Tanystylum occidentalis (Cole, 1904)

Common name(s): Sea spider, pycnogonid

Phylum Arthropoda
 Subphylum Chelicerata
  Class Pycnogonida
   Order Pantopoda
    Family Tanystylidae
Tanystylum occidentalis from under an intertidal rock near the S end of Lopez Island.  Total leg span about 8 mm.
(Photo by: Dave Cowles, July 2006)
Description:  This animal is NOT a crustacean.  As a chelicerate, it has chelicerae instead of jaws.  This species has legs which are longer than the combined length of the proboscis and trunk.  The general outline of the animal is circular.  It has both chelicerae and pedipalps.  Both sexes have an ovigerous pair of legs (photo) (though as in pycnogonids in general, it is the male which carries the eggs).  The chelicerae are reduced to a knob or tubercle, and are small and hard to see.  The pedipalps have 6 or fewer articles.  The body is not covered with setae.  The proboscis is about twice as long as its diameter at the base, and is rounded at the tip (does not taper to a conical point).  The lateral projections from the trunk are not large (in many other species there are obvious lateral swellings of the trunk at the base of each pair of legs).

How to Distinguish from Similar Species:Tanystylum spp have a proboscis which is at least 3x as long as its diameter at the base and tapers to a conical point.  T. anthomasti is covered with setae and is usually associated with Gersemia rubriformis.  Most other species have well-developed chelicerae.

Geographical Range:

Depth Range:

Habitat:  We found it under a rock in the intertidal.

Biology/Natural History:

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Dichotomous Keys:
  Kozloff 1987, 1996
  Smith and Carlton, 1975

General References:

Scientific Articles:

Web sites:

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

In this closeup view one can see the tiny turretlike head with 4 eyes (near the left end of the body, between the left (front) pair of legs).  The proboscis is much larger than the head and extends to the left of the body.

Here is an even closer view of the turret-like head, which appears as a small tubercle covered with 4 eyes, and also of the proboscis

In this ventral view, the small ovigerous legs can be seen on the underside of the first body segment (left side, just to the right of the proboscis).  Here the animal is extending its other, walking legs upward and away from the camera.  The proboscis is to the left.  Females of some families lack ovigerous legs and in other families they are reduced in females.

Pycnogonids are frequently found clinging to hydroids, as here on the hydroid Aglaophenia sp.

Authors and Editors of Page:
Dave Cowles (2006):  Created original page