Yoldia seminuda (Dall, 1897)

Common name(s): Crisscross Yoldia

Synonyms:  Cnesterium scissurata, Yoldia scissurata
Phylum Mollusca
 Class Bivalvia
  Subclass Protobranchia
   Order Nuculida  (Palaeotaxodonta)
Yoldia seminuda trawled from 15-18 m depth off Canoe Island, San Juan Island, WA.
Captured July 1987 and preserved before photographing.  The foot can be seen extending from the anterior end of the shell.
(Photo by: Dave Cowles Sept 2006)
Description:  Clams in Order Nuculida have valves similar to one another.  The hinge plate has taxodont dentition.  The shell is aragonitic, longer than high and has no radial ribs.  The periostracum is smooth.  They are protobranchs, so their gills are simple platelike leaflets suspended in the mantle cavity.  They have large palps near the mouth which they use to gather food.  Members of Family Yoldiidae have an external hinge ligament, the interior of the valves is not pearly, they have siphons and a pallial sinus, they have a chondrophore, and the shell gapes at theposterior end (to the right in the photo above).  Yoldia seminuda has a flattened (not swollen) shell, the posterior end is rather pointed rather than truncate.  It differs from other members of the family in that the valves have fine concentric sculpturing which does not coincide with the concentric growth lines, but instead crosses over them (photo).  The umbones are tiny and central.  The dorsal margin of the shell anterior to the umbo is slightly convex.  Shell is white with a smooth, shiny, yellow or greenish tan periostracum.  Rarely over 4 cm long.

How to Distinguish from Similar Species:  Other Yoldia species do not have the concentric lines on the shell which cross the growth lines.  Macoma yoldiformis is a Macoma clam which also is white with a smooth, shiny periostracum but, among many other differences, does not have taxodont dentition.

Geographical Range:  Arctic ocean to San Diego, CA

Depth Range:  Subtidal, 15-150 m.

Habitat:  In fine sand and mud

Biology/Natural History:  This group lives in the sediment and eats detritus which is picked up by extending the long palps into the sediment and moving detritus toward the mouth by ciliary action.  Unlike other groups of clams, the gills are used for respiration only--not for feeding.

Yoldia is a protobranch bivalve, meaning its gills are bipectinate and it does not feed using its gills (see above).  It is also a Palaeotaxodont because its shell valves are equal and have taxodont dentition.

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Dichotomous Keys:
  Kozloff 1987, 1996
  Scott and Blake, 1998

General References:
  Harbo, 1997
  Morris, 1966 (as Y. scissurata)

Scientific Articles:

Web sites:

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

Strong side light (here from above, from the dorsal side) shows the fine concentric striations on the shell that cut across the concentric growth lines.  The growth lines are centered on the umbo, while the other striations are centered to the right (posterior to) the umbo.  The foot can be seen protruding from the anterior end of the shell to the left.

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