Phylum Annelida Segmented Worms.

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1 Phylum Annelida Segmented Worms

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3 Five main animal clades: Parazoa? Radiata Lophotrochozoa Ecdysozoa
Trochophore larva Five main animal clades: Parazoa? Radiata Lophotrochozoa Ecdysozoa Deuterostomia Protostomia

4 Coelomates Two major evolutionary lineages (clades) based on embryonic development Protostomia and Deuterostomia Three coelomate groups Protostomia (Protostomes) Lophotrochozoa Ecdysozoa Deuterostomia (Deuterostomes)

5 Protostomia Lophotrochozoa Deuterostomia Ecdysozoa Parazoa Radiata
Choanoflagellate ancestor

6 Coelomates Protostomia (Protostomes) Spiral cleavage
Cell divisions diagonal to polar axis, therefore spiral arrangement of cells Cleavage is determinate Each cell is destined for a specific fate No stem cells Blastopore develops into the mouth Coelom formed by schizocoely

7 Protostomes Lophotrochozoa Ecdysozoa – animals that molt
Platyhelminthes Nemerteans Mollusks Annelids Lophophorate phyla Rotifers Ecdysozoa – animals that molt Nematodes Arthropods Animals in the lophotrochozoa have either a lophophore or a trochophore larva

8 Lophophore is a circular tuft of cilia
Lophophoran Anatomy Lophophore is a circular tuft of cilia

9 Segmentation in developing annelid larva
Trochophore Larva Segmentation in developing annelid larva

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11 Coelomates Three major clades of coelomates Protostomia Deuterostomia
Lophotrochozoa Ecdysozoa Deuterostomia

12 Five main animal clades: (Parazoa) Radiata Lophotrochozoa Ecdysozoa Deuterostomia

13 Protostomes Lophotrochozoa Ecdysozoa – animals that molt
Platyhelminthes Nemerteans Mollusks Annelids Lophophorate phyla Rotifers Ecdysozoa – animals that molt Nematodes Arthropods Lophophore is a ring of tentacles, often horseshoe-shaped or coiled; trochocophore larva

14 Coelomates Deuterostomia (Deuterostomes) Radial cleavage
Cell divisions parallel or at 90°, therefore cells directly above or below each other Cleavage is indeterminate Cells are pleuripotent “stem cells” Blastopore becomes the anus Coelom formed by enterocoely

15 Deuterostomes Echinoderms Hemichordates Chordates

16 Ecdysozoa Porifera Cnidaria Ctenophora Platyhelminthes Nemertea Mollusca Annelida Nematoda Tardigrada Onychophora Arthropoda Hemichordata Chordata Echinodermata Rotifera Lophophorate phyla Ecdysis Segmentation Protostome pattern of development Radial symmetry Deuterostome pattern of development Bilateral symmetry, 3 tissue layers, body cavity Tissues Multicellularity Choanoflagellate ancestor Parazoa Radiata Lophotrochozoa Deuterostomia Protostomia

17 Segmentation Three classes Polychaeta Oligochaeta Hirudinea Few Hairs

18 Identifying Characteristics
Segmentation (metamerism) Chaetae (setae) bundles of chitinous cylinders held together by sclerotinized protein

19 Emerging patterns in evolution
Coelom Schizocoely Segmentation Metamerism – body parts repeated in each segment Each segment can carry out all survival functions Ventral nerve cord

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21 Segmentation Annelids are the first phylum to show segmentation of the body also known as metamerism Each metamere, or segment, carries out all the functions necessary for any organism to survive. To build a bigger (better?) animal each segment was repeated linearly creating serially homologous metameres, with each identical to the one next to it. Metamerism is a third type of symmetry along with radial and bilateral

22 Segmentation Ancestral metameric unit probably had:
A mass of nervous tissue and related nerves to coordinate its functions Circular and longitudinal muscles to allow it to change its shape using a hydrostatic skeleton An excretory system to eliminate wastes Gonads to produce gametes. These structures are all derived from a combination of mesoderm and ectoderm.

23 Segmentation The alimentary tract was the only part of the system that wasn't metamerically arranged Advantages of linear processing of ingested food by a complete gut were now a liability. Need to get nutrients from where they were being absorbed by the gut to all of the isolated body segments

24 Circulatory System Distribution of nutrients was achieved by the closed circulatory system Supplied each segment Had blood vessels that ran the length of the animal.

25 Emerging patterns in evolution
Segmentation Coelom Schizocoely Enterocoely Ventral nerve cord

26 Annelids Emerging patterns in evolution
Ventral nerve cord nerve cord

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28 Niches of Annelids Annelids have radiated into a number of niches
Parasites: leeches (and myzostomarians) Filter-feeders of particulate matter suspended in the oceans: feather duster (tube) worms Predators of other invertebrates: Nereis Consumers of soil or sediments: earthworms Most significant ecological role played by annelids is reworking of soil and sediments. Soils may harbor 50 to 500 earthworms per m2 Keep soils aerated Their castings (feces) fertilize the soil.

29 Niches of Annelids Many polychaetes and oligochaetes, and even a few leeches, are burrowers that constantly rework the sediment through which they burrow In addition, they may ingest and excrete large quantities of sediments or soils. Some sandy beaches may harbor 32,000 burrowing annelids per m2, which collectively may ingest and excrete 3 metric tons of sand per year!

30 Niches of Annelids Metameric arrangement of the coelomic spaces allowed the first annelids to burrow into the rich organic sediments of the ocean bottom where they fed on a food source that no other group of animals was exploiting. How???????

31 Niches of Annelids Terrestrial oligochaetes are highly adapted for burrowing Extensive streamlining of body No sensory structures on the head No parapodia Reduction in the number of setae which are still involved in locomotion.

32 Niches of Annelids Parasitic leeches also show adaptations for their niche The spacious coelom essential for burrowing has been lost Coelom has become reduced to only a series of spaces and sinuses that surround the internal organs.

33 Annelid Taxonomy Through most of the 20th century Annelida was split into three major groups: Polychaeta, Oligochaeta (earthworms etc.) and Hirudinea (leeches). Oligochaeta and Hirudinea form a clade comprised of several thousand species, and should be referred to either as Oligochaeta or Clitellata This group may well belong inside Polychaeta, thus making Polychaeta synonymous with Annelida

34 Diversity of Segmented Worms
Polychaetes - many bristles Lugworms Clam worms Bristleworms and lots more Oligochaetes - few bristles Earthworms Hirudinea Leeches Should perhaps be grouped with Oligochaetes as Class: Clitellata, because this anatomical feature is unique to these two groups of worms

35 Diversity of Segmented Worms
Polychaetes are the most primitive annelids Probably evolved in the Precambrian Niches Sedentary forms Burrowers Tube worms Errant forms Swimmers Crawlers Use modified parapodia

36 Canadia - a Middle Cambrian polychaete from the Burgess Shale deposit in British Columbia

37 Fossundecima another polychaete from the Carboniferous Period
Fossundecima another polychaete from the Carboniferous Period. This fossil is from the Mazon Creek deposits near Braidwood IL. It has been preserved in a concretion that has been split open.

38 Antarctic featherduster worms

39 Christmas tree worms

40 Diversity of Segmented Worms
Fireworms - polychaetes Eat fire corals Bristles can break off in skin Venom causes long-lasting burning sensation

41 Diversity of Segmented Worms
Feather-duster Worm, Eudistyla sp. Clam Worm Nereis

42 Clam Worm Nereis

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45 Setae = chaetae

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48 Lugworms - live in J-shaped tubes in sediments. Deposit feeders.

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60 Reproduction in Annelids
Sexes in annelids Most earthworms and leeches are monoecious (hermaphroditic) Possess a specialized set of segments called the clitellum Internally the reproductive structures are located in distinct segments Polychaetes are dioecious (separate sexes) Some oligochaetes and polychaetes can also reproduce asexually by budding.

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63 Development Trochophore larva
Polychaete eggs hatch into a particular type of planktonic larva - the trochophore Which later metamorphoses into a juvenile worm.

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67 Later stage in development - note the three sets of chaetae

68 Larva - note nerves (black lines)

69 Head of young adult Nereis - note jaws

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71 Development Segments are formed sequentially in annelids and are established during development from growth zones located at the posterior end of the body The youngest segment in the body of an annelid is always the most posterior.

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73 Epitoky Epitoky in polychaetes
Unusual mode of reproduction unique to polychaetes Worm undergoes a partial or entire transition into a pelagic, sexually reproductive morph known as an epitoke Polychaete epitokes can often be seen swarming around submerged lights during summer nights In many cases, epitoky involves loss or degeneration of digestive structures and enhancement of swimming, sensory, and gonadal structures.

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76 Syllid epitokes Female Male

77 Hirudo medicinalis Medicinal leech Parasitic
Adults feed on the blood of mammals Young leeches feed on frogs instead of mammals because their jaws are not strong enough to bite through mammalian skin Attaches to the host by means of its two suckers and bites through the skin of its victim Simultaneously, the leech injects Anaesthetic so that its presence is not detected Anticoagulant in order for the incision to remain open during the meal - hirudinin

78 Hirudo medicinalis Vasodilator Hyaluronidase Increases blood flow
Enzyme that breaks down “bonding agent” in connective tissue

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80 Medicinal Leeches The leech's main therapeutic benefits are not derived from the average 5 mls of blood removed during biting (although this may provide dramatic relief at first), but from the anticoagulant and vasodilator contained in the leech saliva. permit the wound to ooze up to 50 mls of blood for up to 48 hours leech bites will bleed (ooze)an average of six (6) hours goal is to produce an adequate venous outflow from the tissue by adjusting the number of leech applications and thereby bite wounds to suit the clinical applications; for example, 6 leech bites

81 16 Hours Postoperatively: Photograph shows severe venous congestion in the reimplanted ear following surgery.

82 48 Hours Postoperatively: 4 leeches have been applied every 8 hours.

83 72 Hours Postoperatively3 leeches applied every 8 hours

84 Two Months Postoperatively:

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