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Table 8b
(Cestodes)
Differential
Morphology of the Diagnostic Stages of Helminths Found in
Humans: Eggs (Cestodes)
| Species | Size | Shape | Color | Stage of Development When Passed | Specific Features and Variations |
| CESTODES | |||||
| Taenia saginata Taenia solium |
35 mm. Range, 31-43 mm. | Spherical with thick striated shell. | Walnut brown. | Embryonated. 6-hooked oncosphere present inside a thick shell. | Thick, striated shell. Eggs of T. solium and T. saginata are indistinguishable and species identification should be made from proglottids or scoleces. "Taenia" spp. should be reported if only eggs are found. |
| Hymenolepis nana | 47 mm × 37 mm. Range, 40-60 mm × 30-50 mm. | Oval. Shell consists of 2 distinct membranes. On inner membrane are two small "knobs" or poles from which 4 to 8 filaments arise and spread out between the two membranes. | Colorless, almost transparent. | Embryonated. 6-hooked oncosphere inside shell. | Polar filaments. |
| Hymenolepis diminuta* | 72 mm. Range, 70-86 mm × 60-80 mm. | Round or slightly oval. Striated outer membrane and thin inner membrane with slight poles. Space between membranes may appear smooth or faintly granular. | Yellow. | Embryonated. 6-hooked oncosphere inside shell. | Resembles H. nana but lacks polar filaments. Poles are rudimentary and often hard to see. |
| Dipylidium caninum* | 35-40 mm. Range, 31-50 mm × 27-48 mm. | Spherical or oval. 5-15 eggs (or more) are enclosed in a sac or capsule. | Colorless. | Embryonated. 6-hooked oncosphere inside shell. | Eggs are contained in a sac or capsule which ranges in size from 58mm to 60 mm x 170 mm. Occasionally capsules are ruptured and eggs are free. |
| Diphyllobothrium latum | 66 mm × 44 mm. Range, 58-76 mm × 40-51 mm. | Oval or ellipsoidal with an inconspicuous operculum at one end and a small "knob" at the other end. | Yellow to brown. | Unembryonated. Germinal cell is surrounded by a mass of yolk cells which completely fills inner area of shell. Germinal cell is usually not visible. | Egg resembles hookworm egg but has a thicker shell and an operculum. |
*Usually found in lower animals, only occasionally found in humans.
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