Phylum Chordata: Fishes and Amphibians

• Phylum Chordata covers the distribution and variety of fishes and amphibians

Phylum Chordata

• Exhibits bilateral symmetry and a segmented body plan
• The notochord, or skeletal rod, is present at some stage
• Features a tubular nerve cord
• The anterior end of the nerve cord is typically enlarged, forming a brain
• Has pharyngeal gill slits at some point during its life cycle, which may or may not be functional
• Has a postanal tail that usually projects beyond the anus at some stage, but may or may not persist
• Possesses a heart with dorsal and ventral blood vessels and a closed blood system
• Has a complete digestive system
• The skeleton is present and well-developed in some vertebrates
• Has a cartilage or bony endoskeleton present in the majority of members, referred to as vertebrates

Characteristics of Fish

• Poikilothermic animals, meaning their body temperature varies with the environment
• Possess fins, gills, and scales
• There exists approximately 28,000-30,000 species
• ~60% are marine, living primarily in marine environments
• The remainder live in freshwater
• ~1% move between salt and fresh water throughout their life cycle
• Fish live in freshwater, saltwater and brackish water environments
• Nutrition type includes Benthophags which feed on bottom-dwelling organisms
• Nutrition type includes planktophags which feed on plankton
• Nutrition type includes Rapacious which are predatory feeders

Classification of Fish

• Agnatha encompasses jawless fishes like lampreys and hagfish
• Chondrichthyes includes cartilaginous fishes like sharks and rays
• Osteichthyes includes bony fishes, encompassing Actinopterygians (ray-finned fishes) and Sarcopterygians (lobe-finned fishes)

Superclass Agnatha (Jawless Fishes)

• Characterized by a slender, eel-like body shape with rounded features
• Possess soft skin containing mucous glands but lack scales
• Sucker-like oral disc
• A digestive system lacking a stomach
• External fertilization

Hagfishes (Myxiniformes)

• Enter dead or dying organisms through an orifice or by digging
• Consume prey from the inside out, leaving skin and bones

Lampreys (Petromyzontiformes)

• Includes sea lamprey (Petromyzon marinus) and European river lamprey (Lampetra fluviatilis)

Class Chondrichthyes (Cartilaginous Fishes)

• Have caudal (tail) fin, first and second dorsal fins, and an anal fin
• Have claspers, ventral surface, nostril and pectoral fin

Types of Fins

• Caudal fin, dorsal fin, pectoral fin, pelvic fin, anal fin, adipose fin

Types of Caudal Fins

• Heterocercal in which the vertebral column turns upward into an upper lobe: exemplified by sharks
• Protocercal in which the vertebral column extends to the tip of the tail without any distinct lobes: seen in primitive chordates
• Homocercal in which the vertebral column extends to the middle of the tail, and the tail is symmetrical: found in most advanced bony fishes
• Diphycercal in which the vertebral column extends to the tail's tip, and the tail is symmetrical, resembling a lance: present in lungfish and some primitive fishes

Types of Fish Scales

• Placoid scales are characteristic of sharks and rays and consist of a flat, rectangular plate lying on the dermis, with a raised spine projecting towards the surface

Characteristics of Cartilaginous Fishes

• Includes around 950 species
• Examples include the great white shark (Carcharodon carcharias), rabbit fish (Chimaera monstrosa), and southern stingray (Dasyatis americana)
• Body has caudal (tail) fin, first and second dorsal fins, and an anal fin
• Also has claspers, pectoral fin, ventral surface, nostril and a snout

Sharks (Selachiformes)

• Example measurements include: bale shark is 46ft, Basking shark is 33ft, great white shark is 23 ft, megamouth shark is 15ft, nurse shark is 13 ft, mako shark is 8ft, blacktip reef shark is 6.5ft, bonnethead shark is 3.4ft, and dwarf lantern shark is 6 inches

Rays (Batoidea)

• Have dorsal fins that are reduced, or absent and also have a reduced caudal fin, or absent
• Features pectoral fins, pelvic fins, and spiracle, as well as gill slits on the underside
• An example includes the Eagle ray (Myliobatis)

Chimaeras (Halocephali)

• An example includes the Spotted Ratfish (Hydrolagus colliei)

Superclass Osteichthyes (Bony Fish)

• The skeleton is more or less bony, representing the primitive skeleton
• The vertebrae are numerous, and the notochord may persist in part
• Includes a tail that's usually homocercal
• Possesses skin with mucous glands and embedded dermal scales of three types including ganoid, cycloid, or ctenoid
• Some possess no scales, and no placoid scales
• Fins are both median and paired, with fin rays of cartilage or bone
• Terminal mouth with many teeth (some toothless); has jaws
• Respiration occurs through gills supported by bony gill arches and covered by a common operculum
• Swim bladder is often present with or without duct connected to the pharynx
• Has three types of scales: ctenoid, cycloid and ganoid, as well as placoid scales

Classifications of Bony Fish

• Lobe-finned fishes (Sarcopterygii)
• Ray-finned fishes (Actinopterygii)

Class Sarcopterygii (Lobe-finned Fish)

• Have nostrils that open into the mouth, lungs, and paired lobed fins
• Divided into Subclass Coelacanths (Coelacanthimorpha)
• Divided into Subclass Lungfish (Dipnoi)

Subclass Coelacanthimorpha (Coelacanths)

• More specialized than other sarcopterygians
• Possess a unique spiny first dorsal fin rather than a lobate one
• Three-lobed caudal fin with a middle fleshy, fringed lobe
• A rostral organ involving a rostral cavity, with several openings on the snout associated with electroreception
• Today, a small, endangered population of 200-600 fish exists

Order Ceratodontiformes (Lungfishes)

• An example includes the African Lungfish (Protopterus annectens)

Class Actinopterygii (Ray-finned Fishes)

• Family: Sturgeon and paddlefishes (Acipenseridae)
• Includes the Shortnose Sturgeon (Acipenser brevirostrum), Atlantic Sturgeon (Acipenser oxyrhynchus), and Lake Sturgeon (Acipenser fulvescens)

Sturgeon (Acipenseridae)

• An example includes the White Sturgeon, or Acipenser transmontanas

Order Lepisosteiformes

• Family Gar (Lepisosteidae)
• All seven species of living gars typically inhabit backwater areas of lakes and rivers, such as oxbows and bayous
• An example is the Aligator Gar, or Atractosteus spatula

Order Amiiformes

• Family Bowfin (Amiidae)
• Bowfins are living relics
• They have a long, soft-rayed dorsal fin that arches in a bow over most of the length of its body
• Generally, they are a scarce fish and of no commercial value
• An example is Bowfin (Amia calva)

Division Teleostei (The Teleosts)

• Teleost means roughly “perfect bone”
• Refers to their evolutionary position as the most advanced of the living bony fish
• Includes examples like the Swordfish (which is Xiphias gladius), Flying fish which is Exocoetus volitans, Atlantic herring which is Clupea harengus, and Barrel-eye which is Opisthoproctus soleatus, as well as Ocean sunfish, or Mola mola

Teleostei (Teleosts)

• Order Eels (Anguiliformes)
• Examples include the European eel, or Anguilla anguilla, the Short-finned eel or, Anguilla australis australis, and the Japanese eel, or Anguilla japonica

Eels (Anguiliformes)

• Includes the European eel (Anguilla anguilla) and Sea eel (Conger conger)

Clupeiformes.

• Includes the Atlantic herring, or Clupea harengus) and Baltic herring, or Clupea harengus membras
• This group also includes the Sprat (Sprattus sprattus balticus) and Anchovy (Engraulis encrasicholus)
• Features the Twaite shad (Alosa fallax)

Salmoniformes

• Smelt, or Osmerus eperlanus
• Whitefish, or Coregonus lavaretus) and the Salmon, or Salmo salar alongside the Trout, or Salmo trutta

Cypriniformes

• Roach (Rutilus rutilus)
• Bitterling (Rhodeus sericeus)
• Barbel (Barbus barbus)
• Bleak (Alburnus alburnus)
• Goldfish (Carassius auratus)
  • Rudd (Scardinius erythrophthalmus)

Siluriformes

• Catfishes and Electrical catfish (Malapterurus electricus)
• Includes Asian walking catfish, which is defined as Clarias batrachus and Wels (Silurus glanis)

Gadiformes

• Burbot (Lota lota)
• Cod (Gadus morhua)

Perciformes

• Includes Barramundi cod, Perch, and Pike Perch.

Scorpaeniformes

• Encompasses bullhead sculpin, bull-rout, and lumpsucker

Pleuronectiformes

• Includes examples like Turbot (Psetta maxima) and Flounder (Platichthys flesus)

Characteristics of Amphibians

• The study of these creatures is called herpetology
• Amphibians on Earth for 300 million years
• ~7,000 amphibian species known, nearly 90% are frogs
• Amphibian diversity is largely in the tropics
• Amphibians are tetrapods, though some are legless or have reduced limbs
• Ectothermic, their body temperature varies with the surrounding environment
• Lack an exoskeleton or scales
• Smooth skin with many mucous glands, and in some species, poison glands
• Respire by gills, lungs, and skin, utilizing buccal pumping
• Three-chambered heart, consisting of two atria and one ventricle
• Mouth usually large with small teeth in upper or both jaws
• Have muscular tongues that can be protruded in many species
• Possess urinary bladders and excrete urea as waste
• Have ten pairs of cranial nerves
• Are of separate sexes
• Fertilization is mostly internal in salamanders and caecilians, and mostly external in frogs and toads
• Tend to require water or moist environments for reproduction

Amphibian Locations

• Largely in the tropics
• Can be found in water, dry land, underground or in trees

Threats to Amphibians

• Climate changes that can decease effective moisture that lead to habitat loss, increased risk of disease and changes to development and their phenology

Smallest and Largest Amphibian

• The smallest amphibian in the world is Paedophryne amauensis
• It is a frog that's native to New Guinea
• It measures just 7.7 mm in length and is the world's smallest vertebrate
• Discovered in August 2009
• The largest amphibian in the world is Andrias davidianus, or The Chinese Giant Salamander
• Those salamanders can be up to 1.8 meters long and weigh 65 kg

Orders of Amphibians

- Salamanders (Urodela, Caudata) are the first order
- Frogs and toads (Anura) are the second order
- Caecilians (Gymnophiona) are the third order

Salamanders (Urodela/Caudata)

• Consist of complete metamorphosis and eyelids
• Adults have eyelids and no gills slits
• Larvae have four pairs of gills slits Hynobiids are typically small to moderate size Adults of most genera are terrestrial with developed lungs. Larvae have external gills and caudal fins
• Has two families: Hynobiidae and Cryptobranchidae

Sirenoidae

• 3 suborders include cryptobranchoidea, salamandroidea, and sirenoidea
• They have long tails and usually two pairs of limbs of about equal size, although hindlimbs are absent in Sirenidae
• The Urodeles are found in almost all temperate and tropical regions of the world
• Primitive limbs, carnivorous and ectothermic
• Eggs are fertilized internally Cryptobranchidae

Lengths of Salamanders

• Most are under 15cm long
• Thorius pennatulus which is only 2cm long
• Chinese Giant which can be up to 180cm.

Other Charateristics of Salamanders

• Secrete a mucus to maintain their moiture and salt balance
• Skin can also secrete poison
• Shed their outer skin

Additional Facts about Family Hynobiidae

• Has complete metamorphosis
• Adults have eyelids and no gill slits
• Larvae have four pairs of gill slits
• Hynobiids are generally small to moderate in size
• Larvae have external gills and caudal fins

Family Cryptobranchidae

• Shows an incomplete metamorphosis
• Adults lack eyelids and have one pair of gills slits
• Larvae have caudal fins and short gills

Mexican Axolotl

• Has special attributes that include
• Neoteny
• Metamorphose
• Can be endangered and live up to 15 years

Mount Lyell Salamander

• Discovered in 1915
• Only lives in the United States
• No lungs
• Special type of locomotion

Proteiidae

• Proteus attains a total length of about 300mm
• Necturus reaches 400mm and has a robust body, four digits on all feet, pigmented skin and small but normal eyes

Lungless Salamanders (Plethodontidae)

• A family that includes both woodland and Grotto salamanders

“True” Salamanders (Salamandridae)

• Examples include Black Alpine Salamander (Salamandra atra), and Fire Salamander (Salamandra salamandra), as well as Great Crested newt (Triturus cristatus) and Smooth newt (Triturus vulgaris)

Caecilians (Gymnophiona)

• Ceylon caecilian (Ichthyophis glutinosus)
• This species also exists as the Ringed Caecilian (Siphonops annulatus)

Facts about Frogs and Toads (Anura)

• Have long and forward sloping ilium
• Fused tailbone or urostyle
• No tail
• Shorter forelimb than hindlimb
• More than 6,000 species
• Can be found in the tropics to subarctic regions
• Live in water, dry land, underground, or in trees
• Have a semipermeable skin that makes them sensitive to dehydration
• External fertilization
• Typically lay eggs in the water that hatch and the eggs hatch

Families within "Frogs and Toads"

• Disc-Tongued Frogs (Discoglossidae)*
  • Barbourula busuangensis
  • European Fire-bellied Toad (Bombina bombina)
  • Common midwife toad (Alytes obstetricans)