Key--Class Pycnogonida

Phylum Arthropoda
 Subphylum Chelicerata

Taken primarily from  Kozloff, 1987, 1996 p. 296 (Copyright 1987, 1996, University of Washington Press.  Used in this web page by permission of University of Washington Press)
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1a  Legs thick, shorter than (or at least not conspicuously longer than) the combined length of the proboscis and trunk; outline of the animal as a whole oval or elliptical; without chelicerae or pedipalps; without conspicuous spiny projections 2
1b Legs usually much longer than the combined length of the proboscis and trunk (pycnogonids of this type are usually awkward and gangly, but sometimes are fairly compact); outline of the animal as a whole approximately circular; with either chelicerae or pedipalps, or both; often spiny or setose 3
2a Color uniform (ivory to pink); height of dorsal tubercles, when these are present, not greater than their basal diameter Pycnogonum stearnsi
2b Color not uniform (generally light brown with dark lines, or with clear areas between dark patches); height of dorsal tubercles greater than their basal diameter Pycnogonum rickettsi
3a With both chelicerae and pedipalps (the pedipalps are conspicuous and have several articles); chelicerae either with functional chelae or with chelae reduced to knobs (juveniles of some species, however, have chelae that are lost as the animals mature); ovigerous legs usually present in both sexes and conspicuous 4
3b With chelicerae, but without pedipalps; chelicerae with chelae and conspicuous; ovigerous legs reduced or entirely absent in females 17
4a Chelicerae with 2 basal articles; small chelae sometimes present (the chelae may, however, be reduced to nonfunctional knobs) 5
4b Chelicerae with a single basal article (scape); with a chela or a knoblike second article (or the entire appendage may be reduced to a knob or to an elongate, tuberclelike structure) 7
7a Chelicerae reduced to knobs or tubercles 8
7b Chelicerae consisting of a basal article (scape) and either a well developed terminal chela that extends beyond the proboscis or with a knoblike article (if functional chelae are present in sub-adults, these do not extend beyond the proboscis) 11
8a Each chelicera consisting of an easily recognized, papillate process; a gangly species with rather long and slender legs, these often with brownish purple bands; pedipalps with 9 articles Ammothea hilgendorfi
8b Chelicerae small and difficult to see; animal rather compact; pedipalps with 6 or fewer articles 9
9a Body covered with short setae, thus appearing hairy; associated with the alcyonacean Gersemia rubriformis Tanystylum anthomasti
9b Body not covered with short setae (it may, however, have sparse spines); not normally associated with Gersemia 10
10a Proboscis about twide as long as its diameter at the base, rounded at the tip, trunk very compact, the lateral projections indistinct Tanystylum occidentalis
10b Proboscis at least 3 times as long as its diameter at the base, tapering to a blunt, subconical tip; trunk not so compact as in T. occidentalis, the lateral projections touching, but distinct Tanystylum sp.
11a Chelicerae conspicuous, chelate, extending beyond the proboscis; pedipalps slender, with 5 articles; total diameeter, when the legs are outstretched, sometimes exceeding 5 cm; usually subtidal 12
11b Chelicerae usually reduced to knobs in the adult, but if chelae persist, the chelicerae are shorter than the proboscis; pedipalps with 8 articles; total diameter less than 2 cm; includes some intertidal species 13
13a Adults not chelate 14
13b Adults chelate, the dactyl and fixed finger arcuate (a seasonal parasite of mussels in central California; found at least as far north as Boiler Bay, Oregon, but the habitat on the Oregon coast is not known) Achelia chelata
14a Dorsodistal edges of first coxal articles with fingerlike projections or short outgrowths 15
14b Dorsodistal edges of first coxal articles without fingerlike projections or short outgrowths (there may, however, be low knobs or wartlike eminences on the lateral projections of the trunk) Achelia latifrons
17a Lateral projections very close together; auxiliary claws minute and inconspicuous; legs slender (intestine bright green, its branches clearly visible in the legs; eye tubercle at least twice as high as broad) Anoplodactylus viridintestinalis
17b Lateral projections separated by at least half their diameter; auxialiary claws small but well developed; legs stout Phoxichilidium femoratum

Taxonomic Levels Represented in This Key:

  Achelia latifrons (tentative identification)
   Ammothea verenae (Found at local hydrothermal vents, not in the key)
  Phoxichilidium femoratum
  Pycnogonum stearnsi
  Tanystylum occidentalis

Page created by Dave Cowles, 2006
Edited by: Dave Cowles, 2009