Phylum Annelida Segmented Worms

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

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

Protostomia Lophotrochozoa Deuterostomia Ecdysozoa Parazoa Radiata Choanoflagellate ancestor

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

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

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

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

Coelomates Three major clades of coelomates Protostomia Deuterostomia Lophotrochozoa Ecdysozoa Deuterostomia

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

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

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

Deuterostomes Echinoderms Hemichordates Chordates

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

Segmentation Three classes Polychaeta Oligochaeta Hirudinea Few Hairs

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

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

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

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.

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

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.

Emerging patterns in evolution Segmentation Coelom Schizocoely Enterocoely Ventral nerve cord

Annelids Emerging patterns in evolution Ventral nerve cord nerve cord

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.

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!

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???????

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.

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.

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

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

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

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

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.

Antarctic featherduster worms

Christmas tree worms

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

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

Clam Worm Nereis

Setae = chaetae

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

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.

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

Later stage in development - note the three sets of chaetae

Larva - note nerves (black lines)

Head of young adult Nereis - note jaws

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.

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.

Syllid epitokes Female Male

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

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

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

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

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

72 Hours Postoperatively3 leeches applied every 8 hours

Two Months Postoperatively: