Scaphopoda

Siphonodentalium lobatum, copyright Natural History Museum Rotterdam.

Belongs within: Rostroconchia.
Contains: Cadulus, Dentalium.

The Scaphopoda, tusk shells, are a group of benthic molluscs with a tubular shell that live buried in the sediment, feeding on micro-organisms. In members of the Dentaliida, the shell generally tapers evenly whereas Gadilida commonly have the shell constricted toward the mouth (Ludbrook 1960). Two pairs of dorsoventral muscles are present in Dentaliida whereas a single pair is found in Gadilida (Steiner 1996). Dentaliida have an encircling sheath around the foot that is expanded laterally and interrupted dorsally (Ludbrook 1960) and the pedal muscles are associated with the body wall along the entire length of the body (Steiner 1996). Gadilida have the foot simple and vermiform, or distally expanded into a symmetrical disc (Ludbrook 1960). The pedal muscles are separated from the integument in the distal part of the foot in Entalina and are entirely separate from the body wall in Gadilimorpha; instead, they occupy a central position in the body and attach to the dorsoventral muscles at the diaphragm between intestinal sinus and perianal sinus (Steiner 1996). The disc of the foot has a digitate periphery in the genus Entalina; the shell of Entalina is Dentalium-like and strongly ribbed (Ludbrook 1960).

Characters (from Ludbrook 1960): Marine, bilaterally symmetrical mollusks protected by an external elongate, tubular, tapering, calcareous shell, open at both ends and generally somewhat curved. Concave side of shell dorsal, convex side ventral; aperture or anterior opening larger, apex or posterior opening simple or variously slit or notched, some forms with terminal pipe. Shell substance of three distinct layers. Shell secreted by mantle of same shape, larger (anterior) opening of which is contracted by muscular thickening of mantle, giving egress to long conical foot; smaller (posterior) opening serving as outlet for organic waste and genital products. Mouth furnished with radula, borne on cylindrical snout and surrounded by rosette of lobes; a cluster of threadlike, distally enlarged appendages known as “captacula” springing from its base. No eyes or tentacles; otocysts present. Liver 2-lobed, symmetrical; gut strongly convoluted, anus ventral and somewhat anterior, kidney openings near it. Heart rudimentary; no gills, respiration performed by general integument. Nervous system with well-developed ganglia united by commissures. Gonad simple, sexes separate, reproduction without copulation.

<==Scaphopoda [Cirrhobranchiata, Lateribranchiata]
    |  i. s.: Paleodentalium Gentile 1974 PR79
    |         Quasidentalium Gentile 1974 PR79
    |         Throopella Greger 1933 [Throopellidae] L60
    |           `--*T. typa Greger 1933 L60
    |--Gadilida [Siphonodentaliidae] L60
    |    |--Entalina Monterosato 1872 GO06, L60 [incl. Eudentalium Cotton & Godfrey 1933 L60; Entalinidae]
    |    |    |--*E. tetragona (Brocchi 1814) L60 (see below for synonymy)
    |    |    |--E. platamodes (Watson 1879) [=Siphodentalium platamodes; incl. E. quadrata Henderson 1920] E52
    |    |    `--E. quinquangularis (Forbes 1843) L60, E52 [=Dentalium quinquangulare E52]
    |    `--Gadilimorpha [Siphonodentalioida] S96
    |         |--+--Cadulus GO06
    |         |  `--Pulsellum Stoliczka 1868 L60 [incl. Siphonentalis Sars 1878 L60; Pulsellidae S96]
    |         |       |--*P. lofotense (Sars 1864) [=Siphonodentalium lofotense] L60
    |         |       `--P. affine GO06
    |         `--+--Wemersoniellidae S96
    |            `--Gadilidae S96
    |                 |--Gadila Gray 1847 L60 (see below for synonymy)
    |                 |    |--*G. gadus (Montagu 1803) [=Dentalium gadus, Cadulus (*Gadila) gadus] L60
    |                 |    |--G. braziliensis (Henderson 1920) S11
    |                 |    |--‘Helonyx’ jeffreysii N79
    |                 |    `--G. tolmiei (Dall 1897) SW11, O27 [=Cadulus tolmei O27]
    |                 `--Siphonodentaliinae S96
    |                      |--Calstevenus Yancey 1973 SB93, PR79
    |                      |    `--C. arcturus Yancey 1973 SB93
    |                      `--Siphonodentalium Sars 1859 (see below for synonymy) L60
    |                           |--S. lobatum (Sowerby 1860) (see below for synonymy) L60
    |                           |--S. eboracense Watson 1879 H09
    |                           |--S. quadrifissatum Pilsbry 1898 O27
    |                           `--S. quinquangulare PP64
    `--Dentaliida [Dentalioida] S96
         |  i. s.: Laevidentaliidae S96
         |           |--Pseudantalis Monterosato 1884 PR79, L60
         |           |    `--*P. rubescens (Deshayes 1825) [=Dentalium rubescens] L60
         |           |--Rhytiodentalium Pojeta & Runnegar 1979 PR79
         |           |    `--*R. kentuckyensis Pojeta & Runnegar 1979 PR79
         |           |--Plagioglypta Pilsbry & Sharp 1897 SB93, L60
         |           |    |--*P. undulata (Münster 1844) [=Dentalium undulatum] L60
         |           |    `--P. iowaensis [=Coleolus iowaensis] PR79
         |           `--Laevidentalium Cossmann 1888 L60
         |                |--*L. incertum (Deshayes 1825) [=Dentalium incertum] L60
         |                |--L. arnoldi Lamprell & Healy 1998 MG-H11
         |                |--L. callipeplum (Dall 1889) [=Dentalium callipeplum] E52
         |                |--L. ecostatum (Kirk 1880) [=Dentalium (Laevidentalium) ecostatum] P61
         |                |--L. longitrorsum (Reeve 1842) MG-H11
         |                |--L. morganianum (Wilckens 1922) [=Dentalium (Laevidentalium) morganianum] S98
         |                `--L. perlongum (Dall 1881) [=Dentalium perlongum] E52
         |         Gadilina Foresti 1895 L60 [Gadilinidae S96]
         |           `--*G. triquetra (Brocchi 1814) [=Dentalium (*Gadilina) triquetrum] L60
         |         Omniglyptidae S96
         |--Rhabdus Pilsbry & Sharp 1897 L60 [Rhabdidae S96]
         |    `--*R. rectius (Carpenter 1865) [=Dentalium rectius] L60
         `--+--Fustiaria Stoliczka 1868 L60 [Fustiariidae S96]
            |    |--*F. circinata (Sowerby 1823) [=Dentalium circinatum] L60
            |    `--F. rubescens GO06
            `--Dentaliidae S96
                 |--Dentalium L60
                 `--Prodentalium Young 1942 L60
                      |--*P. raymondi Young 1942 L60
                      `--P. martini (Whitfield 1882) SB93

*Entalina tetragona (Brocchi 1814) L60 [=Dentalium tetragonum L60, Siphonodentalium tetragonum N79; incl. S. pentagonum Sars 1864 N79, Dentalium quinquangulatum Reeve 1872 N79]

Gadila Gray 1847 L60 [incl. Helonyx Stimpson 1865 L60, Loxoporus Jeffreys 1883 L60; Gadilinae S96]

Siphonodentalium Sars 1859 [=Siphodentalium Monterosato 1874; incl. Siphonodontum Locard 1886, Tubidentalium Locard 1886; Siphonopoda, Siphonopodidae] L60

Siphonodentalium lobatum (Sowerby 1860) [=Dentalium lobatum; incl. D. vitreum Sars 1851 non Gmelin 1791, *Siphonodentalium vitreum] L60

*Type species of generic name indicated

REFERENCES

[E52] Emerson, W. K. 1952. The scaphopod mollusks collected by the first Johnson-Smithsonian deep-sea expedition. Smithsonian Miscellaneous Collections 117 (6): 1–14.

[GO06] Giribet, G., A. Okusu, A. R. Lindgren, S. W. Huff, M. Schrödl & M. K. Nishiguchi. 2006. Evidence for a clade composed of molluscs with serially repeated structures: monoplacophorans are related to chitons. Proceedings of the National Academy of Sciences of the USA 103 (20): 7723–7728.

[H09] Hedley, C. 1909. The Marine Fauna of Queensland: Address by the President of Section D. Australasian Association for the Advancement of Science: Brisbane.

[L60] Ludbrook, N. H. 1960. Scaphopoda. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt I. Mollusca 1: Mollusca—General Features, Scaphopoda, Amphineura, Monoplacophora, Gastropoda—General Features, Archaeogastropoda and some (mainly Paleozoic) Caenogastropoda and Opisthobranchia pp. I37–I41. Geological Society of America, and University of Kansas Press.

[MG-H11] McEnnulty, F. R., K. L. Gowlett-Holmes, A. Williams, F. Althaus, J. Fromont, G. C. B. Poore, T. D. O’Hara, L. Marsh, P. Kott, S. Slack-Smith, P. Alderslade & M. V. Kitahara. 2011. The deepwater megabenthic invertebrates on the western continental margin of Australia (100–1100 m depths): composition, distribution and novelty. Records of the Western Australian Museum Supplement 80: 1–191.

[N79] Norman, A. M. 1879. The Mollusca of the fiords near Bergen, Norway. Journal of Conchology 2: 8–77.

[O27] Oldroyd, I. S. 1927. The Marine Shells of the West Coast of North America vol. 2 pt 1. Stanford University Press: Stanford University (California).

[PP64] Peres, J. M., & J. Picard. 1964. Nouveau manuel de bionomie benthique de la mer Mediterranee. Recueil des Travaux de la Station Marine d'Endoume, Bulletin 31 (27): 5–137.

[PR79] Pojeta, J., Jr & B. Runnegar. 1979. Rhytiodentalium kentuckyensis, a new genus and new species of Ordovician scaphopod, and the early history of scaphopod mollusks. Journal of Paleontology 53 (3): 530–541.

[P61] Powell, A. W. B. 1961. Shells of New Zealand: An illustrated handbook 4^th ed. Whitcombe and Tombs Limited: Christchurch.

[S11] Simone, L. R. L. 2011. Phylogeny of the Caenogastropoda (Mollusca), based on comparative morphology. Arquivos de Zoologia 42 (4): 161–323.

[SB93] Skelton, P. W., & M. J. Benton. 1993. Mollusca: Rostroconchia, Scaphopoda and Bivalvia. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 237–263. Chapman & Hall: London.

[SW11] Smith, S. A., N. G. Wilson, F. E. Goetz, C. Feehery, S. C. S. Andrade, G. W. Rouse, G. Giribet & C. W. Dunn. 2011. Resolving the evolutionary relationships of molluscs with phylogenomic tools. Nature 480: 364–367.

[S96] Steiner, G. 1996. Suprageneric phylogeny in Scaphopoda. In: Taylor, J. D. (ed.) Origin and Evolutionary Radiation of the Mollusca pp. 329–335. Oxford University Press: Oxford.

[S98] Stilwell, J. D. 1998. Late Cretaceous Mollusca from the Chatham Islands, New Zealand. Alcheringa 22 (1): 29–85.

Last updated: 11 August 2021.