INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM EUMETAZOA (EUMETAZOA)

DIVISION TRIPLOBLASTIC (TRIPLOBLASTICA) OR BILATERAL (BILATERIA) ANIMALS

SUBDIVISION SPIRALIA (SPIRALIA)

PHYLUM FLATWORMS (PLATHELMINTHES)

SUBPHYLUM TURBELLARIANS (TURBELLARIA) OR ARCHIDERMATA

SUPERCLASS ARCHOPHORA (ARCHOPHORA)

CLASS POLYCLADS (POLYCLADIDA)

Marine inhabitants, with the exception of a single freshwater species from the island of Borneo. Most species prefer shallow depths in warm and tropical waters. However, some species are found at depths down to 1,000 m. They are relatively large in size (up to several centimeters in length) and often brightly colored. The body is leaf-shaped. In many species, the anterior end of the body bears a pair of tentacles and numerous eyes. Statocysts are absent. The Mouth is located in the middle of the body or closer to the posterior end.

In most species, the Pharynx is strongly muscular; it is capable of protruding from the mouth, capturing, engulfing, and sucking out prey. In some species, the mouth and pharynx are elongated along the body axis, allowing the worms to

capture quite large prey. The midgut is highly branched (Fig. 110, c), and in the species Thysanozoon hrochii, the Branches of the intestine extend into special dermal papillae located on the DORSAL SIDE OF the body (Fig. 118). The Ovaries and Testes appear as numerous small glands; some species possess a special sucker posterior to the female genital opening. Development proceeds with metamorphosis, and they are characterized by the Müller's larva (Fig. 114).

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Fig. 118. Polyclad turbellarian Thysanozoon brochii (after Joffe)