Possibly Nymphon gracile
Good mama sea spider did not drop her bundle of eggs despite the stress of this photo op. Photo bomb in lower left by tiny (2 mm) Eubranchus misakiensis.
Tiny, about 1/3" across.
Sea spiders, also called Pantopoda or pycnogonids, are marine arthropods of class Pycnogonida. They are cosmopolitan, found especially in the Mediterranean and Caribbean Seas, as well as the Arctic and Antarctic Oceans. There are over 1300 known species, ranging in size from 1 to 10 millimetres (0.039 to 0.39 in) to over 90 cm (35 in) in some deep water species. Most are toward the smaller end of this range in relatively shallow depths, however, they can grow to...