Phylum Chordata

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Phylum Chordata
Subphyla

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Subphylum Urochordata(Sea Squirts)
- Subphylum Cephalochordata (Lancets)
- Subphylum Craniata (hagfishes & vertebrates)
- Infraphylum Hyperotreti(hagfishes)
- Infraphylum Vertebrata (vertebrates)

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Subphylum Craniata

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The hagfishes and all vertebrates are CRANIATE: possess a skull that surrounds the brain & some sensory organs
- skull may be either bone or cartilage (2 types of connective tissue)

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Infraphylum Hyperotreti:
Hagfishes

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- all marine, in benthic (bottom) region, ~60 species
- feed on inverts in sediment, may enter live/dead fish and eat from inside
- most primitive craniates

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Hagfishes:
Anatomy

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Skull consists of cartilaginous bars
Retain notochord through adult stage
Body is elongate (eel-like)
Lack jaws; mouth with 4 pairs of tentacles
Lack paired fins
- Either lack eyes or have vestigial eyes
- Possess slime glands, are excessively slimy
- Circ system partly open, partly closed
- Have a main branchial heart & several accessory hearts

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Infraphylum Vertebrata:
Vertebrates

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- characterized by VERTEBRAE, hollow rigid structures that form tube surrounding & protecting dorsal nerve cord
- vertebrae may be of bone or cartilage

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Class Petromyzontida:
Lampreys

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- marine & freshwater
- larvae filterfeeders, adults lgly parasitize other fish
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Class Ptromyzontida:
Lamprey Anatomy

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- Lack jaws; have sucking mouth with teeth and rasping tongue
- Eel-like body form
- No scales or paired fins
- Gill slits (7) on side of head (water enters and exits through slits)
- Skeleton made of cartilage
- Can tolerate very high iron levels in blood and tissues
- Only juveniles retain notochord

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Lamprey Reproduction

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- Many lampreys live as adults in the ocean but in rivers as juveniles
- Typically return to river to mate
- Juveniles are called ammocoete larvae

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Class Chondrichthyes: Sharks, Skates, Rays & Allies

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- primarily marine, few freshwater
- carnivore or scavengers
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Chondrichthyes: External Anatomy

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- Cartilaginous skeleton
- Have moveable jaws with teeth
- Ventrally located mouth
- Paired appendages (fins)
- Heterocercal (asymmetrical) tail
- Gill slits (5-7) on side of head
- Water enters through mouth or spiracles (specialized openings through which water enters)
- Have a CLOACA, or common external opening to urinary & reproductive tract

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Chondrichthyes: Scales

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tractChondrichthyes: Scales
- Sandpaper-like skin, covered with placoid scales (flattened rectangular base plate which is embedded in the skin)
- These are lost in adult ratfishes & chimaera
- Teeth are modified placoid scales, in rows

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Chondrichthyes:
Internal Anatomy

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- Breathe via gills; all but skates (which use spiracles) aerate gills via the mouth
- Possess a liver to remove wastes from blood
- Blood cells produced in spleen and Leydig’sorgan
- Spiral valve in lower intestine; increases surface area for absorption
- Lack swim bladder or lung, sink if not swimming
- Large brain size for body size in many species

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Subclass Elasmobranchii: Sharks, Skates and Rays

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Sharks are:
- Elongate; fast swimmers
- Somewhat laterally compressed
- Mostly predatory w sharp teeth
- Among largest living fish
- Skates & rays are:
- Dorso-ventrally flattened
- Mostly benthic, some shallowly burrow
- Some filter feed while swimming
- Some have stingers or electric charge

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Subclass Holocephali: Chimaeraor ratfishes or ghost sharks

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- Gills are covered with OPERCULUM (like bony fishes)
- Plate-like crushing teeth for feeding on molluscs
- Many have venomous spine anterior to dorsal fin

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Bony fishes:
General Characteristics

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- Both marine & freshwater species; some capable of limited time out of water (lungfishes)
- Carnivores, herbivores, detritus feeders, some filter feeders

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Bony Fish:
External Anatomy

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- Skeleton made of bone (except in paddlefish and sturgeons)
- Jaws with limited mobility, many with teeth
- Terminal or ventral mouth
- Paired fins
- Homocercal(symmetrical) tail
- Single gill opening on each side, covered by bony operculum (pumps water)

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Class Sarcopterygii: Lobe-finned Fishes

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- Small group; 8 living species
- Fins are lobed and connected to body by single bone; lack rays
- Can “walk” across substrate on these fins
- Lungfishes have air-filled sacs used as lungs in gas exchange (can withstand drought)
- Direct ancestor of land vertebrates
- Very likely that these should not be included in the same Class as the remaining fish

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Class Actinopterygii:
Ray-finned Fishes

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- No muscular lobes associated with fins
- Instead, fins are thin layers or skin with thin bony rays
- Swim bladders (gas-filled sacs) function to regulate buoyancy
- Includes vast majority of living fishes

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Fishes:
Feeding and Digestion

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- Most modern fishes are predators, usually swallowing prey whole
- Some are filter-feeders
- Some are herbivorous (e.g., carp, wood-eating catfish)
- Complete digestive system like other vertebrates
- Stomach stores food
- Small intestine primary site of digestion and absorption

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Fishes:
Circulation and Gas Exchange

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- CLOSED circulatory system
-Two-chambered heart pumps blood through arteries, capillaries, and veins
- Red blood cells contain HEMOGLOBIN
- Most fish exchange gases primarily w gills (a few have lungs)
- Counter-current exchange (water & blood flow in opp directions)m inc efficiency

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Fishes:
Nervous System I

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- Central nervous system w brain & spinal cord
- Receptors for temperature, touch, smell, vision, hearing, & balance
- Ear often connects to swim bladder to aid in sound detection
- Eyes lidless & lens moves back & forth to focus (unlike other vertebrates)
- Lateral-line system –sensory pits along side detect motion, perhaps low frequency sounds
- Most fish display electroreception (detect electrical fields generated by other organisms)
- Some (e.g., sharks) find prey this way
-Some fish (e.g., electric eel) produce strong current for defense & to shock

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Fishes: Osmoregulation

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- Freshwater fish naturally absorb water, lose electrolytes (salts & other ions) thru diffusion
- Marine fish naturally absorb electrolytes, lose H2O thru diffusion
- Fish kidneys & gills are the primary osmoregulatory organs

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Freshwater Fishes:
Osmoregulation

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- Actively absorb ions across gills
- Reabsorb little water in kidneys
- Much dilute urine
- Do not drink water

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Saltwater Fishes:
Osmoregulation

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- Eliminate ions by excretion, defecation, and active transport across gills
- Reabsorb much water in kidneys
- Small amounts of strong urine
- Drink water

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Fishes:
Osmoregulation and Excretion

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Diadromousfishes migrate between freshwater and saltwater and must have both mechanisms
- Some marine fish (e.g., sharks) store N-ous wastes (urea) in tissues to reduce the concentration gradient
- Most N-ous waste in form of NH3 & is excreted across gill surfaces
- Remainder excreted through cloaca as urea, creatine, or creatinine

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Fishes:
Reproduction

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- Sexual reproduction, external(most) or internal fertilization
- Most oviparous, some ovoviviparous, and a few viviparous
- Most have limited or no parental care of embryos (lay many eggs)
- Some brood embryos (e.g., seahorses) or even provide post-hatching care of young (e.g., catfishes)