BIOL 101 Lecture 12-Arthropods II

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  • Homework 4 is available and due tonight @ 11:59 PM!

  • Quiz 3 will be online Thursday, March 6 (Lec. 11-12)

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Lecture 12 Learning Objectives

  • Synapomorphies: Identify the shared synapomorphy among Myriapoda, Crustacea, and Hexapoda.

  • Myriapoda and Crustacea Synapomorphies: List specific synapomorphies associated with these groups.

  • Chilopoda vs. Diplopoda: Differentiate between these two Myriapoda classes.

  • Appendages: Distinguish between uniramous (single branched) and biramous (two branched) appendages.

  • Crustacea Classification: Distinguish the classes Branchiopoda, Maxillopoda, and Malacostraca within Crustacea.

Myriapoda Overview

  • Meaning: "Numerous foot"

  • Respiration: Utilizes spiracles which lead to tracheae for gas exchange.

Historical Context

  • Pneumodesmus newmani: An ancient myriapod dating back 428 million years, noted for likely possessing spiracles, indicating it was possibly terrestrial.

Myriapoda Characteristics

  • Tagmata Structure: Myriapods have two tagmata: head and trunk, featuring numerous uniramous appendages.

  • Antennae and Eyes: Loss of compound eyes, with multiple simple eyes present.

Major Clades

  • Chilopoda (Centipedes):

    • One pair of legs per trunk segment, up to 175 pairs.

    • Modified first pair of legs into venomous fangs, active predators, hiding under rocks and logs.

  • Diplopoda (Millipedes):

    • Two pairs of legs per trunk segment; first four segments typically have one pair.

    • Herbivores with robust mouthparts; exhibit cuticle heavy armor for protection.

Crustacean Biology

  • Diversity and Examples: Crustaceans include crabs, lobsters, shrimp, and barnacles – approximately 67,000 species.

  • Habitat: Primarily aquatic and marine, utilizing gills for respiration; can be free-living or sessile.

Crustacea Characteristics

  • Synapomorphies: Include compound eyes on stalks, two pairs of antennae, biramous joint appendages, and the cephalothorax-abdomen tagmata.

  • Feeding Structures: Adaptable appendages serve various functions such as feeding defense, and mating.

Ecdysis (Molting) in Crustaceans

  • Phases of Ecdysis:

    • Step 1: Separation of old procuticle from the epidermis with new epicuticle secreted.

    • Step 2: New exocuticle secreted while the old endocuticle dissolves.

    • Step 3: Old cuticles are shed during ecdysis.

    • Step 4: New cuticle stretches and unfolds, with new endocuticle being secreted post-molt.

Crustacea Diversity

  • Three Major Clades: Branchiopoda, Maxillopoda, and Malacostraca.

    • Branchiopoda: Small aquatic species like fairy and brine shrimp; help in ecosystem functioning as zooplankton.

    • Maxillopoda: Includes barnacles and copepods, featuring diverse life forms from free-living to parasitic.

    • Malacostraca: Largest group with significant ecological and economic importance, includes crabs, lobsters, and shrimp.