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Questions and Answers
Where does the male genital opening of the leech lie?
Where does the male genital opening of the leech lie?
What is the primary function of the salivary glands in leeches?
What is the primary function of the salivary glands in leeches?
What aids in the storage capacity of the leech's crop?
What aids in the storage capacity of the leech's crop?
How does respiration occur in leeches?
How does respiration occur in leeches?
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What type of reproduction do leeches primarily engage in?
What type of reproduction do leeches primarily engage in?
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What is primarily responsible for the collection of nitrogenous wastes in leeches?
What is primarily responsible for the collection of nitrogenous wastes in leeches?
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During reproduction, where does the fertilization of leech eggs take place?
During reproduction, where does the fertilization of leech eggs take place?
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Which of the following statements about the trochophore larva is true?
Which of the following statements about the trochophore larva is true?
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What anatomical feature is absent in leeches that is often found in other annelids?
What anatomical feature is absent in leeches that is often found in other annelids?
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How many segments does the common freshwater leech Hirudo medicinalis typically have?
How many segments does the common freshwater leech Hirudo medicinalis typically have?
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What is the primary environment where polychaetes are commonly found?
What is the primary environment where polychaetes are commonly found?
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Which characteristic is absent in polychaetes?
Which characteristic is absent in polychaetes?
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What type of feeding mechanism is employed by polychaetes such as Nereis?
What type of feeding mechanism is employed by polychaetes such as Nereis?
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How is the parapodium structured in polychaetes?
How is the parapodium structured in polychaetes?
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What is the function of the pharynx in the feeding system of Nereis?
What is the function of the pharynx in the feeding system of Nereis?
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What role do the setae in the parapodia of polychaetes play?
What role do the setae in the parapodia of polychaetes play?
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Which of the following best describes the developmental process of polychaetes?
Which of the following best describes the developmental process of polychaetes?
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What is the excretory organ found in each segment of polychaetes?
What is the excretory organ found in each segment of polychaetes?
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Study Notes
Polychaeta
- Bristle worms live in marine environments, frequently in shallow intertidal zones.
- Many are carnivores, feeding on invertebrates.
- Body has numerous chaetae.
- A head region with eyes, tentacles, and palps is present.
- Each segment bears one pair of parapodia.
- A clitellum is absent.
- Sexes are separate, and development is indirect, involving a trochophore larva.
Sand Worm (Nereis)
- Body divided into many segments (200+).
- Segments separated by intersegmental grooves.
- Well-developed head region, consisting of:
- Prostomium: Carries the mouth and sensory organs (4 eyes, 2 tentacles).
- Rest of the body bears parapodia.
Parapodia
- Each parapodium consists of a dorsal notopodium and a ventral neuropodium.
- Dorsal notopodium has a dorsal cirrus with a chaetae bunch.
- Ventral neuropodium has a ventral cirrus with a chaetae bunch.
- Parapodia are supported by dorsal and ventral acicula (long setae).
Parapodium Functions
- Locomotion.
- Respiration (increase respiratory surface).
- Sensation.
Nereis Internal Anatomy
- Body wall with muscles (circular and longitudinal).
- Coelomic epithelium..
- Dorsal and ventral blood vessels.
- Digestive system (mouth, pharynx, esophagus, crop, stomach, intestine, anus).
- Nephridia (excretory organs).
- Nerve cord.
- Eggs.
- Respiratory capillaries.
- Setae.
Nereis Feeding and Digestive System
- Carnivorous, feeding on crustaceans.
- Mouth is below the prostomium, leading to a muscular pharynx.
- Pharynx is lined with thickened cuticle.
- Numerous small teeth and two jaws are thickened in specific areas of the pharynx.
- Prey is captured by mouth jaws.
- Teeth pull food into the pharynx.
Nereis Digestive System Details
- Pharynx leads to a narrow esophagus with bilobed esophageal glands.
- Followed by a long intestine without a typhlosole.
- Ends with rectum and anus.
Nereis Excretory System
- One pair of nephridia per segment (except some anterior and posterior ones).
- Each nephridium consists of a syncytial mass with a coiled nephridial tubule opening at both ends.
- Nephrostome (opening in coelom) is in anterior segment.
- Nephridiopore (opening to the outside) is ventral at base of parapodium.
- Nitrogenous waste (mainly ammonia) is collected from coelomic fluid and blood.
- Cilia move waste to the outside via nephridiopores.
Nereis Blood Vascular System
- Dorsal blood vessel.
- Ventral blood vessel.
- Parapodial capillaries.
- Perineural blood vessels.
- Dorso-intestinal vessel.
- Ventro-intestinal vessel.
- Intestinal capillaries.
Reproduction and Life Cycle
- Sexes are separate.
- Gametes bud from gonads and mature in coelom.
- Gonoducts and gonopores are absent.
- Males mature near the surface, attracting females.
- Segments with gonads rupture to release eggs and sperm into water.
- Fertilization occurs in water, forming zygotes.
- Zygotes develop into trochophore larvae.
Trochophore Larva
- Has preoral ciliated ring used for swimming.
- Apical sensory plate with cilia.
- Complete gut with mouth and anus.
- Nephridia and mesodermal cells are present in the larva.
- Cilia are lost, and the larva settles to the bottom to become a young worm.
Hirudinea (Leeches)
- Live in aquatic and damp terrestrial environments.
- Fixed number of segments, subdivided into secondary annuli.
- Reduced head, no tentacles.
- No chaetae or parapodia.
- Terminal suckers (for attachment and locomotion).
- Sexes are separate, and development is direct in a cocoon.
Hirudo Medicinalis (Medical Leech)
- Freshwater annelid.
- Blood-feeding ectoparasite.
- Two suckers.
- Anterior sucker encloses the mouth and has 3 jaws.
- Posterior sucker is non-perforated.
- First five segments have 5 pairs of eyes.
- Remaining segments have papillae.
- Body consists of 33 segments but divided into 5 annuli (variaion between anterior and posterior).
- Nephridiopores (17 pairs) open ventrally; anus in front of posterior sucker.
- Male genital opening on segment 11; female on 12.
Leech Locomotion
- Uses body movements and suckers to move.
Leech Digestive System and Nutrition
- Modified for blood-feeding.
- Mouth with 3 jaws to cut skin.
- Suctorial pharynx.
- Crop with lateral diverticula to store blood.
- Stomach.
- Intestine, opening externally via anus.
- Salivary glands secrete hirudin (anticoagulant).
Leech Respiration and Excretion
- Respiration occurs through skin.
- Excretion is performed by 17 pairs of nephridia in segments 7-23.
Leech Reproductive System
- Hermaphroditic (both male and female reproductive organs present).
- 9 pairs of testes.
- Common vas deferens, epididymis.
- Male genital opening on segment 11.
- Two ovaries, oviducts, vagina.
- Female genital opening on segment 12.
- Cross-fertilization common.
- Fertilized eggs are laid in cocoon for development.
- Direct development.
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Description
Test your knowledge about Polychaeta, the fascinating group of bristle worms found in marine environments. This quiz covers their anatomy, including the structure and function of parapodia, as well as their reproductive strategies and habitats. Dive into the details of their unique characteristics and discover more about these interesting organisms.
