Type II microtrich sensilla of amphipods: variations in external morphology and distributional patterns
Scanning electron microscopic observations of type II microtrichs on the integument of selected amphipods show that these sensilla vary in length from less than 2 to 25 μm and, with few exceptions, their external morphology is similar. Typically, these microtrichs occur in two dorsal and two lateral clusters on each somite. Exceptionally, there is a series of circumferential clusters. Sexually mature males of some amphipod species have many additional lateral clusters on somite 11. Type II microtrichs are also present on the telson but absent from the head. The most prevalent cluster pattern is a row in the form of a J, but this may be modified into a Y, a semicircle, or a curvilinear pattern.