INVERTEBRATE ZOOLOGY IN THREE BOOKS - BOOK 1 - H.I. Shcherbak - 1995

SUBKINGDOM MULTICELLULAR ANIMALS (METAZOA)

SECTION TRUE METAZOANS (EUMETAZOA)

PHYLUM RIBBON WORMS (NEMERTINI)

Nemertines are predominantly free-living marine predators. Around a thousand species have been described, 33 of which are found in the Black Sea.

They combine traits typical of Flatworms with features of a much higher level of Organization. A distinctive characteristic of nemertines is a long proboscis at the anterior end of the body that retracts into a specialized proboscis sheath (rhynchocoel). Nemertines possess a well-developed Skin-Muscle sac with ciliated epithelium; they lack a true body coelom, and the spaces between Internal Organs are filled with parenchyma. The Digestive System is complete, featuring not only foregut and midgut, but also a hindgut that opens into an anus. The excretory system is of the protonephridial type. Nemertines also feature a well-developed closed Circulatory system. The Nervous system consists of two pairs of cerebral ganglia, with two lateral nerve cords extending from the ventral pair and connected by transverse commissures.

Nemertines are dioecious animals with numerous simply constructed Gonads. The phylum Nemertini comprises a single Class bearing the same name.