lab/lecture 13: arthropoda 1 - trilobites

Question 1

Describe (Phylum) Arthropoda.

Answer 1

Segmented bodies, jointed appendages, exoskeleton of chitin (cuticle), molting (ecdysis); most diverse phylum (85–99% of animal species).

Question 2

Describe (Subphylum) Trilobitomorpha.

Answer 2

Extinct Paleozoic arthropods; calcified exoskeleton, three longitudinal body lobes (axial + two pleural), body divided into cephalon, thorax, pygidium; compound eyes or blind.

Question 3

Describe holochroal eyes.

Answer 3

Small, closely packed lenses under a corneal cuticle; ~3,000 lenses/eye; wide vision, similar to modern arthropods.

Question 4

Describe schizochroal eyes.

Answer 4

Larger, separated lenses with individual corneal cuticle; stereoscopic vision, fewer lenses, better depth perception.

Question 5

Describe trilobite body regions.

Answer 5

Cephalon (head, often with glabella), thorax (segmented), pygidium (fused tail); often with genal spines.

Question 6

Describe moulting in trilobites.

Answer 6

Shed exoskeleton (ecdysis) by splitting along facial suture; suture types: proparian, opisthoparian, gonatoparian, lateral.

Question 7

Describe pygidium size types.

Answer 7

Micropygous (tiny tail), heteropygous (slightly smaller), isopygous (equal), macropygous (larger tail).

Question 8

Describe (Order) Redlichiida.

Answer 8

Large Cambrian trilobites, semicircular cephalon, long genal spines, many thoracic segments, tiny pygidium, big eyes.

Question 9

Describe (Order) Agnostida.

Answer 9

Cambrian–Ordovician, tiny, no eyes, cephalon ≈ pygidium, only 2–3 thoracic segments; likely planktonic.

Question 10

Describe (Order) Corynexochida.

Answer 10

Cambrian–Devonian, varied glabella, opisthoparian sutures, often isopygous, 7–8 thoracic segments.

Question 11

Describe (Order) Lichida.

Answer 11

Cambrian–Devonian, often spiny, large size, broad glabella, opisthoparian sutures, large pygidium.

Question 12

Describe (Order) Phacopida.

Answer 12

Ordovician–Devonian, large glabella, no genal spines, large schizochroal eyes, proparian sutures, enroll when stressed.

Question 13

Describe (Order) Ptychopariida.

Answer 13

Cambrian–Devonian, simple tapering glabella, many thoracic segments, small pygidium, common.

Question 14

Describe (Order) Asaphida.

Answer 14

Cambrian–Silurian, median ventral suture, usually macropygous.

Question 15

Describe (Order) Proetida.

Answer 15

Ordovician–Permian, large vaulted glabella, genal spines, opisthoparian sutures, 8–10 thoracic segments, isopygous.

Question 16

What are trilobite limbs like?

Answer 16

Biramous (two-branched) appendages for walking, swimming, or feeding.

Question 17

How did trilobite modes of life vary?

Answer 17

Burrowers, benthic grazers, swimmers, floaters; eye reduction suggests deep-water or blind forms.