
Belongs within: Clypeasteroida.
The Echinarachniidae are a group of sand dollars known from the Oligocene to the present of the North Pacific, as well as the present day north-western North Atlantic (Durham 1966).
Characters (from Durham 1966): Medium-sized to large; petals well developed, anterior petal more open than paired petals; interambulacrum 5 may be discontinuous; interambulacra 0.7 or less width of ambulacra at ambitus; four genital pores; periproct marginal to inframarginal; food grooves with central trunk.
<==EchinarachniidaeD66 |--Nipponaster Durham 1952 [=Pseudoastrodapsis Durham 1953]D66 | `--*N. nipponicus (Nisiyama 1934)M89 [=Astrodapsis nipponicusM89, *Pseudoastrodapsis nipponicusD66] |--Tenuiarachnius Durham 1955D66 | `--*T. kleinpelli (Grant & Hertlein 1938)M89 (see below for synonymy) |--Kewia Nisiyama 1935D66 | |--*K. blancoensis (Kew 1920) [=Scutella blancoensis]M89 | `--K. marquamensis Linder, Durham & Orr 1988SG93 |--Remondella Durham 1955D66 | |--*R. gabbi (Rémond 1863) [=Clypeaster gabbi]M89 | `--R. waldroniM89 |--Echinarachnius Gray 1825 (nom. cons.)M89 [=Phelsumaster Lambert & Thiéry 1914D66, Phelsumia Pomel 1883D66] | |--*E. parma (Lamarck 1816)M89 (see below for synonymy) | |--E. mirabilisD05 | `--E. placentaJ64 |--Astrodapsis Conrad 1856 [=Asterodapsis Agassiz 1872, Astrodaspis (l. c.)]D66 | |--*A. antiselli Conrad 1856M89 [=*Asterodapsis antiselliD66] | |--A. brewerianusD66 | `--A. spatiosusM89 `--Vaquerosella Durham 1955D66 |--*V. andersoni (Twitchell 1915) [=Scutella andersoni]M89 |--V. norrisiM89 `--V. vaquerosensisD66
*Echinarachnius parma (Lamarck 1816)M89 [=Scutella parmaM89, *Phelsumaster parmaD66, *Phelsumia parmaD66; incl. Echinarachnius asiaticus Michelin 1859D05, E. atlanticus Agassiz 1841D05]
*Tenuiarachnius kleinpelli (Grant & Hertlein 1938)M89 [=Echinarachnius gabbii kleinpelliM89; incl. Scutella gabbi tenuis Kew 1915 non Echinarachnius tenuis Yoshikawa 1898D66]
*Type species of generic name indicated
References
[D05] Döderlein, L. 1905. Arktische Seeigel. In: Römer, F., & F. Schaudinn (eds) Fauna Arctica. Eine Zusammenstellun der arktischen Tierformen, mit besonder Berücksichtigung des Spitzbergen-Gebietes auf Grund der Ergebnisse der Deutschen Expedition in das Nördliche Eismeer im Jahre 1898 vol. 4 pp. 373–394. Gustav Fischer: Jena.
[D66] Durham, J. D. 1966. Clypeasteroids. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt U. Echinodermata 3 vol. 2 pp. U450–U491. The Geological Society of America, Inc., and The University of Kansas Press.
[J64] Jeffreys, J. G. 1864. Report of the committee appointed for exploring the coasts of Shetland by means of the dredge. Report of the British Association for the Advancement of Science 33: 70–81.
[M89] Mooi, R. 1989. Living and fossil genera of the Clypeasteroida (Echinoidea: Echinodermata): an illustrated key and annotated checklist. Smithsonian Contributions to Zoology 488: 1–51.
[SG93] Simms, M. J., A. S. Gale, P. Gilliland, E. P. F. Rose & G. D. Sevastopulo. 1993. Echinodermata. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 491–528. Chapman & Hall: London.