Lecture 29: Lophotrochozoa and Two Groups - Annelids and Flatworms

● What are the two key traits discussed that are seen in Lophotrochozoans?

1. a lophophore

2. trochophore

1. lophophore

• circular or U-shaped ring of hollow, ciliated tentacles around mouth

• it functions in food collection and gas exchange

1. trochophore

• swimming, ciliated larval stage

• moves and pulls in food by beating a band of cilia

● Do all members of Lophotrochozoans have the traits that led to the name of the group?

no, likely present in common ancestor and lost in species w/ out it

● What does the term “zoa” mean?

animal

Flatworms

○ Diversity

• 3 major groups

  • Planarians:

    • free-living (terrestrial & aquatic

  • Flukes:

    • obligate animal parasites

  • Tapeworms

    • obligate animal parasites

    • ribbon-like bodies made up of small segments

    • lack cephalization and gut

    • attach to digestive tract of host and absorb nutrients across their epidermis

Flatworms

○ Symmetry

bilateral symmetry

Flatworms

○ Mesoderm / blastopore

• no respiratory or circulatory system

• every cell must be near the surface, thus flat

Flatworms

○ Cavities

acoelomate

Flatworms

○ CNS and Cephalization

• free living flatworms have cephalization

  • parasitic flatworms: some have reduced CNS and no head

Flatworms

○ Segmentation

many have segmented appearance but generated in a very different way than “normal” segmentation

● Which two groups of flatworms are all animal parasites?

• fluke

• tapeworms

  • obligate animal parasites

  • ribbon-like bodies made up of small segments

  • lack cephalization and gut

  • attach to digestive tract of host and absorb nutrients across their epidermis

● Which group of flatworms has free living species

Planarians

Flatworms

● What has happened to the biological features of many of the animal parasites?

probs lost even tho common ancestor had it

Annelids

○ Diversity

includes fan worms, tubeworms, earthworms, leeches

Annelids

○ Symmetry

bilateral symmetry

Annelids

○ Mesoderm / blastopore

• well developed organ systems (circulatory, excretory, nervous)

• most have thin, permeable body wall that serves for gas exchange; restricted to aquatic or moist habitats

Annelids

○ Cavities

coelomate

Annelids

○ CNS and Cephalization

• yes

• a separate nerve ganglion controls each segment

Annelids

○ Segmentation

• yes

• the coelom in each segment is isolated from the coelom in other segments

• isolated coeloms serve as hydrostatic skeleton

○ Describe how earthworm use segmentation in relation to their movement

segments divide the coelom into fluid-filled compartments; these are separated by hepta

○ Describe what setae are and how earthworms use them as part of their movement

• made from chitin

• present in most annelids (except leeches)

• serve as anchor points in locomotion

○ Describe how earthworms use muscles as part of their movement

• movement in annelids is coordinated by circular and longitudinal muscles that work with the hydroskeleton skeleton

• circular muscles contract to make the segment skinny; longitudinal muscles contract to make segments fat

○ Why does it matter for earthworm movement that water is incompressible?

so the organism can use it to apply force or change shape

○ What is a hydrostatic skeleton in earthworm?

use a cavity filled with liquid (eg water) to move, provide structure, change shape, etc

● Tubeworms

○ How do they get their energy?

• live in deep sea vents and have no mouth or digestive system

• survive via mutualistic symbiosis w/ bacteria

• bacteria make all the “food” they need