold blooded)

Chondrichthyes (cartilaginous fish) • Differences 1. All are marine animals 2. Endoskeleton is made up of cartilage 3. Scales are placoid type and are minute 4 Gills not cover by operculum. 5. Swim bladder or lung absent; have oil filled liver to provide neutral buoyancy. 6. Tail is heterocercal 7. Ventral mouth. 8. Fins are without rays. Similarities Osteichthyes (bony fish) • Differences 1. Inhabits freshwater & marine. 2. Endoskeleton is made up of bone 3. Skin is covered by cycloid, ctenoid or gonoid scales 4 Gills covered by operculum. 5. Air bladder is present in many species 6. Tail is homocercal, diphycercal or heterocercal 7. Mouth is usually terminal or subterminal 8. Paired pectoral and pelvic fins supported by bony rays. Similarities

cartilaginous fish (Shark) Male sharks have paired intromittent organs called claspers. Claspers are modifications of the pelvic fins and are located on the inner margin of the pelvic fins. Females do not have claspers.

Oreochromis niloticus (Linnaeus, 1758) Kingdom: Animalia Phylum : Chordata Class : Actinopherygii (Rayfinned fishes) Order : Perciformes (Perch like) Family : Cichlidae (Cichlidae) Genus : Oreochromis Species : Oreochromis niloticus

The principal types of scales are the cycloid scales of salmon and carp, the ctenoid scales of perch, the placoid scales of sharks and rays, the ganoid scales of sturgeons and gars. Fish scales are produced from the mesoderm layer of the dermis, which distinguishes them from reptile scales