Core Course No ZOOA P1T GroupA Topic No 2 Bilaterally symmetric triploblastic true coelomate animals Body vermiform elongated divided into three regions anteriormost ID: 935350
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Slide1
The segmented worms
ANNELIDA
Core
Course No. ZOOA –
P1T
,
Group-A
,
Topic
No.
2
Slide2Slide3Bilaterally symmetric, triploblastic, true coelomate animals.
Body vermiform , elongated, divided into three regions,
anteriormost
protostomium (bears brain and sensory organs), posteriormost pygidium (bears anus)and intermediate metamerically segmented trunkThey locomote by epidermal chitinous bristles chaetae (absent in leeches and few polychaetes) Gut straight and tubular , from anterior mouth till posterior anus, digestion extracellular.Respire mostly by moist body surface, but through gills in some tube dwellers (Arenicola sp., Cirratulus sp.). Respiratory pigments such as Haemoglobin, chlorocruorins and haemerythrin are found in blood plasma and coelomocytes.Closed vascular system comrised of contractile dorsal vessels(in few modified into heart), ventral vessels and intermediate capilary plexus.Nervous system is ladder like , comprised of brain and double ventral nerve cords (segmentally arranged ganglia and lateral projections).Excrete by means of filtration nephridia, i.e segmentally coiled tubes known as metanephridia (rarely protonephridia)Sexes separate or united, develoment direct (Oligochaeta, Hirudinea) or indirect through trochohore larva (polychaeta)They inhabit Aquatic (marine, freshwater) and terrestrial habitats.
BAUPLAN AND FUNCTION
Slide4Annelid Body Plan
chaetae
Slide5Slide6Annelid Characteristics
Defining Characteristics
One or more pairs of
chitinous
ChetaeThe phylum includes polychaetes, earthworms, leeches, and vestimentiferansPhylum Annelida6True segmented wormsMetameric segmentation
Slide7Body Structure
The body is a tube within a tube
Phylum Annelida
7
The coelom is important to annelids for:The epidermis is what secretes the tough cuticle
Slide8Systems
Integument- epidermis is one cell layer with mucous gland that secrete a moist cuticle.
Skeletal
-hydrostatic (using coelom)
Muscle- longitudinal and circular muscles Each segments muscles are independent of the other segments.Digestive- complete, complex, with absorption and digestive glands and excretory cells.
Slide9Systems (continue)
Excretory- a pair of
metanephridia
per segment.Respiratory –generally through skin, some through parapodia; tubeworms have gills.Circulatory- closed system, use hemoglobin as oxygen carrier.Nervous- dorsal brain; ventral, double, solid nerve cord, with segmental ganglia in each segment.Endocrine- hormones secreted by nervous system.Reproductive- Dioecious in Polychaeta; no special organs, posterior end becomes gonads.Monoecious in Oligochaeta and Hirudinea; Clitellium.
Slide10Locomotion
On each side of the animal is a
parapod
(
parapodia) consisting of fleshly lobes, which are supported by chitinous rodsEach parapod have chetae, which can be sharp (protection), and aid in locomotionPhylum Annelida10
Slide11Feeding
Phylum Annelida
11
Annelids range from carnivores, herbivores, scavengers, deposit feeders, and filter feeders
With very few defenses, many remain in a burrow or secreted tube Carnivores can capture prey with strong jaws and quickly drag it back to its burrowCan use a muscular pharynx = eversible proboscis
Slide12Digestive System
Phylum Annelida
12
Slide13Circulatory System
Blood flows entirely in closed vessels
Some spp. have hearts
Blood contains hemoglobin, which increases oxygen carrying ability
Phylum Annelida13
Slide14Excretory & Nervous System
Phylum Annelida
14
Nervous system
Slide15Slide16Slide17Reproduction
Phylum Annelida
17
Sexes are usually separate with gonads occurring in each segment
Some species have gonad specific segmentsBreeding is usually seasonal (spring or fall)As gametes mature they fill the coelom and are released by the nephridiaFertilization can be internal or external Trochophore larvae develop, which are remarkably similar to the Molluscs
Slide18Phylum Annelida
Ancestral Traits
Coelomate
Lophotrochozoan
- non-molting protostomesProtostomeClosed circulatory systemCephalizationDerived TraitsSegmentationMetamerismSeptaSetaeBristlesMyelinated neurons~ 40K species of annelidsSpirobranchus giganteusChristmas tree worm
Slide19Barnes,1994
Classification
Slide20Slide21Class P
olychaeta (Poly= many; Chaeta=bristles)
Elongated,
metamerically
segmented body, antrior head is comprised of prostomium (bearing eyes, antennae and palps) and peristomium (bearing cirri).Each trunk segment typically bears a pair of bilateral fleshy paddle like outgrowths, Parapodia (fecilitates locomotion and gas exchange) bearing bundles of chaetae.Parapodia are biramous (two branches), dorsal notopodium and vental neuropodium both lobes bearing its own cluster of chaetae. Both lobes are supported internally by acicula (singular aciculum), which are chitinous skeletalrodsRespiration generally by means of body surface, in some forms specialized unprotected gills are present, which are modified parapodial outgrowth.Excretion,occasionally by protonephridia (forms lack or have reduced hemal system), but mainly through metanephridia.Digestive system with an eversible buccal region and protrusible pharynx.Reproduce sexually, sexes separate (gonochoric), exhibit epitoky (synchronous maturation and mating), fertilization external.Develoment indirect, though Trochophore larval stage.Exclusively marine, Clitellum absentExample: Aphrodite (sea mouse), Nereis (rag worms), Chaetopterus (paddle worms), Arenicola (lug worms), Sabella (fanworms), Glycera (tounge worms) etc.
Slide22Slide23Class O
ligochaeta(Oligo= few; Chaeta=bristles)
Streamlined body, well developed segmentation, four bundles of chaetae per segment, the small
prostomium
and pygidium devoid of appendages. They possess a Clitellum (reproductive structure), a thick glandular epidermal covering, encircling and thus forming a girdle around a series of anterior segments.Their head is indistinct, without eyes and tentacles and cirri, The locomote and burrow by means of body wall musculature, cheatae are less distributed along the body, parapodia absent. Respiration generally by means of moist body surface, except few posessing true gills.They have various numbers (one to five pairs) of pulsatile muscular hearts (modified circumenteric vessels), Excretion by metanephridial system.Reproduce sexually, sexes united (hermahrodite), exhibit cross fertilization (interchange of sperm between copulating pairs), fertilization external.Develoment direct. Within cocoon secreted by clitellum. Most are fresh water or terrestrial inhabitants, a few are marine.Example: Pheretima, Lumbriculus, Tubifex, Nais, Branchiura, Megascolex,
Slide24Slide25Class H
irudinea
Elongated body,
dorsoventrally
flatenned and tapered anteriorly, bearing small anterior sucker and large, disc shaped posterior sucker.Body made up of 33 segments, head is composed of 6 segments (reduced prostomium and next 5)bears several ocelli (dorsally) and ventrally anterior sucker (surrounding mouth), Trunk is composed of 21 segments (6-26), followed by Posterior sucker composed of 7 segments (27-33), anus located dorsally on (or near) the last trunk segmentTrunk is divided into preclitellar region, clitellum spanning 3 segments (9-11) and conspicuous only during reproductive period, and the last postclitellar region, Coelom is reduced due to expansion of overlying connective tissue compartment, also the coelomic cavity is continuous and uninterrupted (no septa and mesenteries)Excrete by means of 10-17 pairs of metanehridia (1pair per segment), located in the middle third of the body.Locomote by inchworm like crawling and swimming, they also burrow, fecilitated by body wall musculature and both the suckers.They are Hermaphrodite (cross fertilize), reproductive structures are restricted to anterior few segments, fertilization internal, development direct and occurs inside cocoons secreted by clitellum. colonize marine, freshwater and terrestrial habitats. Example: Hirudo, Hirudinaria (cattle leech), Aulostoma (horse leech), Glossiphonia, Piscicola, Branchiobdella,
Slide26Slide27Slide28Slide29Earthworm
Slide30Slide31Slide32Slide33Slide34Metamerism
Slide35The phenomena where individuals body is made up of a number of identical units known as
segments/
metameres
,
each of which bears similar internal and external components and are repeated one after the another.OccurrenceAnnelid and arthropod lineChordate lineCestode lineFeaturesOnly confined to trunkIdentical units bears segmental (separated) and integrating component (continuous)Co ordination between segmental and integrating componentsOrigin of MetamerismGonocoel theoryCyclomerism theoryCorm theoryTypes
Slide36Advantages of
Metamerism
Efficient energetics during locomotion
Scope for
tagmosis by means ofRestrictionDivergenceFusion
Slide37ETC
Slide38Slide39Slide40Slide41Slide42Slide43Slide44Sources
E.E. Ruppert et al., Invertebrate Zoology , 7
th
Edition, Cengage Learning, 2004
R.C. Brusca and G.J. Brusca., Invertebrates, 2nd Edition, Sinaur Associates, 2003