Chapter 30: Protostome Animals

Protostome characteristics

- triploblastic

- bilateral symmetry

- mouth forms first

2 major derived traits of protostomes

•Anterior brain that surrounds the entrance to the digestive tract

•Ventral nervous system with paired or fused longitudinal nerve cords

2 clades of protostomes

- lophotrochozoans

- ecdysozoans

lophotrochozoans

derive their name from having a trochophore larva and a lophophore

- bryozoans, entoprocts, brachiopods, phoronids

- some (flatworms, ribbon worms, annelids, mollusks) have spiral cleavage

lophophore

- U-shaped ring of hollow ciliated tentacles around the mouth

- functions in food collections

- almost all animals with this are sessile as adults

Ecdysozoans

- have external cuticle secreted by epidermis

Ecdysozoans cuticle

- purpose: protection & support

- to grow, cuticle must be shed and replaced with a larger one (ecdysis)

cuticle in arthropods

- exoskeleton thickened by proteins and chitin

- waterproof polysaccharide

- restricts movement and gas exchange

arthropod movement

evolution of appendages

appendages of arthropods

- movement

- food capture

- gas exchange

- copulation

- sensory perception

- hard exoskeleton allowed for walking on dry land and not drying

arrow worms controversy

- 180 species

- evolutionary relationships debated because not lophotrochozoans because no trochophore larva

- blastopore gives rise to anal opening which would say they are deuterostomes

- ventral nerve cord and spiral cleavage which would say they are protostomes

- THEY ARE PROTOSTOMES

arrow worms

- transparent

- head, trunk, tail

- most swim in open sea, others live on sea floor

- diffusion: gas exchange and waste excretion

- no circulatory system: wastes and nutrients moved by cilia that line coelom

- predators of planktonic organisms

hermaphroditic

- each individual produces both male and female gametes

arrow worms larva stage

- no larva stage: mini adults hatch from eggs

Bryozoans and Entoprocts

- colonial

- external body walls secrete material that forms a "house"

- most are marine

Bryozoan colony

- individuals are small, connected by strands of tissue

- individuals may be specialized for feeding, reproduction, defense, or support

- colonies formed asexually but can be sexual or asexual reproduction

sexual reproduction

sperm released into water and carried to another individual

•Eggs are fertilized and brooded internally, then larvae are released to find new attachment sites.

Bryozoans vs Entoprocts

Anus location

- Bryozoans- outside ring of tentacles/lophophore

- entoprocts- center of ring of tentacles/lophophore

Food particles movement

- Bryozoans- tip to base of tentacles

- Entoprocts- base to tip of tentacles

Coelem

- Bryozoans- three-part coelom

- Entoprocts- acoelomate

flatworms

•Dorsoventrally flattened; no gas transport system, so every cell must be near the surface --> diffusion

•Free-living flatworms have cephalization and glide over surfaces by broad bands of cilia.

flatworms digestion

•Digestive tract: mouth opens into a blind gut, often highly branched, which increases surface area for absorption of nutrients.

endoparasite examples

tapeworms and flukes

- hermaphrodites

- energy put into reproduction

flat worm hosts in complex life cycles

- snails

- mammals

Rotifers

mostly in fresh water.

•Tiny (50-500 mm), but have specialized internal organs and a complete gut.

•Body cavity is a pseudocoel that functions as a hydrostatic skeleton, but most propel themselves by cilia.

corona

ciliated organ on the head

corona function

- beating cilia sweep food particles into the mouth and into the mastax

- an organ that grinds the food

ribbon worms

1200 species.

•The rhynchocoel (a fluid filled cavity) contains a hollow, muscular proboscis.

•Muscle contractions expel the proboscis explosively from an anterior pore. It may be armed with sharp stylets to pierce prey and release toxins.

•Most are small; some may be up to 20 meters long.

brachiopods

-solitary marine animals with two-part shells connected by a ligament

- 2 halves of the shell are dorsal and ventral

- live attached to a substrate

- feed using lophophores

annelids

- clearly segmented

- septae separates coelom in each segment

- separate nerve ganglion controls each segment

- most have thin permeable body wall

annelids habitats

aquatic or moist

thin permeable wall of annelids function

gas exchange

2 major annelid groups

- polychaetes (many hair) and clitellates

pogonophorans

group of polychaetes

2 groups of clitellates

- oligochaetes (few hair)

- leeches

polychaetes

- mostly marine

- burrow in soft sediments

- have one or more pairs of tentacles for prey capture or filter feeding

- parapodia on each segment

- setae

parapodia in polychaetes

- gas exchange and sometimes for movement

setae in polychaetes

- stiff bristles

- protrude from parapodia

- provides grip

pogonophorans

- tube worms

- hemoglobin in tentacles imparts red color

tube worms with pogonophorans

- live near deep hydrothermal vents

- live in tubes made of chitin

pogonophorans acquisition of nutrition

- dissolved organic matter

- have endosymbiotic bacteria in a trophosome --> bacteria fix carbon using energy oxidation of H2S

clitellates

- oligochaetes and leeches

- earthworms burrow in and ingest soil

oligochaetes

- oligochaetes have no parapodia, eyes, tentacles, and few setae

- oligochaetes are hermaphroditic

leeches

- lack parapodia and tentacles

- no segmentation

- segments forms suckers on each side

- freshwater and terrestrial

- ectoparasites

- make incision in host and secrete anticoagulant

Suckers in leeches

- temporary anchors that aid in movement

mollusks 3 main components

foot, visceral mass, mantle

foot of mollusk

- large

- muscular structure

- locomotion and support of internal organs - has been modified in diff groups

visceral mass of mollusks

heart, digestive, excretory, and reproductive organs

mantle of mollusks

- Fold of tissue that covers organs in the visceral mass; secretes the calcareous shell.

- Extends beyond the visceral mass to form the mantle cavity. Contains gills for gas exchange.

4 major clades of living mollusks

- chitons

- gastropods

- bivalves

- cephalopods

chitons

- 8 overlapping calcareous plates surrounded by girdle

- scrape algae and organisms from rocks with radulla

- cling with large foot

chitons calcareous plates function

protection of organs and muscular foot

gastropods

- snails

- slugs

- naudibranchs

- limpets

- abalones

gastropods movement

- gliding on foot but in a few species it is a swimming organ

naudibranchs and slugs

- lost shells

- can be toxic and have strong colors for warning (aposematic coloration)

- or camouflaged

mollusks in terrestrial habitats

- land snails & slugs

- mantle issue modified into highly vascularized lung

bivalves

- clams

- oysters

-scallops

- mussels

bivalves structure

-hinged, two-part shells

- many use foot to burrow into mud or sand

bivalves feeding

- bring water in the incurrent siphon

- filter food particles with large gills

- water exits through excument siphon

cephalopods

- squids

- octopuses

- nautiluses

cephalopods

- high degree of mobility: water can be forcibly ejected from body cavity "jet propulsion"

- head has complex sensory organs

- eyes are comparable to vertebrates

- arms and/or tentacles used for movement and prey capture

early cephalopods

- chambered shells

- living species: nautilus

octopuses

- lost shells

- allow them to pass through small openings

- developed nervous system & brain of non-vertebrates

2 types of ecdysozoans

- worm like- limbless

- limbed

limbless ecdysozoans

nematodes

limbed ecdysozoans

- tardigrades

- velvet worms

- arthropods

nematodes

- roundworms

- unsegmented

- thick, multilayered cuticle

- gas and nutrient exchange occurs through cuticle and gut wall

- 1 cell thick

- microscopic

pharynx in nematodes

- muscular anterior organ

- moves material through gut

mode of nutrition among nematodes

- scavengers

- predators

- parasites

nematodes in humans cause...

- trichinosis

- elephantiasis

model organism in genetics

Caenorhabitis elegans

- easy to cultivate

- matures in 3 days

- has a fixed number of body cells

- genome completely sequenced

arthropods

ecdysozoans with limbs

- paired, jointed appendages

4 major arthropod groups

- chelicerates: spiders and scorpions

-myriopods: millipedes and centipedes

- crustaceans: shrimps, crabs, and barnacles

- hexapods: insects

mandibulates

- myriopods

- crustaceans

- hexapods

- mandibles used for chewing, biting, holding food and sensory antennae

tardigrades and velvet worms

- unjointed appendages

trilobites

anthropod ancestors

- abundant fossil record

- jointed legs appeared in trilobites

chelicerates

- sea spiders, horseshoe crabs, arachnids

- head has 2 pairs of appendages modified into mouthparts (chelicerae)

two-part body of chelicerates

- cephalothorax

- abdomen

horseshoe crabs

- changed very little over their evolutionary history - example of living fossil

- common shallow marine waters along eastern North America and Asia

- come into intertidal zone in large numbers to mate and lay eggs

arachnids

- spiders, scorpions, harvestmen, mites, and ticks

- simple life cycle: mini adults hatch from eggs and begin independent life

mites and ticks

parasites of plants and animals

spiders and predators

- chelicerae inject venom into prey

- some have excellent vision for prey capture

- others spin elaborate webs to snare prey

myriapods (centipedes and millipedes)

- head and a long, flexible trunk with many pairs of legs

- centipedes: 1 pair of legs per segment

- millipedes: 2 pairs of legs per segment

crustaceans

- decapods: shrimps, lobsters, crayfishes, and crab

- isopods: pill bugs

- other groups: amphipods, ostracods, branchiopods, copepods, barnacles

crustaceans structures

- 3 body regions: head, thorax, abdomen

- head segments: fused and 5 pairs of appendages

- thoracic and abdominal segment: 1 pair of appendages each

hexapods

- 6 legs

- insects & wingless relatives of insects

- limbs in insects are in thoracic region

insect body plan

- head: 1 pair of antennae

- thorax: 3 pairs of legs and 2 sets of wings in most groups

- abdomen: no appendages

metamorphosis

- substantial physical changes occur between life stages

- indirect development

indirect metamorphosis

- changes are gradual

- ex) grasshoppers and roaches

complete metamorphosis

- changes are dramatic

- ex) butterflies