Kingdom Animalia – Phylum Chordata Major Characteristics found in all chordates: 1. Notochord – a stiff but flexible rod along the length of the body 2. Dorsal hollow nerve chord – neural structure that develops into the brain and and central nervous system 3. Pharyngeal gill slits – openings or grooves found on the cavity behind the mouth (found in all chordates at least at some stage of their life cycle) 4. Post-anal tail

Kingdom Animalia – Phylum Chordata Subphylum Urochordata : Tunicates - ~1400 entirely marine species, including sea squirts. Sessile, filter feeders… Body may look like that of a sponge but they have a leathery outer protective layer called the tunic that feels very different from sponges… internally, they are quite complex…

Kingdom Animalia – Phylum Chordata subphylum urochordata Although urochordates are sessile, they typically have motile larvae that truly exhibit all the chordate characteristics… In a few cases however (i.e. salps); the urochordates retain the larval form even as adults, remaining motile…

g Also, tunicates may be solitary… … or colonial What would be the advantages or disadvantages of each of these lifestyles?

Kingdom Animalia – Phylum Chordata Subphylum Cephalochordata : Lancelets - ~ 29 species of small “fish-like” organisms with all the typical “fish” characteristics, other than a backbone… They live on soft bottoms, and use gill slits to filter feed…

Kingdom Animalia – Phylum Chordata Subphylum Vertebrata : The vertebrates represent a diverse group of animals… Simply put however, they are chordates with a backbone. Their backbone (or vertebral column, or spine) is made up of a dorsal row of hollow skeletal elements that protect the nerve cord (or spinal cord).

Marine Fishes Class Agnatha – Jawless fishes … feed by suction and help from their round muscular mouth with rows of teeth… Include hagfish (or slime eels) that feed on dead or dying organisms… sometimes from the inside out!!! … include about 20 species. Other agnathans include lampreys which either feed on invertebrates, or attach to other fish and such their blood… include about 30 species.

Marine Fishes Class Chondrichthyes – Cartilaginous fishes; with about 1000 different species, they include the different species of sharks, rays, skates, and ratfish. Cartilaginous fishes have well developed jaws and teeth; Typically have a ventral mouth; and, have rough, sandpaper-like skin because of tiny scales… In fact, their teeth are simply modified scales!!

Marine Fishes Class Osteichthyes – Bony fishes; the most prominent group of vertebrates, they include about 24,000 species. In addition to having a bony skeleton, there are some other major differences between bony and cartilaginous fishes.

Marine Fishes Bony and cartilaginous fishes also have very different strategies for maintaining their position within the water column. Most bony fishes use a swim bladder for lift, whereas most sharks rely on the swimming generated lift that is a function of the fluid dynamics of their fins and tail. Both groups do however use bands of muscle called myomeres to generate the basic undulating motions of the body. There are many exceptions though…

Marine Fishes There is however great variation to the basic themes of movement, as well as the body shapes that are best adapted to different environments and different swimming habits…

Marine Fishes - Coloration The color of bony fishes is typically found in special cells in the skin called chromatophores. Different chromatophores, each with varying amounts of pigments, can dictate the basic color pattern of the different fishes. Many fishes can even change their coloration based on their environmental conditions (for predation, avoidance of predation, and communication with others of the same species). Examples of general fish coloration patterns: Warning coloration Cryptic coloration Disruptive coloration Countershading

Marine Fishes – Circulatory System The circulatory system of all fishes are based on a two-chambered hearts that pump blood to the gills, from where the oxygenated blood is carried to the body through arteries and capillaries, before returning to the heart through the veins.

Marine Fishes – Circulatory System The mechanism for irrigating the gills is different for bony and cartilaginous fishes. Cartilaginous fishes: Bony fishes:

Marine Fishes – Circulatory System Gas exchange occurs in the gills, where a counter-current flowing blood/water system allows for very efficient oxygenation of the blood…

Marine Fishes – Sensory System Marine fishes have well developed nervous and sensory systems. Many have a great sense of smell. Their nostrils open to olfactory sacs on both sides of the head. Some sharks can detect blood at concentrations as little as one part per million! Fishes detect taste with their taste buds in their mouth, as well as on their barbels (whisker-like organs found around the mouths of some bottom dwelling fishes). Most fish have a somewhat well developed sense of vision. Some shallow water bony fishes have color vision, but most fishes do not… also, focusing is done by moving the lens as supposed to changing it’s shape… Some cartilaginous fish have sensory organs around the head called ampullae of Lorenzini. They can detect week electrical fields that may be used for navigation, as well as for detecting prey. Most fishes can also perceive sounds with their inner ear, and they can detect changes in their position within the water column using their ear stones or otoliths… (nerve cells detect changes in positioning).

Marine Fishes – Sensory System (cont.) Finally, many fish have a lateral line that allows them to sense vibrations in the water…

Marine Fishes – Reproductive System A few species of fishes are hermaphroditic, but most have separate sexes… Sexes are not always definitive though, with many species exhibiting sex reversal. What are the advantages of each of these strategies? Depending on the species of the fishes, they all have a wide range of behaviors associated with mating. Also, different species exhibit internal versus external fertilization; and, oviparity, viviparity, and ovoviviparity strategies are all utilized… What may be the advantages and disadvantages of each? Want extra credit? How about a report on strange mating behaviors of some fish?

Basic classification of vertebrates and fishes: By the way: Fish – single individual or more than one individual of the same species. Fishes – more than one kind of fish.