Surely, you haven’t had enough information about pycnogonids yet, have you? Here’s another species, Tanystylum bealensis, collected off the British Columbian coast. That’s a ventral view of the male, and those bunches of grapes everywhere are eggs and babies—males do the childcare in this group. These animals also live in relatively shallow water, in the lower intertidal zone, so it was possible to collect thousands of them and develop a complete staging series. Below the fold I’ve put some illustrations of the larvae, which are even cuter.
The eggs are sheltered on a specialized male appendage, the oviger, and held there through the first instar. You can see a couple of the little guys on the photo above. In later instars, they inhabit the fronds of a hydrozoan, Plumularia setacea, sucking on tasty gonophores and other tissues. Plumularia is also rather pretty:
Anyway, here’s the developmental series. Sea spiders exhibit a vivid pattern of prolonged anterior to posterior development: the embryo basically forms just the head of the animal, and then limbs are steadily added and modified from front to back as development proceeds. Imagine a human baby born as just a head, and then later sprouting arms, and later still popping out a couple of legs…that’s how sea spiders grow.
Gillespie JM, Bain BA (2006) Postembryonic development of Tanystylum bealensis (Pycnogonida, Ammotheidae) from Barkley Sound, British Columbia, Canada. J Morphol. 267(3):308-17.