ANNELIDS Instructor: Almonther I. Alhamedi The Islamic University of Gaza Department of Biology
[email protected] : E-mail http://site.iugaza.edu.ps/mhamedi :Web page GENERAL CHARACTERISTICS Segmentation Septa
highly developed between segments Each segment is also known as a metamere Each metamere has a parapodia with numerous setae
GENERAL CHARACTERISTICS Integument- epidermis is one cell layer with mucous gland that secrete a moist cuticle. Muscle- longitudinal and circular muscles Each segments muscles are independent of the other segments. Digestive- complete, complex, with
typhlosole for absorption and chloragogen cells acting as digestive gland and excretory cells. As the liver function. Excretory- a pair of nephridia per segment. GENERAL CHARACTERISTICS
Respiratory -through skin, some through parapodia; tubeworms have gills. Circulatory- closed system, use hemoglobin as oxygen carrier. Nervous- dorsal brain; ventral, double, solid nerve cord, with ganglia in each segment. Endocrine- hormones secreted by nervous system.
Annelids are to be found in marine, fresh-water and terrestrial habitats. Annelids are hermaphrodites The larva is the trochophore. Coelomate. CNS of preoral ganglia linked by
connectives to a pair of ventral ganglionated cords. CLOSED VERSUS OPEN CIRCULATORY SYSTEMS HYDROSTATIC
SKELETON Earthworm Phylum Annelida ANNELID BODY PLAN Setae
PHYLUM ANNELIDA Class Polychaeta Marine worms Nereis class
Oligochaeta Subclass Hirudinae earthworms
Leeches Lumbricus Hirudo CLASS POLYCHAETA
Approximately 63% of all annelids species are placed in the class Polychaeta and mostly marine. Polychaeta possess at least 1 pair of eyes and at least 1 pair of sensory appendages (tentacles) on the anterior most part of the body (the prostomium). The body wall is extended laterally into a series of thin,
flattened outgrowths called parapodia Parapodia function in: 1- Gas exchange between the worm and its environment. 2- Locomotory function in many species due to the presence of chitinous support rods called acicula ( Fig. 13.3a).
3- In addition, siliceous, chitinous, or, more rarely, calcareous bristles called setae protrude from each parapodium POLYCHAETE ANATOMY
POLYCHAETE ANATOMY (CROSS SECTION) Polychaete Larvae class Oligochaeta
Approximately 3,500 oligochaete species have been described. Only about 6.5% of oligochaete species are
marine, most are found in fesh-water or terrestrial habitats. The common earthworm, Lumbricus terrestris, is a familiar example (Fig. 13.12a. Oligochaetes have more streamlined appearance compared with most polychaete annelids. parapodia are lacking and the anteriormost region of the
body, the prostomium, lacks sensory structures, such as eyes and tentacles. Oliogchaetes do have setae, but the setae are less densely distributed along the body. Oligochaete Excretory System
CLASS HIRUDINEA includes the leeches, and has approximately 500 to 630 described species. Most leeches occupy freshwater or terrestrial habitats; only a small proportion from the species is marine. There are no parapodia and no setae. -(Fig. 13.15b and 13.16).
-The body is generally not separated into compartments by septa, and the continuous coelomic space is largely filled with connective tissue, or mesenchyme (Fig. 13.17). Leeches locomote over solid substrates by using suckers as temporary anchores. These suckers are formed from groups of segments at
the bodys anterior and posterior ends (Fig. 13.16 and 13.18). LEECHES Leeches are generally ectoparasitic, feeding either on the blood of other invertebrates or, more commonly,
on the blood of vertebrates. Many parasitic species possess 3 toothed jaws within the mouth; leech uses these jaws to make an incision in the host. Other species have a protrusible proboscis, through which blood is removed from the host. An application of Hirudo medicinalis, the medical
leech, help in 2 ways: 1-Drains off the excess blood from the finger, 2-Injects an anticoagulant-hirudin- that keeps the blood flowing out from the bite-wound long after the sated leech has dropped off.
Hirudo medicinalis LUMBRICUS clitellium clitellium
dorsal ventral Lumbricus EARTHWORM
DISSECTION Cross section Return to
EARTHWORM CROSS SECTION taxonomy
