MINI EXAM 8 (Annelids and Mollusca)
What is a protostome?
During gastrulation, the first opening of the embryonic gut forms the MOUTH.
Lineage order of Annelids (broadest to most specific)
Eumetazoa--{____Bilateria--{___Protostomia--{____Lophotrochozoa--{_Annelida
The largest invertebrate (also largest mollusk) is _________________
Giant squid
What structure is used by a typical Bivalve to collect food out of the water?
Gills!
Which portion of a mollusc produces the shell?
Mantle (secretes calcium to make shell)
Annelid feeding summary
Many feeding modes: filter feeders, carnivores, herbivores, scavengers, deposit feeders (detritivores), blood-sucking parasites (leeches). Carnivores and herbivores often have a long, muscular, protrusible pharynx. Deposit and filter-feeding tube worms use ciliated tentacles coated with mucus to trap and transport food particles to the mouth
Annelids key innovation is metamerism. What is this?
Metameres are repeating body segments, often with similar internal structure. It allows for greater flexibility, compartmentalization, complexity, and larger size, leading to greater species diversity.
Annelid Digestive System summary
NEW: complete gut (i.e. digestive tract) with a separate mouth and anus. GUT: compartmentalized into specialized regions (e.g. mouth, cavity, muscular pharynx, esophagus, crop, gizzard, intestine, etc.) depending on feeding habit.
Annelid Excretory System summary
NEW: increased activity requires increased metabloism which requires more efficient excretory system to eliminate metabolic N-wastes (urine) Pairs of METANEPHRIDIA in almost all metameres are composed of a ciliated funnel that sweeps coelomic fluid into a coiled tubule that filters out toxic N-waste from fluid and capillary blood, osmoregulates water, with N-waste and water exiting through a pore as urine. *metanephrium pore exits to the outside (urine)
Lineage (phylogeny) of Mollusca
Order of broadest to most specific: Eumetazoa--{__Bilateria--{__protostomia--{__Lophotrochozoa--{__Mollusca (clams, snails)
Coelom of Annelids is partitioned into metameres internally by ___________
Septa
What is the ecological function of annelids?
They are burrowing detritivores that are important in both marine (freshwater) and terrestrial (land) ecosystems by ingesting and breaking down organic debris and recycle nutrients in soil & sediments. Terrestrial earthworm burrows also aerate soil that helps with drainage.
Capillaries in body wall fulfill what purpose?
They exchange O2/CO2 by diffusion. Ones in gut can pick up nutrients and connect the two major blood vessels.
True or false? Annelids are protostomes
True
What is a typhlosole? (in annelids)
Typhlosole: a dorsal U-shaped infolding of the intestine that increases the SA for absorption of digested food
Annelid Nervous System summary
a pair of cephalic ganglia ("brain") attached to a double or fused ventral nerve chord that runs the length of the worm with pairs of additional ganglia and nerve branches in each metamere. various sensory structures (chemoreceptors, mechanoreceptors, and photoreceptors or ocelli) nervous system on ventral surface unlike humans each metamere also has a ganglion which provides local control to what goes in in that particular metamere
Which of the following structures is found in Mollusca and not in Annelida? a. gills b. circulatory system c. excretory system d. ventral nerve cord
a. Gills
The complete gut runs ______________ through the metameres and coelom
all the way
Which organ system in Annelids is NOT metameric? a. nervous b. excretory c. digestive. d. circulatory
c. digestive system
What is the energy source for synthesis of organic molecules in a vent ecosystem?
chemical bonds in inorganic molecules (best answer)
Annelids are the first group of organisms to have a ____________________ system and a ________________ gut (mouth & anus!)
circulatory (closed circulatory system); complete
Annelids are the first group so far to have a TRUE _______________ (body cavity)
coelom (annelids are coelomate)
Class Oligochaeta (annelids)
earthworms, and relatives, including leeches (previously in their own class Hirudinea)
Class Oligochaeta
earthworms, relatives, and leeches EARTHWORMS: -terrestrial with short, stiff SETAE along both sides to gain traction against oil particles -mostly detritivores ("eat" soil) with specialized gut regions -important soil aerators and nutrient recyclers EARTHWORM reproduction: --1st. hermaphrodites exchange sperm --2nd, clitellum (giant segment looks like scarf on earthworm) secretes a mucous cocoon that slides forward collecting eggs and sperm, then slides off. Zygotes undergo DIRECT development (terrestrial, so no trochophore larvae) & emerge as young worms. --3rd, ______________________________________________________________________ Aquatic Oligochaetes: -mostly small, slender worms associated with sediment and aquatic plants -some used as bait or aquarium fish food -marine species in sediment *LEECHES (~500 spp., mostly freshwater) --monoecious with direct development --many are ectoparasites w a posterior sucker that attached to host; anterior sucker at mouth used to suck blood. --no setae; no internal septa --salivary glands secrete an anaesthetic & anticoagulant (Hirudin) that has medicinal use. --segmented *leeches were used for blood-letting 2,500 years ago in India, Greece, and Egypt; popular again in 1800s in the West. *leeches used today in finger and ear reattachment and reconstructive surgery; the hirudin in leech saliva keeps blood flowing into surgical sites and prevents blood clotting.
In annelids, dorsal blood vessel carries blood _______________ (anteriorly)
forward
Molluscs General Body Structure
four general body regions of Mollusca: see HAM 1. Head: sensory organs, mouth 2. Foot: muscular 3. Visceral (body) mass: digestive, reproductive, circulatory organs 4. Mantle tissue: secretes the SHELL (if present); encloses MANTLE CAVITY that contained "Ctenidia" (aka "GILLS")
HAM
hypothetical ancestral mollusc (before specialization) SEE DIAGRAM
Annelid originated as ____________ species then _______________ then _________________
marine, terrestrial, parasitic (started out w saltwater forms of life)
Class Polychaeta (annelids)
marine; mostly benthic (in/on substrate); some are tubeworms (also includes marine beardworms) *most ancient class with ~8k species *paraphyletic-represents ancestral state *Marine *a pair of bilobed parapodia "appendages" with SETAE on each metamere (for movement and gas exchange) *externally fertilized eggs develop into trochophore larva (indirect development)
In annelids, ventral (underside) blood vessel moves blood ___________________
posteriorly
Annelida are also referred as the _________________ worms
segmented
Class Polychaeta
some are filter-feeding tube worms & live in burrows that they make. (ex. Christmas-tree tube worms, peacock tube worms, serpulid tube worms, feather duster tube worms.) some are "beardworms" --some in marine sediments, others in the DEEP SEA at HYDROTHERMAL VENTS --highly modified, fast-growing polychaetes --no gut; mutualistic chemosynthetic bacteria supply worm with organic food molecules (bacteria living inside worms)
Septa are _____________
structures that form a boundary between different metameres (they separate the coelom into separate units)
Other than cephalopods, molluscs have an OPEN circulatory system. An open circulatory system is defined by _____________________
the blood doesn't stay within the blood vessels all the time. It is pumped through different structures. **This type of circulatory system is common in less-mobile or moving animals.
How many tissue layers do Annelids have?
three (triploblastic: endo, meso, ecto-derms)
What is the function of parapodia?
(on most metameres) increase the SA for gas exchange with the environment (simple diffusion into and out of blood capillaries) and movement *muscles (oblique muscle, longitudinal muscle, circular muscle) attach to chitinous rods to move the parapodia
Squid & Octopus defense mechanisms
*Chromatophores: pigment-containing cells regulated by muscles for camouflage or signaling (e.g. mating rituals) *blue-ringed octopus has deadly venom and aposematic (i.e., warning) coloration *an ink sac releases a cloud of ink (melanin) to distract predators
Class Gastropoda (Phylum Mollusca)
*Largest molluscan class (~80%) *common on land and freshwater! 1. Aquatic Snails (conchs, whelks, periwinkles, etc.) -mostly marine, some freshwater -body has undergone torsion; most have coiled shells -radula for feeding: herbivores, carnivores, and detritivores -most are dioecious -an OPERCULUM is present in most aquatic snails. It is a trap door structure on the dorsal side of the foot that closes the aperture (opening) of the shell when the animal (snail) retracts (defense; prevent drying out) -aquatic snails often lay eggs in strings of protective capsules -freshwater snails lay eggs on plants above water ________________________________ Anatomy of marine snail: *mantel flap *inhalent siphon *etc. SIPHON: draws fresh H2O from one side over gills for gas exchange, then water carries wastes away. (draws water in and blows across mantel cavity) _________________________________ Marine Slugs (sea hares & nudibranchs) -have secondarily undergone DETORSION of body. -sea hares have REDUCED shell; sea slugs have NO shell -ctenidia (gills) often replaced by other gill-like respiratory surfaces that increase SA -monoecious (exchange sperm) -nudibranchs (sea slugs) can have chemosensory rhinophores -many nudibranchs use "stolen weapons" *some feed on cnidarians and store functional nematocysts in cnidosacs at the tips of outgrowths of their gut called cerrata (also increases area for gas exchange) -sea hares can have ink glands to confuse predators _______________________________________________________________________________ Land Snails & Slugs (Terrestrial gastropods) -have "lungs" (essentially a convergent form): modified vascularized region of the mantle (no ctenidia because no water for gas exchange) -land slugs have undergone detorsion and have lost their shell -no operculum
Information on slide after shell types
*Mulberry whelks use their radula to bore holes into the tops of the barnacles (and oysters) and pull out flesh. *Moon snail HUGE foot extended *Hole in a bivalve made by the radula of a predatory moon snail
Class Bivalvia (Phylum Mollusca)
*Not very mobile organisms *the "bivalves" (scallops, clams, cockles, mussels, oysters, etc.): shells divided into 2 parts. *ctenidia (gills) used for respiration AND filter feeding! *shell modified into right and left valves w dorsal hinge and moved by muscles (allows "swimming") *anterior region but no "head" as such & no radula *foot often modified for digging into sediments --UMBO: the oldest part of the shell --RIDGES show were mantle has successively laid down *a dorsal HINGE ligament connects the 2 shelled "valves" & ADDUCTOR MUSCLES move the 2 valves. --contraction closes, relaxed opens ***UNIdirectional water flow over ctenidia facilitated by posterior incurrent and excurrent SIPHONS (derived from the mantle!) *Scallops can have multiple "simple eyes" along mantle edge that detect motion, light, dark, and chemosensory tentacles *Burrowing bivalves can have long SIPHONES (incurrent and excurrent) -siphons are extensions of the mantle -permit water to enter and exit cavity and reach gills while buried *Destructive wood-boring "shipworms" are actually bivalves PEARLS! (layers of calcium carbonate ("nacre") deposited concentrically around an irritant that gets lodged between the mantle and shell.
Mollusca brief overview
*Phylogenetic position and characteristic *variation in body form in three major classes *basic anatomy *diversity (4 minor classes) --1. Gastropoda --2. Bivalvia --3. Cephalopoda --4. Rotifera (Phylum)
Shell Types
*TORSION: happens to the body (visceral mass) *COILING: happens to shell Basic shell is straight or usually coiled, with new shell deposited by the mantle at the margin of the open end ('aperature") during growth. Limpets (straight shell) Snails (coiled shell) **Shells have varied antipredator defenses (spines, thickness) _________________________________________________________________________ COILING types: 1. Sinistral (left-handed) coiling 2. Dextral (right-handed) coiling (aperture opening right)
"HAM" to Gastropoda (snails)
*body undergoes torsion (twisting) *shell undergoes coiling
"HAM" to Cephalopoda
*foot becomes lobed into tentacles *highly developed head with complex eyes and different mouth parts *shell is reduced or lost (in most)
Octopus Reproduction
*male transfers a spermatophore (sperm packet) to female using a modified arm (hectocotylus); then he dies *females attach eggs to a substrate; some die, others may seal themselves up in a den to lay eggs, then care for the eggs (up to 6 months); after the eggs hatch, she dies. *DIRECT DEVELOPMENT (baby octopuses hatch out)
Phylum Mollusca "soft-bodied animals"
*second-largest animal phylum (~110,000 extant spp.) *marine, freshwater, terrestrial *range from 1 mm to 18 m long
Gastropod body torsion
*see a 180 degree rotation of the visceral mass during development: RESULT: this moves the mantle cavity & anus from the rear to an anterior position over the head. BENEFIT: better water flow over gills. PROBLEM: anus fouls water SOLUTION: mantle forms an anterior SIPHON to direct H2O over gills and keep anus away from it.
"HAM" to Bivalvia
*shell becomes bivalved with a hinge & muscles
Class Cephalopoda (Phylum Mollusca)
*squids, octopuses, nautilus, and cuttlefish *shell can be present, reduced, or lost *all predators with beak-like jaws and often a radula *highly developed head and sensory organs ***only molluscs with a closed circulatory system (higher pressure delivers blood more rapidly: seen in active animals) *swim via jet propulsion (portion of mantle forms a funnel) *foot is lobed and forms arms & tentacles *direct development (basically hatch as adults) (no larvae); dioecious; die after reproduction *pigment cells (chromatophores) for color changes; INK (for defense) _______________________________________________________________________________ *Chambered Nautilus (most ancient extant group): -shell has gas-filled chambers that regulate bouyancy -ONLY extant cephalopod with a predominant shell _____________________________ SQUID (reduced, internal shell called the "PEN') -more open water animals CUTTLEFISH (reduced, internal shell called the "cuttlefish bone:" often seen in birdcages) ----> BOTH squid and cuttlefish have 8 arms with 2 tentacles (with suction discs), lateral "fins" & a reduced internal shell. ______________________________ Octopuses -lost shell completely (can squeeze into tiny openings) -most intelligent invertebrate -suction discs on 8 arms -octopus eye is the most complex among invertebrates; similar to human eye in many ways (iris, lens, vitreous humor and retina), but the octopus eye evolved independently of the human eye (i.e. analogous)
General characteristics of Mollusca
*triploblastic, organ level *bilateral *protostome, lophotrochozoan *true coelom (like annelids) -trochophore & VELIGER larva Gas Exchange: --mainly by GILLS (NEW) called Ctenidia (mollusc gills) in the Mantle Cavity --MANY, THIN gill filaments increase the SA for gas exchange ___________________________________________________________________________ Circulatory System: --OPEN circulatory system (closed in cephalopods) (NEW!) --Multi-chambered HEART (1-2 atria, 1 ventricle) (NEW!) *heart sits in the "pericardium space" (the reduced coelom) *O2-rich blood leaves ctenidium (gill) in a vein, enters atrium of heart, then ventricle, then ventricle pumps blood out to organs in the hemocoel through an artery and capillaries. *O2-poor blood collects in capillaries, then goes to gills to pick up O2. *blood contains oxygen-carrying pigment (Hemocyanin) (NEW!) ______________________________________________________________________________ Excretion: --most have paired metanephridia (not new; aka nephridia) to osmoregulate (water balance) and excrete N-waste. ____________________________________________________________________________ Nervous System: --ventral nerve chords (not new) in foot, various ganglia & sensory organs ___________________________________________________________________________ Digestive System: --complete gut (not new) often with regional specialization --RADULA: a tongue-like organ bearing rows of sharp "teeth" used in feeding (scraping, tearing, drilling, etc.) ____________________________________________________________________________ Reproduction: --both monoecious and dioecious spp. --usually internal fertilization --Indirect development via trochophore larva; in some cases it develops into a VELIGER larva (NEW!: seen in bivalves, gastropods & scaphopods); but....CEPHALOPODS have DIRECT development!
Three traditional classes of Annelids
1. Polychaeta- marine, ecologically diverse, parapodia (appendages/legs). some are filter-feeding tube worms & live in burrows that they make. (ex. Christmas-tree tube worms, peacock tube worms, serpulid tube worms, feather duster tube worms.) 2. Oligochaeta- earthworms & relatives, terrestrial, freshwater, marine (saltwater) 3. Hirudinea- leeches (ectoparasites), freshwater & marine As traditionally used both Polychaetes and Oligochaetes are paraphyletic (Hirudinea is within Oligochaetes and Oligochaetes are within Polychaetes)
4 Minor Classes of Mollusca
1. Scaphopoda (tusk, tooth shells) --deposit feeders --live buried in sand; related to bivalves? 2. Polyplacophora (chitons) --grazing herbivores --found in shallow, marine (saltwater) habitats --multi-part shell, body is not segmented --distantly related to all other Mollusca 3. Monoplacophora (closest to HAM) --Living with fossil taxon w single shell. --uncertain place in phylogeny --live in deep sea --modern species discovered in 1950s 4. Aplacophora --deep sea, lack shell --distantly related to all other Mollusca
Molluscan classes (extant: not extinct)
7 total (only know the main 3) MAIN 3: 1. Bivalvia (clams, mussels) 2. Gastropoda (snails, slugs) 3. Cephalopoda (octopus, squid, cuttlefish, nautilus) _____________________________________________________________________________ 4. scaphopoda (tusk, tooth, shells) 5. polyplacophora (chitons) 6. monoplacophora 7. aplacophora
Why do annelids need to live in fairly moist places?
Annelids have a moist outer cuticle (like flatworms) of collagen secreted by epidermal cells. It is NOT molted!
Why are transport systems needed in Annelids?
Because the septal divisions do not allow coelomic fluid to transport nutrients and metabolic wastes to cells for diffusion.
Annelid reproduction and development summary
Both monoecious and dioecious species exist, but earthworms and leeches are monoecious (hermaphrodites) Some undergo DIRECT development (young resemble adults: e.g. terrestrial earthworms); Some with INDIRECT development (marine species): embryo becomes a swimming TROCHOPHORE larva that goes through stages growing into an adult. --as the larva grows, metameres are added posteriorly.
The polychaeta and oligochaeta classes are sometimes combined in a new class called Class ________________
Clitellata
Annelid movement summary
Coelom still serves as a hydrostatic skeleton (like platyhelminthes) Outer circular & inner longitudinal muscles (as in flatworms; reverse of cnidaria) & septa allow metameres to move independently. Have stiff chitinous SETAE (bristles) which provide leverage against sediments RESULTS: more complex movement ***earthworms move using alternating waves of circular muscle contraction (elongates and constricts worm) and longitudinal muscle contraction )shorten and thickens worm) : SIMILAR to PERISTALSIS
