Chap 33: Invertebrates

Parazoa

Introduction

• Choanoflagellates are the ancestors of the animal kingdom

• Sponges are the closest animal to these ancestors

Phylum Porifera: Sponges

• Basic Characteristics

• Sessile

• No nerves or muscles but can respond to events in the environment.

• No true tissues

• Have porous bodies through which water is drawn in

• Spongocel: the central cavity

Figure 33.1 Review of animal phylogeny

Figure 33.3 Anatomy of a sponge

Filter Feeders

SpongesSponges

• How do we know that sponges are related to the early choanoflagellates?

• The cells of the choanoflagellates and the choanocytes are similar in terms of molecular makeup.

• Presence of spicules: these are sharp fibers made of calcium carbonate

• Some of the fibers are not so rigid and made of collagen protein and this is what the bath sponges are made of.

• Sponge Sex

• They are hermaphroditic so they can produce both sperm and egg cells. Eggs reside in a gelatinous layer, the mesohyl, while the sperm cells are released out the osculum.

• Cross fertilization can occur

• Fertilization occurs in the mesohyl and the zygotes develop flagellum and swim away from the parent.

SpongesSponges

• Asexual reproduction is possible by fragments of a sponge breaking off and developing into a new organism

• Regeneration is possible.

Radiata

Introduction

• Possess true tissues

• Radially symmetrical

• Embryos possess ectoderm and endoderm (diploblastic)

Phylum Cnidaria: hydras, jellies, sea anemones and corals

• Basic Characteristics

• Possess a gastrovascular cavity

• Single opening for mouth and anus

• Two body forms (plans)

• Polyps: adhere to a substratum and extend tentacles

• Medusa: “mouth-down” version; mobile by drifting and contracting of the bells.

Figure 33.4 Polyp and medusa forms of cnidarians

Figure 33.4bx Jelly medusa

Figure 33.6 Cnidarians: Hydrozoans (top left), jelly (top right), sea anemone (bottom left), coral polyps (bottom right)

Figure 33.5 A cnidocyte of a hydra

Carnivorous

CnidariansCnidarians

• Carnivorous

• Cnidocytes: a specialized cell that causes the projects of a stinging capsule called a nematocyst.

• Class Hydrozoa

• Hydras

• Can reproduce by budding (asexual) with conditions are good

• Can reproduce sexually forming dormant zygotes if conditions are harsh.

Figure 33.7 The life cycle of the hydrozoan Obelia (Layer 3)

• Class Scyphozoa

• Jellies

• Class Anthozoa

• Sea anemones and corals

• Occur only as polyps, attached to a substrate.

Phylum Ctenophora: Comb jellies

• 100 species of comb jellies

• The descriptor, “comb” comes from the 8 rows of fused cilia.

Figure 33.8x2 Ctenophore

Figure 33.8x1 Sea gooseberry, Pleurobrachia pileus

Combs

rows of cilia are used for locomotion

Comb jellies and cnidarians are in different phyla. Both are radiate and diploblastic.

Tentacles: capture food with their adhesive structures (colloblasts). These colloblasts when stimulated by touch will release a sticky thread.

Protostomia: Lophotrochozoa

Introduction

• Protostomes represent Bilateral Symmetry (see Fig 33.1, pg 647)

• Protostomes are the planaria, flatworms, earthworms, mollusks, arthropods such as insects, crayfish, spiders.

Phylum Platyhelminthes: Flatworms

• Introduction

• many parasitic species (tapeworms)

• marine and freshwater as well as terrestrial flatworms

• Triploblastic: possess endo- ecto- and mesoderm

• being triploblastic allows them greater complexity in organ development.

• Acoelomates, that is there is no space between their outer body wall and digestive digestive tract.

• Possess a gastrovascular cavity with one opening (like hydra)

• Class Tubellaria

• Planarians

• Digestion

•Carnivorous

•Gastrovascular cavity

• Respiration and Circulation

•One-cell layer thick for diffusion of gases

•Food is distributed by the branching of the gv cavity.

Figure 33.9x A flatworm

• Movement

•Beating cilia on a secreted mucus layer

• Nervous System

•More sophisticated then cnidarians

•Can learn to modify responses to the environment

•Possess eyespots to detect light

•Lateral flaps for hearing

• Excretion

•Gases diffuse out

•Flame cells circulate water over ducts that carry water and salt to the exterior.

• Reproduction

•They can regenerate (asexual) by the parent simply splitting in the middle and each half regenerates

•Sexual reproduction: cross fertilize

•Hermaphroditic but not fertilize themselves

Figure 33.10 Anatomy of a planarian

• Classes Monogenea and Trematoda

• Flukes (such as Schistosoma or blood flukes)

• Digestion

•Parasitic and possess suckers

• Reproduction

•Their internal spaces are filled with reproductive organs because that is all they need to worry about being parasites.

• Class Cestoidea

• Tapeworms

• Digestion

•Parasitic with the head or scolex possessing suckers and hooks that lock onto your intestine.

• Reproduction

•Body parts are units of proglottids which are sacs of sex organs containing eggs.

Figure 33.11 The life history of a blood fluke, Schistosoma mansoni

• Reproduction (cont’d)

•Proglottids leave the person’s body with the feces. An intermediate host such as pigs, cattle, pick up the eggs that develop into larvae and are embedded in their muscle tissue. We eat the muscle tissue, larvae get into our intestine and mature.

Figure 33.12 Anatomy of a tapeworm

Phylum Rotifera (Rotifers)

• Basic Characteristics

• Pseudocoelomates: that is, they have a body cavity but it is not completely lined by mesoderm. The acoelomates do not have a body cavity and the coelomates have a body cavity completely lined by mesoderm.

• Possess a complete digestive tract with a mouth and anus

• Water is drawn in through the mouth by cilia

• A pharynx bears jaws for grinding food (microorganisms)

• Fluid the pseudocoelom serves as a skeleton as well as medium in which nutrients and wastes are transported.

• The pseudocoelom is also the circulatory system

• Undergoes parthenogenesis, the production of females from unfertilized eggs.

• Some species produce two types of eggs: one undergoes parthenogenesis and produces females, the other develops into males by parthenogenesis. These males survive just long enough to produce sperm. Fertilization occurs, zygotes form that withstand drought conditions and then develop into a female.

Figure 33.13 A rotifer

Phylum Lophophorate

• Identifying Characteristic

• Lophophore or a horseshoe-shaped piece of body wall that bears ciliated tentacles that surround the mouth.

• Cilia draws water in, traps food

• Have true coeloms lined by mesoderm

• Brachiopods

• possess a hinged shell with its two halves being dorsal and ventral and not like clams which have lateral shells.

Figure 33.14 Lophophorates: Bryozoan (left), brachiopod (right)

Lophophore

Phylum Nemertea or proboscis worms

• Basic Characteristics

• Body shaped is ribbon like

• Excretory System: gas diffusion through body wall

• Possess eyespots like flatworms.

• Unique Features

• Complete digestive tract

• Closed Circulatory System: blood within vessels; no heart but blood is moved by muscle contraction on the vessels thus squeezing the blood throughout the body.

Phylum Mollusca

• Examples: snails, slugs, oysters, clams, octopuses, squids

• Where they live

• mostly marine, terrestrial

• Skeleton

• external made of calcium carbonate

• octopuses and squids have internals skeleton or they have lost their skeleton completely

• Body Plan

• 3 main parts

• Foot: muscular; for movement

• Visceral Mass: contains internal organs

• Mantle: tissue that hangs over the internal organs and also secretes the shell.

•Also produces a water filled chamber for gills, anus and excretory pores for clams and other similar mollusks

• Digestive System

• Radula: scraps food from surfaces

• Complete digestive system (see next slide)

Figure 33.16 Basic body plan of mollusks

• Reproduction

• Separate sexes with ovaries and testes located in the visceral mass.

• Snails can be hermaphroditic

• Trochophore: ciliated larval stage

Figure 33.17 A chiton

• Class Polyplacophora

• Chitons (not chitin)

• have 8 dorsal plates

• use radulas to obtain food from surfaces

Figure 33.18 The results of torsion in a gastropod

• Class Gastropods

• Torsion: a characteristic feature where the contraction of a muscle during embryonic development and uneven growth places the anus and mantle cavity above the head. Advantage? To possibly locate these structures more centrally over the body.

• One of few inverte-brates to have successfully populated land.

• Land snails have a moist lining for gas exchange. No gills unless it is aquatic.

Figure 33.18x Garden snail

Figure 33.19 Gastropods: Nudibranchs (top left and top right), terrestrial snail (bottom left), deer cowrie (bottom right)

Sea Slugs

• Class Bivalvia

• Examples: clams, oyster, mussels, scallops

• Muscular System

• Adductor muscle which closes the two shells

• Movement

• by a foot that gets extended out of the shell

• can also be used to anchor the clam

• mostly sedentary• Respiration

• has gills that water flows over

• water is taken in through the incurrent siphon and out of the mantle cavity through the excurrent siphon

Figure 33.21 Anatomy of a clam

• Digestive System

• water that is brought in through the incurrent siphon brings in food particles that get trapped on mucus that is on the gills.

• cilia beat to food these food particles to the mouth

• no radula for the scraping of food• Nervous System

• Scallops possess eyes

Figure 33.20 A bivalve: Scallop

Eyes are between the

two halves.

• Class Cephalopoda

• Examples: octopuses, squids

• Digestive System

• Carnivorous: eat clams

• Possess jaws

• Inject poison to immobilize prey

• Possess a mouth

• Skeletal System

• Nautiluses have an external skeleton; otherwise the shell is greatly decreased or lost

• Movement

• Water is drawn into the mantle cavity and fired out the excurrent siphon. The siphon can be pointed for directional movement.

• Most live on the ocean bottom

• Circulatory System

• Closed circulatory system

• Nervous System

• Well-developed

• Brain is able to learn

• Well-developed sense organs

Figure 33.22 Cephalopods: Squid (top left and bottom left), nautilus (top right), octopus (bottom right)

What’s the big deal about the Phylum Annelida or segmented worms?

• Presence of a coelom or body cavity

• provides space for digestive organs

• acts as a cushion to protect these internal organs

• separates the muscular outer body wall from the muscular intestine

• provides space for fluid to support the body (a hydrostatic skeleton)

• Segmentation

• the body plan of animals is becoming localized to certain areas. This theme is present in many other animals.

Phylum Annelida or the segmented worms like earthworms.

• Habitat: soil, marine, freshwater.

• Digestive System

• Specialized into several areas or compartments:

• pharynx

• esophagus

• crop

• gizzard

• intestine

• eats its way through soil, digest soil and waste is “deposited” as castings.

• ecological role: aerates soil; improves texture

• Circulatory System

• Closed

• Hemoglobin is the oxygen carrying pigment

• Dorsal blood vessel with 5 pairs of vessels serve as a pumping mechanism to get blood into the ventral blood vessel and distributed

• Blood is carried right to the skin for gas exchange

• Excretory System

• Functioning unit is the metanephridia. Located in each segment of the earthworm’s body

• Liquid and wastes are removed from the segments through a funnel called a nephrostome that will carry the wastes to the outside and excrete it through a small pore.

• Nervous System

• Possesses a collection of nerve cells, ganglia, one ganglia on each side of the pharynx.

• Nerves run through a nerve cord that runs to the end, the ventral nerve cord

• Along the ventral nerve cord are collections of nerves into ganglia from which nerves branch out laterally

• Muscular System

• Move by inserting bristles or setae into soil and using two sets of muscles, longitudinal and circular.

• Reproductive System

• Hermaphroditic but they do not fertilize themselves

• Sperm is exchanged

• The clitellum secretes a mucous cocoon that slides dorsally along the earthworm, picks up the eggs and exchanged sperm and continues towards the anterior and slides off. This cocoon contains the developing embryos.

Figure 33.23x External anatomy of an earthworm

Figure 33.23 Anatomy of an earthworm

• Class Oligochaeta

• earthworms

• Class Polychaeta

• possess many setae for movement

• These setae are attached to a structure called a parapodia that have lots of blood vessels, can exchange gases and function in respiration.

• Class Hirudinea

• leeches

• parasitic lifestyle in marine and freshwater

• contact with skin can be made with enzymes or with jaws. An anesthetic is released so host does not feel the biting.

• Hirudin: anticoagulant so the blood keeps on flowing. Digestive system here is not too complicated.

Figure 33.24 Annelids, the segmented worms: Polychaete (left), feather-duster worm (middle), leech (right)

Protostomia: Ecdysozoa

Introduction

• Roundworms, arthropods (crustaceans, spiders, insects) all molt or lose their outer skeleton (exoskeleton) so they are in a “clade” called ecdysozoa because they go through ecdysis or the loss of the exoskeleton.

Phylum Nematoda (Caenorhabitis elegans or C. elegans)

• Habitat

• moist soil or in marine or freshwater, moist parts of plants and in the body fluids and tissues of animals.

• Skeleton

• has an external cuticle (exoskeleton) that it molts

• new one is secreted.

• Digestive System

• similar to annelids, a complete digestive tract.

• Circulatory System

• No circulatory system

• Nutrients are transported through the body cavity’s fluid

• Reproductive System

• sexual reproduction

• internal fertilization

• Ecological Importance

• decomposition of matter; recycling of nutrients

• Human Impact

• the roundworm, Trichinella spiralis, causes trichinosis which you get from eating undercooked pork. The cyst of the roundworm is in the muscle tissue you eat, finds its way to the intestine and burrows into the intestine to mature. The offspring can infect other body tissues (heart muscle) causing death.

Figure 33.25ax Nematode, C. elegans

Figure 33.25a Free-living nematode

Mouth

Figure 33.25b Parasite nematode, Trichinella spiralis

Distinguishing Features of the Arthropods

1. Importance of the exoskeleton

a) allowed the move to land by some arthropods

b) protection in sea and on land

c) prevented water loss on land; cuticle is impermeable to water.

d) structural support since there is no water to “hold up” the appendages.

2. Segmentation

a) This represents the “segmentation” or “blocking of the embryo into regions of development. Eyes go in the “first segment” or the head region and then different appendages are developed towards the posterior end.

b) Hox genes are responsible for determining what organ goes in what segment.

2. Segmentation

a) This represents the “segmentation” or “blocking of the embryo into regions of development. Eyes go in the “first segment” or the head region and then different appendages are developed towards the posterior end.

b) Hox genes are responsible for determining what organ goes in what segment.

c) As the Hox genes duplicated and mutated more segmentation of the bodies occurred producing greater diversity

• Skeleton

• hard chitinous exoskeleton or cuticle, lost and reformed

• jointed appendages

• Body segments are specialized for attachment of appendages or sensory reception, reproduction

Phylum Arthropoda

• Habitat: diverse and everywhere are the crustaceans, insects, spiders.

• Senses and Nervous System

• eyes, smell, antennae for touch and smell

• Localization of nerves towards the head, known as cephalization, is a distinguishing feature.

• Circulatory System

• Open

• Fluid is called hemolymph, not blood

• Heart and short arteries but no extensive vessel development. Hemolymph is pumped into the sinuses which surround the tissue. Here the tissues pick up nutrients that they need and get rid of waste.

• Hemolymph reenters heart through ports called ostia

• Respiratory System

• Aquatic arthropods have gills

• Terrestrial arthropods can take gases into through pores at the body surface, through tracheal systems or ducts and branch to distribute gases at the tissues.

• Arthropod Phylogeny and Classification

• 4 main lineages of arthropods

• (1) Trilobites

• now extinct

• lots of segmentation which again is a major distinction as animals became more sophisticated.

• (2) Chelicerates (spiders, horseshoe crabs)

• have chelicerae which are the clawed appendages like in a crayfish; possess a single lens eye

• appendages are a bit more specialized than the trilobites

• the chelicerae are the distinguishing appendage

• the horseshoe crabs have changed very little but has existed for 100’s of millions of years

• known as the “living fossil”

Figure 33.27 A trilobite fossil

• Chelicerates (cont’d)

• possess book lungs as respiratory surfaces. These are “pages”of respiratory surfaces for gas exchange between the hemolymph and the air.

• Arachnids have 6 pairs of appendages, the chelicerae, the pedipalps used for sensing or feeding and the 4 pairs of walking legs.

• Webs of silk are part of capturing food. Silk is a protein.

Figure 33.30b Spider anatomy

• (3) Insects

• possess mandibles or lower jaws for chewing

• possess antennae and compound eyes (many focusing elements)

• Distinguishing feature to their success: flight

• Important in pollination of plants (coevolution)

• Complete digestive system

• Open circulatory system with hemolymph and sinuses

• Excretory System: Malpighian tubules which extend from the digestive tract, extract waste from the hemolymph.

• Respiratory System: Tracheal system of branched tubes extending from the pores or spiracles in the chitinous exoskeleton and carry oxygen right to the tissues.

• Insects (cont’d)

• Nervous System: ventral nerve cord, ganglia throughout the body. The two ventral nerve cords come together at the head and from the brain. Antennae, eyes as sense organs.

• Insects undergo metamorphosis

Incomplete metamorphosis: several moltings as the body develops in proper portions to become an adult with each molting.

Complete metamorphosis: larval stage looks different from the adult (caterpillar) and metamorphosis occurs during the pupa stage as the caterpillar, in the cocoon becomes an adult.

• Reproduction is internal, sexual. Deposited sperm is stored in a spermatheca.

• (4) Crustaceans

• thrived in aquatic environments while the insects and arachnids thrived on land.

• Multiple appendages: 2 pairs of antennae; 3 or more mouthparts; walking legs

• Respiration: smaller ones can exchange gases across a thin cuticle but larger crustaceans have feathery gills.

• Circulatory system: open; heart with hemolymph in vessels and then into sinuses.

• Excretory system: some wastes (N) can diffuse across the cuticle and salt wastes are regulated by salt glands.

• Reproductive system: sexual reproduction

• Common species: isopods, copepods (food at the base of the aquatic food chain, eaten by fish), decapods (lobsters)

Figure 33.35 Crustaceans: Lobster (top left), banded coral shrimp (bottom left), barnacles (right)

Barnacles have shells of CaCO3 and use the appendages to filter food from water.

Deuterostomia

Basic Characteristics

• radial cleavage

• mouth forms at the opposite end of the blastopore

• body cavity or coelom develops from the archenteron

• Examples of deuterostomes: sea stars, fish, amphibians, reptiles, birds and mammals.

Phylum Echinodermata

• Examples: sea stars, sea urchins, sea cucumbers.

• Basic Characteristics

• sessile or slow moving

• water vascular system: water is taken in by tube feet and passed through channels under pressure that aid in movement, feeding and gas exchange.

• Reproductive system: sexual where gametes are released into the water.

• It is the larvae of the echinoderms that possess the bilateral symmetry that relates them to the chordates.

Figure 33.38 Anatomy of a sea star

• Class Asteroidea (sea stars)

• Digestive system: turn stomach inside out, out through its mouth and in-between the shells of its prey. Digestive juices are secreted / released into the shell of the clam.

• Regeneration of body parts and one genus can grow an entire body from a piece of an arm.

• Class Ophiuroidea (brittle stars)

• Digestive system: suspension feeders, scavengers.

• Class Echinoidea (sea urchins and sand dollars)

• muscles move their spines around

• possess tube feet but no arms like sea stars

Figure 33.37 Echinoderms: Sea star (top left), brittle star (top right), sea urchin (bottom left), sea lily

(bottom right),

Phylum Chordata

• Include invertebrates such as the sea squirts, lancelet and the vertebrates (fish, amphibians, reptiles, birds, mammals)

•Once again, the grouping of echinoderms such as sea stars with humans into the phylum chordata is due to their similarity in embryonic development.