Animal Diversity Flatworms, Mollusks, Annelids Chap 23

LOPHOTROCHOZOA These animals are members of the group LOPHOTROCHOZOA because they either have a feeding structure with tentacles called a lophophore or a ciliated larvae called a trochophore. They are protostomes and have bilateral symmetry.

lophophore

Trochophore larvae

FLATWORMS

General characteristics Solid bodies, no coelom Have tissues and three embryonic layers: ectoderm, mesoderm, endoderm bilateral symmetry and cephalization (sensory organs in their heads) Digestive sac with ONE opening, parasitic ones have no digestive system and absorb nutrients from host No circulatory system, rely on diffusion

3 cell layers

Classes of Flatworms Planarians: Free-living, eyespots for sensing light, simple brain, mouth/anus on ventral surface (mouth attached to muscular pharynx for feeding) Move by muscles and cilia Can regenerate

Planarian

A Planarian extending its pharynx to feed.

They are cephalized- have a HEAD!

Regeneration in Planaria

Gastrovascular cavity Eyespot Notice the branching of the gastrovascular cavity. This increases surface area for diffusion and absorption. Mouth/anus

Flukes Parasitic, live on body fluids Ex- schistosoma – causes schistosomiasis (snail fever), has two hosts: people’s intestines and snails, causes muscle pain and fever

Schistosoma Worm – causes schistosomiasis or snail fever

In terms of socioeconomic and public health impact, schistosomiasis, also known as snail fever, is second only to malaria as the most devastating parasitic disease in tropical countries. An estimated 200 million people in 74 countries are infected with the disease — 100 million in Africa alone.

Tapeworms Ribbon-like made of many reproductive segments attached to a head with hooks and suckers Absorbs food from host’s intestines Segments break off and are excreted Multiple hosts including fleas

TAPEWORM Scolex

Each segment is basically made of reproductive organs.

General characteristics Soft bodies, external or internal shells Complete digestive tract – two openings, can take in more variety of food Many diverse forms

An internal shell of a cuttlefish Called a “cuttlebone” and used in bird cages for birds to gnaw on.

Internal shell of a squid - a “pen”

Many feeding types - some are sessile so filter-feed (oysters) - some are herbivores (snails) - some are predators (octopi)

Beak of an octopus

All share at least one of the following body parts 1) radula – filelike feeding organ 2) mantle – covers internal organs; may secrete a shell 3) ctenidia – flat gills in mantle cavity (land ones lost gills)

A radula of a mollusk

mantle

They pump blood in spaces called a hemocoel. They have an OPEN circulatory system in that blood is not always in vessels. They have a foot used for crawling, digging, or modified into tentacles.

Squid Foot – modified into tentacles Mantle Visceral Mass

Open circulatory system

Reproduction Some are hermaphrodites, but they cross- fertilize by exchanging sperm (love-darts)

3 Main Classes Gastropods – stomach-foot animals, slugs, snails Pelecypods – bivalves, two shells that are hinged, clams Cephalopods – head-foot animals, well- developed nervous systems, carnivorous, squid, octopus

Cephalopods

Pelecypods Clams, scallops, oysters, mussels

Gastropods

Importances of the mollusks 1.Food source 2.Cleaning up water – can monitor pollution 3.Symbiotic relationships with bacteria in swamps

Pretty smart animals.

Annelids Segmentation Closed circulatory system True coelom – acts as hydrostatic skeleton Muscles (longitudinal, circular) Earthworms eat organic matter, aerate the soil and fertilize it with their feces called castings

Coelom

Circulatory System - have a closed circulatory system where blood stays within the blood vessels - in the earthworm, the blood in the dorsal vessel moves toward the head and towards the tail in the ventral vessels. These are connected by ring vessels. The dorsal vessel pumps the blood. Dorsal Blood Vessel Ventral Blood Vessel Ring Vessels

Reproduction Earthworms reproduce sexually; some are hermaphroditic and exchange sperm and store them in special sacs (seminal receptacles). The clitellum, a noticeable band around the earthworm, secretes a mucus ring into which eggs and sperm are released. A cocoon forms around the eggs until they hatch.

Seminal receptacles store sperm

Annelid Reproduction Annelids swap sperm during sexual reproduction.

Cocoons – contain fertilized eggs

Giant Earthworms!

leeches External parasites with suckers at both ends Used in medicine to help healing Produce an anticlotting chemical Live in water or moist areas

Tubeworms are annelids too. Their bodies are inside of the tube.

Importances of the Annelids Aerate and fertilize the soil Food source Decomposers