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Morphology Ecology and taphonomy   Age range and collections

Mellopegma

Helcionelloida - Helcionellida - Stenothecidae

Synonymy list
YearName and author
1976Mellopegma Runnegar and Jell
1980Mellopegma Runnegar and Jell p. 111
1989Mellopegma Missarzhevsky p. 179
2002Mellopegma Landing et al. p. 298
2002Mellopegma Parkhaev p. 36
2002Mellopegma Sepkoski, Jr.
2004Mellopegma Parkhaev p. 602
2005Mellopegma Bouchet et al. pp. 107, 241
2011Mellopegma Vendrasco et al. pp. 11A:6-7

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RankNameAuthor
kingdomAnimalia()
Bilateria
EubilateriaAx 1987
Protostomia
Spiralia
Schizocoela
RankNameAuthor
phylumMollusca
classHelcionelloidaPeel 1991
orderHelcionellida
superfamilyYochelcionelloidea
familyStenothecidae
genusMellopegma

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.

Diagnosis
ReferenceDiagnosis
M. J. Vendrasco et al. 2011Stenothecid 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).