Chapter 27: Mollusks and Annelids

Chapter 27: Mollusks and Annelids

Section 2: Annelids

Annelids

·  The soft-bodied earthworm is the most common terrestrial, or land-dwelling, segmented worm

·  There are approximately ______species of segmented worms that live in moist soil, in fresh water, and in the sea

·  Segmented worms, or ______, live just about everywhere in the world

What Is an Annelid?

·  Phylum ______

·  An annelid is a round, wormlike animal that has a long, segmented body

·  Annelids range in size from tiny aquatic worms less than half a millimeter long to giant earthworms more than 3 meters long

·  Annelids also vary greatly in color, patterning, number of bristles, and other superficial features

Form and Function in Annelids

·  The many segments of an annelid’s body are separated by internal walls called ______

·  Most of the body segments are virtually identical to one another

·  However, some segments are modified to perform special functions

·  For example, the first few segments may carry one or more pairs of ______, several pairs of ______, and other ______

______

Feeding

·  The digestive tract extends from the ______to the ______

·  Food enters through the mouth and travels through the gut, where it is ______

·  Like mollusks, annelids have evolved structures and behaviors that allow them to use a wide variety of foods

·  One feeding organ that has evolved many different forms in different groups of annelids is the ______, or the muscular front end of the digestive tube

·  Many annelids can extend the pharynx through the mouth

·  In carnivorous annelids, this type of pharynx usually has two or more ______attached to it

·  When a suitable animal approaches, the worm lunges forward, rapidly extends the pharynx, and grabs the prey with its jaws

·  When the pharynx returns to its normal position, it carries the food back to the ______

Respiration

·  Aquatic annelids often breathe through ______

·  Terrestrial annelids take in oxygen and give off carbon dioxide through their ______

·  Because the skin must stay moist to make gas exchange possible, ______

______

·  To help guard against this, terrestrial annelids, such as earthworms, secrete a thin protective coating called a ______to hold moisture around them

Internal Transport

·  Annelids typically have ______organized around two blood vessels that run the length of their bodies

·  In each body segment is a pair of smaller vessels called ______

______that connect the two main blood vessels and supply blood to the internal organs

·  In annelids such as earthworms, several of the ring vessels near the anterior end of the worm are larger than the other ring vessels and have muscle tissue in their walls

o  These vessels are often called ______because they contract rhythmically and help pump blood through the system

Excretion

·  Annelids produce two kinds of wastes

o  ______pass out through the anus at the end of the gut

o  Wastes resulting from cellular metabolism are eliminated by ______

§  A pair of nephridia in each body segment removes waste products from the body fluids and carries them to the outside

Response

·  Many annelids are active animals with ______

______

·  The ______sits on top of the gut at the front end of the body

·  Two large nerves pass around the gut and connect the brain with a pair of ganglia below

·  From these ganglia, a ventral nerve cord runs the entire length of the worm

·  Nerves from each segment of the worm enter and leave the nerve cord at a pair of small ganglia

·  These nerves help carry messages from sense organs and coordinate the movements of muscles

·  Sense organs are best developed in the ______

______of annelids

o  Have sensory tentacles, statocysts, chemical receptors, and two or more pairs of eyes

·  Many other annelids have much simpler sensory systems

o  Earthworms have no specialized sense organs

o  They rely on simple sensory cells in the skin

Movement

·  Annelids have ______in their body walls

o  ______muscles

§  Runs from the ______of the worm to the ______

§  When contracted, they make the worm ______

o  ______muscles

§  Runs in circles around the body of the worm

§  When contracted, they make the worm ______

Reproduction

·  Most annelids reproduce ______

·  In some annelids, the sexes are separate

·  However, annelids such as earthworms and leeches are hermaphrodites that undergo ______

·  Although an individual worm produces both sperm and eggs, it rarely fertilizes its own eggs

·  Instead, worms pair up, attach themselves to each other, and exchange sperm

·  Each worm stores the sperm it has received in special sacs

·  When eggs are ready for fertilization, a band of thickened, specialized segments called the ______secretes a mucus ring into which eggs and sperm are released

·  The ring then slips off the worm’s body and forms a ______that shelters the eggs

Sandworms, Bloodworms, and Their Relatives

·  Class ______

o  Common and important marine worms

o  Polychaetes are characterized by paired paddle like appendages on their body segments

o  These appendages are tipped with ______

o  Polychaetes live in cracks and crevices in coral reefs, in sand, mud, and poles of rocks, and even out in the open water

Earthworms and Their Relatives

·  Class ______

o  Contains earthworms and related species

o  Oligochaetes are annelid worms that live in soil and open water

o  Most oligochaetes live in soil or freshwater

o  Oligochaetes have fewer bristles than polychaetes

Leeches

·  Class ______

o  Contains the ______, most of which live in tropical countries

o  Freshwater organisms that exist as external ______, drinking blood and body fluids from their host

o  All leeches have powerful suckers at both ends of their bodies

o  These suckers are used to attach a leech to its host

·  Leeches penetrate the skin of their host in one of two ways

o  Use a muscular ______

§  Tubular organ that they force into the tissue of their host

o  Use razor sharp ______

§  Once the wound has been made, the leech uses its muscular pharynx to suck blood from the area

·  Both types of leeches release a special secretion from their salivary glands to prevent ______as they drink it

·  Some leeches also produce a substance that ______the wound – thus keeping the host from knowing it has been bitten

·  During feeding, a leech can swallow as much as ______its weight in blood

o  Can take up to ______to digest

o  A leech can live for a ______before it must feed again

How Annelids Fit into the World

·  Important in many habitats

o  Aquatic species are food for many fish, crab, and lobster

o  Earthworms perform an essential task in ______

______

§  By constantly burrowing through the ground, they help ______the soil

§  Without the efforts of these annelids, the structure and fertility of farm soils would degenerate quickly, lowering ______

______