ECHINODERMATA, HEMICHORDATA, AND CHORDATA

Chapter 14 & 15

Echinodermata

A phylum of deuterostome marine animals (e.g., sea stars, sea urchins) characterized by a water vascular system, tube feet, and pentaradial symmetry in adults.

Water Vascular System

A network of fluid-filled canals in echinoderms used for locomotion, feeding, and gas exchange; it connects to tube feet.

Tube Feet

Small, flexible, fluid-filled structures connected to the water vascular system that aid in movement, feeding, and attachment in echinoderms.

Pedicellariae

Tiny, pincer-like structures on the skin of many echinoderms that help keep the surface free of debris and sometimes aid in feeding or defense.

Dermal Branchiae (Papulae)

Skin gills or small projections on the body wall of echinoderms that function in respiration.

Pentaradial Symmetry

A body plan arranged in five (or multiples of five) around a central axis, typical of adult echinoderms.

Phylum Hemichordata

A deuterostome phylum whose members (e.g., acorn worms) share traits with both echinoderms (larval forms) and chordates (pharyngeal slits).

Stomochord

A dorsal outpocketing of the gut in hemichordates, once thought to be homologous to the chordate notochord but is not.

Pharyngeal Slits (in hemichordates)

Openings in the pharynx that allow water to exit; also found in chordates.

Chordata

The phylum that includes all vertebrates and two groups of invertebrate chordates. Distinguished by the notochord, dorsal hollow nerve cord, pharyngeal slits, post-anal tail, and endostyle (or thyroid).

Notochord

A flexible, rod-like structure that extends the length of the body in chordates, providing skeletal support for muscles.

Dorsal, Hollow Nerve Cord

A nerve cord that runs along the dorsal (back) side in chordates; it develops into the central nervous system (brain and spinal cord) in vertebrates.

Pharyngeal Slits or Pouches (in chordates)

Openings in the pharynx that function in filter feeding or develop into gill supports or other structures in vertebrates.

Endostyle

A ciliated groove in the floor of the pharynx in chordates (e.g., tunicates and lancelets); homologous to the thyroid gland in vertebrates.

Post-anal Tail

A tail extending beyond the anus, a chordate feature used in locomotion in many species.

Cephalochordata (Lancelets)

A subphylum of chordates (e.g., Amphioxus) that retain the key chordate features (notochord, dorsal nerve cord, pharyngeal slits, post-anal tail) throughout life.

Urochordata (Tunicates)

A subphylum of chordates whose motile larval stage has the chordate characters; adults become sessile and lose some of these features (e.g., notochord, tail).

Vertebrata

A subphylum of chordates characterized by a vertebral column (backbone) that replaces or encloses the notochord.

Conodonts

Extinct jawless vertebrates known from their tooth-like microfossils; among the earliest vertebrates to have mineralized elements in the mouth.

Ostracoderms

Extinct, armored jawless fishes from the Paleozoic era, lacking paired fins but having heavy dermal bone.

Gnathostomes

Jawed vertebrates (fishes with jaws and all tetrapods). Jaws evolved from modifications of anterior pharyngeal arches.

Placoderms

Extinct group of heavily armored jawed fishes that lived during the Devonian period.