Caecum (Fartulum)

Caecum circumvolutum, from Ortigosa et al. (2018). Scale bar = 0.2 mm.

Belongs within: Truncatelloidea.

Stop giggling

Published 11 May 2009

The minute marine gastropod Caecum (Fartulum) occidentale, all of 2.5 millimetres long. Photo by Maurio Pizzini.

It has to be admitted that some organisms have rather unfairly copped it when it comes to the names that biologists have chosen to bestow upon them. There are birds called Turdus and Arses, a beetle called Dermestes haemorrhoidalis, even the fungus Rectipilus doesn’t sound entirely comfortable. Compared to those unfortunates, today’s subject perhaps got off lightly. Still, I don’t think I would want to be known as Fartulum.

Fartulum is a taxon in the gastropod family Caecidae. Depending on where you look, it’s treated as either its own genus or a subgenus of the genus Caecum (ranking issues again, not really important). Species of Fartulum are distinguished from other species of Caecum or closely related genera by their combination of a cap-shaped apical plug (more on that in a moment) and perfectly smooth mature shell without the rings or ridges of other caecids.

Caecum (Fartulum) magatama, even smaller at 1.8 millimetres. Photo from here.

Caecids are one of the more distinctive groups of gastropods. They belong to the superfamily Rissooidea, so are closely related to families with periwinkle-type shells such as Rissoidae and Hydrobiidae, but quite honestly you wouldn’t know it to look at them. Mind you, first you’d have to be looking at them, and not many people do that. Not because they’re uncommon, but because they’re tiny. Many would be pushing it to get past two millimetres. Even if you were sharp-sighted enough to spot a caecid, you might dismiss it as a fragment of something else. Caecids start out life as a flat-spiralling shell, but after a couple of turns the whorls open up and the caecid leaves its tight spiral (Carpenter, 1861). In Caecum and its subgenera or related genera, the growing gastropod then produces an apical plug with which it seals off the upper part of the shell, so the living animal is restricted to the anterior section. With no internal tissue holding it in place, the forsaken spire breaks off, so the mature caecid is a short, slightly curved tube, open at one end and plugged at the other (Carpenter, 1861, described Fartulum specimens as looking like “tiny sausages”). As the caecid continues to secrete new shell at the front, it draws forward the plug at the back and continues to shed old shell.

Caecids are detritivores, and live buried in marine sediment, or among sponges or algae. Despite their obscurity, they are far from uncommon. For instance, an ecological survey of the intertidal zone at Mazatlán Bay on the Pacific coast of Mexico by Olabarria et al. (2001) found Fartulum to be the most abundant deposit-feeder there by a fairly significant margin.

Systematics of Caecum (Fartulum)
<==Caecum (Fartulum Carpenter 1857) [incl. Defolinia Weisbord 1962, Levia Folin 1875]APS-P86
    |--C. (*F.) laeveO27
    |--‘Fartulum’ bakeri Bartsch 1920O27
    |--C. (F.) chinense Folin in Folin & Périer 1868APS-P86
    |--C. (F.) circumvolutum Folin in Folin & Périer 1867APS-P86
    |--‘Fartulum’ hemphilli Bartsch 1920O27
    |--C. (F.) inclinatum Folin in Folin & Périer 1869APS-P86
    |--C. (F.) limpidum Folin in Folin & Périer 1874APS-P86
    |--C. (F.) malleatum Folin in Folin & Périer 1868APS-P86
    |--C. (F.) mauritianum Folin in Folin & Périer 1868APS-P86
    |--C. (F.) microcyclos Folin 1879APS-P86
    |--C. (F.) modestum Folin in Folin & Périer 1868APS-P86
    |--‘Fartulum’ moorei Marincovich 1973BC01
    |--‘Fartulum’ occidentale Bartsch 1920O27
    |--‘Fartulum’ orcutti Dall 1885O27
    |--C. (F.) orientale Folin in Folin & Périer 1868APS-P86
    |--C. (F.) sardinianum Folin in Folin & Périer 1870APS-P86
    |--C. (F.) senegambianum Folin in Folin & Périer 1870APS-P86
    |--C. (F.) striatum Folin in Folin & Périer 1868APS-P86
    |--C. (F.) subquadratum Carpenter 1858APS-P86
    |--C. (F.) succineum Folin 1879APS-P86
    |--C. (F.) syriacum Folin in Folin & Périer 1869APS-P86
    |--C. (F.) venosum Folin in Folin & Périer 1867APS-P86
    `--C. (F.) vestitum Folin in Folin & Périer 1870 (see below for synonymy)APS-P86

Caecum (Fartulum) vestitum Folin in Folin & Périer 1870 [incl. C. buccina Folin 1870, C. carmenensis Folin 1870, C. veracruzanum Folin 1870]APS-P86

*Type species of generic name indicated

References

[APS-P86] Arnaud, P. M., Cl. Poizat & L. v. Salvini-Plawen. 1986. Marine-interstitial Gastropoda (including one freshwater interstitial species). In: Botosaneanu, L. (ed.) Stygofauna Mundi: A Faunistic, Distributional, and Ecological Synthesis of the World Fauna inhabiting Subterranean Waters (including the Marine Interstitial) pp. 153–176. E. J. Brill/Dr W. Backhuys: Leiden.

[BC01] Boyko, C. B., & J. R. Cordeiro. 2001. Catalog of Recent type specimens in the Division of Invertebrate Zoology, American Museum of Natural History. V. Mollusca, part 2 (class Gastropoda [exclusive of Opisthobranchia and Pulmonata], with supplements to Gastropoda [Opisthobranchia], and Bivalvia). Bulletin of the American Museum of Natural History 262: 1–170.

Carpenter, P. P. 1861. Lectures on Mollusca, or “Shell-fish” and their Allies. Prepared for the Smithsonian Institution. Congressional Globe Office: Washington.

Olabarria, C., J. L. Carballo & C. Vega. 2001. Spatio-temporal changes in the trophic structure of rocky intertidal mollusc assemblages on a tropical shore. Ciencias Marinas 27 (2): 235–254.

[O27] Oldroyd, I. S. 1927. The Marine Shells of the West Coast of North America vol. 2 pt 3. Stanford University Press: Stanford University (California).

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