Category: Invertebrate Unit

Unsegmented Worm

Unsegmented Worms

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Phylum Platyhelminthes
Characteristics

  • Called flatworms because bodies are flattened dorso-ventrally

  • Acoelomate – solid bodies without a lined body cavity
  • Have 3 body layers — outer ectoderm, middle mesoderm, & inner endoderm
  • Bilaterally symmetrical
  • Show cephalization (concentration of sensory organs at anterior or head end)
  • Body cells exchange oxygen & carbon dioxide directly with environment by diffusion
  • Single opening into gastrovascular cavity; two-way digestive tract
  • Some are parasites & others are free-living
  • Parasitic worms have thick cell layer called tegument covered with a nonliving cuticle covering their bodies as protection inside hosts
  • Includes 3 classes — Turbellaria (planarians), Trematoda (parasitic flukes), & Cestoda (parasitic tapeworms

Class Turbellaria

  • Most are marine but includes freshwater planarian (Dugesia)

Planarians

  • Spade-shaped at the anterior end & have two, light-sensitive eyespots
  • Can sense light, touch, taste, & small
  • Have 2 clusters of nerve cells or ganglia to form a simple brain
  • Nervous system composed of a nerve net
  • Capable of simple learning
  • Move by tiny hairs or cilia over a mucus layer that they secrete
  • Feed by scavenging or protozoans
  • Have a single opening or mouth located at the end of a muscular tube called the pharynx which can be extended when feeding
  • Flame cells help remove wastes to excretory pores

  • Hermaphrodites that cross-fertilize eggs that are then deposited into a capsule until hatching in 2-3 weeks
  • Reproduce asexually by fragmentation

Class Trematoda

  • Includes parasitic flukes
  • About 1 cm long & oval shaped

  • Require a host to live
  • Have both oral & ventral suckers to cling to host & suck blood, cells, & body fluids
  • Oral sucker around mouth at anterior end sucks blood
  • May be endoparasites (live inside a host) or ectoparasites (live on the outside of host
  • Covered in tough, unciliated tegument
  • Nervous & excretory systems like turbellarians
  • Hermaphrodites
  • Have a long, coiled uterus that stores & releases 10,000+ eggs
  • Eggs released through genital pore & develop into larva
  • Show complex life cycles
  • Life cycle of sheep liver fluke:
    * Adult liver flukes live in sheep liver & gall bladder where they mate & form eggs
    * Eggs enter intestines, pass out with feces, & hatch in water
    * Larva enter snails, asexually multiply, then leave snail & form cysts
    * Cysts (dormant larva with hard, protective covering) clings to grass
    * Sheep ingest cysts when they eat grass
    * Cysts hatch in digestive tract & bore through intestines into bloodstream
    * Mature & reproduce in the liver

  • Schistosomiasis (disease caused by parasitic blood flukes) infects people in Asia, Africa, & South America causing intestinal bleeding & tissue decay that can result in death

Class Cestoda

  • Includes tapeworms
  • Adapted for parasitic life
  • Tough outer tegument prevents being digested by host
  • Anterior end called scolex contains hooks & suckers for attachment to intestine of host

  • Long, ribbon-like bodies up to 12 m in length
  • Nervous system extends length of body but lacks sense organs
  • Lacks mouth & digestive tract but absorbs digested nutrients from host
  • Grows by making body segments called proglottids
  • Each proglottid produces eggs & sperm that cross-fertilize with other segments & also self-fertilize (hermaphrodites)
  • Oldest, mature proglottids containing eggs at posterior end break off & pass out with feces
  • Life cycle of beef tapeworm:
    * Cattle eat grass with proglottids containing fertilized eggs
    * Eggs hatch into larva & bore through cow’s intestine into bloodstream
    * Larva burrow into cow’s muscle & form cysts
    * Humans eat beef (muscle) & cysts travels to intestines
    * Cyst breaks open & adult beef tapeworm forms


BEEF TAPEWORM LIFE CYCLE

Phylum Nematoda
Characteristics

  • Called roundworms
  • Includes Ascaris, hookworms, Trichinella, & pinworms
  • Pseudocoelomates have fluid-filled body cavity partially lined with mesoderm
  • Pseudocoelom contains the body organs & provides hydrostatic skeletal support for muscles
  • Have long slender bodies that taper at both ends

  • Covered with flexible cuticle
  • Digestive tract with anterior mouth & posterior anus; called one-way digestive tract
  • Separate sexes in most species
  • Most are free living
  • Some are parasites on plants & animals
  • Ascaris is a parasitic roundworm living in the intestines of pigs, horses, & humans
  • Ascaris life cycle:
    * Enter body in contaminated food or water & hatch in intestines
    * Larva bore into bloodstream & carried to lungs & throat
    * Larva coughed up, swallowed, & return to intestines to mature & mate
    * Block the intestine causing death

  • Hookworm eggs hatch in moist soil & larva bore through bare feet of new host 
  • Trichinella are human parasites caused by eating undercooked pork containing the cysts
    * Cause disease called trichinosis
    * Cysts cause muscle pain & stiffness


 CYSTS IN CONTAMINATED PORK

Phylum Rotifera
Characteristics

  • Known as rotifers or wheel animals
  • Transparent, free-swimming microscopic animal
  • Freshwater & marine
  • Have a ring of cilia around mouth that rotates like a wheel to bring in food
  • Feed on unicellular algae, bacteria, & protozoa
  • Have a muscular organ called the mastax behind the pharynx to chop food
  • Nervous system composed of anterior ganglia & 2 long nerve cords
  • Show cephalization (head end)
  • Have 2 anterior, light-sensitive eyespots

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Sponge & Cnidarian Study Guide

Study guide for Sponge, Cnidarians, & Ctenophores

·         Know relatives of the jellyfish
·         How are sponges different from other animals
·         Know characteristics of all invertebrates
·         Know characteristics of sponges
·         What is the function of collar cells in sponges
·         What are spicules
·         Know characteristics of adult sponges
·         Be able to explain skeletal support of sponges
·         How do sponges obtain their food
·         What helps draw water into a sponge
·         What is the function of amebocytes in sponges
·         How does excess water leave a sponge
·         What is the purpose of gemmules in sponges
·         What is a hermaphrodite
·         How can sponges reproduce
·         Know animals that capture prey by using nematocysts
·         What are the 2 distinct life stages of cnidarians
·         Describe nematocysts
·         What organisms have tentacles with stinging cells
·         Know examples of cnidarians
·         Describe the life of a planula larva
·         Know the life stage that is dominant in sea anemones
·         What organisms would be anthozoans
·         Know the dominant life stage of jellyfish
·         Know the main characteristics of ctenophores

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Sponges & Cnidarian

Sponges, Cnidarians, & Ctenophores

Phylum Porifera
Characteristics

  • Includes marine & freshwater sponges
  • Found in the kingdom Animalia & subkingdom Parazoa
  • Sessile as adults
  • Simplest of all animals

  • Contain specialized cells, but no tissue
  • Asymmetrical
  • Bodies filled with holes or pores for water circulation
  • Marine sponges are larger & more colorful than freshwater sponges
  • Range in size from 2 centimeters to 2 meters
  • Osculum is single, large body opening at the top for water & wastes to leave
  • Spongocoel is the body cavity of sponges
  • Have only 2 cell layers (ectoderm & endoderm) separated by jellylike material
  • Flagellated cells called choanocytes or collar cells line their internal body cavity
  • Flagella of choanocytes beat & pull in water containing food which the collar traps

 

  • Spongin is a network of flexible, protein fibers making up the sponge’s skeleton
  • Spicules are tiny, hard particles shaped like spikes or stars in the  skeleton of some sponges
  • Spicules are made of calcium carbonate or silica

Feeding

  • Sponges are filter feeders that remove plankton (food) from the water that is brought in through pores lined with collar cells
  •  Flagella pull in bacteria, protozoans, & algae that sticks to collar of choanocytes where it is digested
  • Amebocytes are specialized cells in sponges that can roam to pick up food from choanocytes & distribute it to all other parts of the sponge
  • Amebocytes also transport carbon dioxide & wastes away from sponge cells
  • Excess water & food leaves through the excurrent osculum

Reproduction

  • Sponges can reproduce asexually by external buds that break off & form new sponges or stay attached to form sponge colonies
  • Gemmules are specialized, internal buds formed by sponges during cold or dry weather that can survive harsh conditions
  • Gemmules consist of a food-filled ball of amebocytes surrounded by a protective coat with spicules & released when adult sponge dies
  • Gemmules break open when conditions improve & the cells form new sponges

  • Sponge can also asexually regenerate missing parts or a new sponge from a small piece of sponge
  • Sponges are hermaphrodites (produce both eggs & sperm), but they exchange sperm & cross-fertilize eggs during sexual reproduction
  • Planula is the flagellated, free-swimming larva that forms from the zygote
  • Planula larva eventually settles to the bottom & attaches to develop into an adult, sessile sponge

Classes of Sponges

  • Calcarea are chalky sponges with calcium carbonate spicules
  • Hexactinella includes glass sponges & the Venus flower basket with silica spicules
  • Demospongiae include horny & bath sponges with only spongin or spongin & silica spicules
  • Sclerospongiae are coral sponges & have spongin & silica and calcium carbonate spicules

Phylum Cnidaria
Characteristics

  • Includes marine organisms such as jelllyfish, Portuguese man-of-war, coral, sea anemone, & sea fans
  • Hydra is a freshwater cnidarian

  • All carnivorous
  • Have 2 cell layers (epidermis -outer & gastrodermis-inner) with a hollow body called gastrovascular cavity
  • Contain a jelly-like layer between epidermis 7 gastrodermis  called mesoglea
  • Single opening (mouth/anus) to gastrovascular cavity where food & water enter & wastes leave; called two-way digestive system
  • Have tentacles around mouth to pull in water & capture food

  • Have a simple nerve net with to help with movement & senses
  • Sessile members include corals, sea anemones, & sea fans
  • Have radial symmetry as adults

  • Contain stinging cells called cnidocytes in their tentacles that contain coiled stingers called nematocysts that can shoot out & paralyze prey 

Body Forms

  • Have 2 basic body forms —polyp & medusa

 


MEDUSA
POLYP

 

 

  • Polyp forms are usually sessile with upright tentacles arranged around the mouth at the top and with a thin layer of mesoglea
  • Polyps are the asexual stage
  • Corals, hydra, & sea anemones exist in the polyp form as adults 


CORAL POLYPS

  • Medusa forms are usually free-swimming, bell-shaped animals with tentacles that hang down around the mouth and with a thick layer of mesoglea for support
  • Medusa are the sexual stage
  • Jellyfish & Portuguese man-of-war are medusa form as adults
  • Some cnidarians are dimorphic or go through both polyp & medusa stages in their life cycle

Life cycle of a jellyfish
JELLYFISH LIFE CYCLE

  • Some are solitary (Hydra) others are colonial (corals)
  • Three classes include Hydrozoa (hydra), Scyphozoa (jellyfish), & Anthozoa (sea anemones & corals)

Hydrozoa

  • Includes freshwater, sessile hydra (exists only as polyps) 
  • Portuguese man-of-war (exists as colony of polyps & medusa)
  • Group of cells called basal disk produces sticky secretion for attachment & can secrete gas bubbles to unattach & let hydra float
  • Hydra also move by somersaulting (tentacles bend over to bottom as basal disk pulls free)
  • Tentacles pull food into gastrovascular cavity where enzymes digest it
  • Reproduce asexually by budding during warm weather & sexually in the fall
  • Hermaphrodites that release sperm into water to fertilize eggs of another hydra


HYDRA

Scyphozoa

  • Includes bell-shaped jellyfish
  • Medusa stage is dominant in the life cycle
  • Tentacles may be meters in length & carry poisons that cause severe pain or death
  • Have both asexual polyps & sexual medusa stages in their life cycles
  • Adult medusa stage releases eggs & sperm into water
  • Fertilization produces ciliated planula larva that settles to the bottom, attaches, & forms tentacles 
  • New medusa bud off of reproductive polyps & form adult jellyfish

jellyfish life cycle photo
JELLYFISH

Anthozoa

  • Include corals in a limestone case & sea anemones
  • Called “flower animals”
  • All marine
  • Sea anemone is a sessile, polyp-form that uses its tentacles to paralyze fish
  • Some anemones in the Pacific Ocean live symbiotically with the clownfish sharing food & protecting each other

#22A

  • Corals are small, colonial polyps living in limestone cases
  • Coral reefs form as polyps die & provide a home and protection for other marine animals
  • Reefs form in warm, shallow water & only the top layer has living polyps
  • Algae may live symbiotically with coral supplying them with oxygen

Phylum Ctenophora

Characteristics

  • All marine
  • Includes comb jellies

  • Have eight rows of fused cilia called “comb rows”
  • Largest animal to move by cilia
  • Move by beating cilia
  • Lack cnidocytes but have cells sticky cells called colloblasts that bind to prey
  • Colloblasts located on two ribbon-like tentacles
  • Have sensory structure called apical organ to detect direction in the water
  • Most are hermaphrodites (make eggs & sperm)
  • Produce light by bioluminescence
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Squid Dissection

              Squid Dissection

Objectives:

As a result of this lesson, students will be able to:

  1. Locate and identify major external and internal features and organs of a squid.
  2. Understand and use basic dissection techniques and terms.
  3. Critically examine the functions of several squid features and organs.

 

Teaching Notes: This lab is a very thorough dissection of a squid and can be adapted to different grade levels. Teachers should try the lessons, considering which parts are most appropriate for their students and curriculum. The descriptions use complex dissection terminology. Be certain students understand the vocabulary of dissection prior to beginning the lab.

These lessons were tested with middle school students ages 11 to 13. They followed procedures and understood concepts well. The skills necessary to do all steps in the dissection are within the normal ability range of middle school students.

 

Materials:

  • squid*
  • scissors
  • toothpicks (for probes and pointers)
  • drawing paper
  • forceps
  • hand lens (5x recommended)
  • small cups (ketchup cups work well)
  • dissecting pan (or lunch trays)
  • paper towels
  • diagram of squid
  • wash bottle
  • microscope (optional)
  • dissecting scopes (optional)
  • slides (optional)
  • slide covers (optional)

 

*Look for squid at the local supermarket in the seafood and frozen foods sections. You may have to order it in advance. For areas that have them, you can also go to the local fish market or oriental food stores, or you can deal directly with fishermen.

 

 

Teaching Notes: Squid specimens tend to deteriorate rapidly. Keep all squid frozen until the morning before dissection. Thaw the squid in the refrigerator. If the entire dissection cannot be completed in one day, do the external activities while the specimens are still partly frozen, and the internal activities the next day after squid are thawed.

Squid may have tentacles or arms missing. Individual squid vary internally, and their relative maturity determines which organs are formed well enough to be seen clearly, and which have lost (or have yet to gain) their shape and coloration. Please advise students that they may not see everything shown in the enclosed diagram. Tissue shrinks and organs become misshapen quickly. To help maintain the freshness of the specimen, cover it with a wet paper towel as you work so it does not dry out so quickly.

Finally, this lesson is a tactile experience. You may want to explore this aspect through sensory activities, written descriptions, poetry, and/or artwork. Encourage students to experience the many textures found inside and outside the squid’s body. Moving fingertips along the suckers is suggested as well – the suckers do not scrape or hurt if you are gentle with them.

 

Procedure

 

  • Orientation:

Place the squid with the dorsal (back) side up in the dissecting pan. This means put the side with the funnel down and the fin side up. Make sure the tentacles and arms are towards you. Locate the head, eyes, beaks (mouth), arms (8), two longer feeding tentacles, fins, mantle, and skin. Use the hand lens to examine the suckers on the tentacles and arms as well as the spots on the skin, which are chromatophores.

 

Step 1A

 

What are the differences between arm and tentacle suckers? Where are the suckers located on the feeding tentacles as compared to the location of the suckers on the arms?

 

Step 1B

 

How do you account for the different locations of the suckers on the tentacles and the arms? What are chromatophores?

 

  1. The Mouth and Beaks: Locate the dark beaks in the center of the mouth.

    Step 2A

     

     

    Open and close the beaks, noting how the ventral beak overlaps the dorsal beak. How is this different from a parrot’s beak? Before you pull out the beaks, imagine what they will look like on the inside. With tweezers, remove the beaks and place beaks together with dark pointed parts opposite one another. Manipulate them (open and close) as if the squid were eating. What makes them work in this way?

    Step 2B Step 2B

     

     

    In order to remove the radula (a ribbon with rows of teeth on a tongue-like muscle) from inside the mouth, make small incisions in the edge of the mouth. With tweezers, locate the small, folded, plastic-like radula between beaks and remove it. It is usually very small, yellow or white in color. What is the radula’s function?   Store the radula and the beaks in water in a small cup if you are going to do a microscopic examination.
    Drawing of Squid Radula
  2. Funnel:
  3. Turn the body over, ventral side up, and locate the funnel (a deflated fleshy tube located at the base of the head). A squid swims by squirting water from the mantle through the funnel. The direction it swims depends on which way the funnel is aimed. Move the funnel and note its flexibility.

    Step 3

     

     

  4. External Anatomy:
  5. Orient the squid so that the tentacles are away from you, at the top of the dissection tray. Spread out the arms, tentacles, and fins. Draw and label the external parts of the squid: arms, tentacles (have suckers only at the tips), head, eyes, fins, mantle, funnel, tail, suckers, beaks (where each would be found on an intact squid) and mouth. If something cannot be seen, draw an arrow to show where it should be.  

    Step 4 Step 4

     

     

    If you have time, slice open an eyeball and locate the lens, pupil, retina, and iris (colored part of the eye). Look for the creamy white brain between the eyeballs. For assistance in identifying these parts, refer to the illustration below.

    Diagram of cephalopod eye

     

     

  6. Opening the Mantle:
  7. Keep the squid on its back (the side opposite the funnel). Using forceps, lift up the opening to the mantle behind the funnel (near the head) and separate the mantle from the internal organs. Close the forceps firmly so as to “pinch” the mantle flesh to keep it taut, cut along the ventral midline of the mantle, from its opening all the way to the tail. Be careful to keep the scissors lifted away from the internal organs so they are not damaged.  

    Step 5 Step 5

     

     

  8. Locating and Removing Reproductive Organs:
  9. Locate the gonad (reproductive organ) in the posterior end (refer to diagram for shape and location).

    Step 6A

     

     

    Upon opening female specimens, the large, firm, white nidamental glands are seen first. Males do not have nidamental glands. The glands lay on top of the other internal organs. These glands create the gelatinous matrix that envelops the eggs. In order to proceed further, carefully remove these glands. In females the eggs are jelly-like in a conical sac at the posterior end of the mantle. The male genital duct is a white, fluid-filled sac in the posterior end of the mantle. The sperm are stored in thin tubes in an elongated sac behind and along one gill.

    Step 6B

     

     

  10. Gills:
  11. Find the gills. These are the long, feather-shaped organs that are attached to the sides of the mantle and extend along the anterior half of the mantle. Identify the gill hearts, one on the posterior end of each gill (these are small, flat and white). Questions: Why are they white and our hearts are red or purple? The squid has a third heart (the systemic heart) that pumps blood to the rest of the body.

    Step 7

     

     

    Challenge: Why does it have separate hearts for the gills alone?
  12. Digestive Tract:

  13. Step 8A

     

     

    The long, silvery dark tube on the bottom of the liver (but appearing to be on top of the liver because of the squid’s inverted position) is the ink sac. Be careful not to break it open. Locate the stomach and caecum. These lie together as one white, silky-looking tube, like a deflated bladder and a coiled sack. The bunched up organs that look like human intestines are digestive ducts for the squid. If you are curious about the liver, wait to cut it open until the end of the dissection. It contains a lot of brown, oily liquid which may obscure other organs. If possible, open the stomach and examine its contents. Many squid will have bits of partially digested crustaceans (pink and white pieces), or tiny fish scales and bones.  

    Step 8B

     

     

  14. Removing the Ink Sac:
  15. Find and carefully remove the silvery-black ink sac that lies connected to the intestine. To do this, pinch the opening of the sac (near the back of the funnel) with forceps while gently pulling up and cutting the connective membrane along its length. After cutting about 1/3 to 1/2 of it, hold the sac with your fingers and pull the sac off the liver. Be careful not to puncture it. Squid ink stains clothing and skin. Place the sac in a small cup for later use with the gladius (pen).  

    Step 9 Step 9

     

     

  16. Removing the Gladius (Pen):
  17. The gladius is a long, clear feather-shaped structure used to support the mantle and for organ attachment. It and the cranium, or brain case, make up the “skeleton” of the squid. It feels like plastic and is made of tissue similar to a shrimp shell. There are two ways to remove it: from the tail or from inside the cut-open mantle. To remove it from inside the open mantle, grasp the head and organs firmly, and rotate them to the side with your left hand while holding on to one side of the mantle with your right hand and pulling away gently. Pulling the gladius out is like removing a splinter from your skin. You may need to cut away connective tissues that hold the gladius in place.

    Step 10A Step 10A

     

     

    The gladius is revealed, lying along the dorsal midline of the mantle.  

    Step 10B Step 10B

     

     

    Grab the forward end of the gladius and pull it carefully from its slot in the mantle. It may be helpful to have one person hold down the lower mantle while the other removes the gladius. To remove from the tail end, rotate the organs to one side, cutting connective tissues. Make sure the mantle is slit along the internal dorsal midline all the way to the tip of the tail. Pry out the tail end of the gladius and pull straight back, away from the body.

    Step 10C Step 10C

     

     

     
  18. Writing with the Gladius (Pen) and Squid Ink:

  19. Step 11A Step 11A

     

     

    Cut one end of the ink sac open and press it against the bottom of the cup with forceps or toothpick. You can also hold one end and push the ink out with your finger, as you would toothpaste from a tube. This will release the ink. Dip the pointed tip (the anterior end) of the gladius into the ink, filling the tip with the dark fluid. Then, using only the ink-filled tip of the gladius, write your name on your squid illustration or paper. If there is enough ink, create and write the name of your dissected squid under its picture. If the ink seems dry and pasty, add one drop of water at a time to create fluid ink. Though this is an unusual way to write, squid ink was actually used to write and draw in ancient times, and it is used today in some cultures. Unfortunately, it tends to fade over time (except from your clothes!).

    Step 11B

     

     

  20. Internal Anatomy:
  21. Draw, label, and identify the function of the following internal parts of the squid:
    • stomach
    • caecum
    • hearts (systemic and gill)
    • gills
    • reproductive organs
    • ink sac
    • liver (digestive gland)
    • gladius
    • brain
    • eyeball

     

  22. Microscope Slide Option:

    Step 12
    Step 12

     

     

    The following parts of the squid make excellent specimens for microscopic study:

    • eggs from the ovaries
    • suckers
    • nidamental glands
    • tips of arms and tentacles
    • spermatophores
    • connective membranes (thinly-sliced: mantle, fin, arm muscle)
    • radula
    • stomach contents
    • liver fluids
    • skin and chromatophores
    • portions of the eye
    • beak

     

    Teaching Note: Most of these are useful only for a dissecting microscope.

    Questions for further Investigation:

    • Identify the differences between the tentacles and the arms. Why are they different?
    • How are squid mouths and beaks like your jaw and teeth? How are they different?
    • How does the squid use the funnel and mantle for locomotion?
    • How does the squid obtain oxygen from the water?
    • How do squid reproduce?
    • Why are the chromatophores important to the squid?
    • What are the relatives of the squid?
    • What are the characteristics of cephalopods and of mollusks?
    • Why is it difficult to identify stomach contents?
    • What is the function of the fins?
    • What organ systems are the same or different from vertebrates?

    When finished, clean your area completely. Return all equipment and wash your hands. The squid odor will remain for a little while. Lemon juice will alleviate the odor if you find it offensive. To dispose of your specimen, wrap it in plastic or a zip-lock bag and throw it away. You may want to feed it to your cat, cut it up for fish bait, or even serve it as tonight’s calamari. Bon Appetite! Visit Clyde’s Kitchen on this website for tasty squid recipes!

 

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Starfish Dissection

 

Starfish Dissection

Introduction:

Echinoderms are radially symmetrical animals that are only found in the sea (there are none on land or in fresh water). Echinoderms mean “spiny skin” in Greek. Many, but not all, echinoderms have spiny skin. There are over 6,000 species. Echinoderms usually have five appendages (arms or rays), but there are some exceptions.

Radial symmetry means that the body is a hub, like a bicycle wheel, and tentacles are spokes coming out of it (think of a starfish). As larvae, echinoderms are bilaterally symmetrical. As they mature, they become radially symmetrical.

Most adult echinoderms live on the bottom of the ocean floor. Many echinoderms have suckers on the ends of their feet that are used to capture and hold prey, and to hold onto rocks in a swift current.

Sea Stars
Sea StarSea stars (group name Stelleroidea) are sometimes called starfish, though they are not real fish (they lack both vertebrae and fins). There are two sub-types of sea stars:

  • Asteroideas are the true sea stars and sun stars.
  • Ophiuroideas are brittle stars and basket stars.

The differences between the two sub-types lies in how the arms connect to the central disk. Ophiuroids have arms that do not connect with each other. There is a distinct boundary between arm and central disk. Asteroids have arms that are connected to each other. Also, it is harder to tell with asteroids where the central disk ends and the arms begin.

The sea star’s top surface (or skin) looks spiny if you examine it. If you look very closely you will notice that there are different types of growths on the surface. Some bumps are used to absorb oxygen, they are called dermal branchiae. Pedicellaria are pincher-like organs used to clean the surface of the skin. Barnacle larvae could land on a sea star and start growing if it were not for these organs.

How Do Sea Stars Move?
Underside of a Sea StarEach sea star had hundreds of tiny feet on the bottom of each ray. These are tube feet, or podia. These tiny feet can be filled with sea water. The vascular system of the sea star is also filled with sea water. By moving water from the vascular system into the tiny feet, the sea star can make a foot move by expanding it. This is how sea stars move around. Muscles within the feet are used to retract them.

Each ray of a sea star has a light sensitive organ called an eyespot. Though it can not see nearly as well as we do, sea stars can detect light and its general direction. They have some idea of where they are going.

Sea Star Anatomy

Can Sea Stars Grow New Arms?
Given enough time, sea stars can grow back arms that have been damaged or removed. For a few species, the severed arm can grow back into a complete sea star! For most sea stars, however, a severed limb dies.

What Do Sea Stars Eat?
Sea stars eat many things. A sea star’s diet can include: barnacles, snails, sea urchins, clams, and mussels. A few species, such as the spiny star of the North Atlantic, eat other sea stars! Many sea stars eat mussels and clams in an interesting way. They surround the shell and use the suckers on their feet to pull the two shells (or valves) apart. The sea star has enough force in its arms to actually bend the shell! This creates an opening between the two shells that is only .01 inches wide. Using this tiny gap, the sea star puts its stomach into the clam’s shell and eats its insides. When it is done, nothing is left but an empty shell.

Materials:

Preserved starfish, dissecting pan, scissors, scalpel, forceps, T-pins, pencil, lab apron, safety glasses

Procedure:

 

 

Dorsal view of starfish showing external anatomy

Ventral view of starfish showing external anatomy

Dorsal view of a dissected starfish showing rectal cecum, anus, madreporite, pyloric stomach, pyloric duct

Dorsal view of a dissected starfish showing madreporite, stone canal, cardiac stomach, and ampullae

Dissection showing where cardiac stomach opens into the mouth

Close up of madreporite and stone canal

Dorsal view of a dissected starfish showing pyloric caecum and pyloric ducts

Dorsal view of a dissected starfish showing gonads and ampullae

Ventral view of starfish showing external anatomy

Starfish Prelab

 

Starfish Prelab

1. In what phylum are starfish found?

2. What is the habitat for starfish?

3. On what do starfish feed?

4. What system in their body helps them catch & hold their food?

5. What does echinoderm mean in Greek? Why is this a good name for this group?

 

6. Name 2 classes of echinoderms & a member of each class.

 

7. Where does water enter a starfish? Where does it leave?

 

Pzsol Mollusks

 

Mollusks

Answer Key: (Students may have a different order.)
   


mollusca
slugs
clams
octopus
nautilus
marine
coelomate
trocophore
invertebrate
snails
visceral
mantle
radula
gastropods
torsion
hemolymph
hemocoel
cephalopods
bivalvia
nudibranch
nocturnal
tentacles
pteropod
adductor
oyster
scallop
foot
siphon
incurrent
squid
chromatophores
propulsion

 

Mollusk

Mollusks


All Materials © Cmassengale  

Phylum Mollusca
Characteristics

  • Soft-bodied invertebrate covered with protective mantle that may or may not form a hard, calcium carbonate shell
  • Includes chitons, snails, slugs, clams, oysters, squid, octopus, & nautilus
  • Second largest animal phylum
  • Have a muscular foot for movement which is modified into tentacles for squid & octopus
  • Complete, one-way digestive tract with a mouth & anus
  • Have a fully-lined coelom
  • Cephalization – have a distinct head with sense organs & brain
  • Have a scraping, mouth-like structure called the radula
  • Go through free-swimming larval stage called trochophore


Trochophore Larva

  • Body organs called visceral mass lie below mantle
  • Have circulatory, respiratory, digestive, excretory, nervous, & reproductive systems
  • Bilaterally symmetrical
  • Most have separate sexes that cross-fertilize eggs
  • Gills between the mantle & visceral mass are used for gas exchange
  • Includes 4 classes — Polyplacophora (chitons), Gastropoda (snails, slugs, nudibranchs, conchs & abalone), Pelecypoda or Bivalvia (clams, oysters, & mussels), & Cephalopoda (squid, octopus, & nautilus)


SNAIL, CLAM, CHITON, & SQUID

Class Polyplacophora
Characteristics

  • All marine
  • Have a shell divided into 8 over-lapping plates
  • Live on rocks along seashore feeding on algae


CHITON

Class Gastropoda
Characteristics

  • Head has a pair of retractable tentacles with eyes located at the ends
  • Have a single shell or valve (snails) or none (slugs)
  • Known as univalves
  • Snails
    * May be marine, freshwater, or terrestrial
    * Aquatic snails breathe through gills & use their radula to scrape algae for food
    * Terrestrial snails use their mantle cavity as a modified lung & saw off leaves
    * Retreat into shell in dry periods & seals opening with mucus
    * Have open circulatory system
    * Secrete mucus & use muscular foot to move
    * Land snails are hermaphrodites
    * Aquatic snails have separate sexes
    * Use internal fertilization

  • Slugs
    * Live in moist terrestrial areas
    * Lack a shell


SLUG

  • Pteropods
    * Called “sea butterflies”
    * Marine
    * Have a wing-like flap for swimming


“SEA BUTTERFLY”

  • Oyster Drills
    * Radula modified to drill into oyster shells


OYSTER DRILL

  • Nudibranch
    * Marine slug
    * Lacks shell


NUDIBRANCH

Class Bivalvia or Pelecypoda
Characteristics

  • Sessile or sedentary
  • Includes marine clams, oysters, shipworms, & scallops and freshwater mussels
  • Filter feeders
  • Have two-part, hinged shell (2 valves)
  • Have muscular foot that extends from shell for movement
  • Scallops clap valves together to move

  • Shell secreted by mantle & made of 3 layers — outer horny layer protects against acids, middle prismatic layer made of calcium carbonate for strength, & inner pearly layer next to soft body
  • Mantle secretes substance called “mother of pearl” to surround irritants like grains of sand
  • Oldest, raised part of shell called umbo
  • Powerful anterior & posterior adductor muscles open & close shell
  • Lack a distinct head
  • Have an incurrent & excurrent siphon that circulate water over the gills to remove food & oxygen

INTERNAL CLAM ANATOMY

  • Have heart & open circulatory system
  • Nervous system made of 3 pairs of ganglia, nerve cords, & sensory cells that detect light, chemicals, & touch
  • Separate sexes with external fertilization of eggs

Class Cephalopoda or Amphineura
Characteristics

  •  Includes octopus, squid, cuttlefish, & chambered nautilus  
  • All marine  

 

NAUTILUS OCTOPUS SQUID

 

  • Most intelligent mollusk
  • Well developed head
  • Active, free swimming predators
  • Foot divided into tentacles with suckers
  • Use  their radula & beak to feed
  • Closed circulatory system
  • Lack an external shell
  • Highly developed nervous system with vertebrate-like eyes
  • Separate sexes with internal fertilization

  • Squid
    * Largest invertebrate is the Giant Squid
    * Large, complex brain
    * Ten tentacles with longest pair to catch prey
    * Use jet propulsion to move by forcing water out their excurrent siphon
    * Chromatophores in the skin can help change squid color for camouflage
    * Can squirt an inky substance into water to temporarily blind predators
    * Have internal shell called pen
    * Female lays eggs in jellylike material & protects them until hatching


GIANT SQUID

  • Octopus
    * Eight tentacles
    * Similar to squid
    * Crawls along bottom looking for prey


OCTOPUS

  • Chambered Nautilus
    * Has an exterior shell
    * Lives in the outer chamber of the shell
    * Secretes gas into the other chambers to adjust buoyancy


NAUTILUS

Economic Importance of Mollusks

  • Used  by humans for food
  • Pearls from oysters
  • Shells used for jewelry
  • Do crop & garden damage
  • Serve as intermediate hosts for some parasites such as flukes
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