Question

renatocysts (Cnidae) are structures unique to the Chidaria. Describe their structure and us this phylum. (5 + 5 Points)

Answer 1

Nematocysts are cell organelles found in specialized cells called cnidocytes or cnidoblasts, which are modified epidermal interstitial cells. A Cnidoblast is an oval or rounded cell with a conspicuous nucleus lying on basal side. Inside the cnidoblast is present an oval or pyriform sac or bladder that is filled with a toxin called hypnotoxin, which is a mixture of proteins and phenols. The outer end of the capsule is invaginated into a long, hollow and tubular filament or thread tube, coiled like a watch-spring inside the sac itself. The base of the thread tube is swollen to form a butt, which carries three large spines, called barbs or stylets and three spiral rows of minute spines. The bladder is covered on the top by a lid or operculum, near which lies a hair-like process, the cnidocil that acts like a trigger for the discharge of the thread tube. Cytoplasm of cnidoblast may contain contractile muscle fibrils and a restraining thread at the base, called lasso, which prevents the nematocyst from being thrown out of cell. Otherwise cnidoblast has cell organelles similar to a normal cell and at base it is attached to an epithelio-muscle cell. Nematocysts may occur scattered throughout the body surface, except the basal disc. They are abundant on the tentacles and hypostome. On tentacles they form “battery of nematocysts” which are used for paralyzing the prey. A battery consists of one or two large central nematocysts surrounded by 10-12 smaller ones.

Uses of nematocysts - Nematocysts are produced by nematoblasts, or cnidoblasts, and are used for capturing and paralyzing prey or for defense. Each nematocyst contains a coiled, hollow thread that can have barbs or spines and often contains poison.