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Belongs within: Vetigastropoda.
Contains: Brookula (Brookula).
The Skeneidae are a group of small marine gastropods with a porcelaneous, usually widely umbilicate shell (Knight et al. 1960).
Dilemma Elachorbis
Published 30 December 2024
The figure above, taken from Suter (1915), shows the holotype of Elachorbis helicoides, a tiny marine gastropod that was found in New Zealand during the Miocene period. This species was described by Hutton (1877) from the White Rock River formation of Canterbury, under the name of Cyclostrema helicoides. The small, flat-spired shell was only 3.5 mm in diameter with a broad umbilicus. The outer whorls were marked by strong spiral striae, resulting in the outer margin of aperture being subpentagonal. On the underside of the shell, strong radiate folds emerged from the umbilicus. When redescribing the species, Suter (1915) assigned it to the genus Circulus. It was later placed in Elachorbis by Finlay (1926), though authors have differed on whether Circulus and Elachorbis should be maintained as distinct genera.
The broader relationships of Elachorbis have also been subject to dispute. Hutton’s placement of it within Cyclostrema implies a relationship with an assemblage of small archaeogastropods that has variously been referred to the Cyclostrematidae, Liotiidae or Skeneidae. However, even in its original description Hutton expressed some uncertainty whether his helicoides should be placed in Cyclostrema and Adeorbis. These two genera refer to taxa that, though closely similar in external appearance, belong to widely separated lineages. Adeorbis is referrable to the Tornidae, a caenogastropod family and therefore having its last common ancestor with the cyclostrematids more than 300 million years past. Elachorbis was variously regarded as either an archaeogastropod or caenogastropod for more than a century, only being confirmed as the latter with the availability of molecular data (Goto et al. 2021). The difficulty of distinguishing such evolutionarily divergent lineages is an excellent example of the challenges that bedevil mollusc palaeontologists, forced to sort convergent taxa on the basis of their bare shells only.
Systematics of Skeneidae
<==Skeneidae [Delphinoideinae, Skeneadae, Skeneinae]
|--Morchia Adams 1860F26
|--Dikoleps Höisaeter 1968H92
|--Tharsiella Bush 1897 [=Porcupinia Cossmann 1900 non Haeckel 1887, Porcupina (l. c.), Tharsis Jeffreys 1883]KC60
| `--*T. romettensis (Seguenza ex Granata 1877) (see below for synonymy)KC60
|--Philorene Oliver 1915KC60
| `--*P. texturata Oliver 1915KC60
|--Haplocochlias Carpenter 1864KC60
| `--*H. cyclophoreus Carpenter 1864KC60
|--Kaawatina Bartrum & Powell 1928KC60
| `--*K. turneri Bartrum & Powell 1928KC60
|--Leucorhynchia Crosse 1867KC60
| `--*L. caledonica Crosse 1867KC60
|--Munditiella Kuroda & Habe 1954KC60
| `--*M. ammonoceras (Adams 1863) [=Cyclostrema ammonoceras]KC60
|--Norrisella Cossmann 1888KC60
| `--*N. pygmaea (Deshayes 1863) [=Turbo pygmaea]KC60
|--Pakistania Eames 1952KC60
| `--*P. antirotata Eames 1952KC60
|--Pondorbis Bartsch 1915KC60
| `--*P. alfredensis Bartsch 1915KC60
|--Pygmaerota Habe 1958KC60
| `--*P. duplicata (Lischke 1872) [=Cyclostrema duplicatum]KC60
|--Rhodinoliotia Tomlin & Shackleford 1915KC60
| `--*R. roseotincta (Smith 1871) [=Cyclostrema roseotinctum]KC60
|--Tiburnus deGregorio 1890 [incl. Platychilus Cossmann 1888 non Jakolev 1874, Simochilus Harris & Burrows 1891]KC60
| `--T. eborea (Conrad 1833) [=Natica eborea; incl. Turbo naticoides Lea 1833, *Tiburnus naticoides]KC60
|--Delphinoidea Brown 1827BR17 [=Delphionoidea Brown 1844KC60]
| `--*D. unispiralis (Montagu 1803) [=Helix unispiralis]BR17
|--Daronia Adams 1861KC60
| `--*D. spirula (Adams 1850) [=Cyclostrema spirula]KC60
|--Partubolia Iredale 1936W93
| `--*P. blanchaW93
|--Dillwynella Dall 1889KC60
| |--*D. modesta Dall 1889KC60
| `--D. errataW62
|--Lophocochlias Pilsbry 1921KC60 [incl. Aqabarella Alhejoj, Bandel & Al-Najjar 2016 (n. n.)BR17; Aqabarellidae]
| |--*L. minutissimus (Pilsbry 1921)KC60 [=Haplocochlias minutissimusKC60; incl. Aqabarella pulchellaBR17]
| `--L. procerus Rubio & Rolán 2015 [incl. *Aqabarella urdunensis Alhejoj, Bandel & Al-Najjar 2016 (n. n.)]BR17
|--Leptogyra Bush 1897KC60
| |--*L. verrilli Bush 1897KC60
| `--L. alaskana Bartsch 1910O27
|--Dolicrossea Iredale 1924 [=Doliocrossea (l. c.)]KC60
| |--*D. labiata (Tenison-Woods 1876)KC60 [=Crossea labiataP61]
| `--D. vesca Finlay 1927P61
|--Tubiola Adams 1863KC60
| |--*T. (Tubiola) nivea (Gmelin 1791) [=Turbo niveus]KC60
| `--T. (Partubiola Iredale 1936)KC60
| `--T. (*P.) blancha (Iredale 1936) [=*Partubiola blancha]KC60
|--Lissotestella Powell 1946KC60
| |--*L. tenuilirata (Powell 1931) [=Lissotesta tenuilirata]P61
| |--L. cookiana Dell 1956P61
| |--L. rissoaformis (Powell 1931)P61 [=Lissotesta rissoaformisD56]
| `--L. tryphenensis (Powell 1931)P61
|--Zalipais Iredale 1915W93
| |--*Z. lissa (Suter 1908)P61 [=Delphinoidea lissaP61, Cyclostrema lissaKC60]
| |--Z. benthicola Powell 1927P61
| |--Z. parva Finlay 1924P61 [=Z. lissa parvaF26]
| `--Z. turneri Powell 1939P61
|--Lodderena Iredale 1924KC60
| |--*L. minima (Tenison-Woods 1878)KC60 [=Liotia minimaP61]
| |--L. formosa Powell 1930P61
| `--L. nana Powell 1930P61
| |--L. n. nanaP61
| `--L. n. pooki Fleming 1940P61
|--Lodderia Tate 1899 [incl. Cyclostremella Tate 1898 non Bush 1897]KC60
| |--*L. lodderae (Petterd 1884)KC60 [=Liotia lodderaeP61]
| |--L. eumorpha (Suter 1908)P61 [=Cyclostrema eumorphaF26, Elachorbis eumorphaF26]
| | |--L. e. eumorphaP61
| | `--L. e. cookiana (Dell 1952)P61 [=Crosseola cookianaD56]
| `--L. waitemata Powell 1940P61
|--Ganesa Jeffreys 1883KC60
| |--*G. (Ganesa) pruinosa Jeffreys 1883KC60
| |--G. (Granigyra Dall 1889)KC60
| | `--G. (*G.) limata (Dall 1889) [=Cyclostrema limatum]KC60
| `--G. (Lissospira Bush 1897)KC60
| `--G. (*L.) proxima (Tryon 1888) [=Cyclostrema proximum]KC60
|--Skenea Fleming 1825BR05
| |--*S. serpuloides (Montagu 1808) [=Helix serpuloides, Delphinoidea serpuloides]KC60
| |--S. andersoni Janssen 1978TTE93
| |--S. nitida [incl. S. laevis]J64
| |--S. planorbisN79
| |--S. radiostriata Janssen 1978TTE93
| `--S. verreauxiiC64
|--Elachorbis Iredale 1915W93
| |--*E. tatei (Angas 1878)P61, K90 [=Cyclostrema tateiP61]
| |--E. cingulatus (Bartrum 1919) [=Circulus cingulatus]F26
| |--E. diaphana Finlay 1924P61
| |--E. helicoides (Hutton 1877) [=Circulus helicoides]F26
| |--E. politus (Suter 1917) [=Circulus politus]F26
| `--E. subtatei (Suter 1907)P61
|--Parviturbo Pilsbry & McGinty 1945MASC88
| |--*P. rehderi Pilsbry & McGinty 1945KC60
| |--P. calidimaris Pilsbry & McGinty 1945W62
| |--P. francesae Pilsbry & McGinty 1945W62
| |--P. insularis Rolán 1988BC01
| |--P. miliumW62
| |--P. stearnsii (Dall 1918)PP78
| |--P. venezuelensis Weisbord 1962W62
| `--P. weberi Pilsbry & McGinty 1945W62
|--Crossea Adams 1865 [=Crosseia Fischer 1885]KC60
| |--*C. miranda Adams 1865KC60
| |--C. bellulusTW76
| |--C. biconica Hedley 1902H09
| |--C. gatliffi Hedley 1902H09
| |--C. inverta Hedley 1907H09
| |--C. minuta Petterd 1884 [=Fossarus minutus non Michaud 1827]F27
| |--C. parvula Tenison-Woods 1879F71
| `--C. striata Watson 1883H09
|--Liotella Iredale 1915KC60
| |--*L. polypleura (Hedley 1904)P61 [=Liotia polypleuraP61, Brookula (*Liotella) polypleuraKC60]
| |--L. aupouria Powell 1937P61
| |--L. incertaF26
| |--L. indigens Finlay 1927P61
| |--L. mackenae Dell 1956P61
| |--L. neozelanica (Suter 1908)F26
| |--L. rotula (Suter 1908)P61
| `--L. rotuloides Powell 1937P61
|--Brookula Iredale 1912S98 [incl. Vetulonia Dall 1913KC60; Brookulidae]
| | i. s.: B. densilaminata (Verco 1907)W93
| |--B. (Brookula)P61
| |--B. (Aequispirella Finlay 1924)P61
| | |--B. (*A.) corulum (Hutton 1884) [=Scalaria corulum]P61
| | |--B. (A.) enderbyensis Powell 1931P61
| | |--B. (A.) finlayi Powell 1933P61
| | |--B. (A.) iredalei Finlay 1924F26
| | `--B. (A.) tenuilirata Finlay 1924F26
| `--B. (Liocarinia Laseron 1954)KC60
| `--B. (*L.) disjuncta (Hedley 1903) [=Liotia disjuncta]KC60
|--Lissotesta Iredale 1915KC60
| |--*L. micra (Tenison-Woods 1877)KC60 [=Cyclostrema micraP61]
| |--L. ambigua Dell 1956P61
| |--L. aupouria Powell 1937P61
| |--L. benthicola Powell 1927P61
| |--L. bicarinata Powell 1940P61
| |--L. caelata Powell 1937P61
| |--L. conoidea Powell 1937P61
| |--L. consobrina Powell 1940P61
| |--L. decipiens Powell 1940P61
| |--L. errata Finlay 1927P61
| |--L. exigua (Suter 1917) [=Lissospira exigua]F26
| |--L. granum (Murdoch & Suter 1906)P61 [=Cirsonella granumF26]
| |--L. oblata Powell 1940P61
| `--L. otagoensis Dell 1956P61
`--Cirsonella Angas 1877KC60
|--C. weldii (Tenison-Woods 1877)H09 [=Cyclostrema weldiiH09; incl. *Ci. australis Angas 1877W93, P61]
|--C. accelerans Fleming 1948P61
|--C. consobrina Powell 1930P61
|--C. cubitale Hedley 1907H09
|--C. densilirata Suter 1908P61
|--C. laevis (Johnston 1880) [=Adeorbis laevis]F27
|--C. laxa Powell 1937P61
|--C. paradoxa Powell 1937P61
|--C. parvula Powell 1926P61
|--C. pisiformis Powell 1937P61
|--C. propelaxa Dell 1956P61
|--C. simplex Powell 1937P61
|--C. variecostata Powell 1940P61
`--C. waikukuensis Powell 1937P61
*Tharsiella romettensis (Seguenza ex Granata 1877) [=Oxystele romettensis, *Porcupinia romettensis, *Tharsis romettensis]KC60
*Type species of generic name indicated
References
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