sea spider

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various predatory marine arthropods of the class Pycnogonida, having a small body, four pairs of long walking legs, and a proboscis.

from The Century Dictionary.

• noun Some marine animal whose appearance suggests a spider.

from the GNU version of the Collaborative International Dictionary of English.

• Any maioid crab; a spider crab. See maioid, and Spider crab, under spider.
• Any pycnogonid.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any arthropod in the taxonomic class Pycnogonida.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any of various small spiderlike marine arthropods having small thin bodies and long slender legs