Observations on spear replacement in Xiphinema dentatum (Nematoda: Longidoridae)

The process of spear (odontostyle + odontophore) replacement was determined by studying juveniles of Xiphinema dentatum in different phases of moulting. The process is subdivided into eight distinct phases, each readily identified by characteristic morphological features. The replacement odontostyle takes the functional position by assembling the new stoma behind the lining of the old cheilostoma, at the level where the replacement odontostyle inserts into the old odontophore during early moulting. A new spear is produced by the formation of the new odontophore behind the base of the new functional odontostyle, which was formed either during the previous moulting, or during embryogenesis (spear of the second stage juveniles). The most obvious event during spear replacement is development of a large space, void of tissues, in the region of the old chcilostoma, where a delicate sleeve-like membranous structure, coaxial with the old stoma, was observed. This extends posteriorly from about the old amphids to the lip region border of the newly forming stage. There are two, dorsal and ventral, flap-like cuticular extensions of the base of the cheilostoma lining. In the postlabial region there are, most likely four, sabre blade or carrot-like cuticular extensions.