Fig. 4
Type 1 postembryonic development of Pycnogonida. a-f Sequence of postembryonic instars of Achelia alaskensis up to the first juvenile instar (modified from [70], reproduced with permission of Hokkaido University). Dorsal view always on the left side, ventral view on the right side. Note strictly sequential development of the walking legs. The late protonymphon larva in (a) shows slight elevations of walking leg pair 1 posterior to the ovigeral larval limb (potentially the second larval instar of postembryonic development, the actual hatching having not been observed)