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					CHAPTER 33 INVERTEBRATES
Kathryn Callan and Jessica Fagioli

A. Parazoa

        1. Phylum Porifera: Sponges are sessile with porous bodies and choanocytes

                Sponges have no nerves or muscles, but instead have individual cells

                Sponges range in height from 1cm to 2m. Most sponges are marine. Sponges draw
                 water in through their pores into a central cavity called the spongocoel and then flow
                 the water out through a larger opening called the osculum.

                Almost sponges are suspension-feeders which are animals that collect food particles
                 from water passed through some sort of food trapping device.

                Lining the inside of the spongocoel are flagellated choanocytes. The flagella generate a
                 water current, and the collar traps food particles that the choanocytes then ingest by
                 phagocytosis.

                A sponge consists of two layers of cells separated by a region called the mesohyl and
                 wandering through mesohyl cells are amoebocytes. Amoebocytes have many functions
                 including taking up food from the water and from choanocytes, carrying nutrients to
                 other cells and forming form tough skeletal fibers within the mesohyl.

                Most sponges are hermaphrodites which means individuals function as both a male and
                 female in sexual reproduction.

                Their gametes arise from choanocytes or amoebocytes. Their Eggs reside in the
                 mesohyl, but sperm cells are carried out of the sponge by water currents. Fertilization
                 occurs in the mesohyl where the zygotes develop into larvae.

                Sponges are capable of extensive regeneration.

B. Radiata

        1. Phylum Cnidaria: Cnidarians have radial symmetry, a gastrovascular cavity, and cnidocytes

                Cnidarians have a sac with a central digestive compartment called the gastrovascular
                 cavity. A single opening to this cavity acts as both a mouth and anus. There are two
                 variations on this: polyps and medusas.

                              o Polyps are cylindrical forms that adhere to the substratum by the aboral
                                 end of the body and extend their tentacles, waiting for prey.
                            o Medusas are a flattened mouth down version of the polyp. It moves
                              freely in the water by a combination of passive drifting and
                              contractions of the belly shaped body.

              Cnidarians are carnivores that use tentacles to capture prey and push the food into the
               gastrovascular cavity. The tentacles have cnidocytes which are cells that aid in defense
               and capturing of prey. The cnidocytes contain cnidae also known as nematocytes which
               are stinging capsules.

               a. Class Hydrozoa

                      Most hydrozoans alternate polyp and medusa forms depending on the different
                       environmental conditions.

               b. Class Scyphozoa

                      The medusa generally is the life cycle of the Scyphozoa. Most coastal medusas
                       go through a small polyp stage during their life cycle.

               c. Class Anthozoa

                      They only occur as polyps. Coral animals secrete hard external skeletons. Each
                       polyp generation builds on skeletal remains of earlier generations to construct
                       “rocks” which we call coral.

       2. Phylum Ctenophora: Comb jellies possess rows of ciliary plates and adhesive colloblasts

              Most of them are marine. They range in size from 1 to 10cm. Most are spherical but
               there are a few that are get longer and are ribbon like. They are the largest animal to
               use cilia for locomotion.

              A sensor helps with the orientation of the comb jelly, and there are nerves running from
               the sensory organ to the cilia that coordinate movement. Most comb jellies have a pair
               of retractable tentacles called colloblasts which capture food.

C. Protostomia: Lophotrochozoa

       1. Phylum Platyhelminthes: Flatworms are acoelomates with gastrovascular cavities

              There are about 20,000 species of flatworms living in all different kinds of habitats.

              Flatworms are triploblastic. The middle embryonic tissue contributes to the
               development of more complex organs and organ systems. Thus flatworms are
               structurally more complex.

              In common though with radiate animals flatworms do have a gastrovascular tract cavity
               with only one opening
   Flatworms are divided into four classes:

    a. Class Turbellaria

           Turbellarians are nearly all nonparasitic and mostly marine. Planarians thrive in
            ponds and streams. Planarians are carnivores.

           Planarians lack specialized organs for gas exchange and circulation. The flat
            shape of the planarian places all of the cells close to the surrounding water and
            the gastrovascular cavity distributes the food throughout the body. Waste
            diffuses directly from the cells into surrounding environment.

           Planarians move by using cilia and some tubellarians use their muscles to swim
            through water.

           A planarian has a head with a pair of eyespots that can detect light and flaps
            that can detect smell. Planarians have a complex nervous system.

           Planarians reproduce asexually through regeneration.

    b. Classes Monogenea and Trematoda

           This class lives as parasites. Many of them have suckers to attach to their hosts
            and they have tough coverings that protect them. Their reproductive organs fill
            almost their entire interior.

           Trematodes parasitize a wide range of hosts and most species have complex life
            cycles.

           Most monogeneans are external parasites of fish and have a relatively simple
            life cycle.

    c. Class Cestoidea

           Tapeworms are parasitic and mostly live in vertebrates. The tapeworm head
            also called scolex has suckers and hooks that lock the worm to the intestinal
            lining of a host.

           Posterior to the scolex is a ribbon of proglottids which are sacs of sex organs. A
            tapeworm absorbs food predigested by the host.

           Mature proglottids are released from a tapeworm and leave the host with its
            feces. In one life cycle the feces get into an intermediate host (pigs or cattle)
            and then humans eat the meat from these animals. Then the tapeworms
            mature inside the human. These creatures can cause intestinal blockage and
               nutritional deficiencies. Fortunately there is a drug that can kill the mature
               tapeworm.

2. Phylum Rotifera: Rotifers are pseudocoelomates with jaws, crowns of cilia, and complete
digestive tracts

      Rotifers live mainly in freshwater but some live elsewhere. They range in size from
       about 0.05 to 2.0mm.

      Rotifers have complete digestive tract which is a digestive tube with a separate mouth
       and anus. Internal organs lie within the pseudocoelom which is a body cavity. Fluid in
       this pseudocoelom serves as a hydrostatic skeleton and as a way of transportation.

      Rotifers have a crown of cilia that can draw things into its mouth and posterior to its
       mouth is a region called the pharynx bear jaws that grinds its food.

      Rotifers reproduce in unusual ways:

           o   Some use parthenogenesis which is a type of reproduction where females
               produce more females from unfertilized eggs.

           o   Others produce two types of eggs that develop by parthenogenesis, one type
               forming females and the other type forming degenerative males. The males
               survive long enough to fertilize eggs, forming resistant zygotes that can survive
               when a pong dries up.

3. The lophophorate phyla: Bryozoans, phoronids, and brachiopods, are coelomates with ciliated
tentacles around their mouths

      The lophophorate animals share a distinctive structure called the lophophore. This
       structure is a horseshoe shaped or circular fold in the body wall bearing ciliated
       tentacles that surround the mouth

      The anus lies outside the whorl of tentacles. The cilia draw water toward the mouth
       between the tentacles which help trap food particles.

           o   Bryozoans- are colonial animals that look like moss. In most species the colony is
               encased in a hard exoskeleton with pores through which the lophophores. Most
               of them live in the sea.

           o   Phoronids- are tube dwelling marine worms ranging from 1mm to 50cm. Some
               live buried in sand within tubes of chitin extending its lophophore from the
               opening of the tube.
              o   Brachiopods- the two halves of the brachiopod shell are dorsal and ventral to
                  the animal. A brachiopod lives attached to its substratum opening its shell
                  slightly to allow water to flow in.

4. Phylum Nemertea: Proboscis worms are named for their prey-capturing apparatus

         A proboscis worm’s body is structurally acoelomate, but it contains a small fluid –filled
          sac. The sac and fluid hydraulics operate an extensible proboscis which the worm uses
          to catch prey with

         Proboscis worms range in length from less than 1mm to more than 30m. Nearly all of
          them are marine.

         Proboscis worms have two unique features:

              o   Closed digestive tract

              o   Closed circulatory system- the blood is contained in vessels thus making it
                  distinct from fluid in the body cavity.

5. Phylum Mollusca: Mollusks have a muscular foot, a visceral mass, and a mantle

         Most mollusks are marine but some live in freshwater and some even live on land.

         All mollusks have three main parts:

              o   Foot- uses for movement.

              o   Visceral mass- containing all of its internal organs.

              o   Mantle- a fold of tissue that drapes over the visceral mass and secretes a shell.

         Most mollusks feed by using an organ called the radula.

         Many mollusks have separate sexes but some are hermaphrodites like snails.

          a. Class Polyplacophora

                 Chitons are marine animals with oval shells divided into eight dorsal plates.

                 Chitons like to cling to rocks and they eat the algae.

  .       b. Class Gastropoda

                 Is the largest mollusk class. Most gastropods are marine.

                 A unique aspect of them is a process called torsion in which the body rotates
                  during development.
              Most gastropods are protected by single spiraled shells. Many gastropods have
               distinct heads with antennas.

              To move around they use an elongated foot and to feed they use the radula.

       c. Class Bivalvia

              Bivalves have two shells that are hinged at the mid-dorsal line. The adductor
               muscles draw the two halves together.

              The mantle cavity is used for feeding as well as gas exchange.

              They are suspension feeders which means they must lead very inactive lives.

       d. Class Cephalopoda

              Cephalopods are built for speed. Cephalopods use jaws to bite their prey and
               then inject poison to immobilize them. The mouth is at the center of its
               tentacles. A mantle does cover the visceral mass but the shell is reduced in size
               and sometimes even missing.

              They have foot that has become modified into a muscular siphon and parts of its
               tentacles and head.

              Cephalopods are the only mollusk to have a closed circulatory system and they
               also have a well developed nervous system with a complex brain.

              The ancestors of the cephalopods were most likely shelled mollusks that
               became predators and lost its shell later in evolution.

6. Phylum Annelida: Annelids are segmented worms

      Annelids live in many diverse environments.

      The coelom of the earthworm is partitioned by septa, but the digestive tract,
       longitudinal blood vessels, and nerve cords penetrate the septa and run the length of
       the animal.

      They have a digestive system that has a few specialized regions: the pharynx, the
       esophagus, the crop, the gizzard, and the intestine.

      They have a closed circulatory system which consists of a network of vessels are
       containing blood with oxygen-carrying hemoglobin.

      They have dorsal and ventral vessels that are connected by segmented pairs of vessels.
       The dorsal vessel and five pairs of vessels that circle the esophagus of an earthworm are
       muscular and pump blood.
              They also have a brain like pair of ganglia.

              Earthworms are hermaphrodites but they can cross-fertilize.

               a. Class Oligochaeta

                        This class includes earthworms and many aquatic species.

                        An earthworm basically eats its way through the digestive the soil, extracting
                         nutrients as the soil passes through its digestive tract.

                        Undigested material is egested as casting through the anus.

                        Farmers like earthworms because they till the soil and their castings improve
                         the texture of the soil.



               b. Class Polychaeta

                        Each segment of a polychaete had a pair of paddlike structures that are called
                         parapodia. These are the locomotion structures. Chitin forms their setae.
                        Most polychaetes are marine. They either drift and swim, crawl, or live in tubes
                         that they create from broken sea shells and mucus.

               c. Class Hirudinea

                        This class is made up of leeches, which mostly live in fresh water, but some live
                         on land in moist vegetation.
                        The leeches either feed off other invertebrates, but some suck plod from
                         animals. In order to do this, the leech attaches to its host with a blade-like jaw,
                         secrete an enzyme which burns a hole in the host, and then secretes an
                         anesthetic. Then, in order to keep the blood from coagulating, the leech
                         secretes hirudin and then sucks as much blood as it can hold.
                        Today, leeches are used medically for treating bruised tissue and improving
                         circulation.
                        Coelom- provides hydrostatic skeleton, allows new methods of locomotion,
                         provides body space for storage and complex organ development.
                         Segmentation- allows for a high degree of specialization of body regions.

D. Protozoa: Ecdysozoa

       1. Phylum Nematoda: Roundworms are nonsegmented pseudocoelomates covered by tough
       cuticles
      Roundworms are found in aquatic habitats, wet soil, moist plan tissue and tissue and
       bodily fluids of animals.
      Their bodies are nonsegmented, their bodies range from <1mm to more than a meter in
       length. The end tapers to a fine tip and the head is most of a blunt tip.
      Its body is covered with a cuticle cover and this is periodically shed and replaced.
      They have a complete digestive tract, but no circulatory system. Nutrients are
       transported via fluid in the pseudocoelom.
      They usually reproduce sexually, the sexes are mostly separate and females are usually
       larger than males. Fertilization is internal and the female may deposit 100,000 or more
       fertilized eggs a day.
      The worms living in moist soil play an important role in decomposition and nutrient
       cycling. Some of these include agricultural pests that attack the roots of plants.
      Humans host at least 50% of this species.

2. Arthropods are segmented coelomates with exoskeletons and jointed appendages

      The arthropod population is estimated at a billion billion individuals.

       a. General Characteristics of Arthropods

                Arthropods have segmentation, a hard exoskeleton and jointed appendages.
                 Their body segments and appendages are specialized for a great variety of
                 function.
                Its body is completely covered in an exoskeleton. This exoskeleton can be think
                 and hard or thin and flexible. It provides protection and points of attachment.
                 It is strong and almost impermeable to water.
                The animal must periodically shed its exoskeleton, in order to make room for a
                 newer and larger one. This process takes a lot of energy and leaves the animal
                 vulnerable for a short time.
                Arthropods have well-adapted sensory organs, including eyes, olfactory for
                 smell, and antenna for touch and smell.
                They also have an open circulatory system. Here, hemolymph is pumped
                 through short arteries by the heart. It surrounds the tissues and organs.
                Arthropods have a variety of organs that are specialized for gas exchange. Most
                 of the aquatic species have gills with feathery extensions. Terrestrial arthropods
                 have internal surfaces specialized for as exchange.

       b. Arthropod Phylogeny and Classification

                The four main evolutionary lineages are: trilobites, chelicerates, uniramians and
                  crustations.
                      o Crustations- primarily aquatic, have jaw-like mandibles, have one or two
                          pairs of sensory antennae and usually a pair of compound eyes.
             o Chelicerates- are named for their claw-like feeding appendages,
                 chelicerae. Have simple eyes.
             o Uniramians- have one pair of antennae
       The exoskeleton was used primarily for protection and muscle anchorage, but as
         the animals moved to the land, the exoskeleton helped to solve the problems
         of water loss and structural support.

c. Trilobites

       They were common in the shallow seas during the Paleozoic era but then
          disappeared. They have pronounced segmentation but there was little
          variation in their appendages.

d. Spiders and Other Chelicerates

       The eurypterids or water scorpions lasted longer than the trilobites did. They
          were predators in the main and fresh water and they were up to 3 mm long.
          Their appendages were more specialized than trilobites. Most of the marine
          chelicerates are extinct.
       The majority of modern chelicerates are found on land. These include
          scorpions, spiders, ticks and mites. Some of these are parasitic arthropods.
          (ticks, mites)
       Arachnids have a cephalothorax that has 6 pairs of appendages. Their functions
          are either locomotion or sensing and feeding. Spiders use their fang-like
          chelicerae, which are filled with poison, to attack their prey. As it chews the
          prey, it spills digestive juices on the tissue and it softens so that the spider can
          suck it up.
       Spiders have book lungs, stacked plates contained in an internal chamber.
       The spider can catch flying insects with a web of silk proteins. All spiders perfect
          the web on the first try.

e. Millipedes and Centipedes

       Millipedes- wormlike, legs are two pairs per segment, eat decaying leaves and
          other plant matter
       Centipedes- terrestrial carnivores, head has a pair of antennae and three pairs
          of appendages, each segment of trunk region has one pair of walking legs.

f. Insects

       This species outnumbers all other forms of life combined. They live almost
          everywhere possible.
       Entomology is the study of insects
       The oldest insect fossil dates back to 400 million years ago.
      The success of insects is attributed to their flight. It uses flight to escape
         predators, find food, find mates, and disperse to new habitats. Most insects
         have one or two pair of wings that come from the thorax. Since the wings are
         not true appendages, they do not have to sacrifice walking legs in order to fly.
      Dragonflies were among the first insects to fly. The wings of bees and wasps
         are hooked together, and the wings of butterflies function in a similar fashion.
         Beetles have the posterior wings hat function for flight.
      The insect has several complex organ systems. They have a complete digestive
         system that is regionally specialized. There are discrete organs that function
         to breakdown food and absorb nutrients. They also have an open circulatory
         system. The Melpighian tubes are organs that remove metabolic wastes from
         the hemolymph.
      The nervous system of an insect consists of a pair of ventral nerve cords. They
         meet at the head where the sensory organs are connected.
      Many insects undergo metamorphosis as they develop.
           o Incomplete metamorphosis- the young resemble the adults but are
                smaller and with different body proportions.
           o Complete metamorphosis- these insects have larval stages specialized
                for eating and growing, this looks completely different from the adult
                stage.
      Insect reproduction is usually sexual with separate male and female
         individuals. The adults come together once they let each other know they are
         from the same species. Colors, odors and sounds are used.
      Fertilization is internal and most species deposit the sperm cell directly into
         the female’s vagina. Many insects mate only once in a lifetime. The female
         lays her eggs on a food source so that when they hatch, they can begin eating.
      Insects can be an advantage and a disadvantage for humans. They can
         pollinate crops, but they can spread disease.

g. Crustaceans

      They thrive in marine and freshwater environments. They have multiple
         appendages that are extensively specialized. They are the only arthropods
         that have two pair of antennae. They have walking legs on the thorax and if
         they lose an appendage, it can be regenerated.
      Small crustaceans have gas exchange across thin cuticle areas but larger ones
         have gills.
      The sexes are separate in most crustaceans. In some species, males use a
         special appendage to insert sperm into the female’s reproductive pore.
      Isopods- one of the largest groups of crustaceans, mostly a small marine
         species.
                        Copepods- among the most numerous of all animals, important members of the
                           marine and freshwater plankton communities.
                        Decapods- relatively large crustaceans, hardened exoskeleton, most are marine.

               h. How many times did Segmentation Evolve in the Animal Kingdom?

                        The majority of biologists used to think that arthropods evolved from a annelid
                           ancestor.
                        There are three new hypotheses
                             o Segmentation had separate evolutionary origins.
                             o There were two separate origins of segmentation
                             o Segmentation evolved just once
                        The research field is “Evo-devo”

E. Deuterostomia

       1. Phylum Echinodermata: Echinoderms have a water vascular system and secondary radial
       anatomy.

              Echinoderms are slow-moving animals. Its internal and external parts radiate from the
               center. Its hard plates are covered with a thin skin.
              The echinoderms have the water vascular system. This is a network of hydraulic canals
               branching into extensions called tube feet. These tube feet function in locomotion,
               feeding and gas exchange.
              Sexual reproduction between echinoderms is separate. They release their gametes into
               the water.
              Echinoderms are bilaterians. But adult echinoderms are not perfectly symmetrical.
              All 7,000 echinoderms are divided into six classes. These are: Asteroidea, Ophiuroidea,
               Echinoidea, Crinoidea, Holothuroidea, and Concentricycloidea.

               a. Class Asteroidea

                        Sea stars have 5 arms radiating from a central disk. These arms have tube feet
                         on the underside. They can act as suction disks. These are used for locomotion
                         or capturing prey. The sea star secretes digestive juices which digest its prey in
                         its own shell.

               b. Class Ophiuroidea

                        The brittle stars have distinct central disks and its arms are long and flexible,
                         they do not have suckers on their tube feet.

               c. Class Echinoidea
              For the most part, these have no arms, but they do have 5 rows of tube feet
               that function in slow movement. They also have muscles to pivot their long
               spines

       d. Class Crinoidea

              Sea Lilies are attached to the substratum by stalks, feather stars crawl around by
               using their long flexible arms. They use their arms for suspension feeding

       e. Class Holothuroidea

              They lack spines, the hard exoskeleton is reduced, and they have tube feet,
               some of which are developed as feeding tentacles.

2. Phylum Chordata

      This phyla consists of two subphyla. These are the invertebrates and those with
       vertebra.
      They have similar evolutionary paths

				
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