MEDICAL BIOLOGY, ANATOMY, HUMAN PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedoniuk 2010

BIOLOGY

CHAPTER 2. BIOGEOCENOTIC LEVEL OF LIFE ORGANIZATION AND HUMAN PLACE IN IT

2.5. MEDICAL ARACHNOENTOMOLOGY

Phylum Arthropoda

Class Crustacea

The Class comprises approximately 25,000 species inhabiting predominantly marine and freshwater environments. It is divided into two subclasses: Entomostraca (lower crustaceans) and Malacostraca (higher crustaceans).

Lower crustaceans (such as Daphnia, Cyclops, and Diaptomus) dwell in the Water Column and constitute a major component of plankton. A distinctive morphological feature is their long, branching antennules, which maintain buoyancy and serve for locomotion, along with the presence of a single unpaired simple eye (Fig. 2.41).

Fig. 2.41. Female cyclops (Cyclops strenuus):

1 - eye; 2 - antennule; 3 - antenna; 4 - cephalothorax; 5 - free thoracic segments; 6 - abdominal segments; 7 - caudal furca; 8 - egg sac; 9 - intestine; 10 - Ovary; 11 - longitudinal thoracic Muscles.

They are of substantial ecological importance as a primary food source for numerous fish species and cetaceans, and they also contribute to the biological self-purification of water bodies. Medical significance: Cyclops and Diaptomus serve as intermediate hosts for helminths, specifically the broad fish tapeworm (Diphyllobothrium latum) and the guinea worm (Dracunculus medinensis).

Higher crustaceans primarily inhabit marine and freshwater environments (including crayfish, crabs, lobsters, spiny lobsters, shrimp, and hermit crabs). Only woodlice and certain crabs (such as the robber crab) have adapted to terrestrial life. Medical significance: freshwater crayfish and crabs in East Asian countries and the Russian Far East act as intermediate hosts for the lung fluke (Paragonimus ringeri).