The Fish: Part 1

• Genesis 1:26 “have dominion over the fish of the sea”
• Main food source
• Good form of fertilizer
• Used to make glue
• Entertainment (aquariums)
• Three classes of fish
• Class Agnatha
• Class Chondrichthyes
• Class Osteichthyes 

Class Osteichthyes

• Characteristics
• Most fish we think of are in this class.
• Some unusual members such as sea horses
• Typical flat, spindle-shaped body
• Others flat on the bottom, round like a pencil, can look like boxes, pyramids, or balls
• Usually less than 1 meter in length 
• Support and Movement
• Bony skeletons (Bone is cartilage hardened by mineral deposits)
• Vertebral column and skull of bone
• Ribs, pectoral, and pelvic girdles are often cartilage (but can be bone)
• Move through the water by the whipping motion of its body. 
• The power comes from wavy, muscular bands found in the fish’s trunk and tail.
• Fish are denser than water, so why do they float
• Swim bladder: thin-walled sac in the body cavity that enables fish to control its depth and maintain it without swimming.
• Gases diffuse in and out of the SB through the bloodstream. 
• Fins
• Used for guidance or slow swimming movement. 
• Unusual ones: 
• Sea robin uses its pectoral fins to “walk”
• Walking catfish can hold water in its gills, and walk across land for long distances
• Flying fish use them for gliding through the air
• Can go 55 km/h and up to 46 m

• Body Coverings
• Overlapping scales. The number does not change, just the size in proportion to their bodies.
• Some fish, like some catfish are scaleless. 
• Some catfish have bony plates. 
• Sturgeon have rows of large enamel-like plates.
• Special glands beneath the scales secrete mucus.
• Nearly waterproof coating
• Lubricates the fish for smoother movement through the water (reduces friction by 66%)
• Chromatophores: branched cells responsible for producing some of the pigment in fish scales.
• Some fish can change their color or pattern
• Change color in response to temp., diet, states of excitement, and physical condition.
• Digestion
• Feed on plankton, worms, insects, other fish, and even some mammals.
• Ingested through mouth (which often contains teeth to bite or hold prey)
• Fish mouths vary depending on their prey
• The direction of the mouth points to where it eats
• Food passes through a flexible throat, or pharynx and a short esophagus into a saclike stomach for storage.
• Digestion occurs in a short intestine.
• Short tubes called pyloric ceca (at junction of stomach and intestines) secrete digestive enzymes.
• Liver, near stomach, secretes bile to aid in digestion of fats.
• Most fish have a gallbladder (stores and exerts bile) and a pancreas (secretes other digestive enzymes).
• Indigestible food eliminated via the anus.

• Respiration
• Almost all fish have an operculum: a plate behind the eye on each side of the head.
• Under this is a series of gills 
• Gills consist of two rows of thin gill filaments on a band of cartilage called the gill arch.
• Each gill filament consists of a sac of thin epithelium and richly supplied with blood vessels.
• Gill rakers are a number of cartilage projections on the inner part of the gill arch. They keep food and debris from entering and clogging the gills.
• Circulation
• Circulation of blood enables oxygen and nutrients to reach every cell of the fish.
• 2 chambered heart
• Atrium receives the blood
• Ventricle pumps the blood to the arteries
• Single loop system in which the heart pumps blood only to the gills.

• Nervous System
• Major organs: brain & spinal cord.
• 10 Pairs of cranial nerves branch from the brain
• Many spinal nerves
• Large optic lobe: They could see well if it weren’t for the fact that they live in water.
• Great sense of smell. People taste water, fish smell it.
• Tongue for taste and touch
• No external ears, but can detect sound vibratos 
• Sensor hairs: changes in current (detect pressure and movement changes)
• Reproduction
• Some are ovoviviparous and even viviparous.
• But most are oviparous.
• Eggs are laid and then fertilized externally.
• Females in some species produce hundreds of thousands of eggs.
• When environmental conditions are right, the female spawns (lays eggs)
• The male then covers the eggs with milt (a milky fluid containing sperm)
• The embryo usually forms atop of food material called yolk.
• As the embryo grows, the yolk shrinks.
• Eventually a tiny larval fish escapes the egg and fends for itself.
• This process can take hours to 4 months.

Subphylum Chordata: The Vertebrates

Characteristics

• Dorsal notochord: rod of tough, flexible tissue running the length of the animals body.
• Primary support
• In most chordates, before birth/hatching, it is replaced by vertebrae
• Vertebrae together are called the vertebral column or backbone
• Dorsal tubular nerve chord: 
• Passes dorsal to the notochord/or is incased in the vertebrae
• Connected with the brain at the anterior end of the cord
• Develops into spinal chord
• Pharyngeal pouches: 
• Folds of skin that develop either into gills or various structures of the lower face, neck and upper chest

Classification

• Three subphyla:
• Cephalochordata
• Retain their notochords through their entire lives
• Ex. amphioxus (lancelet): a small eel-like creature that sticks it’s head out of the sand and feeds on filtered plankton
• Urochordata
• Have notochords at the larval stage
• Ex. sea squirts: they pump water through their bodies, they keep their pharyngeal slits through adulthood
• Vetebrata
• Most familiar (95% of all chordates)
• Develop vertebral columns before birth
• We will look at this subphylum in this chapter and the next

Subphylum Vertebrata

• Vertebrate variety:
• Includes fish, amphibians, reptiles, birds, and mammals
• They live virtually every where
• From the ocean floor to the fringes of the atmosphere
• Classification:
• Ectothermic (cold-blooded): cannot generate their own body heat
• Must maintain their body temperature from external sources
• Inactive in cold temp.
• Endothermic (warm-blooded): generate their own body heat through physiological changes
• Relatively active
• Seven classes
• Ectothermic
• Agnatha
• Chondrichthyes
• Osteichthyes
• Amphibia
• Reptilia
• Endothermic
• Aves
• Mamalia
• Support
• Supported by an internal skeleton composed of bone and cartilage
• Support, protect, and surround delicate organs
• Axial skeleton: vertebral column, skull and ribs
• Appendicular skeleton: attachment of limbs
• Pectoral and pelvic girdle
• Circulation and excretion
• Closed circulatory system
• Consists of a heart and blood vessels
• Heart can have 2,3 or 4 chambers, depending on the species.
• Ventral to the vertebral column
• Blood vessels: 
• Arteries: carry blood away from the heart to body tissues
• Capillaries: thinnest branches of the arteries. 
• Pass through the body tissues. 
• Supply them with nutrients and oxygen and remove waste.
• Veins: begin with capillaries and cary blood from tissue back to the heart
• Hemoglobin: a red oxygen-carrying pigment. 
• Blood passes through a pair of kidneys to filter out waste.
• Nutrition
• There are three different types of eating habits in subphylum vertebrate:
• Herbivorous: animals that eat plans.
• Grazing animals such as horses or cows.
• Cellulose is hard to break down so the animal uses grinding teeth
• Carnivorous: animals that feed on other animals
• Sharks, lions, and eagles
• Sharp teeth, beaks, or claws
• Omnivorous: animals that eat both plans and animals.
• Varied types of teeth
• All vertebrates have an alimentary canal that is composed of:
• Esophagus
• Stomach
• Intestines
• Some have a liver, gallbladder, and pancreas
• Reproduction
• Sexes are separate
• Males have a pair of testes and females have a pair of ovaries
• Two types of fertilization:
• External fertilization
• Internal fertilization
• There are three basic methods for development:
• Oviparous: produce offspring from an egg that hatches outside the body
• Viviparous: live offspring that have been nurtured to birth inside the uterus (or similar)
• Ovoviviparous: egg remains in the mother’s body and hatches there, then emerges.
• Behavior
• Inborn
• Behavior from birth, does not need to develop
• Reflex behavior: automatic, involuntary response to stimulus
• Blinking, sucking, recoiling from pain
• Instinct behavior: elaborate behaviors, apparently the result of a stimulus or series of stimulus
• Salmon swimming upstream to spawn, mating rituals, flight or fight
• Conditioned
• A response learned by experience
• Training a dog, elephant, or seal
• Encouraged through reward/“punishment”
• Skunk spraying a dog
• Can be learned by watching other members of the species
• Intelligent
• Ability to use tools to manipulate the environment, reason out a solution to a problem, or communicate with symbols.
• Chimpanzees use rocks to open nuts and sticks to “fish” for insects
• Apes have been taught to learn sign language
• Woodpecker finch uses a cactus spike to dig out bugs
• Nervous system
• Contains:
• Brain
• Spinal cord, 
• Cranial nerves (branch from the brain)
• Spinal nerves (branch from the spinal cord)
• Sensory organs (such as eyes, ears, and taste buds)
• Five lobes of the brain
• Olfactory lobes: receive impulses from the smell receptors
• Cerebrum: controls voluntary muscle activity
• Optic lobes: receive impulses from the eyes
• Cerebellum: coordinates muscle activity and some involuntary activities
• Medulla oblongata: transports impulses to and from the spinal cord, includes some reflexes.

Subphlyum Hexoda: Class Insecta

Introduction

• Nearly 1,000,000 species (80% of all animals)
• Some reasons they are so successful:
• They can fly
• Tremendous reproductive capabilities
• Generally don’t compete for food
• They are a major influence on nature and man

Characteristics

• What makes them different from other arthropods?
• Three pairs of walking legs
• Wings, usually
• Bodies divided into three segments: Head, thorax, abdomen
• One pair of sensory antenna
• Movement
• Three pairs of jointed legs along the thorax.
• Used for movement, but types vary depending on what they are needed for:
• Flies have tiny claws and sticky pads (they can climb on smooth surfaces)
• Bees have fuzzy legs (used for collecting pollen)
• Most have 2 pairs of chitinous wings (although some have 1 pair and a few wingless species exist)
• Only invertebrates that can fly
• Flying styles and speeds vary
• Butterfly flaps wings 5-6 times per second
• Bees flaps wings up to 200 times per second
• Flies fly about 8km/h and dragonflies 40 km/h
• There are four different types of wings that vary based on need and use
• Membranous wings: thin, transparent, and crisscrossed with supporting veins. Most have this type

Membranous Wings

• Scale-covered wings: the flight wings of butterflies and moths are covered with delicate, beautifully colored scales that rub off easily

Scale-covered wings

• Leatherlike wings: grasshopper’s membranous wings covered by a pair of leather like wings 

Leather-like wings

• Horny wings: the front wings of beetles are thick shields that cover most of the dorsal surface of the insect

Horny wings

• Nutrition
• Ingestion:
• Variety of different types of mouthparts called mandibles
• chewing
• sponging
• siphoning
• piercing
• Three main parts of digestive system:
• Foregut: food enters through the mouth, it is moistened with secretions from the salivary glands, passes through to the gizzard where it is thoroughly ground
• Midgut: gizzard opens into the stomach. Digestive juices digest the food.
• Major site of digestion and absorption.
• Hindgut: solid residue left in the midgut after digestion passes through the hind gut, or intestine, and out through the rectum and anus
• Respiration, circulation, and excretion
• Respiratory system of insects is an elaborate system of tubules called tracheae that branch throughout the animal.
• This system is so complete that oxygen is transported throughout the animal without using the circulatory system.
• These tubules open to the outside through a sereis of spiracles, small pores that run along each side of the animal. 
• The insect “breathes” as abdominal contractions pump air in and out of the tracheae.
• The open circulatory system is only involved in the transport of nourishment and collection of waste. No gas exchange.
• Cellular waste is extracted by Malpighian tubes and excreted into the intestine for elimination.
• Irritability
• Anterior “brain” connected to an anterior ganglion and ventral nerve cord.
• Receives information from a variety of sources:
• Smell from antennae.
• Many insects produce chemicals called pheromones to find a mate.
• Antennae can sense humidity and flight speed.
• Taste receptors on the mouth parts.
• Tactile hairs on the antennae, limbs and body
• Compound eyes or several simple eyes
• Some have organs to hear
• Reprodution
• Sexes are separate.
• Females store sperm in seminal receptacle
• As she lays her eggs they are fertilized
• Eggs are protected either by where they are laid (deep in tree bark for example) or with protective coverings.
• Metamorphosis


• Developmental changes in insects is called metamorphosis. 
• This permits various stages to perform different functions.
• Ex. some insects eat only during their immature forms and become adults only to reproduce.
• Only a few species of insects do not exhibit metamorphosis.
• Incomplete metamorphosis (grasshoppers)
• The nymph that hatches looks like a miniature, oddly proportioned adult. 
• As it grows and molts it becomes more like the adult.
• Same diet and habitat for the nymph and adult.
  
  

• Complete metamorphosis (90% of all insects)
• Involves 4 stages: egg, larva, pupa, and adult
• Egg hatches into larva (a segmented wormlike stage)
• Some common names: maggots, grubs, caterpillars
• After period of eating and molting, the larva enters the pupal stage.
• The pupa makes a cocoon around itself (woven silk case).
• Though it is quiet on the outside, it is a period of significant activity and grown. 
• During pupal stage, the organs are dismantled and completely reshaped. 
• Eventually the cocoon opens revealing a fully developed insect. 
• This process is controlled by hormones. 
  
  
  

Subphylum Chelicerata: Class Arachnida

General Characteristics

All have mouthparts called chelicerae (appear as claws or fangs)

Most are completely harmless (some have painful stings, transmit diseases, or can kill you) 

Like insects they have small, compact bodies and long, delicate limbs, but they are not insects. 

Here are the characteristics that separate them: 

4 pairs of walking legs 

Bodies divided into two major segments (cephalothorax and abdomen)

No antennae or mandibles

Respiration by book lungs 

Usually 4 pairs of simple eyes 

 

Class Arachnida

• Characteristics
• 6 pairs of appendages:
• one pair of chelicerae (with poisonous fangs used to paralyze prey)
• one pair of pedipalps used for sensory reception and in males to transfer sperm
• 4 pairs of walking legs

• Nutrition:
• All spiders spin silk used for containing eggs, restraining prey, or building a web.
• Originates as a liquid protein and is released through organs called spinnerets. 
• Not all spiders catch prey in their webs. Some prowl on the group and ambush their prey.
• Once a spider has they prey, they immobilize them with a bite from the chelicerae and inject digestive juices into the victim. 
• The spider then sucks up the partially digested tissues using its stomach and pharynx.

• Respiration:
• Only arachnids have and use book lungs for respiration. 
• Air enters the spider through a slit in the abdomen and flows between folds of the book lungs where gas is exchanged.
• Reproduction:
• The sexes are separate. Females are often larger.
• Male places his sperm in a tiny web sac and stores it in special cavities of his pedipalps. He then transfers it to the female after a courtship offering of food.
• In some species, the female will eat the male after mating.
• As she lays her eggs, they are fertilized by the stored sperm.

 

Subphylum Crustacea

Crustaceans

• Most crustaceans are free-living and aquatic (although there are some parasites and terrestrial species).
• We are going to look at the crayfish as our example of a crustacean. 

The Crayfish

Crayfish

• Covered with a tough exoskeleton
• Divided into three segments: cephalothorax and the abdomen (composed of 6 different segments)
• Beneath the abdomen are a number of paired, small, flipper like appendages called swimmerets (used for swimming and reproduction).
• There are four pairs of walking legs and a pair of prominent chelipeds (or pinchers) attached to the cephalothorax. 

Life Processes

• Movement:
• Muscles
• Legs
• Swimmerets and walking legs
• Nutrition:
• Scavengers: eating virtually any edible material.
• The mouthparts of the crayfish reduce the food to swallowable size.
• Then moves to esophagus then to the anterior part of the stomach where it is ground to fine particles by muscular action and chitinous teeth of the gastric mill.
• The food is sorted in the posterior part of the stomach.
• Food is then moved to the intestines. Undigested food moves through the anus.
• Respiration:
• The crayfish as two sets of feathery gills found in the two lateral gill chambers along the thorax.
• Appendage movement and feathery mouthparts help to keep oxygenated water flowing through the gills. 
• Blood traveling through the thin-walled gills releases carbon dioxide and absorbs oxygen.
• Many can store water in their gill chambers in order to walk on land. The “hold their water” like people “hold their breath.”
• Circulation:
• Open circulatory system.
• Blood collects in the a cavity surrounding the heart. 
• Blood enters the dorsal heart through tiny openings.
• As the heart contracts, valves close to keep the blood from flowing back into the sinus.
• The blood then leaves the heart, bathing the organs with oxygenated blood, to then be collected in the sternal sinus.
• The blood passes again through the gills and the process starts again.
• Excretion:
• Excretion is performed by green glands, which are located near the base of the antennas.
• The green glands filter out waste.
• Fluid wastes are excrete through a pore anterior to the mouth.
• Wastes from the intestines are eliminated through the anus.
• Response:
• Ventral nervous system receives information about the environment from a number of sensory sources.
• Compound eyes
• Antennae
• Antennules, shorter sensory appendages
• Tiny bristles for touch on several appendages
• Statocyst: the organ of balance found at the base of each anteannule
• Reproduction/Regeneration:
• Arthropods cannot reproduce asexually, but as a mode of defense, they can loose an appendage and it will grow back.
• Crayfish mate in the fall.
• The male transfers its sperm to a receptacle in the body of the female using reproductive swimmerets.
• The female stores the sperm until she lays her eggs in the spring. 
• The fertilized eggs are then attached to swimmerets for development. They hatch within 5-6 weeks.
• During the first year, crayfish molt seven times. After that, twice a year for 3-8 years until they die.

The Arthropods

• Phylum Arthropoda includes lobsters, spiders, scorpions, millipedes, and insects. It contains over 1,000,000 species, which is a lot, but scientists believe that only 1/10th of the species have been discovered. It is the most abundant of all the animals. 
• Why should we study this phylum? They live virtually everywhere and their influence upon man and the environment cannot be ignored. They can destroy crops; produce things like wax, drugs, and silk; help maintain cross fertilization; transmit deadly diseases; and some, like spiders, eat mosquitoes!
• Characteristics of phylum arthropoda:
• They have an exoskeleton.





Scorpion's Exoskeleton



• These are made primarily by chitin, a polysaccharide with strong hydrogen bonds.
• Because the exoskeleton is non-living and cannot grow, once the arthropod outgrows their home, they must molt, or shed its covering.
• Enzymes are produced to eat away at the inside of the old exoskeleton while a new exoskeleton is produced underneath the old one.

A scorpion molting





• They have jointed appendages.
• Arthropoda means “joint-footed”
• The muscles of the arthropod move the limbs from within its exoskeleton.
• Variety or forms and functions: 
• spider/grasshopper: jumping and locomotion
• crabs and lobsters: defense
• sensory reception, chewing food, sexual reproduction, etc.
• Body segmentation.
• Arthropods have three body segments:
• Head and thorax (cephalothorax)
• Abdomen

• Open circulatory system
• Dorsal heart

• Ventral nervous system
• Two ganglia joined into a ventral nerve cord. Protected by not only the exoskeleton, but also the bulk of the animal’s body. 
• Near the appendages for command and coordination.

• Antennae: appendages in the head region that provide taste, smell, and touch.
• Sensory bristles
• Eyes: compound (thousands of individual lenses) or simple (one lens)
  
  

  

  Compound Eyes