Siphon whelks are large, benthic marinesnails, or whelks. Penion are commonly called siphon whelks because they have a very long siphon. Species typically have a large, pointed operculum. Radulae have 3 or 4 cusps on lateral teeth and 3 cusps on central teeth. Males have a long, dorso-ventrally flattened penis, and correspondingly females have a large pallial oviduct and albumen gland. However, geometric morphometric investigation of P. chathamensis indicates that secondary sexual dimorphism is not prominent for shell shape or size. Shells of Penion vary significantly in shape, size and colouration, making the distinction of species difficult. Shells are fusiform with a tall spire of roughly equal height to the aperture and siphonal canal combined. Protoconch morphology is also highly variable, from 1.5 - 4.0 whorls in height. The siphonal canal of the shell is often long to protect the elongated siphon. Small shells can be confused with those of Aeneator or Antarctoneptunea.
Ecology
Most species occur in deep water, and inhabit soft sediments on the continental shelf. All species of Penion have a wide ranging diet, and are detritivores and carnivores that actively hunt prey. P. sulcatus is known to feed on mussels and Dosina zelandica zelandica. Members of the genus have similar niche placement to species of Buccinum in the Northern Hemisphere.
Distribution
Penion species are restricted to the Southern Hemisphere. Two extant species are currently classified in waters surrounding Australia and six extant species are documented from New Zealand. Numerous fossil species are recorded in New Zealand, Australia, Argentina and Chile, and Antarctica. In New Zealand, many fossils are found in Wanganui Basin sediments. During the voyage of HMS Beagle, fossils of P. subrectus were among palaeontological samples collected by Charles Darwin from the mouth of the Santa Cruz River in Argentina.
Evolution
Penion is currently classified within Buccinidae, the family of true whelks. Alternatively they have been referred to the family of Buccinulidae. Molecular phylogenetic trees based on mitochondrial genomic and nuclear ribosomal DNA sequence data indicate that Penion is closely related to two genera: Kelletia found in the northPacific Ocean and Antarctoneptunea, distributed in waters surrounding New Zealand and Antarctica. Radulae and opercula morphology is similar between Penion and Kelletia. It is possible that the earliest known fossils of Penion belonging to P. proavitus from the New Zealand Paleocene, actually represent a stem lineage that was the common ancestor of these three genera. In Australian waters, the sister speciesP. mandarinus and P. maximus have overlapping geographic ranges, and may have evolved from a common ancestor via niche differentiation based on prey size and water depth.
Human use
Penion shells are prized by shell collectors. Shells found in middens of historic Māori settlements indicate that P. sulcatus may have been intentionally foraged as a food-source.
Species
Species and subspecies in the genus Penion include:
