99 — Small ostrich foot shell, Pelicaria vermis

Pelicaria vermis, off Pakiri Beach ~20–30m.
Cast up on Kohimarama Beach as part of the
2004 beach replenishment programme.

Pelicaria vermis (flemingi form). A larger and
wider form from Mt. Maunganui's Ocean Beach.

Pelicaria vermis (tricarinata form), Castlecliff
Beach, Jan 1985. Pleistocene fossil form.

All three together. The flemingi form
 is on the far left. The largest is about 50mm.

Pelicaria vermis (Martyn, 1784) is the smaller of the two ostrich foot shells (Family: Struthiolariidae) found in New Zealand waters; it is also the less common of the two. Many more species exist in New Zealand's fossil record, some of which date back at least 40 million years.

Pelicaria vermis is restricted to the North Island and the top of South Island—although this distribution doesn't appear to be temperature related, as they are also found in considerable depths (down to ~300m, where the water is quite cold).

Unlike Struthiolaria papulosa, P. vermis is a direct-developer—meaning that there is no planktonic larval stage, so when the egg hatches out crawls a miniature version of the adult. This direct-development has interesting evolutionary implications, as it is possible for populations to become genetically isolated since there is no planktonic dispersal phase. This is one way new species can arise (a process called speciation).

About 40 years ago it was thought that there were several regional sub-species from various parts of New Zealand. However, it is now considered that there is one, rather variable species, since it turns out that these various forms actually intergrade. Maybe in a few thousand years they might become different species, maybe not...

Ecologically, they feed in a similar way to their larger cousin: buried in the sediment, consuming plankton via currents driven by cilia. However, they appear to differ in that they can tolerate muddier sediments and deeper water.









More info:

https://www.gns.cri.nz/static/Mollusca/taxa/BM514.html