bio 182 lab 7: Mollusca and Annelida

have most advanced body plan! Conserved in evolution of all subsequent animal lineages.

Coelomate animals

body cavity surrounded by mesoderm-derived tissue true body cavity within the mesoderm. Enclosed on inside and out by muscles. A coelom is a cavity lined by an epithelium derived from mesoderm

Coelomates

Freshwater and marine Hinged shell with 2 valves: clamps shut to avoid predators! Strong adductor muscles External fertilization (gametes released into H20) Filter feeders (siphons direct H2O over the gills which trap food particles inside the mantle cavity) Internal Gills Foot used for digging No head or radula! Not needed b/c they filter-feed Eye spots sense light! Mostly sessile...but in extreme scenarios can move Bivalves= two doors or shells. Shell is dorsally hinged. Then mantles of the left and right valves join posteriorly to form a ventral incurrent siphon and dorsal excurrent siphon that direct water throught the clam. The space between the mantle and the visceral mass is the mantle cavity. Water flows into the mantle cavity thru the incurrent siphon (ventral side) water in, over the gills (attached to mantle). Food is filtered by cilia and moved to the labial palps that direct food to the mouth. Filtered water and waste then exits the organism through the Excurrent siphon. Nephridium used to process waste.

Class Bivalvia (clams, scallops, mussels, oysters)

Largest, brightest, & fastest invertebrates!!!! Foot modified into tentacles w/ suckers Closed circulatory system Internal shell (absent in nautilus) Parental care **no skeleton and changes color! Adaptations for Active Predation Advanced cephalization = most intelligent invertebrate **opens jars Largest brain to body mass ratio Complex eye w/ lens Chromatophores = camoflage Statocysts sense sound & gravity Excurrent siphon: jet propulsion Cephalo=head, poda= foot. Lack shells. Closed circulatory system in Mollusks only occurs in this class. Closed circulatory system means that blood is contained in vessels. Giant squid has the largest eyes in the Kingdom of Animalia Cephalopoda characterized by bilateral body symmetry, a prominent head, and a modification of the mollusk foot, a muscular hydrostat, into the form of arms or tentacles.

Class Cephalopoda "head foot" (squid, cuttlefish, octopus, nautilus)

Ancestral Traits of Mollusks & Annelids:

Eukaryotic Heterotrophic True Tissues Bilateral symmetry Complete digestive tract Organs Movement Triploblastic

(false hollow) liquid filled space in which many of the internal organs are suspended. Crude body control because psuedocoel only has muscles on its outside.

Psuedocoelomate

characterized by multiple reproductive cycles over the course of its lifetime. multiple times before death

iteroparous

Oligochaeta Locomotion: 2 Muscle types

1. Circular muscles (encircle worm): contract to lengthen body segments 2. Longitudinal muscles (run length of worm): contract to shorten body segments Alternate contractions of both muscle types against hydrostatic pressure w/in each segment! Segments can move independently!

3 body parts of Mollusca

1. Foot: muscular component of body for moving; highly modified in each Class 2. Mantle : modified epidermis produces GILLS for respiration & secretes a shell in some spp. 3. Visceral mass: collection of organs used for digestion, excretion, and reproduction calcium based shell Many have Radula: Rasping tongue to scrape algae off rocks hot radula action music Diagram not "real" it is simplified rep. to show 3 regions

Second largest animal phylum (110,000 spp.) Marine, freshwater & terrestrial species! "soft-bodied" 4 Classes: (Polyplacophora, Gastropoda, Bivalvia, Cephalopoda,) 3 main body parts: mantle, foot, visceral mass (next slide) Defense: shells or distasteful secretion on skin OPEN Circulation (except Class Cephalopoda) = blood like substance bathes organs in sinuses and then returns to heart

1. Phylum Mollusca (snails, clams, octopi, etc)

Cephalopoda survival

Camouflage Autotomizing limbs: fall off & re-grow! Ink released to escape sharks by dulling smell! Venom in saliva Compactable: hide in tiny places 1) Three defensive mechanisms are typical of octopuses: ink sacs, camouflage, and autotomising limbs. Most octopuses can eject a thick blackish ink in a large cloud to aid in escaping from predators. WHT IS OCTOPUS INK MADE OF?? melanin! 2) An octopus's camouflage is aided by specialized skin cells which can change the apparent color, opacity, and reflectiveness of the epidermis. These Chromatophores contain yellow, orange, red, brown, or black pigments; most species have three of these colors, while some have two or four. This color-changing ability can also be used to communicate with or warn other octopuses. The very venomous blue-ringed octopus becomes bright yellow with blue rings when it is provoked. 4) The blue-ringed octopus is the When under attack, some octopuses can detach their own limbs, in a similar manner to the way skinks and other lizards detach their tails. The crawling arm serves as a distraction to would-be predators; this ability is also used in mating.

are pigment-containing and light-reflecting cells found in amphibians, fish, reptiles, crustaceans, and cephalopods. They are largely responsible for generating skin and eye colour in cold-blooded animals and are generated in the neural crest during embryonic development.Like chameleons, cephalopods use physiological colour change for social interaction. They are also among the most skilled at background adaptation, having the ability to match both the colour and the texture of their local environment with remarkable accuracy.

Chromatophores

Most diverse class (>85,000 spp. = 70%) Only mollusc to successfully invade land! Snails & slugs: 1 lung to breath air (pneumatostome) mucus protects against water loss & predators Snail Gut Torsion = spiral shell creates u-turn Gas exchange: external gills or lung Internal fertilization! Some hermaphrodites! often have a single shell that is often coiled and elaborate. The spiral growth is common in mollusks and results from unequal growth of the two halves of the larva and mantle. Nudibranchs and common garden slug do NOT produce a shell. Radula: a rasping band of teeth for feeding

Class Gastropoda (snails, slugs, nudibranchs)

"hirudin" = anticoagulant found in leeches freshwater ectoparasites, predators of small invertebrates (nematodes, insect larvae) or detritivores Incomplete segmentation - superficial but does not go through entire body plan No parapodia or setae! Suckers (anterior & posterior) hold prey Flattened bodies (vs. Round) Hermaphroditic Sex w/ spermatophore (sperm packet) injected Parental care (not all): Cocoon is brooded 1) Some leeches eat detritus and small inverst, i.e.: worms, snails, insect larvae 2) One group of leeches, the glossiphoniids, has evolved the ability to care for their eggs and young. This care involves both pre-developmental investment (egg yolk) and post-developmental care in the form of nutrient transfer, direct feeding and other forms of care that aid in the survival of the eggs and young.

Class Hirudinea (leeches)

Terrestrial (mostly) detritivores (filter dirt) No parapodia! Small setae for movement & friction Hermaphroditic Clitellum: series of swollen segments; joins eggs & sperm in mucus band & forms coccoon = external fertilization earthworm sex Controlled Coelomate Movement: Extension, anchoring, contraction Motion of earthworms occurs by alternating contractions of circular and longitudinal muscles against hydrostatic (water) pressure within each segment. Oligochates have a prostonium (it often functions like a kind of overlip) priori to the mouth.

Class Oligochaeta"few bristles" (earthworms)

Marine habitat! Sessile in tube or free-swimming Tentacles sense vibrations 2 pairs of simple eyes (ocelli) Body Segments have parapodia & setae: Setae: bristles function in: Movement Defense (poisonous) Filter-feeding (in some) Parapodia (foot-like appendages bearing setae) aid in: Swimming Respiration (highly vascularized) Fireworm: poisonous bristles! Fan worm (sessile in tube) Setae in this class can be used to aid in filtering food and defense. Some species have setae which are filled with poisons that can be used against predators. Nereis are marine worms living in sediment. Parapodia have a large surface area, are highly vascularized with blood vessels,and help the polychaete move and respire. Protruding from the fleshly parapodia are many setae from which the class derives its name

Class Polychaeta (bristle worms, fan worms, & feather dusters) aquatic worms setae = chaeta = bristles

Earliest derived Mollusk! Fossils from Devonian-Ordovician (400+ MYA) Defense: suction onto rocks Exclusively marine -intertidal rocks, nocturnal & slow-moving 8 calcareous dorsal plates Mostly Herbivores: Radula to scrape algae Repro: external fertilization: gametes released into water Gas Exchange: Gills attached to mantle Feed on algae, bryzoans, diatoms, bacteria, and invertebrates.

Class Polyplacophora (chitons): "many plates" Poly= many plac = plate phora = bearing

1. Pharynx: throat 2. Crop: enlarged cavity for food storage 3. Gizzard (stomach): cavity for digestion via enzymes 4. Intestine: linear tube for absorption of broken down food

Digestive System of Annelida

Sexual Reproduction in earthworms

Hermaphrodites: each produces both sperm & eggs Worms intertwine to smear sperm onto other's body, Clitellum slides along body to pick up sperm & unite it with eggs released into clitellum: fertilization Fertilized eggs released into a cocoon secreted by clitellum **Giant earthworm cocoon Each worm produces both sperm and egg. Fertilized eggs are then stored in a mucus band and released into a cocoon. This presents some interesting contrasts with other invertebrate and vertebrate groups that also have parental care but have separate sexes.

3 Advantages to coelomates:

Increased body size Cavity circulates substances Important for Mollusks which lack vessels Increased mobility - more flexibility due to hollow body cavity Fluid cushions organs Protected from impact injuries

Invertebrate, coelomate animals that lack skeletons but gain structural support & leverage for movement from hydrostatic pressure. These soft-bodied animals defend themselves in various ways that include living in a shell or producing distasteful compounds. Mollusks ("soft") probably evolved from a worm-like ancestor into the second most diverse animal phylum. All members share three main body regions, the mantle, foot, & visceral mass. Most are detritivores & herbivores although many bivalves filter feed & cephalopods are advanced predators. Annelids ("ringed"; segmented worms) show advancements including internal compartmentalization and closed circulation. Fan worms and leeches are aquatic, the former filter feeds with highly branched extension while leeches are mostly predators.

Mollusks & Annelids

3 advantages of coelomates

Organs formed inside a coelom can freely move, grow, and develop independently of the body wall while fluid cushions and protects them from impact/shocks. Note: these 3 advantages also apply largely to animals having a pseudocoelom cavity, but the latter has less coordinated movement due to fewer types of muscles that are only capable of simple longitudinal contractions (side-to-side movement results) 1. Increased body size Cavity circulates substances Important for Mollusks which lack vessels 2. Increased mobility - more flexibility due to hollow body cavity 3. Fluid cushions organs Protected from impact injuries

Coelomate & triploblastic body plan Complex organ systems (see next slide) True body segments: repeated sections divided by septa Division of labor: circulatory, digestive, excretory systems separated Closed circulatory system Cerebral ganglia (like a brain) Setae: bristle appendages for different uses Setae modifications distinguish the 3 Classes Include: earthworms, leeches, and less familiar marine and freshwater spps. Segmentation of body is what distinguishes this group from other worms. Each segment is repeated longitudinally and contain parts of the circulatory, digestive, nervous and excretory systems. Classes of annelids are separated by the number of setae (bristle-like appendages FUNCTION VARIES) the species have.

Phylum Annelida = "ringed"(segmented worms)

lengthwise folding of intestine to double surface area for absorption of nutrients increases intestine surface area for more efficient absorption of digested nutrients.

Typhlosole

blood is always retained in vessels.

closed circulatory system

specialized layer of epidermal cells that secretes the shell. Can aid in respiration. Many different external shells: some only remnant internal shell, others have no shell at all

mantle

blood pools in sinuses and bathes the organs directly. Have few large vessels and a heart but no smaller vessels and capllaries

open circulatory system

Irritant stuck between mantle & shell Mantle deposits layers of crystalline shell around sand grain (myth...usually parasite)! 3 yrs later = pearl! Eye boogers

pearls

horny toothed" organ in the mouth. Used for scraping food from rocks.

radula

characterized by a single reproductive episode before death Reproduce only once then die

semelparous