Behaviour

Hippochrenes amplus

Hippochrenes amplus

 

Because Hippochrenes amplus is an extinct genus and species, we can only infer what its behaviour may have been. There are several lines of evidence that we can use:

  1. Systematic relationships
  2. Shell morphology
  3. Symbioses
Systematic relationships

This species belongs to a superfamily (Stromboidea) of which all living species walk with a discontinuous jerking motion, using a strongly muscular and tubular foot. Therefore we may infer that Hippochrenes had a similar shaped foot and walked in the same way.

Many recent stromboids escape bottom predators such as crabs by leaping into the water column using their muscular foot. It has been suggested that the wing of Hippochrenes might then have allowed hydrodynamic gliding of the shell back to the sediment surface away from the predator.

Shell morphology

The adult wing massively extends the area of the shell that may have rested on the sediment. In molluscs wing-like structures commonly act as ‘snowshoes’ to increase a shell’s surface area and prevent the animal sinking into very soft, soupy mud. However, Hippochrenes amplus is found together with the usual range of mud-dwelling molluscs and it is also found in more sandy sediments. Therefore we do not think that the wing acted like a snoeshoe.

Alternatively, the wing may have provided a shelter or chamber into which the animal could extend for walking and feeding, protected from possible predators. We know that Hippochrenes was frequently attacked by predatory crabs or fish from the breakage marks they have left in the edge of the wing. Some Hippochrenes survived these attacks, repaired the lip of their shell and continued to grow.

Symbioses

The wing of live Hippochrenes was commonly encrusted by other marine organisms such as sessile snails, bryozoans (sea mats) and hydroids. Overgrowth of bryozoans and hydroids by later deposited shell layers on the inside of the wing tells us a number of things about the habits of living Hippochrenes snails.

The bryozoans and hydroids encrusted Hippochrenes shells when the snail was alive and still growing.

These organisms are filter-feeders that cannot survive being buried for long periods in mud. This tells us that Hippochrenes lived dominantly on the surface of muddy sediment, not buried within it.

The underside of the wing did not lie flat on the sediment – this would have killed the filter-feeders. So we may conclude that the wing provided a protective shelter over a cavity in which the soft animal could extend to walk and feed yet remain protected from attacks by carnivorous crabs or fish.