Marb 435 1st Edition Lecture 14 Current Lecture Asexual Reproduction Regeneration missing tails tentacles branchiae etc are easily replaced Sometimes a complete worm can be regenerated from a single segment Cloning Budding Fragmentation Fission Sexual Reproduction Most polychaetes only reproduce sexually Mostly gonochoric but some are hermaphroditic Usually paired segmented gonads but may be restricted to certain body regions Germ cells are usually stored in the coelom and can often be seen through the body wall Spawning release of gametes through nephridiopore or rupturing of body wall Epitoke and Swarming Epitoky Formation of a pelagic reproductive individual the epitoke from a benthic nonreproductive individual the atoke Epitoke often shows special adaptations for swimming and for detecting its mate Swarming Many epitokes swim to the surface simultaneously and shed their gametes Usually correlated with the moon phase and the tides These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Females seem to produce a pheromone that attracts males Release of sperm might stimulate females to release eggs Epitoky examples Family Nereididae the entire worms transforms into an epitoke Degeneration of the digestive system Enlarged parapodia with paddle chaetae Family Syllidae Many epitokes are formed by cloning along the length of the worm Each epitoke is a complete sexually mature individual Sipuncula Traditionally considered a separate phylum but now included in the phylum Annelida Body consists of a trunk and an eversible introvert with tentacles at the distal end Habitats Coral rubble Sand and mud Oyster reefs not in Galveston Among roots of mangroves and seagrass Although they have a cryptic lifestyle they can be very common Class Clitelatta Clitellum series of anterior segments enclosed in a thick glandular epidermis enclosing female gonopores or located behind them functions Secretes mucus for copulation Secretes nutritious albumen for eggs Forms a cocoon in which eggs and albumen are deposited Hermaphrodites Copulation and internal fertilization Gonads always restricted to a few segments tagmosis with testes anterior to the ovaries Direct development zygotes develop in the cocoon Brain is not in the prostomium but in an anterior trunk segment Sublcass Oligochaeta About 3500 species Terrestrial earthworms Fresh water small bodied burrowing or living on submerged vegetation Marine small bodied mostly interstitial Well developed segments Prostomium and pygidium lack appendages but prostomium is sometimes elongated almost like an appendage Four bundles of chaetae per segment Number of chaetae per bundle varies from 1 to 25 Chaetae simple and uniform Penis sometimes present Worms attach to each other on their ventral sides in opposite directions Clitellum produces mucus to glue partners together Male gonopores release sperm into the seminal receptacles of the partner Feeding Mostly scavengers feeding on dead organic matter mostly plant material and fungi Earthworms feed on the surface and may pull material into their burrows Deposit feeders eat material that obtained from mud or soil while burrowing Symbiotic bacteria produce cellulase and chitinase Subclass Hirudinea Approximately 700 species Marine freshwater and terrestrial Size range 1 30 cm Freshwater species can be extremely abundant up to 10 000 individuals per square meter Many can estivate survive periods of draught by burrowing into the ground Carnivorous or blood sucking Giant Red Leech is an example shown in class of this subclass Forms and function Typically dorsoventrally flattened Segments at both ends of body specialized to form anterior and posterior suckers Number of segments fixed to 33 but segmentation reduced Superficial annulations mask segment boundaries Chaetae absent Nervous System Similar to that of other annelids Leeches as model organisms for neurobiology Relatively simple system with fixed number of neurons Large sized neurons Coelom and circulatory system No septa and mesenteries Connective tissue fills most of the body Coelomic circulatory system Coelom is continuous throughout the leech body and replaces the hemal system Hirudo medicinalis a k a Medicinal Leech Medicinal use of leeches dates back to 130 BC Today used in grafts and re attachment surgery to enhance blood flow Beneficial properties of leech saliva Anticoagulant hirudin Anesthetic Vasodilator Reproduction Can only reproduce sexually No regeneration Protandric hermaphrodites Internal fertilization Sperm transfer either with penis or by hypodermic insemination Produce spermatophores sperm packages Sperm can be stored for extended periods of time Zygotes develop in cocoon produced by the clitellum