Arthropoda & Chelicerata

Phylum Echinodermata

• Named for their spiny skin.
• Exclusively marine organisms, examples include sea stars, sea cucumbers, sea urchins, sand dollars, and brittle stars.
• No freshwater or terrestrial forms are known.
• Adult echinoderms display pentaradial symmetry and possess a calcareous endoskeleton made of ossicles.
• Early larval stages exhibit bilateral symmetry.
• The endoskeleton develops from epidermal cells, which may contain pigment cells for vivid colors.
• Cells containing toxins, as well as gonads, are present in each arm.
• Echinodermata are deuterostomic.

Class Asteroidea – Sea Stars

• Commonly known echinoderms with variety in shapes, colors, and sizes.
• Distinguished by thick arms (ambulacra) extending from a central disk where organs penetrate.
• Tube feet are used for gripping and grasping prey.
• Ossicles are arranged loosely under the skin and spines are small and blunt.

Class Ophiuroidea – Brittle Stars

• Brittle stars belong to this class.
• Distinguished by long, thin arms sharply demarcated from the central disk.
• Move by lashing arms or wrapping them around objects.
• Thick ossicles with attached musculature may form shields on the surface.

Class Crinoidea – Sea Lilies and Feather Stars

• Sea lilies and feather stars are suspension feeders, with their mouths facing upward.
• Ossicles are well developed, giving the animal a coarse, jointed appearance.

Class Echinoidea – Sea Urchins and Sand Dollars

• Lack arms and are hemispherical or flattened with five rows of tube feet, aiding slow movement.
• Ossicles are fused into a solid shell.

Class Holothuroidea – Sea Cucumbers

• Extended in their oral-aboral axis, featuring five rows of tube feet.
• Demonstrate "functional" bilateral symmetry as adults because the uniquely extended oral-aboral axis compels the animal to lie horizontally rather than stand vertically.
• Reduced ossicles and few, if any, spines are present.

Phylum Chordata

• Key characteristics at some development stage are a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.
• Contains invertebrate clades: Urochordata (tunicates) and Cephalochordata (lancelets).
• Most tunicates and lancelets inhabit the ocean floor and are suspension feeders.

Subphylum Urochordata - Tunicates

• Also known as tunicates.
• "Tunicate" comes from the cellulose-like carbohydrate material, the tunic, covering the outer body.
• Adults lack a notochord, dorsal hollow nerve cord, and post-anal tail, but possess pharyngeal slits.
• The larval form has all four structures.

Subphylum Cephalochordata - Lancets

• Possess a notochord, dorsal hollow nerve cord, pharyngeal slits, and post-anal tail in the adult stage.
• The notochord extends into the head, giving the subphylum its name.
• Extant members are lancelets, named for their blade-like shape.
• They are typically a few centimeters long, bury themselves in sand in warm temperate and tropical seas, and are suspension feeders.

Subphylum Vertebrata

• Exhibit the four chordate characteristics.
• Share derived characteristics that distinguish them from invertebrate chordates.
• Named for the vertebral column made of vertebrae, a series of separate bones creating a backbone.
• In adult vertebrates, the vertebral column replaces the notochord, which is present during the embryonic stage.

Class Agnatha

• Includes lamprey and hagfish.
• Jawless; have a circular mouth with rows of small, sharp teeth.

Class Chondrichthyes

• Includes sharks, skates, and rays.
• Have a cartilaginous endoskeleton.

Class Osteichthyes

• Bony fish.
• Scales are made of bony plates.

Class Amphibia

• Includes frogs, toads, and salamanders.
• Have moist skin that is permeable to gases and water.

Class Reptilia

• Includes turtles, snakes, and lizards.
• Scales made out of keratin.

Class Aves

• Birds.
• Exhibit feathers, toothless beaks, and a high metabolic rate.

Class Mammalia

• Characterized by mammary glands and hair.