Chordates Hemichordates the missing link Even though Echinoderms

Chordates

Hemichordates: the missing link • Even though Echinoderms and Chordates share some characteristics, the hemichordates fall in between – Same developmental characteristics as – Larval phase as seen in Echinoderms – Same key characteristics as Chordates • 90 species, mostly acorn worms or entropneusts usually found in the Benthic region

Key characteristics • • Dorsal, hollow nerve cord Gill slits Notochord Bilateral symmetry, with reduced segmentation, complete digestive tract • Respiratory exchange is through skin • Hybrid circulatory system

Characteristics of Chordates • 3 categories of chordates – Tunicates – Lancelets – Vertebrates • Phylum Chordata are characterized by having a notochord, gill (pharyngeal) slits, and a dorsal nerve cord at some point in their life cycle. – A notochord is a firm tissue mass along the dorsal side. (becomes vertebral – A dorsal nerve cord is a tube of nervous tissue just above the notochord. – estimated 49, 000 species

Special Attributes of Subphyla Urochordata and Cephalochordata • Subphylum Urochordata includes tunicates, colonial drifting salps, and larvacean. – Tunicates pump water to filter feed. – Salps are gelatinous free-floating organisms. – Larvaceans are tadpole-like planktonic organisms thought to resemble theorized ancestor of vertebrates.

• Usually exists as fouling organisms • They are covered by a gelatinous or leathery covering called a tunic • Sessile • They have a tendency to be colonial – They live as individuals in a group – They can live together by sharing a tunic and/or excurrent siphon • Headless, attached tunicates do not resemble chordates – Larval state does • Salps is a rare example of one that remains true

• Feeding is done by allowing water to enter through the incurrent siphon (mouth), it filtered by the sieve-like sac (pharynx – opening derived from gill slit), and the filtered water is expelled through the excurrent siphon – This is where the name for a sea squirt originates

• Subphylum Cephalochordata includes 25 species of lancelet. These small filter feeders of genus Amphioxus are significant because they resemble vertebrates, except they lack vertebrae.

Characteristics of Subphylum Vertebrata • A notochord that has developed into a spinal cord protected by vertebrae and a head with a brain characterize organisms in this subphylum. – Vertebrates consist of the most complex, large, fast, and conspicuous organisms. They include us, the organism that has had the most effect on the global biosphere.

Fish • It is the largest type of vertebrates with over 30, 000 species grouped into 3 different classes – All other vertebrae have 1 class • The classes are jawless, cartilaginous, and bony fish • They are ectotherm (body temperature changes with environment)

Adaptations of fish • Gills= fleshy filaments with tiny blood vessels which is why they are red. – Water enters mouth, passes over vessels in gills adding oxygen and removing carbon dioxide • Fins= fan like structure for moving, balance, and steering • Scales= protects body. Most are overlapping plates of bones • Acclimation • Archimedes principle

Coloration • Chromatophores • Structural colors – Iridohores • Indicates – Mood – Warning coloration – Cryptic coloration – Disruptive coloration – countershading

Feeding • Sharks are carnivorous – Will eat anything regardless of size • Do to the powerful jaws and shaking of the head • Whale sharks, basking sharks and megamouth shark are filter feeders – Utilize gill rakers to filter – Number of teeth and gill slits determine the what they can eat

• Mantas feed on plankton and small fish by filtering • Most bony fish are ___________ – ___________ and ______ – Food can be found in sediments, water column, rock surface, or on other organisms – Use well developed teeth to capture and hold prey until it is swallowed whole

• Food preference varies – Depends on adaptaions and preferences – Grazers eat primarily seaweed • Parrot fish • Plankton feeders are the most abundant

Digestion • Pyloric caeca – slender tubes that secrete digestive enzymes • Liver and Pancreas also release enzymes such as those found in bile • Intestine is straight in carnivores and coiled in others – Spiral valves found in cartilaginous fish

Circulatory System

Gas Exchange • Countercurrent system of flow is an adaptation where blood flows in the opposite directions of water flow – Oxygen transfer is based on diffusion • _____ in red blood cells absorb the oxygen • Red muscles are more heavily used muscle than white muscles – Redness due to extra oxygen stored by protein similar to hemoglobin called myoglobin

Irrigation of Gills

• Gill arches – cartiliganous or bony structures that support the gills – 2 rows of Gill filament on each arch – Gill rakers are on inner surface of each arch • Lamellae – the row of thin plates or disk found one each filament

Locomotion • Most fish swim with a rhythmic side to side motion of body or tail – Creates s-shaped waves that push against the body from head to tail – Myomeres are the bands of muscles along the side of fish allowing the movement • 75% of weight of active swimmers

Sharks lack of swimm bladder • Compensate with large, stiff pectoral fins that provide lift – Similar to planes • Longer upper lobe of tail adds lift by tilting body upwards – Tail reduced in rays and skates • large livers contain large amounts of oil to provide some buoyancy

Bony fish • Due to the swim bladder, bony fish use pectoral fish for maneuverability – Able to make tight turns • Anal fins used as rudders – Steering and stability – Combined with pelvic fins for turning, balance , and stopping • Some use fins purely for swimming – No undulating style of swimming except for speed

Regulation of internal Environment • Unlike other marine organisms, the blood of fish is less salty than seawater – Loss of water through osmosis – To prevent dehydration, they swallow seawater • Kidneys (in combination with Cl cells of gills) excrete excess salts – Water conservation is then possible through small amounts of concentrated urine

The cartilaginous fish method • In most organisms, the job of the kidneys is to remove waste from the blood (urea) and eliminates it through the urine – ___________ • These fish retain the urea in their blood to elevate the amount of solutes in their blood to match that of seawater – ___________ – Any excess salts are eliminated by the kidneys, intestine, and rectal gland

Method used by Freshwater fish • They have the opposite problem in that they are hyperosmotic – As a result, they are constantly absorbing water through their skin and especially gills • Highly efficient kidneys produce extremely diluted urine – This causes a lost in salts and other solutes – To rectify this, they use an active transport system to exchange Na+ from the water for NH 4+ in their bodies and Cl- for CO 32 - to maintain p. H levels

Central Nervous system • Consist of a brain and the spinal cord – Coordinates all body functions and storage – Works with PNS • Brain is protected by bone or cartilage

Various organs and systems • Olfactory sense – Olfactory sacs connected to nostrils contain special cells that give fish developed sense of smell used to detect food, mates, predators, and way home • Sharks are able to detect blood diluted to fractions of a million in water • Salmon can find stream they were born in

• Tastes buds located on lips, fins, and skin – Some contain barbels (whiskers) • s/a catfish which use them to find food on bottom

• Lateral line • ______________________ – Inside the skin and in the bone (or cartilage) of the head – Lined with sensory cells that pick up vibrations • Open to the surface through visible pores • Vibration come from swimming animals and sound waves from water displacement – Allows for obstacle avoidance, predator and prey detection, orientation to currents and position in school

• Inner ears – Located behind the eyes – Fluid-filled canals that pickup sound waves • Contain sensory cells similar to those in the lateral line • Swim bladder can be used to amplify • Also used to maintain equilibrium

Behaviors • Territoriality – Especially common in highly competitive areas s/a coral reefs – Fighting is rarely used • Bluffing is most common form of defense because it avoid injury – Raised fins, darting about, and open mouth – Sounds can be made by rubbing teeth or fin spines – Drum

• Schooling – Some spend entire lives, some only part of life • When part time, it occurs as juveniles or during feeding • Hammerhead sharks are rare cartilaginous fish that school – It is a well-coordinated unit with no visual leader • Vision is a key part in maintaining orientation within group – Some examples of blind fish schools • Group breaks apart during feeding or attacks by predators – Why

Significance of Class Agnatha • This is the class of the jawless fish. – Species include lampreys and hagfish. • Organisms in this class are significant because they may represent the ancestor of bony fish/sharks.

– Scientists theorize that during the Cambrian period the first of three gill arches on a jawless fish evolved into the first jaws. • Having jaws allowed vertebrates to become very successful predators. • Having jaws put organisms in class Chondrichthyes (sharks and rays) and class Osteichthyes (bony fish) near the top of marine food webs.

Agnatha (Jawless) Lamprey Hagfish Round mouths, tube like bodies covered with slimy skin (no scales), cartilage skeleton (tough flexible tissue that is not hard like bone), cuts other fishes and feeds off of their fluids Round mouths, tube like bodies covered with slimy skin (no scales), cartilage skeleton (tough flexible tissue that is not hard like bone), lives in salt water (lampreys are in fresh water),

Characteristics of Sharks and Rays • Class Chondrichthyes includes sharks, rays and their close relatives. – Sharks and rays don’t look similar on the outside, but share a basic anatomy that classifies them together. – Sharks and rays are jawed fish, that lack a swim bladder, and have cartilaginous skeletons. Special Attributes of Sharks and Rays • Sharks and rays are successful predators: – Subclass Elasmobranchii have cartilaginous skeletons. • This characteristic saves energy. Saving energy is one of the things that have made them successful predators. – Sharks have a sense of smell that detect incredibly diluted substances. – Sharks have a “conveyor belt” of multiple rows of teeth. • They swing into place as old teeth wear out and fall away.

Special Attributes of Sharks and Rays (continued) • Sharks and rays have other interesting characteristics: – Both have lateral lines – lines of sensory hair along the length of the body that detect water motion and vibrations. – Unique to elasmobranchs is electroreception – the ability to sense minute electricity created by muscles and nerves. – Sharks and rays have organs called ampullae of Lorenzini which you can see as visible pits near their snouts used to detect the electrical current.

Special Attributes of Sharks and Rays (continued) • Elasmobranchs differ in their reproductive strategy. – Sharks and rays produce fewer, but more mature offspring. – Most fertilize their eggs internally. • The male deposits sperm in the female via a pair of copulatory organs called claspers found at the base of the pelvic fins. • The female lays an egg case in which the juveniles develop for up to six months at which time one or more sharks or rays emerge. – A few shark species are ovoviviparous – the eggs hatch within the mother’s body. • They give birth to live young rather than egg cases.

• The largest fish in the ocean. – Shark size ranges from hand-sized to the whale shark – the largest fish in the ocean. • Whale sharks can reach 14 meters (46 feet). • Basking sharks can reach 10 meters (33 feet). • Megamouth sharks can reach 6 meters (20 feet). – All three are filter feeders that consume plankton.

Special Attributes of Rays • Superorder Batidoidimorpha of subclass Elasmobranchii consists of the rays, which includes skates and guitarfish. – Ray anatomy is well suited to life on sandy bottoms or midwater. – Specially adapted to life in midwater are the eagle ray and manta ray. – Pectoral fins have become “wings” that stretch forward over the gills and are fused to the sides of the head. – Shoulder girdles are flattened and many bones are fused together for rigidity. – No longer need a tail for swimming, the tail has become a defensive whip in some species. – Rays literally fly through the water. – The largest rays are mantas with wingspans exceeding 8 meters (26 feet). – Like the largest shark, the mantas feed on plankton.

Characteristics of Bony Fish • Class Osteichthyes are jawed fish with bone skeletons. – Most have a swim bladder and scales. – Most control buoyancy by adding or releasing gas to/from their swim bladder. • They control the swim bladders with oxygen gas exchanged to and from blood circulation. • Many have a special organ called the gas gland the rete mirabile that take up gases from the bloodstream for the swim bladder. • This allows many species to hover nearly motionless in midwater.

• Most bony fish reproduce externally. – The female lays her eggs, the male immediately fertilizes them. • Their strategy is to produce a vast number of off-spring with only a few expected to survive to maturity.

Characteristics of Bony Fish (continued) • Bony fish have characteristics for life on the reef and for life in the open ocean: – Bony fish have lateral lines that detect water motion and vibrations. – Most open ocean and schooling fish have a torpedo-like streamlined shape that minimizes drag and turbulence. • This fusiform shape is spindle-like, slightly broader at the head and a V-shaped tail. This makes them fast swimmers. • Most open-ocean and schooling fish have a lighter underside and dark topside for concealment. • Bony fish living in reefs and on the bottom use survival strategies more diverse and include concealment and armor instead of swimming. – For this reason, you see far more diversity in color, shape, and size among reef and bottom fish.