BIOL 111: Lab Midterm 2 Review 12-12-17 12:23 AM LAB 6: INVERTEBRATES I Phylum Cnidaria • among simplest of animals (only sponges less complex) • cnidocytes – specialized stinging cells, capture prey, defense • mostly marine: for example, jellyfish and corals • 2 cell layers surrounding a central cavity • radial symmetry with arms/tentacles • 2 Forms: 1) Polyp: sessile, asexual (oral above aboral) 2) Medusa: motile, sexual (aboral above oral) *some show both forms in their life cycle: these are dimorphic Ex. Hydra: -small (3-8mm) freshwater polyp -glides/inches/somersaults/float on gas bubbles -carnivores: tentacles capture prey, subdue with nematocysts stings, partially digested in gastrovascular cavity, absorbed by gastrodermal cells, intercellular digestion occurs >ANATOMY -hypostome: conical elevation with mouth opening at its tip; mouth = mouth and anus -tentacles: food catching arms, contain cnidocytes -gastrovascular cavity: digestion/absorption, respiration in gastrodermis and epidermis -body column: mesoglea + 2 tissue layers (epidermis and gastrodermis) -mesoglea: thin, gelatinous layer = hydrostatic skeleton (: thin dark line) -basal disc (foot): posterior end of body, attaches to substrate (ex. Rocks, plants), locomotion Cell Types: -epitheliomuscular: longitudinal (epi)/circular (gastro), antagonistic à move, engulf partially digested food -cnidocytes: in epidermis, contain nematocysts triggered by cnidocils (bristle-like projections, modified cilia); nematocyst types: stinging/entangling/adhesive -neurons: nerve cells forming a nerve net, runs through mesoglea • sensory cells: type of neuron in epidermis, sensitive to external stimuli -gland cells: in basal disc’s epidermis (sticky substance) & in gastrodermis (digestive enzymes) -interstitial cells: b/n epitheliomuscular cells, small, totipotent (act like stem cells) à cnido. -ciliated cells in gastrodermis = create water currents à food circulates, also: distributes oxygen and removes wastes -no central nervous system or ganglion: signal sent through entire body >REPRODUCTION -either sexual or asexual -sexual: sperm + egg = zygote (union of gametes produced in gonads: testes & ovaries) • some (not most) are hermaphrodites: able to produce both gametes (m and f) • reproduction occurs in the fall, spermàwateràhole in epidermisàegg • zygote forms hard covering and drops to sediments, remains dormant until spring -asexual: budding of new individual through mitosis (2-4 days), genetically identical • summer months, lots of food, parent surviving? Why change! *two different strategies due to alternation b/n stable and unstable conditions -self-fertilization is not advantageous (doesn’t benefit evolution) • receptor proteins on egg cell membranes recognize sperm from self and rejects it • plants of diff. genotypes have structural differences preventing self-pollination • unknown for hydras >FEEDING -for the most part, remains stationary until food drifts to it, brushing its tentacles (opportunistic feeders) -bilateral symmetry would be more beneficial: sensory structures concentrated Ex. Gonionemus -Class Hydrozoa (not Class Scyphozoa, so not technically a jellyfish) -small medusa (d=2.5cm) living in shallow temperate marine waters -some cling to seagrasses their entire life rather than swimming, some are poisonous >ANATOMY -bell: dome-shaped, epidermis, gastrodermis, mesoglea -tentacles: arms hanging from bell, capture prey, attach to objects, 80+/individual -tentacular bulbs: dark swellings at base of each tentacle, interstitial cells à cnidocytes -adhesive pads: attach to seagrass and macroalgae -cnidocytes: stinging cells, spiral swellings (batteries) along tentacles, each contains nematocysts à projects tube à penetrates prey’s tissue à deliver paralyzing poison -velum: shelf under the bell, jellyfish don’t have a velum, epitheliomuscular cells here contract = move -manubrium: tube hanging in bell, homologous to hypostome in hydra, dark square, extracell. digest. -mouth: end of manubrium, ingestion, ringed by oral lobes (fleshy projections), ingestion, anus too -radial canals: 4 canals/extensions of stomach, radiate from manubrium -ring canal: connect w/ radial canals, runs around edge of bell, intercellular digestion -statocysts: small swellings b/n tentacles’ bases, contain stones, orientation à gravity, sensory -gonads: 4 light brown gonads hanging down as ruffles, parallel to 4 radial canals Phylum Annelida • annelida “little rings” • earthworms, tubeworms, leeches = segmented worms • bodies composed of similar segments, ringed appearance and septa internally Ex. Earthworm (lumbricus terrestris) -live in moist oil w/ lots of detritus for food -burrowing à soil is partly pushed and partly swallowed à break up soil particles -soil à digestive tract à cement utilized in lining burrows à air and water à thicker rich topsoil -anterior initiates stronger response due to greater concentration of ganglion >ANATOMY (External) -thin transparent cuticle covers outer surface of worm, secreted by epidermis, protects from desiccation -mucus secreted by glandular cells in epidermis = protective layer, locomotion, respiration -bilateral symmetry: anterior (slightly more cylindrical, thicker), posterior, dorsal (back), ventral (lighter colour, more flattened, small pores visible here) -clitellum (thick band) located closely to anterior end -4 pairs setae on each segment, except first and last (one pair ventral, one pair lateral), 100 segments -Segment 1: mouth, prostomium – fleshy lobe preceding mouth, peristomium – portion around mouth -Segment 9 & 10: ventral, 2 pores/segment à seminal receptacles (store sperm) -Segment 14: ventral, 2 pores = female genital pores -Segment 15: ventral, 2 pores = male genital pores, seminal grooves à sperm à clitellum -Segment 26: ventral, genital setae (hold ventral surfaces together during copulation) -Segment 32-27: clitellum secretes mucus cocoon where eggs and sperm are deposited -Final segment: anus (pore) *annelids have a complete digestive tract w/ mouth and anus separate >LOCOMOTION -circular and longitudinal muscles cause movement -antagonistic muscle types & hydrostatic skeleton -circular muscles contract à pressure on fluid in coelom à segment elongates à push anterior segments forward à longitudinal muscles contract à segment shortens à pull posterior segments fwd -setae anchor segments when others are lengthening and shortening >CIRCULATORY SYSTEM -closed circulatory system -dorsal blood vessel = thin dark purple line, largest blood vessel in body -ventral blood vessel on other side, dark in colour, smaller than dorsal vessel • in each segment: branches of ventral vessel form capillary beds à body à dorsal branches -dorsal blood moves anteriorly, ventral blood moves posteriorly -5 pairs aortic arches: encircle esophagus, act as the heart (pumping organ) -one-way valves for dorsal blood (less pressure so more chance for backflow) >ANATOMY (Internal) -septa: semi-transparent, mark boundaries of each segment -coelom: fluid-filled body cavity, divided by septa, acts as hydrostatic skeleton -all segments (except anterior ones) each contain a portion of the digestive, excretory, nervous, and circ -Digestive system: • digestive tract runs down middle of body, mouth à anus • pharynx: light-coloured swollen structure, pulls soil into digestive tract, radial muscles dilate the pharynx to help ingest detritus • esophagus: thin-walled, lies under aortic arches, partially covered by white reprod. organs • crop: storage pouch, dark-coloured, thin-walled • gizzard: grinds up food, light-coloured, muscular • intestine: long, straight tube extending from gizzard à anus, food & water absorbed • typhlosole: dorsal infolding of intestine running down length of worm, increase area -Reproductive system: -hermaphrodites: both m and f gonads are present in each individual -copulation external, on warm, moist nights -seminal vesicles: male repro, 3 lobes, sperm storage -testes: segments 10 & 11, sperm à sem. ves à vas deferens à m genital pores seg. 15 -ovaries: very small, eggs à oviducts à f genital pores -seminal receptacles: f repro, segments 9 & 10, tiny, round sacs, light-coloured, ventral Copulation: -earthworms lie with ventral surfaces together -anterior ends facing opposite directions -mucous produced by clitellum helps to hold -sperm à seminal grooves à seminal receptacles -2 to 3 hrs -clitellum secretes cocoon made of chitinous material, anterior segments produce mucous tube -eggs released from female genital pores into cocoon à anteriorly à eggs fertilized as they pass over seminal receptacles *fertilization is EXTERNAL à cocoon slipped off à hardens and shrinks on earth’s surface (small seed)à 1 week development, only one individual will complete development > RESPIRATORY SYSTEM -no lungs/gills, no specialized organs -oxygen and carbon dioxide exchanged in capillaries distributed throughout moist epidermis >NERVOUS SYSTEM -pair of ganglia (ganglion): cluster of neurons called the cerebral or suprapharyngeal ganglia • dorsally located, just anterior to pharynx (seg 3) • main center for coordination of sensory & motor functions -subpharyngeal ganglia: below pharynx (seg 4), embedded in pharyngeal muscles, motor functions, reflexes (without these ganglia, movement stops) • without the supra. experiments: still moves, cannot coordinate with environ. stimuli • brain regenerates itself in 2 months -ventral nerve cord: ventral to ventral blood vessel, thin tan string, ganglion (swelling) in each seg -segmental ganglion: 3 pairs segmental