Zoology

 Benefits of multicellularity

Bigger size, specialization of cells, complex reproductive strategies for genetic diversity, systems 

·       Choanoflagellates and metazoans (evidence for and against common ancestry)

Choanoflagellates- single celled protists with a flagellum and microvilli around it

Metazoans- multicellular animals with tissues and organs

Phylum Porifera – sessile, filter-feeding, aquatic

o   why is their evolution puzzling? (compare evidence for poriferans with evidence for ctenophores as the earliest multicellular animal)

Ctenophores (comb jellies) could be the first multicellular animals bc of nervous and muscle systems. Poriferans (sponges) cellular differentiation choanocytes are similar to choanoflagellates, who share a common ancestor w animals

o   General flow of water through a sponge (in ostia > spongocoel > out osculum)

 Water enters through pores (Ostia), then spongocoel (central cavity), choanocytes pull water and trap food particles, exits through osculum.

o   Organized at the cellular level, specialized cells include (what is their function and where are they located?):

–         Choanocytes- filter feeding and creating water current. In the inner chambers lining spongocoel

–         Pinacocyte- epithelial cells that contract and control size of Ostia. Outer surface of sponge protective layer

–         Archaeocyte- can differentiate functions, nutrient transport, digestion, repair, reproduction. Located in the mesohyl 

o   Mesohyl (what is it, what does it contain)

Gelatinous non-cellular layer between the 2 main cell layers of sponge. Contains archaeocytes, spongin, spicules, collagen, water channels. 

o   Spicules/spongin

 Spicules- rigid needle like structures forms skeleton. Made of silica/calcium carbonate

Spongin- flexible fibrous protein forms flexible skeleton. Made of collagen. Found in Demospongiae (think of bath sponge) 

o   Reproduction – asexual (budding, fragmentation, gemmules) and sexual

Budding- small part of parent grows out until it breaks off and becomes new ind. 

Fragmentation- part of sponge breaks off and broken piece grows into new sponge. 

Gemmules- dormant asexual reproductive bodies that are released into the water under unfavorable conditions. Mass of archaeocytes surrounded by spicules. Common in freshwater sponges (demospongiae) 

Sexual reproduction: most hermaphrodites, external sperm released into water and carried to another sponge to fertilize an egg. Has free swimming larva 

o   Ecological roles

Filter feeding and filtration, habitat creation and structural support. Symbiotic interactions, nutrient cycling, biodiversity indicators

o   Sponge body plans:

–         Asconoid: simple sac like structure. Spongocoel central cavity. Filters not efficiently 

–         Syconoid: tubular shape with central spongocoel, inner surface is folded forms radial canals

–         Leuconoid: most complex. Series of incurrent canals into choanocyte chambers then exits excurrent canals. Filters more efficiently 

o   Know sponge taxonomy and defining characteristics of each group (what type of spicules, where do they live, what is their body plans, etc):

–         Class Hexactinellida “glass sponges”

Silica 6 rayed large spicules, syconoid or leuconoid (mostly leuconoid). Found in deep marine environments. Gelatinous transparent look and lack developed mesohyl. Kind of looks like gauze

–         Class Demospongiae “bath sponges”

Silica or spongin, sometimes just spongin. Leuconoid body plan. Freshwater and marine. Spongilla-freshwater sponges. Euspongia-bath sponges

–         Class Calcarea/Calcispongiae “Calcareous sponges” 

Calcium carbonate spicules. Any body plan, asconoid less often. Marine. Simple body structure. Looks like coral

–         Class Homoscleromorpha

Spicules silica if present, small or absent. Rod like spicules. Leuconoid body plan. Distinct epithelial layer with basal membrane. Marine environments shallow water.

Phylum Placozoa defining characteristics

Free living non-parasitic marine invertebrates. Simple body plan, 3 epithelial layers, cilia movement. Feeds by phagocytosis, primarily asexual reproduction

Phylum Cnidaria – aquatic, radial symmetry. Jellies, corals, sea anemone, hydra

o   Organized at the tissue level – how many germ tissues do they have and what are they? 

2 germ tissue layers, Ectoderm (outer) and Endoderm (inner). 

o   Dimorphic life cycle – polyp vs. medusa

Polyp- sessile stage. Has tentacles and basal end attached to substrate. Asexual, budding (hydra, sea anemone, coral)

Medusa- motile stage. Umbrella like body with tentacles hanging downward. Free-swimming and sexual w gametes (Jellyfish and some hydrozoans)

o   General life cycle and variations (compare Scyphozoa to Hydrozoa)

 Scyphozoa (True Jellyfish): Medusa stage, asexual budding of medusa. 

Hydrozoa (Portugese man-o-war): Polyp stage colonial, small medusa. 

o   Body plan

 Radial symmetry, Polyp and Medusa, Ectoderm (epidermis) endoderm (gastrodermis) mesoglea. Nematocysts stinging cells.  

–         Mesoglea

Gelatinous layer between 2 layers, thicker in medusa. 

–         Epitheliomuscular cells

Epidermis, covering and muscular functions. Contractile fibers enable movement. Polyp expansion/contraction and medusa pulsations for swimming. 

–         Nerve net

Decentralized nervous system, composed of connected nerve cells for reflexes and coordination. Maybe 2 in medusa

–         Rhopalia (with ocelli and statocyst) in Scyphozoa and Cubozoa

Rhopalia: Specialized sensory structures along medusa bell. Ocelli: light intensity detecting organs. Statocysts: balancing organs to keep upright position. 

–         Cnidocytes (cells) with nematocysts (organelle)

·       Cnidocil = hair like sensory trigger causes nematocysts to discharge

Cnidocytes- specialized stinging cells mainly on tentacles. Each cnidocyte has a nematocyst, a harpoon-like venomous organelle. Prey capture, defense

o   Feeding

Carnivorous, uses tentacles with cnidocytes to catch prey. Gastrovascular cavity secretes digestive enzymes, gastrodermal cells phagocytosis. GVC distributes nutrients to all body parts. Waste removal through same opening mouth/anus.

o   Mutualistic relationships (know at least 1 example and how each organism benefits)

Sea anemone and clownfish. Clownfish get protection and habitat, anemone gets food scraps and parasite removal. 

o   Know cnidarian taxonomy and defining characteristics of each group (what part of the dimorphic life cycle is dominant in each class, which are colonial, etc.)

–        Class Hydrozoa: Hydroids, fire corals, and Portuguese man-of-war

Polyp dominant. Colonial, has velum (tissue ring for movement), marine and freshwater species. Asexual via budding. Medusa produce gametes

·       Polymorphism + zooids (don’t need to know the names of the different zooids, just that some colonial hydrozoans contain polyps each with specialized functions like eating or reproducing)

·       Portugese man-of-war; pneumatophore (what is it) roots

·       Velum

–         Class Scyphozoa: True jellyfishes

Medusa stage dominant. Has thick mesoglea instead of velum. Solitary not colonial. Rhopalia with ocelli and statocysts. Medusa sexually larva, settles and forms polyp, asexual budding

·       Ephyra

·       No velum

–         Class Cubozoa: Cube or box jellyfishes

Medusa dominant but box shaped bells. Highly venomous, complex eyes. Rhopalia w/ ocelli and statocysts. Medusa sexually, forms polyp, directly transforms to single medusa. 

·       Chironex fleckeri

Australian Box Jellyfish, 1 of most venomous marine animals. Complex eyes. Thousands of nematocysts. 

·       Rhopalia, ocelli, eyes with cornea and lenses

–         Class Anthozoa: Largest class; includes stony corals and sea anemones (Hexacorallia), and soft corals (Octocorallia) (Corals, anemone, sea fans)

Polyp stage only. Exclusively marine, colonial or solitary. Mutualistic w/ zooxanthellae. Asexual budding/fragmentation and sexual/gametes Larvae settle to form new polyps.

·       Reefs, ecological significance

·       Zooxanthellae

o   Dangerous jellies! Be able to compare the sea wasp (Chironex fleckeri) to the Portugese man-of-war (Physalia physalia) – including what class each belongs to – and be able to explain which is more dangerous to humans

Chironex fleckeri (Sea Wasp)- Cubozoa, true jelly, most venomous jellyfish. 

Physalia physalis (Portugese M-O-W)- Hydrozoa, colonial organism, painful but rarely fatal. 

Phylum Ctenophora – defining features, including comb rows, biradial symmetry

Gelatinous marine, 8 rows of cilia “comb rows” for locomotion. Radial + bilateral- biradial. Hermaphroditic, most are transparent  

o   diploblasts: endoderm and ectoderm 

o   Feeding + Colloblasts

Carnivorous on zooplankton crustaceans etc. Colloblasts- specialized sticky cells on tentacles. Touch prey, burst open, sticky substance traps prey. Tentacles retracts brings food to mouth. 

o   Sensory/Statocysts

Lack brain, has nerve net and specialized sensory structures. Statocyst- balancing organ. Has statolith on ring of cilia. Animal tilts and statolith shifts 

Phylum Platyhelminthes (Flatworms) 

·       Bilateral symmetry- left and right side

·       Cephalization- concentrated sensory organs at anterior head region

·       Protostome- blastopore becomes mouth. Spiral cleavage, determinate cell fate

·       Triploblastic- three germ layers (ecto, meso, endo) 

o   Acoelomate body plan (compare this to pseudocoelomate and coelomate)

No body cavity, solid mesoderm filled. Pseudocoelomate- body cavity, not fully lined by mesoderm. Coelomate- body cavity fully lined by mesoderm. 

·       Belong to clade Lophotrochozoa

o   Do not possess lophophore (U-shaped tentacle structure)

o   Some (especially marine) possess trochophore larvae

·       Clade Neodermata: three parasitic classes have syncytial tegument, called a neodermis. Specialized outer body covering. Replaces larval epidermis when parasite inside host. 

Tapeworms (Cestoda) absorb nutrients across tegument. 

·       Free-living (i.e., Turbellaria) have ciliated epidermis

·       General nervous system/nerve ladder: centralized nervous system. Brain at head, 2 longitudinal nerve cords, ladder like structure. 

o   Cephalization at anterior end. Directional movement

o   Ocelli (only in Turbellaria, Monogenea, and juvenile Trematoda – why don’t other groups have these?)

Simple photoreceptors that detect light intensity. Moves away from bright light. Flukes and tapeworms live in hosts with no light. 

o   Auricles (Turbellaria)- chemosensory and mechanosensory projections on sides of head. (little guy in lab) 

o   Reproduction (sexual and asexual), most monoecious (hermaphroditic)- turbellians by fission. Others internal/cross fertilization 

·       Excretion: Flame cells- excretory cells remove water and waste. Has cilia create current to excrete waste.

Protonephridia: excretory system made of tubules. 

·       Know Platyhelminth taxonomy and defining characteristics of each group (which classes are endoparasites, which are ectoparasites, which are free-living, which have digestive systems, which have eyespots/ocelli, for parasitic groups know how they attach to host, etc.)

Platyhelminthes- Free-living and parasitic flatworms. 

o   Class Turbellaria ex. Planaria, marine flatworms w vibrant colors. 

Free living, non-parasitic in terrestrial environments. Clitellum for ciliary gliding. Ocelli for light. 

§  auricles- chemosensory organs to detect food.

o   Class Monogenea- Ectoparasite on fish gills and skin

External attachment. Simple life cycle, no true digestive system-absorbs from host. No ocelli since parasite. 

Opisthaptor- attachment organ with hooks and suckers

o   Class Trematoda (Flukes- endoparasites of vertebrates)

Inside intestines, liver, blood of host. Has digestive system, no ocelli. Oral sucker around mouth and ventral sucker to anchor to host tissues. Complex life cycle w/ multiple hosts. Large number of eggs resistant tegument. 

o   Class Cestoda (Tapeworms- endoparasites of vertebrate intestine) 

Lacks digestive system, absorbs from host through tegument. No ocelli. Scolex (head region) has hooks and suckers. Proglottids- segments filled w/ repro organs break off release eggs. Intermediate host 

Lophotrochozoans (Clade of Protostomia)

·       Lophophore  – what is it, what is it used for, which phyla have it?

Ciliated U-shaped or circular feeding structure surrounding mouth. Filter feeding and respiration. Phoronida, Brachiopoda, Bryozoa. No trochophore larvae.

All lophophorates are lophotrochozoans, but not all lophotrochozoans are lophophorates.

Phylum Mollusca

·       Economics of molluscs (why important?)

Harvested for human consumption and pearls, shells. Filter feeders improve water quality

·       What is adaptive radiation and how do molluscs exhibit this?

Single ancestral group rapidly diversifies into many species. Diversify into various habitats and evolved distinct body forms. 

·       Explain how molluscs fit within clade Lophotrochozoa. What other groups are lophotrochozoans?

Lophotrochozoa because trochophore larvae. Annelida, Platyhelminthes, Lophophorates.

Mollusca Characteristics:

coelomate protostomes (blastopore becomes mouth), fully lined with mesoderm. spiral cleavage, determinate, trochophore larva

o   Where do they live? What do they eat? How big are they?

Marine, freshwater, terrestrial environments. Herbivores filter feeders. Tiny to giant. 

o   common features (know how these are modified within the different classes): which part secretes the shell?

–         Radula- scraper tooth, absent in bivalves. 

–         muscular foot- movement, burrow, attachment. Tentacles in cephalopods, digging in bivalves, gastropods crawl

–         mantle- secretes calcium carbonate to form a shell. Highly developed cephalopods (siphon)

–         shell- provides protection/support. Reduced or absent in cephalopods, thick in bivalves.

·       Respiration: ctenidia (gills) in mantle. Creates water currents. Not in gastropods, they use lungs. Jet propulsion in Cephalopods. 

·       Circulation: open circulatory system. Flows freely through cavity.

·       Digestion: Gastropods: radula. Bivalves: gills (ctendia) then moved by cilia. Cephalopoda: tentacles, jaws, radula, digestive gland. Polyplacophora: radula. Scaphopoda: Tentacle like captacula, no stomach. 

·       Excretion/Osmoregulation: paired metanephridia- tube like excretory organs. open into coelom. Marine and freshwater- ammonia, terrestrial- uric acid. 

·       Nervous/sensory: Paired cerebreal ganglia “brain”. Ventral nerve cords. Cephlapoda highly advanced large brain, image forming eyes. Gastropoda: some simple eyes. Bivalvia- no cephalization, sensory organs. Polyplaco and scaphopoda: simple no brain. 

 pairs of ganglia, ventral nerve cords (usually simpler than annelids and arthropods, cephalopods are major exception) Sensory organs highly specialized

·       Reproduction – know general life cycle and how differs across classes

Dioecious (separate sexes), gastropods hermaphroditic. Indirect development with larval stages (trochophore then veliger then juvenile) 

Trochophore: Free swimming ciliated larva dispersed in water. Most molluscs. Veliger larva more developed, early foot shell mantle. Gastropods and bivalves. Cephalopods no larvae. lay eggs, direct development. Polyplacophora no veliger. 

·       Know the following classes of molluscs, their characteristics, and adaptations to the general mollusc features:

o   Polyplacophora (Chiton -segmented shell) 

8 interlocking dorsal plates. Broad foot and radula. Mantle around shell. 

o   Monoplacophora (Deep sea shells) 

Single, cap-like shell. Multiple pairs of gills, nephridia (kidney) muscles. 

o   Gastropoda (Snails, slugs, limpets, nudibranchs) 

Radula, well developed head

–         Prosobranchs (sea snails)

Marine gastropods with gills, coiled shell. Operculum seals shell. 

–         Opisthobranchs (nudibranchs, sea hares, sea butterflies)

Lost or reduced shell. Dorsal protection for respiration and defense. 

–         Pulmonates (mostly terrestrial snails and slugs)

Lungs instead of gills. No operculum. 

o   Bivalvia (clams, mussels, oysters)

Two-part hinged shell, no head or radula, ctenidia for filter feeding and respiration. Foot modified for burrowing.  

–         Glochidium larva (Freshwater bivalves). A specialized larval stage parasitic on fish gills or fins. Dispersal method. 

o   Scaphopoda (Tusk shells) 

Tubular tapering shell resembles tusk. Burrows, no gills only mantle gas exchange. Captacula- tentacle like structures to capture food. Radula present.

o   Cephalopoda (squid, octopus)

Highly intelligent, well developed nervous system. Closed circulatory system, tentacles, mantle into siphon, image forming eyes but flipped from vertebrates. Chromatophores for rapid color change. 

–         Subclass Nautiloidea

Only cephalopod with external shell, divided into chambers, simple eyes and lots of tentacles. 

–         Subclass Ammonoidea

Spiral extinct marine cephalopods. Related to modern ones. Fossils used for dating rock.

–         Subclass Coleoidea (squid, octopus, cuttlefish)

Shell reduced or absent (cuttlefish cuttlebone). Highly advanced nervous system. Most complex cephalopods. 

Phylum Annelida (segmented worms)

·       Metamerism- true segmentation. Body is divided into repeating units, each with structures nerves nephridia and muscles. Efficient movement, specialization. 

·       Explain how annelids fit within clade Lophotrochozoa. What other groups are lophotrochozoans? Annelids have trochophore larvae, spiral cleavage. Others: mollusca, platyhelminthes. 

·       Characteristics: coelomate protostomes, spiral cleavage, trochophore larva (in marine annelids) 

o   Found in marine, freshwater, terrestrial environments. Filter feeders, scavengers. Range from 1 mm to 3 meters. 

o   common features (know how these are modified within the different classes):

§  metameres/segments: annuli- external grooves marking segmentation. Segments separated by septa

§  chaetae (aka setae): bristle like structures for movement. Reduced in leeches, large in parapodia. 

§  prostomium: Head-like lobe before mouth. Contains sensory organs. Peristomium: First true segment, contains mouth. Pygidium: terminal segment, contains anus. New segments form near here. 

·       Digestive: complete and specialized. Earthworms digest soil for nutrients, leeches specialized (bloodsucking or predation) 

·       Circulation: closed, dorsal and ventral blood vessels connected by segmental hearts. Hemoglobin in blood. 

·       Nervous: cerebral ganglia (“brain”), ventral nerve cord with ganglia in each segment

·       Respiration: diffusion. No specialized respiratory organs. Oxygen diffuses across moist body surface. 

·       Know the following classes of annelids, their characteristics, and adaptations to the general annelid features:

§  Class Polychaeta (Marine Bristle Worms)

Parapodia (bristle bearing appendages used for locomotion, sensation, respiration. Well developed sensory organs, dioecious, trochophore larvae. 

reproduction + epitoke

Epitoky- reproductive ind. (epitoke) detaches and swims to the surface for external fertilization. 

§  Class Clitellata (clitellum, sense organs)

No parapodia. Clitellum: secretes mucus for cocoon formation (reproduction). Hermaphroditic via cross-fertilization. 

·       Oligochaetes/Earthworms

Few, small chaetae (bristles) for locomotion. Deposit feeders/ingest soil digest OM. 

·       Hirunidea/Leeches

Segmented (not internally). Suckers on both ends for attachment. No chaetae or parapodia. Some bloodsuckers, other predators. Uses anticoagulants (hirudin) to keep blood flowing.