Biology 625
ANIMAL PARASITOLOGY
Fall semester lecture note outline

Updated: 08 October 1999

General characteristics

1. A large, specious group of apicomplexans that usually reside in the intestinal tract or body cavity of invertebrates or lower chordates
2. Mature gamonts typically large and usually develop extracellularly
3. Sporozoites, merozoites, and gamonts often possess an anterior adhesive organ
   1. mucron (apical anchoring structure in acephaline gregarines)
   2. epimerite (apical anchoring structure representing a third chamber in cephaline gregarines)
4. Syzygy (pairing of two gametes prior to fertilization. In gregarines, this usually occurs end-to-end) usually present
5. Gamogony generally results in production of similar numbers of male and female gametes in each gametocyte
6. Most gametes isogamous, although some species anisogamous with the male gamete possessing a flagellum or flageliiform-like process
7. Zygotes develop into oocysts while within a gametocyst
8. Nearly all species are homoxenous (single host life-cycle)

Basic taxonomy

1. Order: Archigregarinorida (you will not be tested over this taxon)
   1. Merogony, gamogony, and sporogony present
   2. Gamonts aseptate
   3. Found in marine invertebrates (annelids, ascidians, hemichordates, sipunculids)
   4. Two families and four genera described
2. Order: Eugregarinorida
   1. Gamogony and sporogony present; merogony absent
   2. Most species in arthropods or annelids
   3. Three suborders and about 250 genera known
      1. suborder: Blastogregarinorina (you will not be tested over this taxon)
         1. gamogony with gamonts still attached to intestinal wall
         2. gametes bud off gamonts
         3. anisogamy present
         4. syzygy absent
         5. gametocysts absent
         6. oocysts with 10-16 naked (without sporocyst) oocysts
         7. gamont composed of single structure, without septa (i.e., no protomerite or deutomerite)
         8. mucron present
         9. known from marine polychaetes
         10. only one family and one genus known
      2. suborder: Aseptatorina
         1. gamonts without septa, as single compartment (i.e without protomerite and deutomerite)
         2. some species with mucron or epimerite
         3. syzygy present
         4. about 10 families and nearly 500 named species within over 70 genera
      3. suborder: Septatorina
         1. gamonts or trohozoites divided by septum into protomerite and deutomerite
         2. epimerite present
         3. most species in arthropods
         4. nearly 1200 named species contained in over 150 genera within 3 superfamilies
         5. 4 groups (you will not be tested over these superfamilies)
            1. Superfamily: Porosporicae (life-cycle digenic; 3 known genera)
            2. Superfamily: Fusionicae (life-cycle monogenic; nucleus and endocyte of satellite infected into primite during syzygy; single family and one genus)
            3. Superfamily: Gregarinicae (life-cycle monogenic; nucleus and endocyte of primite and satellite remain isolated until gametocyst formation; associations before gamonts fully mature and enter syzygy)
            4. Superfamily: Stenophoricae (life-cycle monogenic; nucleus and endocyte of primite and satellite remain isolated until gametocyst formation; no associations of gamonts prior to onset of syzygy)
   4. Order: Neogregarinorida (you will not be tested over this taxon)
      1. Merogony, gamogony, and sporogony present
      2. Merogony thought to be derived secondarily
      3. Septate, with epimerite, protomerite, and deutomerite
      4. Thought to be evolved from the Eugregarinorida and perhaps a link with the coccidia
      5. Found in fat body, Malpighian tubules, intestine, or hemolymph of insects
      6. Six families and about 13 genera

Monocystis lumbrici (Suborder: Aseptatorina)

1. oocysts (spores) containing sporozoites eaten by earthworms, Lumbricus terrestris
2. rupture in gizzard
3. sporozoites penetrate gut, migrate through dorsal blood vessels and into hearts; exit hearts
4. enter seminal vesicles (enter blastophores)
5. gradually increase in size
6. exit cells, destroying them, and enter lumen of seminal vesicle
7. mature into gamonts (=sporadins), and reach a size of about 200 micrometers in length
8. attach to host cells in region near sperm duct
9. associate in syzygy (associate in tandem; more anterior member the primite; the posterior the satellite)
10. the pair flatten and a cyst wall forms around the pair, forming a gametocyst
11. each nucleus divides repeatedly
12. nuclei move to periphery of cytoplasm, and bud to become gametes. The representative gametes are different morphologically and are termed anisogametes
13. gametes of each type pair to form a zygote (2N)
14. sporogony occurs (including meiosis), resulting in resistant wall and eight 1N sporozoites
15. gametocytes or oocysts exit in several ways. They may pass through the sperm ducts, the worm may die and degenerate, or they may be eaten along with the entire worm and pass through the gut to the outside world through the predator

Gregarina cuneata (Suborder: Septatorina)

1. oocysts ingested by larval beetles (mealworms), Tenebrio molitor
2. excyst in gut of beetle
3. sporozoites penetrate intestinal cells
4. trophont grows and matures somewhat; attachment structure an epimerite
5. trophozoite detachs leaving the epimerite behind
6. The trophozoites undergo association (pairing of individuals early, so that they undergo maturation prior to sexual maturation). The anterior member of the pair is the primite and the posterior the less elongate satellite
7. further growth and maturation while associated
8. once growth is completed, they can now be termed gamonts and are formally in syzygy; satellite slightly less elongate than primite
9. gametocyst wall secreted
10. each nucleus divides repeatedly
11. nuclei and small amount of cytoplasm partition off to become gametes. The representative gametes are different morphologically and are termed anisogametes
12. gametes of each type pair to form a zygote (2N)
13. sporogony occurs (including meiosis), resulting in resistant wall and 1N sporozoites
14. gametocysts pass out with the feces
15. after several days, chains of oocysts (spores) are extruded explosively as long chains through tubes in a process termed dehiscence.
16. Similar species in mealworms include Gregarina niphandrodes (in the adult beetle), Gregarina polymorpha (in the larvae), and Gregarina steini (in the larvae).