Chapter 33: Invertebrates

 

Spend time with CD Activity 33A – great review for Chs. 32/33

 

I. PARAZOA (no true tissues)—only one phylum in this group = Porifera, the sponges

 

Phylum Porifera (Figs. 33.2 & 32.3)

·        ·        9,000 spp., only 100 fresh water

·        ·        suspension feeders

·        ·        no nerves or muscles

·        ·        no true tissue organization, but 3 specialized cell types:

porocytes--pore-forming cells

               choanocytes--flagellated cells lining interior

               amoebocytes--digest food, transport to other cells

·        ·        form tough skeletal fibers, spicules of CaCO3 or silica; or reinforce with spongin protein

·        ·        hermaphroditic, gametes arise from choanocytes or amoebocytes--may self- or cross- fertilize (eggs stay in mesohyl, sperm released through osculum)

·        ·        multiflagellate zygote develops into larva, released from spongocoel and out through osculum; larva turns “inside out” to place flagellated cells in interior

·        ·        regeneration allows repair, asexual reproduction

·        ·        example in lab: Grantia spicules, dried sponges

 

II. EUMETAZOA (have a layered embryo which undergoes gastrulation) this group includes all phyla other than Porifera

 

A. Radiata radial symmetry, diploblastic (two germ layers in embryo)

                                             ectoderm, endoderm

 

Phylum Cnidaria--hydras, jellyfish, sea anemones, corals

·        ·        Fig. 33.4 diploblastic, with epidermis and gastrodermis in adult; median layer is either mesoglea (non-cellular) or mesochyme (cellular)

·        ·        central gastrovascular cavity with a single opening Fig. 33.4

·        ·        can be sessile polyps, floating medusa, or dimorphic (both body shapes during life cycle, unique to Cnidaria) Fig. 33.4

·        ·        gastrodermal cells are flagellated, secrete digestive enzymes; phagocytize food particles

·        ·        tentacles around mouth/anus armed with cnidocytes with stinging nematocysts (Fig. 33.5)

·        ·        simple muscle and nerves in their simplest form--not true, since not from mesodermal origin--movements coordinated by nerve net

 

3 Classes of Cnidarians (Table 33.1, Fig. 33.6)

A. Hydrozoa eg, Hydra, Obelia

                              most  dimorphic, alternate polyp and medusal stages

                              Hydra is polyp only

               B. Scyphozoa (jellyfish)--         medusal form predominant

 

               C. Anthozoa (flower animals)--sea anemones and corals

                              polyp stage only

                              corals secrete external CaCO3 skeletons, build vast underwater reefs  

                        example in lab:  Hydra

 

Phylum Cnetophora --comb jellies  Fig. 33.8

·        ·        100 spp., all marine

·        ·        1-10 cm in diameter, up to 1 meter long

·        ·        8 rows of comblike plates composed of fused cilia

·        ·        pair of long retractable tentacles for food capture

 

EUMETAZOA continued

 

B. Bilateria (triploblastic) bilateral symmetry, triploblastic (three germ layers)

                                             ectoderm, endoderm, mesoderm (gives rise to muscles)

 

                            1. Acoelomates (having no coelom or body cavity)

 

Phylum Platyhelminthes (flatworms)

·        ·        20,000 spp. including parasitic flukes, tapeworms

·        ·        all are triploblastic, with mesoderm forming true muscle tissue

·        ·        gut still primitive, with only one opening

·        ·        central layer of body solid tissue from mesoderm, no coelom (see Fig. 32.6)

·        ·        increase in nerve function makes them better carnivores, parasites

·        ·        cannot synthesize fatty acids and sterols de novo—makes parasitism attractive

 

4 classes of Platyhelminthes Table 33.2

1. Turbellaria (Figs. 33.9 & 33.10)

·        ·        free-living, marine or fresh-water (planarians)

·        ·        digestion both internal and external, digestive juices spilled onto prey and sucked into pharynx in small pieces; completed in cells lining gastrovascular cavity

·        ·        digestive wastes excreted through “mouth”; CO2 waste diffuses across epidermis

·        ·        ammonia and excess water eliminated via epidermal nephridiopores, a necessary adaptation to terrestrial life

·        ·        movement via ciliated epidermis and mucous secretion on ventral side, muscular undulations to “swim”

·        ·        cephalized nervous system (head not associated with feeding):

               2 eyespots, two nerve ganglia leading to a ventral nerve cords with ladder-like                                              lateral attachments; auricles (earflaps) function in smell, not hearing

·        ·        asexual reproduction-splits in half medially

·        ·        hermaphroditic, can also copulate to cross-fertilize

·        ·        capable of learned responses to stimuli

eg. in lab Dugesia= planaria

 

2. Tremotoda and Monogenea (flukes)

·        ·        parasitic, alternation of sexual and asexual stages with intermediate hosts

·        ·        eg. Schistosoma mansoni (blood fluke, Fig. 33.11)--infects 1/30 of humanity (among the most dreaded parasites of humans)

·        ·        worldwide distribution due to slave trade; most drugs for treatment are toxic

·        ·        means “split body”, from males’ gynecophoral canal

·        ·        adult stage, sexual repro. and eggs develop in blood vessels of human large intestine, pass through wall into feces (unusual in this regard; eggs not shed collect in other organs, including liver and spleen)

·        embryo forms a swimming ciliated larva, the miracidium, which infects a snail (intermediate host)

·        asexually produced larvae escape from snail, penetrate skin of human (primary or definitive host) within one-half hour  to complete life cycle

·        3 weeks in liver to mature, then migrate to large intestine, adults pair for life

Primary phase =fever, skin rash, diarrhea, enlarged liver and spleen

Secondary phase= eggs cause tubercle formation, occlusion of blood vessels

 

3. Cestoidea (tapeworms) Fig. 33.12

·        ·        no digestive system, receives all nutrition from host

·        ·        anterior end, the scolex, armed with hooks to penetrate and attach to host’s intestine

·        ·        body composed of series of immature and maturing proglottids, each containing sex organs (4-70 testes in each!), which mature to egg sacs released with host’s feces

·        ·        larvae encyst in muscle tissue of intermediate host eg. pig, eaten by primary host (human) to complete life cycle

·        ·        examples: Taenia  spp. infect dogs, cats, humans with different intermediate hosts for                                   each (T. solium the most dangerous to humans—10 to 30 ft. long in human intestine, pig as intermediate host; adults live 30 years, can easily contaminate whole family with eggs from feces; cysticeri develop in every organ, including brain, eyes, liver, lungs, heart

Echinococcus granulosus- parasitizes canine family (dog, wolf, fox)

·            ·            Smallest of Taeniidae, but huge larvae

·            ·            human infections can come from family pet that eats deer, moose, caribou, other herbivores (intermed. hosts) which pick up eggs from plants eaten

·            ·            encyst and reproduce asexually in hydatid cysts in muscle, heart, brain of other intermediate hosts, including humans

·            ·            cysts very slow growing, over 20+ years, causing extensive damage; may contain 15 liters of fluid, millions of scolexes)

 

EUMETAZOA continued

 

B. Bilateria (triploblastic) continued

 

2. Pseudocoelomates (having a coelom lined on one side by                                                           mesoderm, complete digestive tracts) Fig. 32.6

 

Phylum Rotifera (rotifers)  Fig. 33.13

·        ·        extremely small but complex, with complete digestive tract and blood vascular systems

·        ·        organs enclosed in a pseudocoelom

·        ·        twin crowns of cilia surround mouth

Examples in lab: live rotifers

 

Phylum Nematoda (roundworms)  Fig. 33.25

 

·        ·        most numerous of all phyla, in numbers of spp. and numbers, period!

·        ·        found EVERYWHERE (aquatic, soil, plant tissues, animal fluids and tissues)

·        ·        important decomposers of soil on land and in oceans

·        ·        complete digestive tract, pseudocoelom

·        ·        Phylum Nematoda (roundworms) con’t.

·        ·        longitudinal muscles capable of contractive movement

·        ·        mostly sexual reproduction with separate sexes and internal fertilization

·        ·        parasites of plant roots, animals eg. pinworms, hookworms

·        ·        eg. Onchoceriasis—River blindness, spread by black flies

 

Eg. trichinosis from Trichinella spiralis, due to eating undercooked pork (Fig. 33.13b)

               juveniles in muscle cysts develop into sexually mature adults in human intestine

                              female produces more juveniles which migrate and encyst in other organs                                                             (heart, muscle) causing nausea, death!

Eg. Dirofilaria immitis—dog heartworm

Eg. Pork roundworm Ascaris  crossed over from pigs to humans, grow up to 18” in human

 

EUMETAZOA continued

 

               B. Bilateria (triploblastic) continued

 

                              2. Coelomates (having a coelom lined on both sides by                                                                                                     mesoderm) Fig. 32.6

 

                                             A. Protostomes spiral and determinate cleavage coelom 

                                         derived from solid mass of mesoderm, splits to form

                                         coelom mouth develops from blastopore

 

Phylum Mollusca

·        ·        simplest of protostomes--no segmentation in bodies

·        ·        50,000 spp. known

·        ·        either soft-bodied (slugs, squids, octopi) or hard-shelled (clams, snails) w/ shells of CaCO3

·        ·        separate sexes with sex organs (some snails hermaphroditic)

 

all have similar features in body plan: (Fig. 33.16)

 

1. muscular foot for movement

               2. visceral mass with embedded organs

               3. mantle--heavy fold of tissue protects the visceral mass, may secrete shell

                              mantle cavity houses gills, anus, excretory pores

               4. may have a radula--rasping organ for scraping up food

 

 

1. Class Gastropoda--40K spp. Figs. 33.19 & 33.19

·        ·        mostly marine (snails and slugs on land)

·        ·        mostly have a shell for protection

·        ·        distinctive torsion in embryo development yields uneven growth, rotation of visceral mass, placing anus and mantle cavity over mouth (Fig. 33.18)

·        ·        radula for grazing; may have teeth or the ability to bore into prey eg. dog whelk preying on limpets

2. Class Bivalvia (Figs. 33.20 & 33.21)

·        ·        clams, mussels, oysters, scallops

·        ·        all have two-sided shell, hinged mid-dorsally

·        ·        powerful adductor muscles to shut shell

·        ·        gills in mantle cavity used in feeding as well as gas exchange (mucous on gills traps suspended food particles

·        ·        no distinct head or radula

·        ·        incurrent and excurrent siphons

 

3. Class Cephalopoda (Fig. 33.22)

·        ·        squids, octopi, cuttlefish, chambered nautilus

·        ·        carnivorous, built for speed

·        ·        shell internal and reduced in squid; lost in octopus

·        ·        movement by squirting water out of excurrent siphon

·        ·        only molluscs with a closed circulatory system

·        ·        well-developed nervous system and complex brain (vital for predators)

 

4. Class Polyplacophora (Fig. 33.17)

·        ·        chitons: marine grazers using radula to cut and ingest algae from rocks

·        ·        externally segmented (8 plates, but no internal repeats of organs)

 

Phylum Annelida (Fig. 33.23)

two important evolutionary innovations:

1. coelom as a hydrostatic skeleton, for attachment of muscles in movement

**2. segmentation = specialization

·        ·        segmented worms eg. earthworm, up to 3 m long

·        ·        segmented coelom + longitudinal muscles = movement; setae also contribute

·        ·        complete digestive system (unsegmented): pharynx, esophagus, crop, gizzard, intestine

·        ·        closed circulatory system, hemoglobin to carry O2, five muscular vessels to pump blood through system

·        ·        each segment has 2 excretory tubes (metanephridia) with ciliated funnels (Fig. 44.16) (nephrostomes) to remove wastes from blood and coelom

·        ·        skin = respiratory organ, must stay moist for gas exchange

·        ·        2 cerebral ganglia, segmental ganglia

·        ·        hermaphroditic; usually cross-fertilize with another worm

·        ·        clitellum secretes mucous band, moved forward and over head by muscular contractions

·        ·        cocoons with embryos develop in soil; able to regenerate via fragmentation

 

3 classes (Table 33.4):

1. Oligochaeta = “few hairs” (2 pairs per segment)

·        ·        earthworms, other freshwater annelids, eat algae, detritus

 

2. Polychaeta = “many hairs”

·        ·        have two parapodia used as gills, in locomotion

·        ·        mostly marine, includes tube worms

 

3. Hirudinea--leeches

·        ·        mostly aquatic, some terrestrial

·        ·        carnivorous or parasitic

·        ·        secrete an anesthetic to numb host as it slits or dissolves the skin

·        ·        hirudin protein prevents blood coagulation 65 Amino acids, may soon be cloned artificially)

·        ·        still used medicinally on bruised tissue, for reattaching fingers, toes, ? to improve circulation, control swelling

 

Phylum Arthropoda (Fig. 33.26)

most successful and numerous of invertebrate phyla AND of all animal phyla

 

1. greater segmentation leading to increased specialization

2. hard exoskeletons (cuticle) of protein + chitin

               important adaptation to land

               protection; prevents drying; points of attachment for muscles

                              but must molt to grow--energy consuming, more vulnerable to predators

               must also solve breathing problem--? how to increase respiratory surfaces

3. specialized organs for gas exchange--gills, book lungs, tracheal system

4. jointed appendages give added versatility in movement, feeding

5. sensory organs, cephalization at anterior end

6. open circulatory system, heart circulates hemolymph through coelom, between sinuses of organs

 

4 groups of arthropods progressing from more to fewer and more specialized segments.  These will probably be grouped as separate phyla in the near future.

 

1. Future Phylum Trilobita  (Fig. 33.27)

·        ·        extinct trilobites

·        ·        present throughout Paleozoic, died out in Permian extinction

·        ·        pronounced segmentation, appendages varying little

 

2. Future Phylum Chelicerata (Fig. 33.28) [Class Arachnida discussed below]

·        ·        spiders, scorpions, mites, ticks, sea spiders

·        ·        horseshoe crab called a living fossil--from Paleozoic

·        ·        named for  their feeding appendages = “lip arm” (clawlike)

·        most marine species now extinct

 

3. Future Phylum Uniramia (insects, centipedes, millipedes) (Table 33.6)

[Classes Diplopoda, Chilopoda, and Insecta discussed below]

·            one set of antennae

·        unbranched (uniramous) appendages

 

4. Future Phylum Crustacea (crabs, lobsters, shrimps, barnacles) (Fig. 33.35)

[Class Crustacea discussed below]

 

Five representative arthropod classes:

Class Arachnida (Fig. 33.29, 33.30)

·        ·        have a cephalothorax, four pairs of walking legs in addition to chelicerae,            

                pedipalps

·        ·        chelicerae--feeding only, often have poison glands associated with

·        ·        pedipalps--sensing (no antennae)

·        ·        gas exchange via book lungs (stacked plates, air drawn in by muscular action)

·        ·        spinnerets produce a protein which solidifies into a web

·        ·        simple eyes (only one lens)

 

Class Diplopoda (Fig. 33.31a)

·        ·        millipedes--two pairs of legs per segment

·        ·        important decomposers (detritivores) of plant matter

 

Class Chilopoda (Fig. 33.31b)

·        ·        centipedes--one pair of legs per segment

·        ·        carnivorous--poison claws on anteriormost trunk segment

 

Class Insecta--most numerous and diverse (Fig. 33.33)

·        ·        mostly terrestrial and freshwater

·        ·        first fossils Devonian (followed plants to land)

 

key evolutionary development:

               flight-wings are extensions of the cuticle, NOT appendages (Fig. 33.32)

anatomy of an insect body (Fig. 33.33)-- Grasshopper

·        ·        body divided into three regions: head, thorax, and abdomen

·        ·        head has antennae, compound eyes (many specialized focusing elements), jawlike mandibles

·        ·        three pairs of legs attached to thorax

·        ·        complete digestive system with specialized organs

·        ·        open circulatory system with heart, hemolymph

·        ·        separate sexes, internal fertilization (some produce live young)

·        ·        excretory organs = Malpighian tubules (remove water, nitrogenous wastes from hemolymph

·        ·        gas exchange via tracheal system--branched, chitin-lined tubes, open at sides via spiracles (can open and close)

·        ·        nervous system--2 ventral nerve cords, dorsal brain

 

metamorphosis for growth:

A. incomplete eg. grasshopper = molting

B. complete, with various heteromorphic stages eg. cicada, butterfly (Fig. 33.34)

1. larval--eating, growing

2. pupa--resting, developing

3. adult--often reproductive only

 

Class Crustacea--mostly marine (Fig. 33.35)

·        ·        2 pairs of antennae

·        ·        highly specialized appendages are biramous (branched, clawlike)

·        ·        appendages on abdomen as well as thorax--can regenerate

·        ·        glands for balancing salts in hemolymph; remove nitrogen wastes via diffusion

·        ·        swimming larval stages important component of zooplankton

 

3 groupings of crustaceans:

 

a) decapods  large eg. lobsters, crayfish, shrimp, crabs

·        ·        some have CaCO3 in exoskeleton, carapace covers dorsal side

 

b) isopods--pill bugs, other marine crustaceans; 10,000 species

 

c) copepods (Class Maxillopoda)

·        ·        very numerous, members of zooplankton

·        ·        krill--major food source for whales

·        ·        barnacles--sessile crustaceans, part of cuticle hardened with CaCO3

 

EUMETAZOA continued

B. Bilateria (triploblastic) continued 

2. Coelomates continued

                        B. Deuterostomes (radial and indeterminate cleavage coelom

                             derived from folds of archenterons anus develops from

                             blastopore.  Echinoderms and chordates, vertebrates share 

                             common features, all are deuterostomes

 

Phylum Echinodermata--7000 spp. (Fig. 33.37)

·        ·        exclusively marine; sessile or sedentary

·        ·        both radial and bilateral symmetry in adult forms

·        ·        bony endoskeleton covered by a thin skin (hard calcareous plates)--precursor to  

                vertebrates

·        ·        unique water vascular system

·        ·        network of vascular canals branching into tube feet (function in feeding, gas 

                exchange)

·        ·        reproduction sexual, separate sexes, gametes released into sea water

·        ·        bilateral larvae metamorphose into radial adults

 

6 Classes of echinoderms

1. Asteroidea--sea stars (Fig. 33.37a, b)

·        ·        central disk, 5 or more arms radiating out, bearing tube feet on ventral side

·        ·        coordinated hydraulic and muscular action creates suction

·        ·        grasps prey (clams, oysters), inverts stomach outside through mouth, secretes 

                digestive juice inside bivalve shells and slurps up the digested mollusc

·        ·        strong powers of regeneration--regrow lost arms slowly

2. Ophiuroidea--brittle stars (Fig. 33.37c)

·        ·        no suckers on tube feet

·        ·        move by lashing arms

3. Echinoidea--sea urchins, sand dollars (Fig. 33.37d)

·        ·        no arms, but five rows of tube feet

·        ·        capable of slow movement

·        ·        muscular movement of spines aids locomotion

·        ·        urchins have complex jawlike structure around mouth for eating seaweeds

4. Crinoidea--sea lilies (Fig. 33.37e)

·        ·        may be sessile (on stalk) or motile

·        ·        arms function in mvmt. and suspension feeding

·        ·        conservative evolution--500 million years old

5. Holothuroidea--sea cucumbers (Fig. 33.37f)

·        ·        5 rows of tube feet, water vascular system

·        ·        tube feet around mouth developed into feeding tentacles

                otherwise different from other echinoderms:

·        ·        elongated in oral-aboral axis (bilateral)

·        ·        much reduced endoskeleton, lack spines

5. Concentricycloidea - sea daisies, recently discovered, deep sea species

Photos and more info about echinoderms: www.meer.org/M37.htm UC