The shape and the idea: 97 — Ostrich foot shell, Struthiolaria papulosa

Monday, 28 November 2016

97 — Ostrich foot shell, Struthiolaria papulosa

Struthiolaria papulosa, Pilot Bay,
Mt. Maunganui, 2015.

The ostrich foot shell Struthiolaria papulosa (Martyn, 1784) is almost ubiquitous on sandy beaches around New Zealand. Examples from the north reach about 70mm and have sharp knobs on the spire whorls, while southern forms (gigas) are larger (~90mm) and are smooth, without sharp knobs. They are considered to be one variable species, as there is a general gradation between the two forms moving north to south.

Struthiolaria papulosa, position buried in sand
while feeding. From Morton (1951).

Struthiolaria papulosa is a deposit feeder and sits just below the surface sediments, using complex ciliary currents to essentially inhale its food. This food consists of coarsely graded detritus and micro-organisms, such as benthic diatoms and Foraminifera. Since they live close to the surface, they are easily disturbed by wave-action and after storms can be washed ashore in their thousands.

The Struthiolariidae have a rich fossil history in New Zealand, although today there are only two extant species: Struthiolaria papulosa and the much smaller Pelicaria vermis (Martyn, 1784). Pelicaria vermis lives in deeper water than S. papulosa and is less common.