Marine Biology Quiz on Elasmobranchii

Character States

• The original condition of a character is called the "primitive character state"
• A character whose state has changed from the primitive state is called a "derived character state"
• For example, the presence of hair is the primitive character state for all mammals. The absence of hair is a derived character state for one subclade - whales.

Clades and Taxa

• Clades are a group of organisms that share a common ancestor.
• A sister group is when two clades diverge from a single lineage and are the same age, but the two clades are not necessarily the same age.
• Taxa is a term for any group of organisms:
  • Species
  • Genus
  • Family

Terms

• Adaptation - a specialized feature that helps an organism survive in its environment
• Specialist - an organism that thrives only in very specific environments
• Generalist - an organism that can survive and thrive in a variety of environments
• Benthic - organisms that live on the substrate or bottom
• Pelagic - organisms that live in the open water column

Global Diversity of Marine Fish

• More species at low latitudes (near the equator)
  • Stable conditions with no seasonality
  • More food available due to warm waters and high productivity
  • More space for organisms to live and specialize
• Species accumulate faster at high latitudes (near poles)
  • Unstable conditions with seasonality
  • Fewer species due to difficult living conditions
  • Competitive exclusion principle: dominant species may restrict the diversity of other species in an area
• Coastal areas can be particularly diverse
  • Coral reefs provide shelter from predators and are a rich source of food

Global Diversity of Freshwater Fish

• Mostly concentrated near the equator focusing on large landmasses with large, warm river systems
  • Amazon and La Plata Rivers (South America)
  • Congo River (Africa)
  • Mekong and Yangtze Rivers (Asia)
  • Mississippi River (North America)

Agnatha: Jawless Fishes

• Primitive vertebrates that originated in the Cambrian period
• Myxiniformes (Hagfishes)
  • Vestigial eye
  • 4 pairs of sensory tentacles
  • Mouth with rasping tongue and keratin teeth
  • Mucus gland pores
  • 12 external gill slits (paired)
  • Slime defense mechanism releases mucin vesicles and skeins of fibrous thread
• Petromyzontiformes (Lampreys)
  • Eye
  • Oral disk with keratin teeth and rasping tongue
  • 7 external gill slits (paired)
  • Anterior and posterior dorsal fins
  • Caudal fin

Chondrichthyes: Cartilaginous Fishes

• Consist of ratfish/chimeras, rays, and sharks
• Maintain buoyancy with a large oil-filled liver and a heterocercal caudal fin.
• Gill openings are independent and physically separate but connected to the esophagus, making them more efficient than pouched gills.
• Respiration modes:
  • Slow-moving, benthic sharks actively pump water across gills with their mouths
  • Spiracle pulls water in and across gills
  • Ram ventilation: forward movement passively forces water across the gills
• Placoid Scales:
  • Present in all species
  • Dermal denticles made of dentine and enameloid
  • Lightweight, highly protective and reduce drag
• Teeth:
  • Made of calcium phosphate
  • Smooth or serrated
  • Replaced throughout life
• Ampullae of Lorenzini:
  • Electroreceptors that detect electric fields
  • Gel-filled pores throughout the body connected to sensory cells
• Synapomorphies:
  • Cartilaginous skeleton
  • Chondrocranium lacks sutures
  • Unsegmented soft fin rays
  • Teeth not fused to jaws
  • Males have claspers for internal fertilization
• Chimeroidea (Ratfish/Chimeras:
  • Gill cover over 4 gill slits
  • Live at depths from 80-2600m
  • Scavengers or invertivores
  • Upper jaw fused to the chondrocranium
  • Males have cephalic claspers
• Elasmobranchii:
  • Includes Selachii (sharks) and Batoidea (rays and skates)
  • Oldest fossil teeth from 418 Mya

Selachii: Sharks

• Pelvic fins usually not anchored to the skeleton by the pelvic girdle.
• Soft fin rays unsegmented

Batoidea: Skates and Rays

• Anatomy: Skates vs Rays
  • Rays are live-bearing (viviporous)
  • Skates are egg-laying (oviparous)
  • Skates have a prominent dorsal fin
  • Rays only have a very reduced dorsal fin
  • Rays are kite-shaped with ship-like tails
  • Skates have fleshy tails
• Skeletal Anatomy
  • Skeleton is cartilaginous
  • Pelvic girdle is fused to the vertebral column, which is a derived feature for Chondrichthyes
  • Scapular girdle is present

Sarcopterygii: Lobe-finned Fishes

• Consist of Dipnoi (lungfish), Actinistia (coelacanths) and Polypteriformes (reedfish)
• Dipnoi (Lungfishes)
  • Cosmoid scales (extinct)
  • Cycloid scales (extant)
  • Distribution of extant species is due to the breakup of the supercontinent Gondwana.
  • Burrowing mechanism to survive during dry periods
  • Aestivation: A period dormancy during drought periods
• Lungfishes can survive up to 5 years during aestivation
• Cranial Anatomy:
  • Ceratohyal (floor of mouth)
  • Clavicle (part of pectoral girdle)
  • Cranial rib (an accessory structure associated with their lung) are involved in breathing and feeding
• Scales:
  • Cosmoid scales (extinct lungfishes)
    • Benefit: durable and provide defense against predators
    • Drawback: poor flexibility
  • Cycloid scales (extant lungfishes)
    • Benefit: flexibility
    • Drawback: Limited defense against predators
• Actinistia (Coelacanths):
  • Vestigial lung derived from the swim bladder
  • Filled with fat, rather than air, and is likely an adaption for buoyancy at great depths
  • Cosmoid scales: likely derived from the fusion of placoid scales
• Polypteriformes (Reedfishes): ~360 Mya
  • Juveniles have external gills, resorbed over time
  • Respire using lungs, but cannot extract sufficient oxygen from water
  • Must periodically surface and gulp air
  • Spiracular breathing:
    • Respire through two spiracles on the top of the head
    • Air can pass through spiracles into the mouth
    • If habitat is desiccating, they can make short over-land excursions

Acipenseriformes: Sturgeons and Paddlefishes

• Acipenseridae (Sturgeons): ~350 Mya
  • 28 species
  • Lack scales, possess five lateral rows of bony plates called scutes
  • Four barbels (sensory organs in front of mouth)
  • Lack teeth
  • Skeleton is largely made of cartilage; many bones do not fully ossify
  • Commercially harvested for their eggs
• Polyodontidae (Paddlefish): ~350 Mya
  • 8 species; only 2 extant
  • Rostrum (paddle) has 2 functions:
    • Provide lift and stability while filter-feeding
    • Counteract the drag created by the lower jaw that drops below the body
  • Lack teeth
  • Lack scales
  • Ampullae of Lorenzini present

Amiiformes (Bowfins): ~250 Mya

• Only 2 species
• Very old lineage
• Vascularized swim bladder can function as a lung
• Protruding tube-like nostrils
• Single-layered cycloid scales

Lepisosteiformes (Gars): ~250 Mya

• 7 extant species
• Vascularized swim bladder can function as a lung (similar to Bowfins)
• Ganoid scales:
  • Rhomboid shape
  • 3 layers
  • Inner bony plate
  • Middle layer of osteodentin
  • Outer layer of ganoine
  • Largely non-overlapping
  • Inflexible and tough
  • Benefit: durable and defense against predators
  • Drawback: poor flexibility

Actinopterygii: Ray-finned Fishes

• Elopiformes (Tarpon):
  • 2 species
  • Cycloid scales
  • Can live in marine and brackish water
  • Obligate air breathers: need to have access to the surface
  • Likely a unique origin from that in lungfish, reedfish, sturgeons, paddlefish, bowfins, and gars
• Anguilliformes (eels):
  • True eels
  • Scales:
    • Freshwater: small, soft, cycloid scales embedded in their epidermis
    • Marine: lack scales, produce mucus for protection
  • Freshwater eels are derived from marine ancestors
    • Lacking scales is viable in marine environments, but not freshwater
  • Fins
    • Freshwater: pectoral fins and continuous dorsal, caudal, and anal fins
    • Marine: continuous dorsal, caudal, and anal fins### Osteoglossiformes
• “Bony Tongues,” about 245 species
• Mostly freshwater
• Cycloid scales, most teeth on tongue and roof of mouth

Ostariophysi

• More than 11,000 species, all freshwater except Antarctica
• Weberian apparatus:
  • Minute bones connecting inner ear to swim bladder
  • Amplify sound waves by resonating through swim bladder
  • Provides enhanced ability to sense vibrations and hear

Cypriniformes

• About 4,500 species, cycloid scales
• Lack teeth on jaws, lack stomachs, many have barbels (whiskers)

Characiformes

• About 2,200 species, well-developed teeth
• Adipose fin: tiny fin by caudal fin, distinct character

Gymnotiformes

• About 240 species
• Lack pelvic and dorsal fins, possess electric organs
• Electric organs produce weak electric fields for navigation
• Electric eels can stun prey

Siluriformes

• More than 3,800 species, majority freshwater
• Adipose fin present
• Usually negatively buoyant, reduced swim bladder, large bony skull
• Lack scales, produce mucus; some have dermal plates
• “Armored” have dermal plates or plates derived from vertebral processes
• Sound production by flicking pectoral fins
• Barbels (whiskers) up to 4 pairs: nasal, maxilla, and 2 pair on dentary
• Some breathe air:
  • Gulp air into modified swim bladder
  • Diffuse air through modified gill arches
  • Gulp air into the modified stomach/digestive tract

Esociformes

• About 10 species
• Esocidae (pikes):
  • 7 species
  • North America, Western Europe, Siberia
  • Sportfish and top predators
• Umbridae (mud minnows):
  • 3 species
  • Mississippi River Basin and eastern US
  • Live in stagnant, low-oxygen waters (marshes, ditches, swamps)

Salmoniformes

• Food and sport fish, adipose fin present

Percopsiformes

• Chologaster: swamp fish live near the surface
• Forbesichthys: spring cavefish live in intermittent surface
• Typhlichthys: southern cavefish live in sub-surface
• Cave adaptations:
  • De-pigmentation: loss of selection for visual signaling, colors are expensive to make
  • Eye-loss: expensive structures, require vitamins, limited utility in dark
  • Elaboration of the lateral line system: mechanosensory (vibrations) and chemosensory (smell) function
  • Flattening of head: possible increase in mouth size and sensory receptor surface area

Acanthomorpha

• Hollow, unsegmented spines along anterior dorsal and anal fin: can be extended for defense, retracted to reduce drag
• Well-developed snout cartilage allows for upper jaw protrusion
• Mostly ctenoid scales: outer bony layer, inner fibrous collagen layer with small spines
  • Highly flexible for mobility
  • Comb-like edge creates turbulence that reduces drag
  • Less protection than placoid, cosmoid, or ganoid scales

Holocentriformes

• Nocturnal, marine, large eyes
• Reddish color provides camouflage in dim light

Batrachoidiformes

• Marine, toadfish

Gobiiformes

• 90% marine, small burrowing species
• Lack swim bladder, actively swim to prevent sinking

Scombriformes

• Marine, mostly pelagic active swimmers
• Fastest swimmers, large predators

Syngnathiformes

• Marine, mimic seaweed and coral
• Males become pregnant and carry young
• Loss of fins: pelvic, sometimes caudal fin
• Seahorses have prehensile tails for grasping, slow swimmers

Synbranchiformes

• Freshwater, labyrinth organ:
  • Vascularized area within branchial arch (gill arch)
  • Diffuses inhaled oxygen into blood
  • Survive on land if moist

Carangiformes

• Mostly large, laterally compressed, silvery fishes
• Remoras have specialized dorsal fin that forms a suction cup
  • Attached to sharks, whales, turtles, tuna, swordfish
  • Commensalism: attachment to host for travel

Pleuronectiformes

• Mostly marine, exhibit eye migration during development
• Ovalentaria: produce adhesive eggs

Pomacentridae

• Farm plots of algae
• Longfin Damselfish has a mutualistic relationship with Mysidium integrum
• Clownfish have mutualistic relationships with anemones

Polycentridae

• Leaf fishes, mimic dead leaves, ambush predator

Cichlidae

• About 1,700 species, East African Great Lakes, significant paradox
• Distributed throughout Africa, Americas, India, and Madagascar
• Freshwater

Perciformes

• Triglidae (sea robins):
  • Marine, possess sensory organs on pectoral fins
  • Used to sift through substrate for food
• Percide (perches and darters):
  • Large-bodied predators: walleye and perches (sport and food fish)
  • Dramatic transition to small bodies: darters
  • Darters lack swim bladders, strictly benthic
• Centrarchidae (sunfishes and black basses)

Labriformes

• Wrasses (more than 400 species) and parrotfishes (about 90 species)
• Wrasses and parrotfishes associate with coral reefs
• Parrotfishes are a sub-clade of wrasses
• Parrotfish teeth are fused into a “beak” for grazing on coral

Lophiiformes

• Mass is mostly head and jaws, large mouths
• Lure used to attract prey: frogfish lures mimic invertebrates, anglerfish lures emit light
• Illicium (rod/stalk): modified dorsal spine controlled by muscles
• Esca (bait/lure): luminescent organ housing symbiotic bacteria

Tetraodontiformes

• Many fins lost or functionally lost, clavus: a pseudocaudal fin acts as a rudder

Fish Swimming Modes

• Body-Caudal Fin (BCF) Swimming:
  • Anguilliform swimming (eels):
    • Swimming with most of the body and caudal fin
    • High maneuverability and flexibility
    • Slow speed, low hydrodynamic efficiency
    • Swimming interrupted by periods of inactivity
    • Cylindrical and elongate body, pointed head, paired fins reduced or absent
  • Carangiform swimming (jacks):
    • Swim with posterior body region and caudal fin
    • Intermediate maneuverability, flexibility, and hydrodynamic efficiency
    • Slow-medium speed; near-constant swimming
    • Laterally compressed
    • Narrow in front of tail, rounded or blunt head, pointed fins
  • Thunniform swimming (tunas):
    • Swim with caudal fin
    • Intermediate body flexibility
    • Low maneuverability, high hydrodynamic efficiency
    • Constant medium-to-high speed swimming
    • Laterally compressed, narrow in front of tail, pointed head, pointed fins
  • Ostraciform swimming (boxfishes):
    • Swim with caudal fin
    • Very little body flexibility
    • High maneuverability, very slow speed, low hydrodynamic efficiency
    • Large pectoral fins used for steering
    • Other fins reduced or vestigial
• Median-Paired Fin (MPF) Swimming:
  • Labriform swimming (wrasses):
    • Swim with pectoral fins
    • Intermediate body flexibility
    • Intermediate maneuverability, slow speed
    • Intermediate hydrodynamic efficiency
    • Swimming in bursts
    • Laterally compressed, long, tapered pectoral fins
  • Rajiform swimming (rays):
    • Swim with pectoral fins, low body flexibility
    • Low maneuverability, slow speed, high stability
    • Low-to-high hydrodynamic efficiency
    • Dorso-ventrally compressed, expanded pectoral fins
    • Benthic species have dorsally positioned eyes
  • Gymnotiform swimming (knife fish):
    • Swim with anal fin
    • Low body flexibility, high maneuverability, slow speed
    • Anal fin expanded along the body
    • Laterally compressed
  • Amiiform swimming (bowfin):
    • Swim with dorsal fin
    • Low body flexibility, high maneuverability, slow speed
    • Elongate, tubular shape
  • Balistiform swimming (triggerfish):
    • Swim with dorsal and anal fin
    • Low body flexibility, high maneuverability, slow speed
    • Tapered head and body (triggerfish and pufferfish)
    • Laterally compressed (triggerfish)
    • Rounded body (pufferfish)

Caudal Fin Types

• Protocercal:
  • Undifferentiated, symmetrical
  • Lampreys and hagfishes
• Heterocercal:
  • Unequal-lobed (upper larger), asymmetrical
  • Passively generated some lift
  • Sharks and sturgeons
• Hypocercal:
  • Asymmetrical: bottom larger
  • Uncommon
  • Flying fish: passive drag to keep from drifting
• Homocercal:
  • Symmetrical, most common
  • Most variable in shape
  • Tunas and wrasses
  • Sub-types:
    • Rounded (sunfishes)
    • Truncate (darters)
    • Lunate (tunas)
• Hemihomocercal:
  • Asymmetrical (without lobes), abbreviated homocercal
  • Bowfin and gar

Locomotion

• Most species use their pectoral fins to some degree:
  • Carangiform/thunniform: use long stiff pectoral fins for steering at moderate-to-high speeds
  • Ostraciform/balistiform: use flexible pectoral fins to supplement dorsal and anal fins for propulsion
• Some species rarely use their caudal fin, but will in certain situations:
  • Labriform/amiiform swimmers: use tail to generate a burst of propulsion
• Anguilliform swimmers: usually benthic, often complex habitat
• Carangiform/thunniform swimmers: pelagic, open water away from structures
• Ostraciform swimmers: coral reefs, but not necessarily benthic
• Labriform swimmers: coral reefs, rarely benthic
• Rajiform swimmers:
  • Undulating pelvic fins: benthic, simple or moderately complex, often sandy areas (many species burrow)
  • Oscillating pelvic fins: pelagic, open water
• Gymnotiform swimmers: complex habitat, but not benthic
• Amiiform swimmers: variable habitat, complex or simple
• Balistiform swimmers: complex habitat