Protostomes & Deuterostomes

Question 1

Synapomorphies of Bilateria

Answer 1

• Bilateral symmetry
• 3 embryonic germ layers (endoderm, mesoderm, and ectoderm)

Question 2

Protostomes

Answer 2

First mouth: blastopore gives rise to the region of the mouth

Question 3

Deuterostomes

Answer 3

Second mouth: blastopore gives rise to the region of the anus

Question 4

Chordata

Answer 4

Part of Deuterostomes

Question 5

Chordata Characters

Answer 5

• Dorsal hollow nerve cord
• Notochord
• Pharyngeal slits
• Post-anal tail
• Endostyle

Note: all 5 characters are present in at least 1 developmental stage in all chordata: some characters are only briefly present while other characters persist into the adult stage

Question 6

Dorsal Hollow Nerve Cord

Answer 6

• Synapomorphy for Chordata (most likely)
• Hollow, fluid-filled structure dorsal to the digestive tract
• Arises from neural plate ectoderm (neural tube)
• Composed of neurons and glial cells
• The dorsal hollow nerve cord in the head expands to form the brain and the central nervous system
• The dorsal hollow nerve cord posterior to the head forms the spinal cord

Question 7

Notochord

Answer 7

• Synapomorphy for Chordata
• Slender rod with a core of cells and fluid surrounded by a tough, fibrous sheath
• Arises from mesoderm
• Reduced or lost during later stages of development in some chordates
• Acts as a major component of the skeleton that provides support for the longitudinal axis of the body in other chordates
• Can bend side to side but can not be axially compressed (length remains the same)

Question 8

Pharyngeal Slits

Answer 8

• Synapomorphy for Deuterostomes (most likely)
• Series of openings in the pharynx
• Slits closed before the embryo is born or hatched in most terrestrial vertebrates

Question 9

Pharynx

Answer 9

• Anterior chamber of the digestive tract just posterior to the mouth
• Arises from endoderm
• Walls of pharynx are penetrated by series of openings at some point during development

Question 10

Post-Anal Tail

Answer 10

• Synapomorphy for Chordata
• Posterior elongation of the body extending beyond the anus
• Notochord extends into this muscular structure
• Contains myomeres in many chordates

Question 11

Myomeres

Answer 11

Segmental blocks of skeletal muscle that are arranged in a series from anterior to posterior and are separated by myosepta

Question 12

Myosepta

Answer 12

Layers of connective tissue that separate myomeres

Question 13

Endostyle

Answer 13

• Synapomorphy for Chordata
• Groove filled with glandular tissue that produces mucus and processes iodine
• Arises from the ventral side of the pharynx during development
• Arises from endoderm
• Homologous to the thyroid gland of vertebrates