Review sheet 8a (Marine Fishes)
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Understand that nekton are actively swimming organisms (can swim against a current)
Understand that cephalopods and some pelagic arthropods are nektonic, but that most nekton
are vertebrates
Know that vertebrates belong to subphylum Vertebrata and phylum Chordata, and so exhibit all
four characteristics of chordates at one point in their lives
Understand that vertebrates differ from other subphyla in phylum Chordata by having a
backbone
Understand that in vertebrates, the vertebrae surround and protect the spinal cord
Understand also that vertebrates have a distinctive head, exhibit bilateral symmetry, and organ
systems
Know that fishes were the first vertebrates, appearing ~500 million years ago
Understand that half of all vertebrates are fish
Understand that fish are broken down into 3 distinct groups: jawless fish (Agnatha),
cartilaginous fish (Chondricthyes), and bony fish (Osteichthyes)
Be able to label the parts of a fish: dorsal fin, pelvic fin, caudal fin, and pectoral fin
Understand that jawless fish (Agnatha) are the most primitive of living fish
Know that jawless fish lack a jaw and have long, cylindrical bodies without scales
Understand that jawless fish (lamprey and hagfish) are not eels (eels belong to Osteichthyes as
they have a jaw)
Understand that hagfish are exclusively marine
Know that cartilaginous fish have an endoskeleton composed of cartilage, not bone
Know that paired fins evolved in cartilaginous fish
Know that cartilaginous fish possess placoid scales, which are rough and pointed backwards
Understand that cartilaginous fish include sharks, skates, rays, and chimeras, nearly all of which
are marine
Understand that the teeth of shark are arranged in rows and lost teeth are replaced by ones
growing behind them (like a conveyor belt)
Know that sharks are efficient swimmers and so have a fusiform, or spindle-shaped body
Understand that many sharks exhibit counter-shading whereby they are lighter on the bottom
and darker on the top
Know that sharks have 5-7 gill slits
Understand that sharks are in serious decline worldwide due to overfishing
Understand that rays and skates are dorsoventrally flattened, with 5 pairs of gill slits on the
ventral (underside) of their bodies
Know that most sharks and rays are demersal, in that they spend most of their time on the
bottom
Know that skates have 2 dorsal fins, rays do not; be able to label a skate vs a ray if given 2
photos on an exam
Understand that chimeras are a small group of cartilaginous fish, also known as ratfishes
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Know that chimeras have only 1 pair of gill slits, which is covered by a flap of skin
Know that bony fish (Osteichthyes) are the most successful and abundant of all fishes
Know that bony fish possess an endoskeleton composed of bone (calcium)
Know that bony fish have cycloid or ctenoid scales
Know that bony fish have a gill flap called an operculum to cover and protect their gills
Understand that most bony fish are ray-finned (not lobe-finned) fishes
Know that flatfish begin their lives are normal (non-flattened) fish, but that during development,
become flattened sideways
Know that winter flounder are right-sided, while summer flounder are left-sided
Understand that there’s always a bigger fish….