Phylum Arthropoda


Subphylum Chelicerata
In the great group of chelicerates are included a variety of "arachnoid"
types, most of which are in highly specialized terrestrial groups. Marine
representatives include the primitive and ancient Xiphosurida ("horseshoe
crabs"), the small and specialized order of Pycnogonida ("sea spiders") of
obscure affinities, and the marine mites (Order Acarina, Family
Halacaridae). Of the latter, about 20 species have been recorded from
southern New England, but the study of these small creatures presents
difficulties, and the interested student is referred to the comprehensive
work of Newell, I.M., 1947. A systematic and ecological study of the
Halacaridae of eastern North America. Bull. Bingham Oceanogr. Coll., 10:
1-232

Class Pycnogonida
Despite the abundance of pycnogonids (about 50 genera and 500 species) in
the seas of the world, the fauna of Woods Hole includes only three common
species: Tanystylum orbiculare, Callipallene brevirostris, and
Anoplodactylus lentus. This group has received little attention in recent
years, although the first good systematic report on them in America was that
on New England Pycnogonida by E. B. Wilson, and their embryology was
described by T. H. Morgan in his doctoral thesis (1891). Most shore
pycnogonids feed upon hydroids and the young stages of many species encyst
or form galls in hydroids. Since our information is still incomplete,
collectors would do well to note the associated coelenterate in making
collections. The following key will separate the common local species, plus
one common north of the Cape; for anything that will not key out, consult
Hedgpeth (1948).

So far this is all I can find , obviously there is little research being
conducted of these creatures . maybe with the escalation of deep sea or
abyssal research will bring more information but for now we're still in the
dark .
A side note , at the following addy you can find a anatomical diagram of the
pycnogonids.

http://www.mbl.edu/html/KEYS/INVERTS/10/pycnogonid.general.gif