ABSTRACT
Nemertines are known from Cambrian rocks; they may be derived from platyhelminth ancestors. An example is Lineus longissimus (bootlace worm).
Body plan Nemertines are bilaterally symmetrical, triploblastic acoelomates (Fig. 1). The body is unsegmented. There is a basement membrane between the ectoderm
and the mesoderm which forms a firm, elastic cover to the extensive longitudinal and circular muscles.
