|Basic info||Taxonomic history||Classification||Relationships|
|Morphology||Ecology and taphonomy||Age range and collections|
Helcionelloida - Helcionellida - Stenothecidae
It was assigned to Procarinariidae by Runnegar and Jell (1976); to Mellopegmidae by Missarzhevsky (1989); to Helcionellidae by Landing et al. (2002); to Helcionelloida by Sepkoski (2002); to Stenothecinae by Parkhaev (2002), Parkhaev (2004) and Bouchet et al. (2005); and to Stenothecidae by Runnegar and Jell (1980) and Vendrasco et al. (2011).
|Year||Name and author|
|1976||Mellopegma Runnegar and Jell|
|1980||Mellopegma Runnegar and Jell p. 111|
|1989||Mellopegma Missarzhevsky p. 179|
|2002||Mellopegma Landing et al. p. 298|
|2002||Mellopegma Parkhaev p. 36|
|2002||Mellopegma Sepkoski, Jr.|
|2004||Mellopegma Parkhaev p. 602|
|2005||Mellopegma Bouchet et al. pp. 107, 241|
|2011||Mellopegma Vendrasco et al. pp. 11A:6-7|
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If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
|M. J. Vendrasco et al. 2011||Stenothecid molluscs with elongate shells (typical l/w >4) that lack a zygion and possess a strongly curved ventral margin.
Laterally compressed, elongate univalves with strongly curved ventral (aperture) margin. Slight coiling (less than half a whorl; cladistic character 4, state 0; Appendix 1), with gently convex supra-apical dorsal margin and concave subapical margin that ends in a flat to downward-sloping shelf. Shell microstructure of outer layer prismatic and inner layer calcitic semi-nacre (character 17, state 1). Tubercles (granules) occur sporadically on surface of internal moulds, revealing shell pores that extend through most or all of the thickness of the shell (character 14, state 1). Inner sculpture of gentle to prominent comarginal ridges (character 6, state 1).