Abstract:
The new genus Trophonella is described from the outer shelf and upper continental slope of Antarctica and islands within the Antarctic Convergence. Four previously known species that had been attributed to the genus Trophon (Trophon scotianus Powell, 1951; T echinolamellatus Powell, 1951; T enderbyensis Powell, 1958; and T eversoni Houart, 1997) are included in Trophonella, as is one new species (Trophonella rugosolamellata) described herein. Trophonella resembles Trophon in gross shell morphology: the members of both genera have large, globose shells, paucispiral protoconchs, prominent axial lamellae, and short siphonal canals. Trophonella differs from Trophon in having shells with evenly rounded whorls that lack a well-defined shoulder; rachidian teeth with distinctive, broadly triangular central cusps, but that lack the marginal cusps of Trophon; characteristic spherical accessory salivary glands; and a circumpapillar fold on the penis that is absent in Trophon. Relationships of the genera Trophon and Trophonella, as well as of the subfamily Trophoninae are reexamined by supplementing the data matrix of Kool (1993b, Table 3) with data for additional taxa. Results support the segregation of Trophonella from Trophon at the generic level. Based on the relationships of the type species of their respective nominotypical genera, Trophoninae is either the sister taxon of a narrowly circumscribed Ocenebrinae, or both are part of a larger clade. A better resolved phylogeny containing a much broader sampling of the more than 50 genus-level taxa that have been attributed to these two subfamilies will be required in order to delineate more precisely the membership of the clade and to identify its diagnostic synapomorphies.
