Terrestrial, marine, freshwater. Repeating segments. Triploblastic. True coelomates – complete gut. Closed circulatory system. Well developed nervous system. Respiratory organs. Protostome development. Metamerism (unspecialized) segmentation. One or more pairs of setae.
Phylum Annelida Ancestral Traits –Coelomate –Lophotrochozoan- non-molting protostomes –Protostome –Closed circulatory system –Cephalization Derived Traits –Segmentation Metamerism Septa –Setae Bristles –Myelinated neurons ~ 40K species of annelids Spirobranchus giganteus Christmas tree worm
Systems IntegumentIntegument- epidermis is one cell layer with mucous gland that secrete a moist cuticle. SkeletalSkeletal -hydrostatic (using coelom) MuscleMuscle- longitudinal and circular muscles Each segments muscles are independent of the other segments. DigestiveDigestive- complete, complex, with absorption and digestive glands and excretory cells.
Systems (continue) ExcretoryExcretory- a pair of nephridia per segment. RespiratoryRespiratory -through skin, some through parapodia; tubeworms have gills. CirculatoryCirculatory- closed system, use hemoglobin as oxygen carrier. NervousNervous- dorsal brain; ventral, double, solid nerve cord, with ganglia in each segment. EndocrineEndocrine- hormones secreted by nervous system. ReproductiveReproductive- –Dioecious in Polychaeta; no special organs, posterior end becomes gonads. –Monoecious in Oligochaeta and Hirudinea; Clitellium.
Annelid Taxomony Class Polychaeta (many bristles) –most numerous # species –marine Hermodice crunculata
Annelid Taxomony Class Polychaeta Class Clitellata –Subclass Oligochaeta (few bristles) Freshwater, marine & terrestrial Lumbricus terrestris
Annelid Taxomony Class Polychaeta Class Clitellata –Subclass Oligochaeta –Subclass Hirudinea Fixed # segments (34) Setae absent Hirudo medicinalis
Annelid Body Plan Setae
Class Polychaeta Highly specialized head regions –Antennae –Sensory palps –Feeding appendages Paired extensions of body (parapodia) Often tube-dwelling –Burrow into substrate and secrete mucus/ CO 3 materials Bispira bunnea sabellid worm Spirobrancheus giganteus
Polychaete Reproduction Most are dioecious-few monoecious Some asexually but sexually more common Trochophore larvae Some species develop specialized segments containing gametes –Epitokes –Segments are released and gametes burst out
Polychaete Asexual Reproduction Epitokes are essentially buds Clues to ancestral origin of segmentation –Segmentation may have been derived from incomplete budding processes
Phylum Annelida 27 Class Oligochaeta Defining characteristics –Pronounced cylindrical glandular region of the body = clitellum Second largest class in the phylum Annelida Most spp. are earthworms, very few are marine
Phylum Annelida 28 Polychaetes and Oligochaetes Oligochaetes differ from polychaetes in several ways: –No parapods, fewer setae (if at all) –Hermaphroditic with sex cells produced in a separate section –No larval stages Giant Gippsland earthworm
Setae: a.k.a. Bristles
Oligochaete Development For terrestrial oligochaetes, development is direct without any larval forms Some aquatic oligochaetes retain a trochophore-like larval stage Site for earthworm anatomy:
Quick and Easy Earthworm Morphology Guide Aporrectodea turgida Lumbricus rubellus -Earthworms can be classified by size, burrowing habits, and color -Number, location and pattern of genital tumescences (GT) and tubercular pubertatis (TP) -Location & shape of clitellum
Common Terrestrial Oligochaetes: Earthworms Eisenia foetida Redworm Octagonal Tail Worm Dendrobaena octaedra This link shows diversity of Oligochaetes!
Earthworm Dissection Return to taxonomy Cross section
Phylum Annelida 38 Subclass Hirudinea Defining characteristics –Posterior sucker Predominately freshwater, but do occur in all seas and moist soil Leeches do not burrow, lack parapods and setae Clitellum only visible during breeding
Horse leech-actually feeds on small worms Haemopis sanguisuga Great Amazon Leech Haementaria ghiliani
Phylum Annelida 41 Leech Anatomy Anterior sucker is small and contains the mouth –Anterior sucker creates a wound with saw like jaws Leeches drink other animals’ blood, usually vertebrates –Can be carnivores, or scavengers; leeches are not set in their feeding habits
Hirudo medicinalis More leech info:
Phylum Annelida 43 Blood Sucker The salivary glands excrete hirudin which prevents the blood from coagulating –May also secrete an anaesthetic and substance to dilate small blood vessels Blood is broken down by symbiotic bacteria that is then used by the leeches Leeches were commonly used in the 19th century for bloodletting –Recent medical uses are to relieve pressure after vascular tissue is damaged –Snake bites or the reattachment of a finger or ear
Phylum Annelida 44 Leech Reproduction Leeches are simultaneous hermaphrodites that lack a free-living larvae stage Fertilization is internal through copulation Development occurs in a cocoon similar to the Oligochaetes