Physical characteristics

Anoplans are differentiated from nemerteans in the class Enopla by the proboscis, which is armed (i.e., there is a stylet attached to it) in enoplans but unarmed in anoplans. Other differences between the two groups include the position of the lateral nervous system and the relationship between the mouth and proboscis; enoplans have a common opening for the mouth and proboscis, while anoplans have separate openings for the two structures. Anopla contains the largest nemerteans. The longest species, Lineus longissimus, is described as being up to 98 ft (30 m) long, and several other hetero- and palaeone-merteans are big and solid worms. Parborlasia corrugatus, for example, is abundant and widely distributed in the Antarctic and can reach lengths up to 6.5 ft (2 m). While most ne-merteans are rather drab in color, the most colorful and strikingly pigmented are found among the anoplans. There have not been many experiments with nemerteans, but a few studies indicate that the coloration and pigmentation are cases of warning coloration. Most nemerteans have toxic and noxious substances in their body—undoubtedly to deter predators. When these substances are accompanied with bright colors and a lifestyle (day active, no hiding, etc.) that does not encourage them to hide from predators, the interpretation of aposematisms seems well founded. In the field, a nemertean is generally recognized by the way it moves. The normal movement is gliding over the surface by help of cilia on the ventral side in combination with mucus produced by the worm. Some species may, under certain circumstances, swim with undulating movements, but only for a short period of time.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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