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Posted: May 18 2012 (Presented as Ensis megistus)

Revised Jul 20 2022

Ensis leei Huber, 2015.  Minor Jackknife Clam

(Previously Ensis megistus Pilsbry & McGinty, 1943)

In the early days the Jackknife Clam found all along the Atlantic coast was reported as E. directus Conrad, 1843 or E. minor Dall, 1899 [later updated to E. minor (Chenu, 1843)].   E. minor is also found in Europe.  More recently researchers recognized that E. directus is a fossil from the Pliocene and that the Jackknife Clam found all along the Atlantic coast sufficiently differed from the European E. minor that it should be treated as a separate species (Lee, 2009; Huber, 2010).  In 1943 Pilsbry and McGinty identified Gulf of Mexico specimens they considered to be a subspecies of E. minor which they named E. megistus.  So, when Lee and Huber ascertained that the Atlantic coast Jackknife was a species distinct from E. minor, they compared it to E. megistus and, as Huber commented, “was unable to draw a line” between them.  As a result, as Huber commented, “Ensis megistus is the valid name to represent this well-known North Atlantic ‘minor jackknife’.”    However, Lee and Huber continued to study the Atlantic coast and Gulf of Mexico taxa and in 2015 Huber published an update and recognized that the two differed sufficiently that the Jackknife Clam found all along the Atlantic coast was a distinct species.  Unable to find another available name, Huber proposed Ensis leei for this species. 

Short version:   There is no E. minor in the western Atlantic (it’s a European species), E. directus is a fossil from the Pliocene, E. megistus is limited to offshore NE Gulf of Mexico, and the species we find all along our Atlantic coast and rarely on west Florida is E. leei

Huber M. (2010). Compendium of Bivalves. Harxheim: ConchBooks.

Huber M. (2015). Compendium of Bivalves 2. Harxheim: ConchBooks.

Lee, Harry G.  2009 Marine Shells of Northeast Florida.  Jacksonville Shell Club, Jacksonville, Florida.

Pilsbry, H. A. & McGinty, T. L. (1943). Ensis minor megistus n. subsp., a west Florida razor clam. The Nautilus. 57(1)

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Posted: Mar 5 2016 and as edited by Lee Jul 8 2022, Harry Lee:

"The shells in this fine report are not Ensis megistus Pilsbry and McGinty, 1943."

"On 11 February, 2014 I looked at the Florida Museum of Natural History's (FLMNH's) extensive holdings of W. Atlantic Ensis and came away with the following impressions:"

"Accounting for the ontogenetic vagaries in various morphometrics of shells from Newfoundland to Alabama (AL), I could not distinguish among the morph in our neighborhood (Sunset Beach, NC, Little Talbot Is., FL, and St. Augustine Beach, FL) and dozens of other lots from N (S or W either) of here. Northern elements, identified as E. directus Conrad, 1844 by many authors over the years, grow larger, but there is considerable overlap in all characters, e.g., five inch shells are not uncommon in NE FL."

"E. megistus is quite different from the the preceding, which is the only regional congener and comprises the overwhelming majority of the FLMNH W. Atl. lots. The small posterior adductor scar, its remoteness from the anterior terminus of the pallial sinus, and the extremely long, slender anterior adductor scar (> 1/3 the length of the valve) are distinctive. I only saw a few specimens from Tampa Bay to Alabama (AL), and these include a PARATYPE!"

"At that time I concluded that the predominant SE US form, often referred to Ensis minor Dall, 1900 [non Chenu, 1843, a European species] by authors, and the often larger New England shell, E. directus of authors, collected by many (including Huber and I) on Revere Beach, MA during the Boston COA Convention in August, 2010, constituted a conspecific cline. For this species I thought the Solen ensis americanus Gould in Binney, 1870 was the first available name [see Lee (2009)]."

"Agreeing with Lee (loc. cit.), Huber (2015: 559-560) considered Ensis directus Conrad, 1844 to be limited to the Pliocene but added that the Gould taxon was unavailable due to junior homonymy with Solen americanus Chenu, 1843, itself a junior synonym of Siliqua patula, another, yet distinctive, denizen of Revere Beach. Unable to find another available name, Huber proposed Ensis leei for this species, which also counts among its misidentifications/synonyms, E. megistus of authors, not Pilsbry and McGinty, 1943."

"Short version: The subject of this vignette is Ensis leei Huber, 2015."

"Huber, M., 2015. Compendium of Bivalves 2. A Full-Color Guide to the Remaining Seven Families. A Systematic Listing of 8'500 Bivalve Species and 10'500 Synonyms. ConchBooks, Hackenheim, Germany. 907 pp., incl. numerous color figs + CD-ROM. May."

"Lee, H.G., 2009. Marine Shells of Northeast Florida. Jacksonville Shell Club, Inc. 204 pp. + 19 color plates. 28 May."

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