Unit 5 Part 2: Intro to Lophotrochozoans, Phylum Platyhelminthes, Phylum Nematoda

$$Lophotrochozoan Phyla:$$

General Characteristics of Lophotrochozoans:

• Bilaterally symmetrical

• Triploblastic

• Protostome: blastopore develops into the anus

$Function of Lophophore Structure:$$$Function of Lophophore Structure:$$

• A horseshoe shaped feeding structure that is a common evolutionary link between members of the phyla. Each member will have this structure at one point in their lives

• Shows evolutionary relationship

==Phylum Platyhelminthes:==

How many species?

• 34,000 species

==Characteristics:==

• Flattened

• ==Triploblastic:== has three tissue layers

• ==Acoelomate== (has no coelom/no body cavity/no organs or organ systems)

• ==Bilaterally symmetrical==

• Unsegmented worms

==Classes of Platyhelminthes (4):==

• ==Class Turbellaria (Planarians!!!!!!)==:

  • Free-living and aquatic

  • Can be both freshwater and marine

  • Predators and scavengers (first true hunters!)

  • 1 cm-60 cm

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==Locomotion:==

• They are bottom dwellers

• They move using cillia and muscular contractions

• They can free swim sometimes

==Digestions:==

• They have an incomplete digestive tract: they only have a mouth but they don’t have an anus

  • Branched digestive systems allows for diffusion of nutrients

  • No circulatory system

  • They have a Pharynx: muscular ingestion organ that is located on their underbelly and attaches to their mouth

  • Chemo receptors on their head that help them find prey

  • ==Chemo receptors==: structures/cells that can sense chemicals/heat in the water to find prey

==Exchanges in the Environment:==

• No respiratory organs

• Gases are exchanged, nitrogenous waste (chemical waste/cellular waste) is eliminated through diffusion through body wall and flame cells

  • ==Flame Cells==: a specialized excretory cell (they operate like kidneys)

==Nervous and Sensory Function:==

• Central ganglia: cluster of neurons located in the head region

• Platyhelminthes can detect touch, water current, and chemicals

• ==Auricles:== projections on the side of the head; help locate food by using chemoreceptors

• ==Ocelli:== “eye spots” that orient the animal towards light

  • Most platyhelminthes (turbeliina) are negatively photoreceptive (meaning they move away from the light)

==Reproduction and Development:==

• Asexually by transverse fission

  • ==Transverse Fission==: They can pinch their bodies together horizontally and make two halfs called zooids. These half each grow the part that they need to become a new turbellina that being either a tail or a head.

• Sexually: ==monoecious== (both male and female reproductive organs in one body)

  • ==Reciprocal sperm exchange between individuals==

  • Fertilized eggs are laid in capsule called coccoon

  • ==Summer capsules==: hatch in a fast time, 2 to 3 weeks and immature animals emerge

  • ==Autumn capsules==: thick walls that resist freezing and drying out; hatch after winter when conditions are favorable

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==Class Trematoda:==

• These are called ==flukes==

• Wide, flat shape

• 10,000 species; that are all parasitic

• They feed on host cells and cell fragments

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==Class Monogenea:==

• External parasites of ==fishes==

• Attach to gill filaments

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==Class Cestiodea:==

• This class includes ==tapeworms==

• They lack a mouth and simple digestive systems

  • Instead these cestiodea absorb nutrition from host through cell wall

• ==Proglottids:== long, repeating sections that each contains a set of reproductive structures

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^^Phylum Nematoda:^^

Main Characteristics:

• ^^Triploblastic^^

• ^^Bilateral^^

• Unsegmented

• ^^Pseudocoelomate (fake body cavity)^^

• ^^Cuticle^^: outer body covering of nematodes that is made of the collagen protein

  • Covers body

• Digestive System:

  • ^^Complete digestive tract^^: mouth and anus

  • Mouth surrounded by lip bearing sense organs

  • Located on the head

Nematode Parasites of Humans:

• ^^Ascaris lumbricodes^^: Affects dogs and cats normally

  • ^^Intestinal roundworm^^

  • 800 million people infected

  • Live in small intestines

  • Eggs exist in the feces that the dog and cats excrete

  • Eggs ingested and move to intestinal tract

• ^^Enterobius vermicularis^^

  • ^^Human pinworms^^

  • Most common roundworms in US

  • Live in lower region of large intestine

  • Females carry eggs out of rectum, deposit them, then die

  • Eggs are swallowed and move to intestines

• ^^Necator americanus^^

  • The New World Hookworm

  • Found in Southern US

  • Live in small intestine

  • Eggs pass out in feces and hatch

  • Larva penetrate the skin, makes way to the intestines

• ^^Trichenella spiralis (pork worm)^^

  • The pork worm

  • Live in small intestines of all carnivores and omnivores

  • Females give birth to live larvae that migrate to muscle tissue

  • Remain infective for years (trichinosis)

  • Transmission: Another animal eats muscle, migrates to that animal’s small intestines

• ^^Wucheria species^^

  • The filarial worms

  • Live in lymphatic system of humans

  • Causes fluids to accumulate in appendages (elephantiasis)

  • Produce larvae: microfilariae

  • Circulates in bloodstream, carried by mosquitoes to next person (intermediate host)