Hemichordates + chaeotognaths

Question 1

What is the defining characteristic of the hemichordates?

Answer 1

a conspicuous dorsal extension of the pharynx forms a buccal tube, or stomochord.

Question 2

What kind of development do hemichordates have?

Answer 2

Deuterostome

Question 3

What chordate characteristic do hemichordates lack?

Answer 3

Notochord

Question 4

What are the two classes of hemichordata

Answer 4

Enteropneusta + Pterobranchia

Question 5

What is the excretory structure of the hemichordates called?

Answer 5

Glomerulus

Question 6

Open or closed circulatory system?

Answer 6

Part open (sinus), part closed (vessels)

Question 7

Where are enteropneusta commonly found?

Answer 7

Common in shallow water; form mucus-lined burrows in sandy or muddy sediment

Question 8

What are the 3 body regions of enteropneusta?

Answer 8

Probiscis, collar, trunk

Question 9

What is the probiscis and what is it used for?

Answer 9

Single coelomic chamber (protocoel), generally conical in shape, highly muscular for burrowing and food collection

Question 10

What is the origin of the coelomic chambers in the collar of certain animals, and where is the mouth located?

Answer 10

The collar contains a pair of coelomic chambers derived from the embryonic mesocoel. The mouth opens on the ventral surface of the collar.

Question 11

What is the trunk?

Answer 11

Bulk of the body. Pair of coelomic compartments derived from embryonic metacoel

Question 12

What is the trunk used for?

Answer 12

External ciliation may aid locomotion

Question 13

What kind of feeders are enteropneusts?

Answer 13

Many are deposit feeders = ingest sediment, extract organic fractions, discard waste sediment. Others are suspension feeders = planktonic organisms adhere to mucus on the proboscis and are transported to the mouth.

Question 14

Describe the tubular digestive system

Answer 14

Mouth => oesophagus => pharynx => intestine => anus
Food moved through gut by ciliary action.

Question 15

Where is the main site of digestion in enteropneusts?

Answer 15

Intestine

Question 16

What is the anterior extension of the pharynx called?

Answer 16

Buccal diverticulum (stomochord)

Question 17

What is the purpose of the stomochord?

Answer 17

May serve to support proboscis.

Question 18

What structure does the dorsal vessel expand into within the collar region, and what additional source contributes blood to it?

Answer 18

It expands into the venous sinus, which also receives blood from the proboscis.

Question 19

Where does blood flow after the venous sinus in the circulatory system?

Answer 19

Into the central sinus.

Question 20

What is the function of the heart vesicle in animals with no distinct heart?

Answer 20

Its muscular ventral wall pulsates against the central sinus, helping move blood.

Question 21

What organ does blood flow to from the central sinus and what is its function?

Answer 21

The glomerulus, which removes metabolic wastes.

Question 22

How does blood travel along the body length?

Answer 22

Through the sinuses of the gut and body wall.

Question 23

What type of circulatory system is described, and what are its main components?

Answer 23

An open circulatory system with two main contractile vessels and a system of sinus channels.

Question 24

What are the features of the nervous system in enteropneusts?

Answer 24

• Epidermal nerve net.
• No brain.
• Dorsal nerve cord (neurochord) present - extends to collar. In some species hollow.
• Few sensory receptors.

Question 25

What are the reproductive traits of enteropneusts?

Answer 25

- Separate sexes. - Gonads in trunk. - External fertilization. - Free-living larva

Question 26

What is the larval stage of enteropneusts?

Answer 26

Tornaria

Question 27

What is the dipleurula theory?

Answer 27

hypothetical ancestral larva, the dipleurula, represents the ancestral form of echinoderms and is a key link in the evolutionary lineage leading to chordates

Question 28

What is defining about pterobranchias?

Answer 28

- Ciliated, anterior tentacles. - U-shaped gut. - Live in rigid tubes. Tube produced by glands on anterior cephalic shield. - Cephalic shield can serve as an attachment organ and as a muscular proboscis to crawl within tube, or on adjacent substrate

Question 29

How are zooids produced in pterobranchia?

Answer 29

Asexual budding from a single larva

Question 30

How do pterobranchs feed?

Answer 30

Suspension feeding using ciliated arms and tentacles

Question 31

What are the defining characteristics of chaetognaths?

Answer 31

1. A series of curved, chitinous, grasping spines on both sides of the head for seizing prey; 2. Lateral stabilizing fins, composed of ectodermal derivatives.

Question 32

Where do chaetognaths live?

Answer 32

All marine, a few benthic, but nearly all pelagic predators

Question 33

How do chaetognaths excrete and do gas exchange?

Answer 33

Diffusion

Question 34

What does the bioluminescent particle cloud produced by Caecosagitta macrocephala do?

Answer 34

confuse predators or make copepod prey reveal themselves

Question 35

What is the function of the ciliated inner linings of the adult body cavity?

Answer 35

They circulate coelomic fluid, aiding in gas exchange and nutrient transport.

Question 36

How do chaetognaths catch prey?

Answer 36

Grasping spines (hooks) and teeth used to capture prey, introduce venom into prey and shove prey in mouth.

Question 37

What kind of photoreceptors are found in the head, and what is their function?

Answer 37

The head has 5 pigment-cup ocelli (simple eyes) oriented in different directions, giving a wide visual field.

Question 38

What is the purpose of the hood?

Answer 38

Hood is withdrawn to expose the spines and teeth during feeding; covers head to streamline when swimming.

Question 39

How do chaetognaths make darting motions?

Answer 39

Alternate contraction of L and R-side longitudinal muscles causes lateral body flexion

Question 40

How is the body of chaetognaths supported?

Answer 40

by hydrostatic nature of internal cavities and well developed musculature (4 blocks longitudinal muscles)

Question 41

What are the lateral fins used for?

Answer 41

reduce rate of sinking when motionless, and for stabilizing body when swimming.

Question 42

What are the tail fins used for?

Answer 42

forward thrust, and aid in flotation.

Question 43

What do chaetognaths feed on?

Answer 43

Active carnivores. Eat planktonic crustaceans (copepods), small fish, and other arrow worms.

Question 44

How do chaetognaths catch prey

Answer 44

Prey captured by darting forward and capture with spines on head.

Question 45

What is the nervous system of chaetognaths, and why is it complex?

Answer 45

Large dorsal cerebral and ventral ganglia connected by circum-enteric connectives. Complex due to being active carnivore

Question 46

What poison is injected into prey

Answer 46

tetrodotoxin (blocks Na2+ transport).

Question 47

How is the toxin produced?

Answer 47

by commensal bacteria (Vibrio alginolyticus) that lives in head region.

Question 48

What reproductive strategy is seen in chaetognaths, and where are the gonads located?

Answer 48

They are simultaneous hermaphrodites, with ovaries in the trunk and testes in the tail.

Question 49

Where do spermatogonia mature in chaetognaths?

Answer 49

Spermatogonia are released from the testes into the body cavity of the tail, where they mature.

Question 50

How is sperm transferred during mating in benthic Spadella?

Answer 50

Through a “hitting action” that transfers a sperm cluster to the mate.

Question 51

Describe the fertilization and development process in chaetognaths

Answer 51

Internal fertilization occurs after “sperm balls” stream to the female gonopore. Eggs are released, and development is direct—no larval stage or metamorphosis, hatch as juveniles.

Question 52

What deuterostome-like features are found in Chaetognaths?

Answer 52

Radial, indeterminate cleavage; blastopore forms anus; enterocoely via archenteron invagination; adult body cavity divided into three compartments lined with mesodermal peritoneum.

Question 53

Why is the evolutionary placement of Chaetognaths uncertain?

Answer 53

They lack a ciliated larval stage, have unique musculature and body cavity, and molecular data (e.g., 18S rDNA) suggest affinities with Nematoda (Ecdysozoa), forming a possible clade with them