33-16-05 barb. copyright © 2002 pearson education, inc., publishing as benjamin cummings teeth of...

33-16-05

Barb

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Teeth of radula-the hardest material

(magnetite) of biological origin

• Most mollusks have separate sexes– However, many snails are outcrossing

hermaphrodites.

• The life cycle of many marine mollusks includes a ciliated larvae, the trophophore.– This larva is also found in marine annelids

(segmented worms) and

some other lophotrochozoans.


Fig. 32.9A trochophore larva.

• The basic molluscan body plan has evolved in various ways in the eight classes of the phylum.– The four most

prominent are the Polyplacophora (chitons), Gastropoda (snails and slugs), Bivalvia (clams, oysters, and other bivalves), and Cephalopoda (squids, octopuses, and nautiluses).


• Marine; oval shapes and shells divided into eight dorsal plates.

• Muscular foot grips the rocky substrate tightly and creep.

• Grazers; use radulas to scrape and ingest algae.


Fig. 33.17

Polyplacophora - chitons

• Gastropoda - > 40,000 species; mostly marine, but also many freshwater species.– Garden snails and slugs have adapted to land.

• Distinctive characteristic - During embryonic development, gastropods undergo torsion in which the visceral mass is rotated up to 180 degrees, such that the anus and mantle cavity are above the head in adults.


Fig. 33.18

Diagrammatic Illustration of Torsion in Gastropod Molluscs

• Most gastropods are protected by single, spiraled shells into which the animals can retreat if threatened.– Other species have lost their shells entirely and may

have chemical defenses against predators (nematocysts from anemones).


Fig. 33.19

Shell-less nudibranchs(sea slugs)

• Many gastropods have distinct heads with eyes at the tips of tentacles.


Conch

• Gastropods are among the few invertebrate groups to have successfully populated the land.

• In place of the gills found in most aquatic gastropods, the lining of the mantle cavity of terrestrial snails functions as a lung – pulmonate snails


• Class Bivalvia -- clams, oysters, mussels, and scallops.

• Bivalves have shells divided into two halves.– The two parts are hinged at the mid-dorsal line, and

powerful adductor muscles close the shell tightly to protect the animal.

– When the shell is open, the bivalve may extend its hatchet-shaped foot for digging or anchoring.


Fig. 33.20

• The mantle cavity of a bivalve contains gills that are used for feeding and gas exchange.

• Most bivalves are suspension feeders, trapping fine particles in mucus that coats the gills.– Cilia convey the

particles to the mouth.– Water flows into mantle

cavity via the incurrent siphon, passes over the gills, and exits via the excurrent siphon.


Fig. 33.21

• Cephalopods - rapid movements to dart toward their prey which they capture with several long tentacles. – Squids and octopuses use beaklike jaws to bite their

prey and then inject poison to immobilize the victim.

• A mantle covers the visceral mass; shell is reduced and internal in squids, missing in many octopi. Onlynautilus has externalshell.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 33.22

• Fast movements by a squid occur when it contracts its mantle cavity and fires a stream of water through the excurrent siphon.– By pointing the siphon in different directions, the

squid can rapidly move in different directions.

• The foot of a cephalopod (“head foot”) has been modified into the muscular siphon and parts of the tentacles and head.


• Unique among mollusks, cephalopods have a closed circulatory system to facilitate the movements of gases, fuels, and wastes through the body.

• They have a well-developed nervous system with a complex brain and well-developed sense organs.– This supports learning and complex behavior.– Squid giant axon located on inside of mantel.

Innervates mantel and causes large contraction leading to forcing a jet of water through syphon.

– Giant axon used as model axon to work out the biophysics of nerve conduction. Large size electrode could be inserted directly into nerve.


• Highly developed eye in cephalopods


• All annelids (“little rings”) have segmented bodies.

• ~ 15,000 species ranging in length from less than 1 mm to 3 m for the giant Australian earthworm.

• Annelids live in the sea, most freshwater habitats, and damp soil.

6. Phylum Annelida: Annelids are segmented worms


The phylum Annelida - three classes: Oligochaeta, Polychaeta, and Hirudinea.


• Oligochaete-

E.g. earthworm Coelom is partitioned by septa, but the digestive tract, longitudinal blood vessels, and nerve cords penetrate the septa and run the animal’s length.


Fig. 33.23

• Digestive system - a pharynx, an esophagus, crop, gizzard, and intestine.

• The closed circulatory system carries blood with oxygen-carrying hemoglobin through dorsal and ventral vessels connected by segmental vessels.

• In each segment is a pair of excretory tubes, metanephridia, that remove wastes from the blood and coelomic fluid.– Wastes are discharged through exterior pores.


• A brainlike pair of cerebral ganglia lie above and in front of the pharynx.

• Earthworms are cross-fertilizing hermaphrodites.– Two earthworms exchange sperm and then separate.

• Some earthworms can also reproduce asexually by fragmentation followed by regeneration.


• Polychaete - Each segment of a polychaete (“many setae”) has a pair of paddlelike or ridgelike parapodia (“almost feet”) that function in locomotion.– Each parapodium has several chitinous setae.– In many polychaetes, the

rich blood vessels in the parapodia function as gills.


Fig. 33.24b

• Most polychaetes are marine.

• Polychaetes include carnivores, scavengers, and planktivores. Many live in tubes with only the tentacles protruding from the tube.– The brightly colored

fanworms trap plankton on feathery tentacles.

– Many build tubes and

Thus called tube worms.


Fig. 33.24c

Chaetopterus

Scale Worms

• Some benthic polychaetes crawl around on the ocean bottom and are covered with large protective scales.

• Many leeches feed on other invertebrates, but some blood-sucking parasites feed by attaching temporarily to other animals, including humans.– Some parasitic species use bladelike

jaws to slit the host’s skin, while others secrete enzymes that digest a hole through the skin.

– The leech secretes hirudin, an anticoagulant, into the wound, allowing the leech to suck as much blood as it can hold.

– Medicinal use of leech.Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• Hirudinea - leeches.

Fig. 33.24d

Prostostomia: Ecdysozoa

Major Phyla:

1. Nematoda – round worms

2. Arthropoda – crabs, insects

spiders

• Undergo ecdysis shedding of exoskeleton.• Ecdysozoa grouping based mainly on molecular data.

Ecdysozoa - Introduction

• ~ 90,000 described species, and ~10x undescribed.• 1 mm to 1m - Ubiquitous habitats. Even in the extreme

cold soil of the Dry Valleys of Antarctica.• Many parasites, including human pathogens – elephantiasis, trichinosis, onchocerciasis (river blindness)

1. Phylum Nematoda

Scottnema lindsayae

(Antarctic soil)

Ascarislumbricoides

(human parasite)

Potato cyst nematode

Wuchereria bancrofti Wuchereria bancrofti Wuchereria bancrofti

Elephantiasis(Wuchereria

bancrofti)

http://www.ce.berkeley.edu/~nelson/ce210a/Ascaris/XF15-21.23.jpeg

Nematoda Characteristics• Cylindrical bodies, chitinous cuticle.• Complete digestive tract.• No circulatory system; use pseudocoelom fluid to

transport nutrients.• Their thrashing motion by

contraction of longitudinal muscles.

• Sexual reproduction.

Fig. 33.24d

Name the most famous nematode ? 3 shared 2002Nobel prize in medicine,

using this worm as a model system for studies in genetic regulation of organ development

and programmed cell death

Caenorhabditis elegans

+ hermaphrodite

Adult:

1090 cells

Programmed death 131 cells

959 cells

1179 cells

Programmed death 148 cells

1031 cells

At hatching: + hermaphrodite 558 cells

560 cells

The worm Noble laureatesm (2002):Sydney Brenner, H. Robert Horvitz, John E. Sulston

Berkeley MIT Sanger,UK

• ~ 1 billion billion (1018) individuals.• ~ 1 million arthropod species described ~67% of spp.• Ubiquitous habitats.• The diversity and success due to: body segmentation, a

hard exoskeleton, and jointed appendages specialization for functions.

2. Arthropoda:

Fig. 33.26

• Cuticle (exoskeleton) - protein and chitin:– thick and inflexible in some regions; protection.– thin and flexible in others; joints.– attachment points for muscles.– relatively impermeable to waterland habitats.– must molt (ecdysis) to grow danger of predation.

Arthropoda Characteristics

• Well-developed sense organs:– eyes, olfactory receptors, antennae.– cephalization; sense organs anterior.

• Open circulatory system.• Coelom much reduced.

• Respiratory system specialized for different habitat. • Aquatic species:

– External gills • Terrestrial species:

– Internal organs (book lungs in arachnids)– Tracheal system in insects.

Arthropod Respiration

(Crabs, lobsters, crayfish, shrimps)

TaditionalTaxonomy:

Phylum

Class:

Arachnida(spiders, scorpions,mites)

Diplopoda(millipedes)

Chilopoda(centipedes)

Insecta(insects)

Crustacea

Arthropoda

Trilobita(trilobites –extinct)

Chelicerata(jaw-like

chelicerae, no antennae, simple

eyes)

Alternate taxonomy:4 major lineages

Phylum:

Uniramia(jaw-like

mandibles, 1pair antennae,complex eyes)

Crustacea

Super-Phylum

Arthropoda

(jaw-like mandibles, 2 pairs antennae,

complex eyes)

• Trilobita

- Earliest arthropods.

- Cambrian (540 mya) to Permian. Extinct ~250 mya.

- Pronounced segmentation; uniform segments and

appendages

- Subsequent arthropod

evolution towards fewer, more specialized segments and appendages.

Fig. 33.27

• Chelicerata • Anterior cephalothorax, posterior abdomen.

– appendages more specialized than trilobites– most anterior appendages modified as chelicerae

(pincers or fangs).• Marine chelicerates – 4 species.

Sea spider

Horse shoe crab-living fossil

http://scilib.ucsd.edu/sio/nsf/fguide/arthropoda6.html

• Terrestrial chelicerates – majority in Arachnida.– Scorpions, spiders venomous predators– Ticks blood sucking parasites– Mites detritus eater; parasites of animals & plants

Fig. 33.29

scorpion mite

tick

http://geology.usgs.gov/postdoc/profiles/lyme-tick.jpg

• Arachnid characteristics

• Cephalothorax has 6 pairs of appendages. – 4 pairs of walking legs.– 1 pair pedipalps sensing or feeding.– Chelicerae usually for feeding. Glands contain

poison.– Spiders inject poison: immobilize preyspills digestive juices

on prey; sucks up liquid

meal.

Fig. 33.30x

• Spider Anatomy• book lungs - stacked plates large surface area for gas

exchange• Spider silk/web – unique prey capturing feature.

Fig. 33.30b

spider spinning cribellate net

Sticky silk

Wool-like cribellate silk

microcrystalline arrays of glycine-rich regions

beta-sheets ofalanine-rich regions

33-16-05 barb. copyright © 2002 pearson education, inc., publishing as benjamin cummings teeth of...

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