Zoology Quiz 2

Two key changes in bilateral symmetry

Polarity development and centralization of sensory cells/organs

Cephalization

Centralization of sensory cells/organs

Flatworms

First bilateral and triploblastic animals (true mesoderm appears)

Rhabdites (Rhabdoids)

Rod-like structures, “mucus” producers, are unique and help to prevent desiccation and with locomotion

Feeding (planarians)

Incomplete gastrovascular system (no anus), intestine with diverticula

Excretion (planarians)

Occurs by diffusion and proto-nephridia

Flame cells (in proto-nephridia)

Filter and get rid of residuals- primitive kidneys

Reproduction (planarians)

Asexual or sexual reproduction

Asexual reproduction (planarians)

Occurs by binary fission, with high capacity of regeneration

Sexual reproduction (planarians)

Hermaphrodites with cross-fertilization capacity

Nervous system (planarians)

Ganglionar system with lateral nerve cords, concentration of organs (light sensitive ocelli on “head”)- primitive brain

Parasitism

Metabolism changes drastically as a result of life history

Adaptations to parasitism

High reproductive ability, ability to attach to the host, simplification or reduction of systems

High reproductive ability

High fertility, life cycle synchronized with host

Ability to attach to host

Holdfasts (suckers, hooks), resistance

Simplification or reduction of systems

No need for “independent metabolism”

Single-host parasites

One life phase in host + free-living phase

Multiple- host parasites

Different stages at different hosts + free-living phase

Intermediate host

The host with eggs or larval parasite

Final host

The host with the adult parasite

Diversity of flatworms

Turbellaria, monogenea, dignea trematoda, cestoda

Monogenea

Single host, low diversity, ectoparasites (on fish gills) attached by the opisthaptor

Opsithaptor

Attachment organ (external hooks) on mongenea

Digenea/ trematoda

Endoparasites with at least one intermediate host, attach to host by suckers

Digenea adaptation to parasitism

Epidermis modified to a syncytial tegument

Syncytial tegument

Cells fused with no membranes in between

Cestoda/ tapeworm

Endoparasites with at least one intermediate host, attached to host by scolex

When infected by cestoda

Removal of proglottids does not terminate the parasitic infection, only scolex removal does it

Gravid proglottid

Proglottid with uterine branches full of eggs

Limitation in flatworms

A solid parenchyma does not provide the best protection/ flexibility

Secondary cavity

Internal cavity surrounding the gut that provides a “tube inside a tube” arrangement of the body

Secondary cavity functions

• Filled with fluid: is an hydrostatic skeleton

• Provides room for organs

• Provides cushion / protection to organs

  • Provides a medium for gas diffusion

Acoelomates

Animals that lack a secondary cavity, the space between ecto- and endo-derm is filled with a mesodermal parenchyma. 1 phylum: flatworms

Pseudocoelomate

Animals with a secondary cavity that is not entirely lined with mesoderm- mesoderm doesn’t cover endoderm. 8 Phyla: roundworms

Coelomates (eucoelomates)

Animals with a true coelom between endoderm and ectoderm. This coelom is fully lined with mesoderm. Lots of phyla: all other bilateral animals

Characteristics of pseudo-coelomate phyla

• Most of them have a pseudo-coelom

• Most of them have an external cuticle

• Most of them have adhesive glands

Pseudo-coelomates phyla

Nematodes, Rotifera, Gastrotricha, Entoprocta, Nematomorpha, Kinorhyncha, Priapulida, Loricifera

Nematodes

Round- or thread-worms, cylindrical with thick cuticle and a pseudo-coelom visible at adult stage

Digestive system (nematoda)

Open- has an anus

Excretion (nematoda)

Occurs by diffusion and excretory ducts, No proto-nephridia

Nervous system (nematoda)

Some cephalization; with nerve ring (brain ganglia) and dorsal and ventral cords

Ascaris lumbricoides

1 host parasite of human small intestine- 25% of humans infected

Trichinella spirallis

Multiple host parasite, adults colonize intestine and newborns migrate through the blood to colonize other organs

Intermediate host (Trichinella spirallis)

Pigs, dogs, cats, rats, etc

Definitive host (Trichinella spirallis)

Humans and other predators

Pattern of clevage

The way mitosis proceeds form a single cell (egg) to a hollow ball of many cells (blastula)

Radial cleavage

Uniform division ending in symmetric blastomeres

Spiral cleavage

Non-uniform division ending in asymmetric blastomeres

Entero-coelous coelom formation

By formation of mesodermal pouches

Schyzo-coelous coelom formation

By proliferation of mesoderm cells and subsequent split

Deuterostome orientation

Blastopore becomes anus, mouth develops after

Protostome orientation

Blastopore becomes mouth, anus develops after

Deuterostomes

Have radial cleavage, enterocoelus formation, and deuterostome orientation

Protostomes

Has spiral cleavage, schyzocoelus formation, and protostome orientation

Metameric body forms

Repetition of systems in each segment ~ 15,000 species

Feeding (annellids)

Complete digestive system- with anus, feeding strategy depends on life history

Excretion (annellids)

Occurs by metanephridia on each segment, they collect residuals from blood and dispose them directly outside

Nervous system (annellids)

Complexity depends on activity, dorsal brain and ventral cord, one ganglion per segment

Diversity of annellids

Earthworms, leeches, and marine worms

Class oligochaeta (earthworms)

Less diverse, few setae, lack parpodia- simple prostomium. No visible sensory organs, uniform segments

Food capture (earthworms)

All deposit feeders, no proboscis/jaws/palps, etc

Reproduction (earthworms)

Hermaphroditic species- they practice cross-copoulation. Gonads in clitellum, a cocoon with eggs is formed

Class hyrudinea (leeches)

No setae, low diversity, predatory or ectoparasites

Segmentation (leeches)

Partially lost (external but not internal)

Food capture (leeches)

Use of suckers for attachment and then sucking of blood or tissues from hosts

Locomotion (leeches)

Suckers are also used for locomotion

Reproduction (leeches)

Hermaphroditic species, cross-copulation (internal), there is a clitellum and a cocoon

Class polychaeta (marine worms)

Have parapodia (un-jointed appendages), acicula (chitin rods) and setae

Mobility (marine worms)

Errant or sedentary

Errant

Move a lot

Sedentary

Move a little

Habitat classification (marine worms)

Pelagic or benthic

Pelagic

Live in water

Benthic

Live in the seafloor

Feeding mode (marine worms)

Suspension feeder, deposit feeders, predatory species

Suspension feeders

Filter water

Deposit feeders

Eat sediment

Predatory species

Proboscis with jaws

Sensory organs (marine worms)

Better developed in errant/predatory polychaetes. Typical organs include: palps, tentacles, eyespots, etc

Reproduction (marine worms)

External fertilization; separate sexes, no clitellum, trochophore larvae

Trochophore

Polychaeta larva

Sipuncula (peanut worms)

Deposit feeders, live in burrows and crevices, have one pair of nephridia. Trochophora larva

Echyura (spoon worms)

Deposit feeders, live in burrows and crevices, 1-3 pairs of nephridia. Trochophora larva

Pogonophora (beard worms)

Sessile organisms (live inside chitin tubes), with no digestive tube. Food comes from mutualism with bacteria and have a special type of metamerism

3 phyla related to polychaeta

Coelomate worms that apparently branched off before metaremism evolved and shaped annellidans

Molluscs

Protostomes, all derived from a worm-snail primitive form to include 7 families and at least 50,000 living species

Snail basic body plan

1. Shell

2. Mantle

3. Mantle cavity

4. Foot

Mollusc shell

Made of calcium carbonate with 3 layers: periostracum, prismatic layer, nacreous layer

Mollusc feeding

Open and complex digestive system, similar to others, except includes a unique structure called radula

Radula

A tonguelike organ with teeth in mollusks used for scraping- not present in bivalves

Mollusc Circulation

Open circulatory system, heart inside coelom

Mollusc Excretion

By Meta-nephridia or “kidney-like” organs

Mollusc excretion process

- Blood collects wastes

- They diffuse into coelom

- Meta-nephridia take them and place them in mantle cavity

Molluscs respiration

Depends on each Class, by gills or lungs located in the mantle cavity

Diversity of Molluscs

Bivalvia, gastropoda, cephalopoda, polyplacophora, monoplacophora, aplacophora, scaphopoda

Bivalvia evolution

1. Shell grows and cover body

2. Compresses laterally

3. Becomes hinged

4. Head shrinks/organs re-arrange

5. Foot becomes a “blade”

Bivalvia

Clams mussels, and scallops. 30,000 species, marine and freshwater. Burrower or sedentary, live in soft- or hard- bottoms. Very important economically

Feeding in bivalves

Deposit or suspension feeders, no radula

Deposit feeders bivalves

Mouth faces down, mantle cavity faces up, some adopt siphons + feeding tentacles. “Eat” sediment, they process the seafloor

Suspension feeders bivalves

Gills filter water and retain food, extensive use of siphons, they increase water clarity, some are ecosystem engineers