Gnathostomulids are delicate wormlike animals less than 2 mm long . The first known species of Gnathostomulida (nath’o-sto-myu’lid-a) (Gr. gnathos, jaw, + stoma, mouth, L .ulus, dim. suffix) was observed in 1928 in the Baltic, but its description was not published until 1956. Since then jaw worms have been found …

Nemerteans (nem-er -te-ans) are often called ribbon worms. Their name (Gr. Nemertes, one of the Nereids, unerring one) refers to the unerring aim of the proboscis, a long muscular tube  and that can be thrust out swiftly to grasp their prey. The phylum is also called Rhynchocoela (ring -ko-se -la) …

The name Mesozoa (mes-o-zo -a) (Gr. mesos, in the middle+ zoon, animal) was coined by an early investigator (vanBeneden, 1876) who considered the group a “missing link”between protozoa and metazoa. These minute, ciliated, wormlike animals represent an extremely simple level of organization. All mesozoans live as parasites or symbionts in …

Taenia saginata (Gr. tainia, band, ribbon) is called the beef tapeworm, but it lives as an adult in the human intestine. Juvenile forms occur primarily in intermuscular tissue of cattle. A mature adult may reach a length of 10 m or more. Its scolex has four suckers for attachment to …

Schistosomiasis, infection with blood flukes of genus Schistosoma (Gr. schistos,divided, + soma, body), ranks among the major infectious dis eases in the world, with 200 million people infected. The disease is widely prevalent over much of Africa and parts of South America, West Indies, Middle East, and Far East. The …

Trematodes are all parasitic flukes, and as adults they are almost all found as endoparasites of vertebrates. They are chiefly leaf like in form with one or more suckers but lack the opisthaptor present in monogenean fluke Other structural adaptations for parasitism are apparent: various penetration glands or glands to …

The released egg is protected by a fairly tough chorion or egg case. Within this the cytoplasm and yolk are contained by a vitelline membrane. Often one or more oil globules are present. Fertilization occurs by a spermatozoon passing through a funnel-shaped micropyle leading to a fusion of the pronuclei …

It is not at all clear why some species have evolved a strategy of producing many small eggs, and others the opposite strategy of fewer, larger ones. The relationships between these characters and the implication for the species can be summarized (Blaxter, 1988) as follow: Fecundity and egg size are …

Vertebrates of both sexes possess a germinal epithelium consisting of germ and somatic cells. The gonads are mesodermal in origin and develop in close association with the nephric system. In elasmobranchs a lateral cortex gives rise to the ovary, and a more medial area becomes the testis. One of these …

According to Karel Liem (1980) most of the enormous variety and range of foods eaten by fishes is obtained through only three basic feeding styles: ram feeding, suction feeding, and manipulation or biting. Virtually all species use one, and, because they are not mutually exclusive, most species use two of …