INVERTEBRATE DIVERSITY SECTION (Biol.201), Spr 2000

Dr. Kathy S. Williams (email kwilliams@sunstroke.sdsu.edu)

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Mollusks and Annelids

Study guide handed out 3/4. First section is concepts; last section is vocabulary words. Please use both to study. You need to know the meaning of the words to communicate about invertebrates animals and their activities. You also need to understand the relevance of the words in the context of how invertebrates function and how their structures indicate the relationship of animals to one another. Use both to prepare for quizzes and the midterm and final exams.

Quiz #2: Explain why the circulatory system of most mollusks limits their activity (i.e, ability to move rapidly for very long).

[Sample answers]

[Note: just telling the type of circulatory system is not a complete response.]

* FIG. 42.17 Role of gas exchange in bioenergetics; Gas exchange across a respiratory surface

* FIG. 42.2 Open and closed circulatory systems

* FIG. 33.16 Basic plan of mollusks — note reduced coelom & enlarged area that is hemocoel

Finish Molluscan diversity: Cephalopods

How to design a mollusk for speed …

Start Annelids … What are the unifying characters that show that mollusks and annelids are more closely related to one another than either are related to arthropods (the next group we’ll discuss)? One is the trocophore larva. (See clade in your lab maunal)

Benefits of Segmentation: Annelids (segmented worms)

Evolution of segmentation: the annelid worms (Annelida). (612-614)

Basic morphology - segmented body in which many body parts are repeated
(= serial homology).

          Body lacks a rigid external covering.

• body is flexible

• thin wall permits gas exchange, when moist (826-827)
 

 Annelids exemplify benefits of a true coelom and advantages gained by repeated segmentation. • body is composed of segments - with a distinct head w/prostomium

• nerve centers in each segment (976-977, * Fig. 48.13)

• compartmentalized hydrostatic skeleton

• well-developed muscles on body wall: longitudinal & circular

(* Fig. 49.23) • gut, muscles, & blood vessels pass through septa, the digestive system has specialized regions (* Fig. 33.23) • paired bundles of setae (bristles) on each segment (1011-1012)

• novel excretory system composed of metanephridia in each segment (880-881, * Fig. 44.16)

Homework for Wed. 3/29:
    In a half page or less,
        Explain how a metanephridium works.

    Make sure you use your own words.  Do not copy from text.

• closed circulatory system (812-813, * Fig. 42.2)

 Three variations on annelid body plan

Majority belong to Polychaeta, marine worms (613-614)

• Polychaetes have a notable adaptation that helps movement & respiration - parapodia.

• Polycheates may also have elaborate structures on heads.

• Specialization to different lifestyles is reflected in different body morphologies.
 

 Two other main groups of annelids: Oligochaeta (like earthworms) & Hirudinea (leeches) share a common ancestor             & thus are more closely related to each other than to the polychaete worms.

Shared features of Oligochaeta and Hirudinea

• lost the trochophore larva stage & reproduce via hermaphrodism

• lack almost all external appendages
 

 Oligochaeta are terrestrial or freshwater "earthworms." (613) • represented by many species living in freshwater & on land
        • have adaptations similar to those of flatworms (Platyhelmenthes) (What are those?)
• most are scavengers What makes oligochaetes different from leeches is not the possession of distinct features - but it’s the lack of things that leeches have.

Hirudinida (leeches) have several unique features for annelids. (614)

Body segments of leeches are not divided into distinct compartments • so move with the aid of suckers
• and have superficial annuli Lifestyles are varied • many are free-living - feeding as predators & scavengers
• many are external parasites of other animals & have characteristics typical of other parasites (What are those characteristics?) Importance of earthworms & leeches to humans directly & indirectly by contributing to natural ecosystem functions.

3/27 Quiz # 3: Match the best answer to the following 3 statements:
    3 questions @ 2 pts each
In an animal,
    1. the respiratory system ...
    2. the circulatory system ...
    3. the excretory system ...
        a) removes digestive wastes from the body
        b) requires arteries & veins.
        c) moves food, mitrogenous wastes , and gases through the body.
        d) functions in gas exchange.
        e) controls water and salt balance.