The ptychocyst, a major new category of cnida used in tube construction by a cerianthid anemone

TLDR: Light, transmission electron and scanning electron microscopy of a cerianthid anemone reveal that the protective tube with which the animal surrounds itself is composed almost entirely of discharged, interwoven cnidae of a heretofore undescribed type.

Abstract: Light, transmission electron and scanning electron microscopy of a cerianthid anemone reveal that the protective tube with which the animal surrounds itself is composed almost entirely of discharged, interwoven cnidae of a heretofore undescribed type.As opposed to the threads of all nematocysts and spirocysts described to date, the thread of the new cnida, to which has been given the name of ptychocyst, is not helically folded, forming a variable number of pleats in circumference (from 5 to 11 observed in the present study), and no pleats in length. The discharged threads are quite long (over 2 mm in some) and are non-isodiametric, tapering from a diameter of about 5 µm at the base to about 2 µm at the tip for an overall reduction in diameter of 2.5 times.The everted thread has a number of fine ridges running along its length which can be seen using phase contrast microscopy and which represent the folds by which the thread is compressed in diameter. The thread tip is closed and the entire thread is unarm...