BIOL 112 Lab 6

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Invertebrate Diversity I

Objectives:

• Differentiate between the three types of Symmetry
• Describe the difference between diploblastic and triploblastic animals
• Describe the three types of body cavities and how they develop
• Describe the sponge body form and explain how they feed
• Distinguish among the Cnidarian classes
• Describe the differences between protostome and deuterostome embryonic development
• State two evolutionary advances of the Nematodes
• Construct a Phylogeny of the Arthropod taxa studied in this lab

Organization

SYMMETRY

asymmetrical: no symmetry

radial: multiple planes of symmetry

bilateral: single plane of symmetry from anterior (head) to posterior (tail)

TISSUES

diploblastic: two layers of tissue (endoderm and ectoderm)

triploblastic: three layers of tissue (endoderm, mesoderm, and ectoderm

BODY CAVITY

acoelomate: No mesoderm

pseudocoelomate: mesoderm on half of cavity (probably endoderm)

coelomate: mesoderm completely surrounding cavity

Sponges

Two clades

1. Silicea — Glass sponges (rigid, brittle skeleton made from silica spicules)
2. Calcarea — Spongey sponges (flexible skeleton made from calcium carbonate)

All sponges are asymmetrical and temporally hermaphroditic

Two major types of sponge cells:

1. Choanocytes ("collar cells") responsible for "churning" the water with flagella
2. Amoebocytes engulf food and transport nutrients throughout sponge body.

Anatomy

• Skeleton: comprised of spicules
• Porocyte: water inlet pores
• Spongocoel: body "cavity" inside sponge
• Osculum: water outlet

Cnidaria

Named after specialized stinging cells called cnidocytes, which contain special organelles called nematocysts.

First group of diploblastic animals, exhibiting an endoderm and ectoderm.

Radially symmetrical

Two primary forms:

1. Medusa: free-floating
2. Polyp: sessile

Some groups alternate between the two, some may skip one or the other.

Hydrozoa

Example: Portuguese Man-of-War

Colonial dominant polyp state, reduced medusa

Polyps reproduce by asexual budding, but medusas are capable of sexual reproduction.

Scyphozoa

Classic Jellyfish

Anthozoa

Corals, Sea Anemones, and Sea Fans

Only polyps; no medusa

May reproduce asexually by fragmentation or sexually by gamete production.

Corals produce calcareous skeleton

Ecdysozoa

"molting" — shed outer cuticle before growing a new one

includes nematodes and arthropods

Triploblastic with three tissue layers: endoderm, mesoderm, and ectoderm.

Two development patterns:

Protostomes

embryonic blastopore becomes the mouth (hence proto– "first", –stome "mouth")

spiral embryonic cleavage

determinant embryonic cells (each cell of embryo will ultimately form a certain body part)

Deuterostomes

embryonic blastopore becomes the anus (hence blasto– "second", –stome "mouth")

echinoderms and chordates

radial embryonic cleavage

indeterminant embryonic stem cells

Nematodes

Roundworms

Pseudocoelomates: body cavity is partially lined with mesoderm.

Parasitic species studied in lab: Trichinella and Ascaris

Arthropods

Most diverse phylum on the planet

oldest known arthropods are 530 million years old (after Cambrian explosion)

three defining characteristics:

• Segmentation of body parts
• Chitinous exoskeleton
• Jointed appendages (arthropod literally means "jointed foot"

Chelicerates

Spiders, horseshoe crabs, scorpions, and ticks

• 1-2 body parts (usually cephalothorax and abdomen
• 4 pairs of legs
• chelicerae: modified appendages that form mouth parts
• pedipalps: appendages next to mouth

Myriapoda

Millipedes and Centipedes

Multiple segments with legs at each segment.

• Millipede segments are made from two fused segments, so 2 pairs of legs per "segment"
• Centipede segments are truly separate: one pair per segment

Hexapoda

Insects

Six legs (as name suggests)

Many modified mouth parts

Ability to fly

Crustacea

Crabs, Lobsters, Barnacles, etc.

Two pair of antennae and branched appendages

Summary of Taxa

Under Domain Eukarya and Kingdom Animalia

• Phylum Porifera — Sponges
• Phylum Cnidaria
  • Class Hydrozoa — Hydra, Obelia, Man-of-War
  • Class Schyphozoa — Jellies
  • Class Cubozoa — Box jellies, sea wasp
  • Class Anthozoa — Sea anemones, most corals
• Grouping Ecdysozoa
  • Phylum Nematoda — Roundworms
  • Phylum Arthropoda
    • Subphylum Chelicerates — Spiders, horseshoe crabs, scorpions, ticks
    • Subphylum Myriapoda — millipedes and centipedes
    • Subphylum Hexapoda — insects
    • Subphylum Crustacea — crabs, lobsters, barnacles, etc.