Flax Snail

Placostylus ambagiosus is a species of flax snail (Māori: pūpū whakarongotaua^[4]), a large air-breathing land snail, a terrestrial pulmonate gastropod mollusc in the family Bothriembryontidae.

Description

This snail has a large (43–97 millimetres or 1.7–3.8 inches long)^[5] shell, which is heavily calcified. The size of the adult shell is habitat dependent,^[5] but the shell shape is not plastic.^[4] Placostylus ambagiosus is highly valued by Te Aupōuri me Ngāti Kurī (the indigenous people of northern New Zealand) as a food source, musical instrument and in the past this snail provided alarm calls at night warning of approaching invaders.^[6]

Distribution

This land snail species occurs in New Zealand. It is restricted to a small fragmented area of Northland Region, including the Aupouri Peninsula and Motuopao Island.^[7] In the past local Māori moved and propagated populations of Placostylus ambagiosus,^[8][9] so today at least three extant populations are found on old pā sites (fortified settlements), along with other species that were cultivated such as karaka (Corynocarpus laevigatus) and harakeke (Phormium tenax).^[10][11]

Biology

This snail feeds at night on fallen leaves on the forest floor.^[5] A favorite plant species is hangehange (Geniostoma ligustrifolium). Placostylus ambagiosus needs year round moisture provided by deep leaf-litter. Eggs are laid in clutches (average 43 eggs) in the shallow hollows in the soil.^[5] The species is slow-growing with a lifespan of 10–22 years and strong site fidelity^[12] The same individual snail has been found under the same food plant for 12 years.^[5] The species is endangered due to predation from rats^[13] and birds,^[14] habitat damage by pigs and horses and competition from introduced snails.^[13]

Hypothetical subspecies

Based on molecular phylogeny (mtDNA) and shell morphology research it was suggested in 2011 by Buckley et al.^[15] that there are no subspecies of Placostylus ambagiosus.^[15] However, in the past, what were thought to be eight extant subspecies and a number of undescribed but distinct populations, were named;^[7] six of these "subspecies" are now extinct^[16] (marked with a †); conservation statuses were given according to the New Zealand Threat Classification System for the extant taxa: "nationally critical" and "nationally endangered":^[17] At least five subspecies of Placostylus ambagiosus can be recognized using shell shape (not size or location) of individuals snails suggesting these represented distinct populations that require protection.^[4]

• Placostylus ambagiosus "Herangi Hill" †
• Placostylus ambagiosus "nouvelle" - nationally endangered
• Placostylus ambagiosus "Haupatoto" - nationally critical
• Placostylus ambagiosus "Kauaetewhakapeke Stream" - nationally critical
• Placostylus ambagiosus "Kohuronaki" - nationally critical
• Placostylus ambagiosus "Poroiki" - nationally critical
• Placostylus ambagiosus "Te Paki" - nationally endangered
• Placostylus ambagiosus "Tirikawa" - nationally critical
• Placostylus ambagiosus ambagiosus Suter, 1906 - nationally critical
• Placostylus ambagiosus annectens Powell, 1938 2
• Placostylus ambagiosus consobrinus Powell, 1938 - nationally critical
• Placostylus ambagiosus gardneri †
• Placostylus ambagiosus hancoxi 1
• Placostylus ambagiosus hinemoa †
• Placostylus ambagiosus keenorum Powell, 1938 - nationally endangered
• Placostylus ambagiosus lesleyae †
• Placostylus ambagiosus michiei Powell, 1951 - nationally endangered
• Placostylus ambagiosus pandora Powell, 1951 - nationally critical
• Placostylus ambagiosus paraspiritus Powell, 1951 - nationally endangered
• Placostylus ambagiosus priscus †
• Placostylus ambagiosus spiritus †
• Placostylus ambagiosus watti Powell, 1947 - nationally critical
• Placostylus ambagiosus whareana Powell, 1951 - nationally critical
• Placostylus ambagiosus worthyi †

References