Marine Exam 3

Chordata

Deuterostomes, including Urochordata, Cephalochordata and Vertebrata

Chordata Defining Characteristics

• Hollow, dorsal nerve cord

• Gills or pharyngeal slits

• Notochord

Urochordata

ascidians, tunicates, salps

Urochordata: Defining Characteristics

ascidians, tunicates, salps.

• Chordate characteristics only in tadpole-like larva

• Body is covered by tunic or test (made of a cellulose-like polysaccharide)

Cephalochordata: Defining Characteristics

lancelets or amphioxus.

• Chordate characteristics present throughout

• Lack backbone

Cephalochordata

lancelets or amphioxus

Vertebrata: Defining Characteristics

sharks, fish, and mammals

• Have backbone (row of skeletal elements called vertebrae)

• Have skull (protects the brain)

• Most* vertebrates have jaws

Vertebrata

sharks, fish, and mammals

Chordates Clades

Craniata (hagfishes and vertebrates) → cranium (skull)

Vertebrata (lampreys and gnathostomes) → with backbones

{Gnathostomata → Vertebrates with jaws}

Agnatha

(Hagfishes and lampreys) Subphylum of Craniata (subclass of chordates) - jawless fishes

Agnatha defining characteristics

hagfishes and lampreys.

Skull (protects brain)

NO backbone

NO jaw

Agnatha feeding

lampreys and hagfishes

• Suction feeding (scavengers use muscular mouth and rows of teeth, on dead or dying fishes)

• Anguilliform morphology (“eel-like” body shape; no scales)

Agnatha defense mechanisms

lampreys and hagfishes. Called slime eels (produce slime and release from mucus gland pores)

Vertebrata

(lampreys and gnathostomes) craniates with backbones

Craniata

(Hagfishes and vertebrates) Chrodates with cranium (skull)

Lampreys

Subclass Agnatha (jawless fishes)

Lampreys

Subclass: Agatha (jawless fishes)

• Have skull

• Have backbone

• DON’T have jaws

Lampreys feeding

Agnatha (jawless fishes)

• Suction feeders (use muscular mouth and row of teeth)

  • Often parasitic → suck blood of larger fish (most scrape and eat algae)

• Anguilliform → no scales

Lamprey ecology

Agnatha (jawless fishes). Found in temperate regions; breed in lakes and rivers and live in sea as adults

Gnathostomata

Clade of chordates → vertebrates with jaws. Clades divided into: Chondrichthyes and Osteichthyes.

Chondrichthyes

Cartilaginous fishes. Subclasses include: Elasmobranchii (sharks, rays) and Holocephali (rat fish).

Chondrichthyes defining characterics

Cartilaginous fishes.

• Skeleton made of cartilage (more flexible than bone)

• Movable jaws (usually with well-developed teeth)

  • Mouth is ventrally located

• Placoid scales (rough sandpaper-like skin)

Elasmobranchii

Sharks and rays. Subclass of Chondrichthyes.

Sharks defining characteristics

• Fusiform body (slips easily through water)

• Heterocercal tail (caudal fin), -upper lobe longer than lower lobe-

• Two dorsal fins and large paired pectoral fin

• Gill slits (5 to 7 located behind the head)

• Powerful jaws with sharp pointy teeth; continually shed. (Rows of teeth to replace teeth when lost (usually while hunting prey).

Sharks variation

Significant variation exists between shark body shapes and ecological preferences.

Sharks Ecological Range

Found in all oceans and most depths (most common in shallow waters). Primarily marine.

Sharks Ecological Role

Top predators and recyclers (often scavengers). Loss of sharks correlates to loss of ecosystem health.

What are sharks fished for

Meat, cartilage, oil and fins

Sharks conservation

Trends in sharks killed yearly have been increasing over the last 10 years. Many are now endangered or threatened.

Skates and rays

Subclass Elasmobranchii. Clade Chondrichthyes.

Skates and rays defining characteristics

• Ventrally located Gills slits

• Pectoral fins (greatly expanded and fused with head)

• Rays have a whip-like tail with spines for defense

  • skates DO NOT

Skates and rays body plans

Dorsoventrally flattened bodies

Skates and rays ecological preferences

Most are benthic (live on the bottom)

Skates and rays ecology

• Some rays expose food by excavating sediment (teeth are modified for grinding and crushing)

• Manta rays fly through ocean using pectoral fins and Filter feed on plankton using gill rakers

Holocephali

Ratfishes. Within Chondrichthyes (cartilaginous fishes).

Holocephali Ecological preferences

Ratfish. Found in deep waters (close to the seabed to better access feeding on benthic invertebrates)

Holocephali body plan

Ratfish. Gill slits (1 pair) and long, rat-like tail

Chondrichthyes Locomotion

• Fishes swim to obtain food, oxygen, mates and escape from predators

• Most fishes (incld. Sharks) swim with side to side motion of body or tail

• S-shaped wave on contractions pushes against water and forces body forward (by myomeres)

Myomeres

Bands of heavy muscle that allow chondrichthyes to swim. Help produce S-shaped wave contractions pushes against water and forces body forward.

Sharks locomotion

• Have large pectoral fins that provide lift while swimming

• Heterocercal tail forces the head upward, (helps maintaining depth while swimming)

• Have a large liver full of oil → helps buoyancy

Chondrichthyes Feeding

• Most cartilaginous fishes are carnivores, and have eclectic diets (mixture of foods)

• Some feed by taking bites from prey larger than themselves

• Some are filter feeders (use gill rakers to eat plankton → planktivores)

Chondrichthyes respiratory system

• Fish get O2 from water flowing over their gills

• Some sharks are obligate ram ventilators

• Some sharks and rays have spiracles

Obligate ram ventilators

Some sharks who must swim continuously to force water over their gills to obtain O2

Spiracles

Some sharks and rays have an opening behind their eyes to pump water over their gills or draw water in through their mouths to obtain O2

Why are chondrichthyes’ gills an efficient way to obtain O2 from seawater?

The maximized surface area and a counter current system of flow

Chondrichthyes’ gills structure

• Cartilaginous gill arches (support gill)

• Gill filaments (increase surface area)

• Lamellae (rows of thin plates that create high surface area)

Chondrichthyes’ countercurrent system

Countercurrent system of flow thar makes for efficient gas exchange.

• water flows over the gills in 1 direction

• blood flows through the gills in the opposite direction

Countercurrent system; same current

Oxygen would diffuse only at the beginning

• Eventually, water and blood would
  reach the same O2 level (diffusion
  stops)

• Max ~50% oxygen extraction

Countercurrent system: counter current

The gradient is maintained across the entire gill

• O keeps diffusing the whole time

• Can extract up to ~80–90% of available O2

Chondrichthyes nervous system and sensory organs

• well developed sense of smell

• Ampullae of Lorenzini (sense organ that can detect weak electrical fields → helps them detect prey at close range

Ampullae of Lorenzini

sense organ in Chondrichthyes (cartilaginous fishes) that can detect weak electrical fields → helps them detect prey at close range

Chondrichthyes reproduction; fertilization

• Ducts lead from ovaries and testes to the cloaca

• Internal fertilization; copulation achieved as male inserts claspers into female cloaca

Chondrichthyes reproduction: early development three types

• oviparous (most)

• ovoviviparous (some)

• viviparous (few)

Oviparous

Type of early development. Lay eggs. Embryo is enclosed in a large leathery egg case, drops to bottom after spawning; Hatch after being laid

ovoviviparous

Type of early development. Eggs develop inside the female and she gives birth to live young.

viviparous

type of early development. embryos absorb nutrients directly from the walls of the females reproductive tract → no egg case

Osteichthyes

“Bony fishes” clade of Gnathostomata

Actinopterygii

“ray finned fishes” class of oseichthyes.

Actinopterygii: Defining Characters

• Bone composes skeleton

• Terminal jaw (more freedom of movement than chondrichthyes)

• Cycloid (or ctenoid scales)

• Operculum (gill cover - protects gills)

• Homocercal tail (similar sized lobes)

Actinoptergii Fin Structure

Composed of bony rays and interconnecting membranes

Actinoptergii - body shape

Large variety of forms.

Actinoptergii - body shape - Fast swimmers

fusiform body shape (streamlined)

Actinoptergii - body shape - bottom dwellers

dorsoventrally flattened

Actinoptergii - body shape - fishes that live among vegetation/rocks

anguilliform (or “eel like”)

Actinoptergii - body shape - slow swimmers

elongated vertically or triangular or round

Components to swimming

Velocity, acceleration, turning and buoyancy (body shape is the compromise between these)

Actinoptergii - acceleration specialists

have large strong tails (sit and wait predators)

Actinoptergii - velocity, cruising specialists

have stiff bodies and quarter moon tails (forked tails)

Actinoptergii - turning, maneuvering specialists

have disc shapes and large pectoral fins

Buoyancy

Osteichthyes (bony fishes) use swim bladder and gas gland.

Swim bladder

allows fish to adjust buoyancy

Gas gland

Allow fish to control secretion of gas from blood into swim bladder

The lateral line

Both Chondrichthyes & Osteichthyes. System of sensory organs. Used to detect:

• movement

• vibration

• changes in pressure

Actinopterygii feeding

ray finned fishes are very diverse. Habits reflected in shape of mouths. have protrusible jaws and thus suction feed.

Osteichthyes feeding

Bony fish are carnivores. Piscivores or eat hard items (corals etc.) or
corallivores or Planktivorous

Piscivores

eat fish. have rows of sharp biting teeth.

Fish that eat hard items (corals, molluscs, crabs)

have teeth fused into crushing plates

Corallivores

Fish that feed on small prey in crevices or coral polyps; have long snouts and small mouths

Planktivorous

fish that filter feed have large mouths and gill rakers

Actinopterygii feeding - protrusible jaw

Give ray-finned fishes have flexibility in feeding habits.

Actinopterygii feeding - suction feeding

rapid opening of mouth creates negative pressure inside mouth and a flow field outside of the mouth. The water and prey are sucked into the mouth

Osteichthyes - respiratory system

use active irrigation to obtain O2 through gills need to swim

Active irrigation

Osteichthyes use counter current exchange to pump water over gills using muscles to move the mouth and operculum to extract dissolved O2

Fish behavior

Schooling - form well defining groups, move in unison.

Schooling, how?

Still in active investigation

Schooling, why?

Three hypothosis:

• Selfish herd hypothesis

• The dilution effect

• The confusion effect

Selfish herd hypothesis

hypothesis for why do fish school. Fishes selfish motivation to reduce their own risk of predation at the expense of their neighbors

The Dilution effect

hypothesis for why fish school. the chance of an individual being eaten is lower the larger the school

The confusion effect

hypothesis for why fish school. coordinated action may serve to confuse predators.

Osteichthyes - reproduction

Almost all are oviparous. Broadcast spawn or lay eggs in a nest and male cares for young.

Broadcast spawn

release eggs directly into water column

Fishes parental care

Males care for young.

Osteichthyes mating systems

Monogamy, polygyny, polyandry and promiscuity

Monogamy

Mating system. One female and one male.

polygyny

mating system. One male and many females.

polyandry

mating system. One female, multiple males.

promiscuity

mating system. both males and females mate with many partners to increase likelihood of fertilization.

Sequential hermaphroditism

Sex change. Can be protogynous or protandrous. Fitness of being one sex is higher, selection favors sex change

protogynous hermaphrodite

female to male sex change

protandrous hermaphrodite

male to female sex change