About Shells 
Shell anatomy, terminology, classification, nomenclature, etc.

Paucispiral vs Planktotrophic Protoconchs

Nov 13, 2013

I've read many researchers' interpretations and they are not all quite consistent, but generally, here's the difference.

Paucispiral literally means "spiral with few turns."

Protoconchs can be classified into two groups:

1. Direct development - where the larval stage is completed in the egg (usually within an egg mass or casing) and teleoconch growth has started by the time the animal/shell is expelled and the animal "crawls away."

2. Lecithotrophic development - where the larva is dispersed into and remains in the water column of the aquatic environment before the larval stage is completed, usually with a yolk sac to provide nutrition for the completion of larval development, but may also be able to feed. Lecithotrophic developers may spend a short or long time in the water column. Lecithotrophic developers that remain in the water column for a fairly long duration (2-3 months) until larvel development is completed are referred to as Planktotrophic. Planktotrophic protoconchs have more numerous whorls, often with distinctive protoconch 1 and protoconch 2 parts of differing sculpture. Planktotrophic protoconchs tend to be tiny, light-weight and translucent.

The number of protoconch whorls in both "direct" and "lecithotrophic" developers is variable, but most often "direct" developers and "lecithotrophic" developers that spend a short time in the water column have protoconchs with only a few whorls, tend to be large, bulbous, heavy, rapidly increasing in width, and opaque [or with the first whorl translucent and subsequent whorl(s) opaque] and are often described as Paucispiral .

Just keep in mind that words like "few," "short time," "numerous" are interpretive and relative, and that Mother Nature has evolved all kinds of variations that often defy clear classification.

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