The Helcionellacea includes two families according to the
Treatise, 1960, the
Helcionellidae, which is the more primitive, and the
Coreospiridae, which is the more derived. The Helconellidae (Wenz, 1938) represented by the genus
Helcionella (Grabau & Shimer, 1909) more closely resembles the
monoplacophoran ancestor, and is characterized by elongate cap-shaped shells. The Coreospiridae (Knight, 1947) which includes
Coreospira (Satto, 1936)
Cycloholcus (Knight, 1947) and
Latouchella (Cobbold, 1921) are more bellerophontiform (shaped like a
bellerophont).
Latauchella has the least amount of apical coiling, and more closely resembles species of
Helcionella.
Coreospira is tightly coiled while
Cycloholcus is open coiled. Both bear some resemblance to the genus
Cloudia in the
Cyrtolitidae, Bellerophontacea. Wagner (2011) reassigned the Helcionellacea (alternatively Helcionelloidea) to the Helcionellida with the following families, Helcionellidae,
Garkielladae, and
Procarinaridae. Parkhaev 2002 added the
Igarkiellidae and expanded the Coreospiridae and Helcionellidae with additional genera. The Procarinaridae, represented by
Procarinaria from the
Upper Silurian of
Italy and the
Czech Republic, was tentatively included in the Cyrolitidae by Knight et al., 1960, and this taxon may or may not belong instead to the Helcionellacea. The stratigraphic gap of the intervening
Ordovician suggests otherwise. ==References==