Phoxichilidium femoratum (Rathke, 1799)

Common name(s): Spiny-thigh sea spider, Sea spider

Synonyms:  Phoxichilidium tubulariae Phoxichilidium femoratum
Phylum Arthropoda 
Subphylum Chelicerata 
Order Pantopoda 
Family Phoxichilidiidae 
Phoxichilidium femoratum found by Joanna Cowles on an Epiactis ritteri anemone in a sea cave at Cape Flattery.  Leg span 1.5 cm.  Since no ovigerous legs are present, this must be a female.
(Photo by:  Dave Cowles, July 2009)
Description:   This pycnogonid (sea spider) has legs which are much longer than the proboscis and trunk.  It has chelate chelicerae but no pedipalps.  The lateral projections  from the trunk which serve as the bases of the legs are separated by at least half their diameter.  The legs are stout, and the auxiliary claws at the ends of the legs are small but well-developed (at least as long as the diameter of the main claw).  The abdomen is at least twice as long as it is wide.  Females of this family have either no ovigerous legs or extremely reduced ones.

How to Distinguish from Similar Species:  In Anoplodactylus viridintestinalis the lateral projections from the trunk which serve as the bases of the legs are very close together, virtually touching.  Its intestine is bright green.  Most other long-legged species have pedipalps as well as chelicerae, plus have well-developed ovigerous legs even in females.  Phoxicholidium quadradentatum (not mentioned in Kozloff key) has extremely short auxiliary claws that are so small they may not even be seen.

Geographical Range:   Dutch Harbor, Alaska to Laguna Beach, CA.  Also common in Europe,Canada, and eastern Russia.

Depth Range:  Mostly subtidal.

Habitat:

Biology/Natural History:   Male pycnogonids carry the eggs, on special anterior ovigerous legs which are lateral to the chelicerae and pedipalps (if present) but anterior to the first pair of walking legs.
In a study of the life history of a related pycnogonid from the North Atlantic, P. tubulariae, Lovely (2005) found that its development was much faster than has been reported for other pycnogonid groups.  P. tubuluriae has a fast developmental mode with an encysted protonymphon larva, with a development time of 21 days as compared to months for other pycnogonids.  The larvae hatched and quickly infested the hydroid Tubularia larynx, where they lived within the gastrovascular cavity.  Later they emerged, destroying the Tubularia polyp.  The abundance of P. tubularia adults peaked in late summer as the hydroid host declined.



 

References:

Dichotomous Keys:
  Carlton, 2007
  Kozloff, 1987, 1996

General References:
  Lamb and Hanby, 2005
  Ricketts et al., 1985

Scientific Articles:
Lovely, Eric C., 2005.  The Life History of Phoxichilidium tubulariae (Pycnogonida: Phoxichilidiidae).  Northeastern Naturalist 12:1 pp. 77-92

Web sites:


General Notes and Observations:  Locations, abundances, unusual behaviors:

Underside
This is a view of the underside of the whole animal
 


The closeup photos below show the head from above and below.  The large chelicerae are readily seen but there are no pedipalps.
Dorsal view Ventral view
Dorsal view.  The large chelicerae flank the proboscis, which is ventral to them.  The rust-colored eye turret is visible behind the chelicerae. Ventral view.  The proboscis is prominent below the chelicerae.  No pedipalps are visible.


Auxiliary claw
In this photo of the tip of the leg of a 3-mm long specimen, the main claw and well-developed auxiliary claw can be seen.  Photo by Dave Cowles, July 2014


Small one
This individual is 3 mm long from proboscis to abdomen.  A photo of the claws on the tip of its foot is above.  Photo by Dave Cowles, July 2014



Authors and Editors of Page:
Dave Cowles (2009):  Created original page
CSS coding for page developed by Jonathan Cowles (2007)