Posted: Mar 15 2010
Costoanachis scutulata (Reeve, 1859)
The difficulty with Costoanachis scutulata has its origins immediately with
Reeve’s original description. Reeve described both C. scutulata and C. sparsa
in the same work (Reeve, L. 1859. Monograph of the genus Columbella.
Conchologia Iconica 11: pls. 1, 24-37). His descriptions are at right.
Both descriptions are poor by today’s standards and would not serve to
actually separate similar species. The only really helpful information might
relate to coloration if “promiscuously tessellated with white dots” can be
considered distinguishable from “sprinkled with chestnut dots and network.”
Reeve appears to be saying C. scutulata is dominated by a chestnut
background with tessellated white dots and C. sparsa is dominated by a
yellowish background with networked chestnut dots. He does note that
C. sparsa has “interstices cancellated,” which would indicate the presence of
spiral sculpture. He mentions only “the last (whorl) smooth, grooved at the
base” for C. scutulata, which could imply a lack of spiral sculpture on the
teleoconch. However, this is doubtful for several reasons, the most significant
to me being that I’ve never seen a Florida Costoanachis species (except
C. sertulariarum) that lacked any spiral sculpture over the entire teleoconch
and above the periphery of the body whorl. C. sertulariarum is readily
distinguished from C. scutulata and C. sparsa since they are “longitudinally
ribbed” over the entire shell and, when ribbed, C. sertulariarum is ribbed only
over the adult body whorl and later portion of the prior whorl. Note also that
Reeve did not report locality data for either shell.
My limited research seems to indicate that for some reason between Reeve (1859) and Radwin (1977) C. scutulata received little or no notice and shells from Florida and near-Florida that looked anywhere close to Reeve’s C. sparsa were identified as such. Abbott (American Seashells 1974) included only C. sparsa and closely matched Reeve’s description thereof. In 1977 Radwin published his work on Columbellidae in the western Atlantic and addressed both these species. His description of C. sparsa closely matched Reeve’s, but his descriptions of C. scutulata differed and were self contradictory regarding the presence of spiral grooves. Radwin indicated that C. scutulata was “cancellated on first 2 postnuclear whorls,” which would mean the presence of spiral sculpture. He continues with, “spiral sculpture almost completely obsolete on later whorls.” He repeatedly notes that there was an “unusual subsutural groove” that “persists to the most recently formed whorl.” Yet, in comparing C. scutulata and C. sparsa, Radwin remarked that “Spiral grooves notably present in the latter species are absent in C. scutulata.” Regarding C. scutulata, Radwin acknowledged that “The validity of this species has been in doubt since Reeve’s original description as a result of his poor figure and his failure to give type locality.” This accurate and exact statement applied equally to Reeve’s C. sparsa, and created a confusion Radwin attempted to clarify, but only confused further. He went on to say, “There is little doubt in my mind, after having examined a photograph of the holotype in the British Museum (Natural History), that this name must be applied to a small, somewhat variable species from Bermuda.” He then stated the range for C. scutulata as “Apparently endemic to the Bermuda Islands.” Radwin’s confusing descriptions of the spiral sculpture of C. scutulata and his restriction to Bermuda set the stage for continuing confusion between these two species. Later workers would have a predisposition to rely upon Radwin’s work and assume C. scutulata was not present in Florida and lump it (if indeed it was present) with the similar C. sparsa. Note that this confusion was also compounded by the misuse of the nomen dubium C. similis (Ravenel, 1861) by some workers for what otherwise were most likely C. sparsa (or possibly C. scutulata) found along Florida’s mid-eastern and south-eastern coast. In 1981 Rehder (The Audubon Society Field Guide to North American Seashells) presented only C. sparsa with no mention of C. scutulata.
When I first collected C. scutulata in the Florida Keys in the late ‘90s it looked like an unusual C. sparsa to me. I was unaware of Radwin at the time. I sought advice from Harry Lee, author of Marine Shells of Northeast Florida 2009. Harry indicated the shell I was finding was indeed not C. sparsa, rather C. scutulata. He noted that Radwin had erred in restricting C. scutulata to Bermuda and that comparison of my Keys shells to C. scutulata in his collection from Bermuda indicated the same species was involved. Harry’s key argument for this conclusion was the similarity in protoconchs (large, dark, globose, paucispiral) and their difference from the protoconch of C. sparsa (white, multi-spiral, acuminate). So, for some time I went merrily along unconfused about these two shells. Then, in 2001 Colin Redfern published his book Bahamian Seashells and subsequently confusion set in again. Colin presented a shell (#414) as C. sparsa that perfectly fit the description of my C. scutulata from the Keys, particularly his indication that his shells had “a brown protoconch of 1.5 smooth, rounded whorls.” There then followed several years of infrequent correspondence between Colin, Harry and myself regarding these shells. I believe it would be enlightening to recount an abbreviated summary of our discussions, since they form the basis for my presentation of C. scutulata.
Feb 19, 2007 - Colin: “I've finally had a chance to take a look at the Costoanachis sparsa/scutulata problem as it relates to material from Abaco. Reviewing scutulata first, the most useful available figure seems to be Kaicher's photo of a syntype. The shell has a prominent parietal swelling that contributes to what Radwin describes as a ‘distinct anal sinus.’ Radwin also cites an ‘unusual subsutural groove’ as being a distinguishing characteristic, but I can find neither of these features on re-examination of more than 250 shells from Abaco."
Mar 8, 2010 – Marlo: “I’m working on a presentation of C. scutulata and want to address this issue (that the ID of your shells is ‘uncertain,’ but more likely scutulata than sparsa). Basically, I believe Radwin’s comment about an ‘unusual subsutural groove’ was just plain a result of poor observation. Harry provided me two C. scutulata from Bermuda and I have examined many of the shells from Florida we’re calling C. scutulata. The Bermudian and Florida shells do indeed fairly consistently display the second (and sometimes first) spiral groove beginning with T-3 as most prominent, but there are subsequent, lesser (and often faint) spiral grooves. For those shells with the periostracum present, these subsequent spirals are often obscured.
Regarding your … comments, while you did not observe ‘an unusual single spiral groove’ on your shells, did you find that the first or second groove were fairly consistently the most prominent?
Frankly, Radwin’s comment about a ‘distinct anal sinus’ is completely spurious (esp. without any more specific description and the fact that he didn’t even mention it in the description section of his presentation). On most Costoanachis the anal sinus is more or less distinct depending upon the maturity of the shell and size of the most posterior tooth.
Do you have any more current thoughts on this matter?”
Mar 8, 2010 – Colin: “It seems to be increasingly unlikely that true C. sparsa occurs on Abaco, but the identification of Abaco material is still a work in progress. The first or second groove is more prominent on some of my shells, but it's not a consistent feature. Incidentally, as I suggested in my previous email, I believe that it was the parietal swelling on Radwin's figured syntype that led him to describe a ‘distinct anal sinus’, rather than the size of the most posterior tooth. This feature is shown most clearly on Kaicher card No. 3846. However, Radwin erroneously referred to that shell as the holotype - there are actually three syntypes of C. scutulata at BMNH, and the other two shells show no sign of a parietal swelling.
An anatomical comparison of 'C. scutulata' from Bermuda and Florida would be helpful, and I think that it's not yet clear whether Abaco material can be referred to that species.”
Marlo: Colin’s comments indicate that he has come to question the shell he presented as C. sparsa, but does not feel the name C. scutulata can be applied (yet).
As indicated in my comments to Colin, Radwin’s work reflects numerous errors and essential omissions. The most glaring omission is the failure to consistently describe protoconchs in his descriptions. It is most disappointing that he failed to address this key shell feature so often relied upon as essential in distinguishing between species. While not a perfect determinant, protoconch differences have proven to be the most effective distinguishing character in the absence of body part or DNA data for corroboration. The two key features other than “distinctive color pattern” that Radwin mentioned and Colin noted (unusual subsutural groove and distinct anal sinus) are easily quite variable across populations and may be particularly variable across geographic distributions. However, my Florida shells, Colin’s Abaco shells, and the samples from Bermuda all have one common character – a protoconch of 2 - 2.25 smooth, swollen brown whorls, including the nucleus. Harry’s recent comments confirming his earlier observations were:
Feb 19, 2010 – Harry: “That was a nice analysis by Colin…. Since what I call Costoanachis scutulata (large, dark, globose, paucispiral protoconch), is represented by shells in my collection taken in Bermuda (that taxon's type locality), and I couldn't find any of the other protoconch type (multispiral, acuminate) in collections made on that island, I am happy with my assignment.
It is clear to me that the protoconchs of Sally's illustrated C. scutulata and C. sparsa type specimens are absent.
Referring to Sally's cards: Intact shells with the color pattern of the holotype of C. sparsa have either type of protoconch, but those with the color pattern of the C. scutulata syntype have only the large, dark, globose, paucispiral protoconch.
As Colin infers, judgment is not based on direct examination of any type material. There may be a different solution. Right now mine works best, I think.”
Marlo: In summary, I have relied upon the protoconch to assign the name C. scutulata to my Florida shells. While I concur with Radwin’s observations regarding the “distinctive color pattern” most commonly displayed by C. scutulata, I cannot consider his “distinct anal sinus” as a distinguishing character. As to Radwin’s comment regarding an “unusual subsutural groove,” at most I can agree that the first and/or second subsutural spiral groove displayed beginning with teleoconch whorl #3 are the most pronounced and that later grooves on a whorl may be faint to absent on some shells and often obscured by the periostracum. Both of these latter two characters are insufficiently “distinctive and constant” and are apparently far too variable to be relied upon as valid species discriminators.
I would very much encourage others with Bermudian shells or familiarity with C. scutulata, esp. in comparison with C. sparsa, to add their observations or comments here on LTS or email me at email@example.com.
So, here’s C. scutulata as I see it. (There are two galleries, so be sure to scroll down.)
We currently (as of 2013) believe Perry & Schwengel's taxon is most probably Costoanachis scutulata (see first slide below).