The nematodes are

Answer: Option C

The nematodes are Triploblastic.
Triblobtastic organisms are those in which there are three primary germ layers: the ectoderm, mesoderm, and endoderm.
Nematodes are very small, slender worms: typically about 5 to 100 µm thick, and 0.1 to 2.5 mm long. The smallest nematodes are microscopic, while free-living species can reach as much as 5 cm, and some parasitic species are larger still, reaching over 1 m in length.  The body is often ornamented with ridges, rings, bristles, or other distinctive structures.