Crustaceans & Myriapods

What are the 6 aspects of tardigrades that are similar to arthropods?

1. Segmented body (but all segments “head homologs”)

2. Cuticle with chitin → must molt (ecdysis)

3. Hemocoel

4. Appendages (4 pairs of lobopod legs)

5. Eutely (fixed cell number) similar to nematodes

6. Stylet mouthparts (feeding specialization)

What are the 4 ways that tardigrades are NOT like arthropods?

1. Legs are NOT jointed (lobopod legs)

2. No tracheae, no respiratory organs

3. All segments share same identity (no tagmata, no differentiated head/thorax/abdomen)

4. Very reduced body plan, microscopic

What are 5 ways that peripatus are like arthropods?

1. Segmented

2. Tracheae for respiration (air tubes)

3. Non-jointed legs ending in claws

4. Antennae on head

5. Shows transitional form toward arthropod segmentation

What are the 4 ways that peripatus are NOT like arthropods?

1. Legs lack true joints

2. Cuticle is soft, not hardened or articulated

3. No compound eyes

4. No tagmata

What are the S.P. Chelicerata

A subphylum of arthropods (that includes spiders, scorpions, and horseshoe crabs) characterized by the presence of chelicerae, which are mouthparts used to grasp and tear food, and typically lack antennae.

What are Eurypterids?

Sea scorpions. Ancient marine arthropods that thrived in the Paleozoic era, known for their large size and predatory behavior.

How do eurypterids influence our understanding of the origins or arachnids?

Their morphology closely resembles that of desert scorpions, suggesting that arachnids may have originated from marine habitats.

What are harvestmen? Are they more like spiders or scorpions?

Daddy long legs.

They are more like scorpions than spiders

What are the 6 main synapomorphies of C. Arachnida?

1. Chelicerae

2. Pedipalps

3. No antennae

4. Prosoma + opisthosoma

5. Book lungs (internal)

6. 4 pairs of walking legs

What are C. Trilobita? What are their 3 characterizing features?

An extinct group of marine arthropods that flourished during the Paleozoic era.

Characterized by:

1. Three-lobed body plan

2. Compound eyes

3. Segmented exoskeleton

What are S.P. Mandibulata? What characterizes them?

A superphylum of arthropods that includes myriapods, crustaceans, and hexapods.

Characterized by having mandibles and distinct body segments.

What are the 4 main Mandibulata synapomorphies?

1. Mandibles

2. Antennae

3. Cephalothorax + abdomen

4. Segmented body with distinct appendages

Define Uniramous vs Biramous

Uniramous - Appendages that consist of a single chain of segments

Biramous - Appendages that are branched into two distinct parts, typically comprising a main axis (endopod) and one or more lateral branches (exopod).

What are S.C. Malacostraca?

A class within the subphylum Crustacea, characterized by a body divided into a head, thorax, and abdomen, and typically having a carapace and numerous jointed appendages.

Crabs, shrimp, lobsters

What is this animal? What are their defining characteristics?

Isopoda (pill bugs)

Dorso-ventrally flattened; same legs

What is this animal? What are their defining characteristics?

Amphipoda (scuds)

Laterally flattened; different legs

What are these animals?

Decapoda (crabs, lobster, shrimp)

A group of crustaceans with ten limbs

What is this animal?

Cladocera (water fleas; daphnia)

What is this animal?

Ostracoda (seed shrimp)

What are these animals?

Copepoda (cyclops)

What is this animal? 

Remipedia (cave crittur)

What is this animal?

Cirripedia (barnacles)

If crustaceans are biramous, how do you explain the crab’s walking legs?

Even though the ancestral crustacean appendage is biramous, in many lineages (e.g., decapods), the exopod is LOST or highly reduced, leaving a functionally uniramous walking leg.

What are C. Chilopoda? What are their defining characteristics?

Commonly known as centipedes. A class of myriapods.

Characterized by:

• One pair of legs per segment

• Venom delivered through forcipules (modified legs)

What are C. Diplopoda? What are their defining characteristics?

Commonly known as millipedes. A class of myriapods

Characterized by:

• Two pairs of legs per fused segment

• Derived from segmental fusion