Scaphopoda

Siphonodentalium lobatum, copyright Natural History Museum Rotterdam.

Belongs within: Rostroconchia.
Contains: Gadilimorpha, Laevidentaliidae, 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 1974PR79
    |         Quasidentalium Gentile 1974PR79
    |         Throopella Greger 1933 [Throopellidae]L60
    |           `--*T. typa Greger 1933L60
    |--Gadilida [Siphonodentaliidae]L60
    |    |--GadilimorphaS96
    |    `--Entalinidae [Entalimorpha]BRW98
    |         |--ContentalinaBRW98
    |         |--PertusiconchaBRW98
    |         |--EntalinopsisBRW98 (see below for synonymy)
    |         |    `--‘Dentalium (*Heteroschismoides) subterfissum Jeffreys 1877 [=*Heteroschisma subterfissum]L60
    |         |--Bathoxiphus Pilsbry & Sharp 1897BRW98, L60
    |         |    |--*B. ensiculus (Jeffreys 1877) [=Dentalium ensiculus]L60
    |         |    |--B. colmani (Palmer 1974)MG-H11
    |         |    `--B. tricarinatumBRW98
    |         `--Entalina Monterosato 1872GO06, L60 [incl. Eudentalium Cotton & Godfrey 1933L60; Entalinidae]
    |              |--*E. tetragona (Brocchi 1814)L60 (see below for synonymy)
    |              |--E. mirificaBRW98
    |              |--E. platamodes (Watson 1879) [=Siphodentalium platamodes; incl. E. quadrata Henderson 1920]E52
    |              `--E. quinquangularis (Forbes 1843)L60, E52 [=Dentalium quinquangulareE52]
    `--Dentaliida [Dentalioida]S96
         |  i. s.: LaevidentaliidaeS96
         |         GadilinidaeS96
         |           |--AnulidentaliumBRW98
         |           |--Lobantale Cossmann 1888BRW98, L60
         |           |    `--*L. duplex (Defrance 1819) [=Dentalium duplex]L60
         |           |--Gadilina Foresti 1895L60
         |           |    |--*G. triquetra (Brocchi 1814) [=Dentalium (*Gadilina) triquetrum]L60
         |           |    `--G. tateiBRW98
         |           `--Episiphon Pilsbry & Sharp 1897BRW98, L60
         |                |--*E. sowerbyi (Guilding 1834) [=Dentalium sowerbyi]L60
         |                |--E. bordaensisBRW98
         |                |--E. johnsoni (Emerson 1952) [=Dentalium (Episiphon) johnsoni]E52
         |                |--E. macilentum (Pilsbry 1911) [=Dentalium (Episiphon) macilentum]E52
         |                |--E. tornatissimumBRW98
         |                `--E. virgulaBRW98
         |         OmniglyptaBRW98 [OmniglyptidaeS96]
         |           |--O. anulosum [=Dentalium anulosum]BRW98
         |           `--O. cerina [=Dentalium cerinum]BRW98
         |--Rhabdus Pilsbry & Sharp 1897L60 [RhabdidaeS96]
         |    `--*R. rectius (Carpenter 1865) [=Dentalium rectius]L60
         `--+--Fustiaria Stoliczka 1868L60 [FustiariidaeS96]
            |    |--*F. circinata (Sowerby 1823) [=Dentalium circinatum]L60
            |    |--F. caesuraBRW98
            |    |--F. rubescensGO06
            |    `--F. stenoschizumBRW98
            `--DentaliidaeS96
                 |--DentaliumL60
                 |--LentigodentaliumBRW98
                 |--Paradentalium Cotton & Godfrey 1933L60
                 |    `--P. intercalatumBRW98
                 |--Prodentalium Young 1942L60
                 |    |--*P. raymondi Young 1942L60
                 |    `--P. martini (Whitfield 1882)SB93
                 `--PictodentaliumBRW98
                      |--P. formosumBRW98
                      |    |--P. f. formosumBRW98
                      |    `--P. f. hiraseiBRW98
                      `--P. vernedeiBRW98

*Entalina tetragona (Brocchi 1814)L60 [=Dentalium tetragonumL60, Siphonodentalium tetragonumN79; incl. S. pentagonum Sars 1864N79, Dentalium quinquangulatum Reeve 1872N79]

EntalinopsisBRW98 [incl. Heteroschisma Simroth 1895 non Wachsmuth 1883L60, Heteroschismoides Ludbrook 1960BRW98, L60]

*Type species of generic name indicated

References

[BRW98] Beesley, P. L., G. J. B. Ross & A. Wells (eds) 1998. Fauna of Australia vol. 5. Mollusca: The Southern Synthesis. Part A. Australian Biological Resources Study: Canberra.

[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.

[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.

[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.

[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.

[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.

Leave a comment

Your email address will not be published. Required fields are marked *