Invertebrate Zoology: A Study Guide - T. A. Dauda 2014

Multicellular Animals
Arthropods
Subphylum Branchiopoda - Class Crustacea - Order Decapoda

The order Decapoda brings together the most highly organized crustaceans, typically of medium to large size. The typical features of their biological Organization are examined in the General characteristics of the Class Crustacea. The order is divided into 3 suborders: Natantia (long-tailed crustaceans); Anomura (soft-tailed crustaceans); Brachyura (short-tailed crustaceans).

Long-tailed crustaceans feature a long abdomen equipped with well-developed appendages. Typical representatives include the narrow-clawed and broad-clawed crayfish, lobsters, spiny lobsters, and shrimp. The narrow-clawed crayfish inhabits rivers flowing into the Black, Caspian, and Azov seas, and is also found in Water bodies of Western Siberia. The broad-clawed crayfish lives in the rivers of the Baltic basin. When colonizing new habitats, the narrow-clawed crayfish tends to outcompete the more commercially valuable broad-clawed crayfish. Large lobsters (over 80 cm long) and spiny lobsters (up to 70 cm) are common in many Regions of the Atlantic Ocean and the Mediterranean Sea. Shrimp inhabit numerous seas; they lead a swimming lifestyle, which explains why their bodies are laterally compressed rather than dorsoventrally flattened like those of other long-tailed crustaceans (see Fig. 49).

Soft-tailed crustaceans possess an abdomen that is softer than that of long-tailed forms. In addition, they often exhibit claw Asymmetry and the underdevelopment of certain abdominal appendages. Typical representatives of this group are hermit crabs. They conceal their abdomen inside appropriately sized empty gastropod shells, which they drag along with them. As they grow, hermit crabs trade their shells for larger ones. A well-known phenomenon is the Symbiosis between hermit crabs and sea anemones (actinians), which attach themselves to the shell. Through this association, the anemones gain mobility, while the crabs receive enhanced protection courtesy of the anemones' stinging Cells and unpalatable nature.

Short-tailed crustaceans have a small abdomen that is permanently tucked beneath a wide cephalothorax. This group comprises true crabs. Crabs are particularly abundant in the Far Eastern seas. The largest among them is the giant Japanese spider crab, in which the span of the middle walking legs reaches 3 m. The stone crab, a medium-sized species equipped with powerful claws, inhabits the Black Sea.

Many decapod crustaceans are consumed by humans. In our country, organized fisheries target the Far Eastern red king crab, freshwater crayfish, and shrimp, alongside the harvesting of lobsters, spiny lobsters, and certain crab species.

QUESTIONS FOR SELF-assessment and review:

1. What structural and physiological features enabled Arthropods to colonize such A wide variety of habitats?

2. Where are crustaceans distributed?

3. What are the external and internal structures of crustaceans?

4. What are the main structural differences between higher and lower crustaceans?