Posted: Jan 4 2015

 

Along the NE Atlantic coast A. versicolor shares its distribution with two similar species:

Angulus agilis (Stimpson, 1857)
Angulus tenellus (Verrill, 1873)

1/1/15, on Conch-L, Bob Fales asked:

"Does anyone have any “surefire” hints on discriminating between Tellina agilis and Tellina versicolor?"

There then followed a few responses and eventually reference to work by Gilbert (1977) examining the taxonomic differences among these three.

Some of the comments responding to Bob were:

1/2 Marlo:

"I’ve seen very few T. agilis, but many, many A. versicolor, but not from the NE coast. I don’t have any really adequate T. agilis to make a presentation, but both Abbott and Mikkelsen/Bieler indicate that the pallial sinus of A. versicolor comes distinctly closer to the anterior muscle scar than it does in T. agilis. If I had a T. agilis with a visible enough pallial sinus I could do a photo comparison.

Abbott considered A. versicolor to have a “nearly straight instead of curved ventral margin (as does T. agilis).” Regarding A. versicolor, I’ve found live and fresh dead specimens to be translucent with exterior color visible from the interior. A. versicolor is one of the most fragile in this group."

1/2 Harry:

"If it's got distinctly pink/purple coloration, it's Angulus versicolor. Sorry, but you wanted "sure-fire," and this response is predicated on a "sure-fire" character set rather than taxonomic rigor.

We have a feature on this one of your bivalve tandem at http://www.jaxshells.org/bti58.htm.

With faded or otherwise pigment-challenged specimens, I suggest looking at the posterior margin of any valve, which is more squared-off and reaches its terminus much more ventrally in this species than in A. agilis. The ventral margin of A. v. is straighter than the arcuate one of A. a.

One character that has struck my eye is the peculiar obliquity (vs. commarginal alignment) of some of the longitudinal grooves on the valve exterior, as shown in the website, seems to be peculiar to A. versicolor, but I can't get at my (NJ) A. agilis specimens at present for confirmation.

Internally, the pallial sinus of A. v. more closely approximates the anterior adductor scar than is the situation with A. a. Maybe like you, I often cannot make out these features even with a good sized lot of well-preserved material at hand."

1/2 Paul:

"Yes, the pink-purple coloration is key; not to be confused with conventional Deep Purple, Purple Rain or other manifestations of the Color Purple."

1/3 Lenny:

"The article cited below should help you distinguish these two species:

Gilbert, W. H. (1977) Taxonomic differences among Tellina agilis , Tellina tenella , and Tellina versicolor . Bull. Amer. Malac. Union, Inc. 1977: 43-48.

Members of the Long Island Shell Club relied on the identification criteria summarized in this ms to identify the Tellina species ..."

1/3 Harry:

"Since this paper, which was actually published in 1978,* is apparently not available on-line, let me offer to scan it for any seriously interested party.

* I recall receiving the journal early the year following the actual July, 1977 meeting/presentation of paper."

1/3 Harry:

"Alan Kabat has informed me that Coan and Kabat (2007: 7) dated the Gilbert publication to late April, 1978.

Coan, E.V. and A.R. Kabat, 2007 [December 27]. The publications of the American Malacological Union/Society. American Malacological Bulletin 23: 1-10.

Gilbert, W.H., 1978 [before April 24]. Taxonomic differences among Tellina agilis, Tellina tenella, and Tellina versicolor. Bulletin of the American Malacological Union, Inc. 1977: 43-48."

Harry's scanned copy is presented below. Gilbert indicated that A. agilis occurs along the most northern region from the Gulf of St. Lawrence south to Cape Hatterus, NC. A. versicolor overlaps in this range only from Cape Cod, Mass., south. So, there should be no confusing these two in Florida.