"Biomantle" isn't a commonly used scientific term. It's possible you're thinking of a similar term, or it might be a more specific, localized term.

Here are some possibilities:

1. Biofilm: This is a thin, slimy layer of microorganisms that adhere to surfaces. It's a very common phenomenon in nature and plays important roles in various ecosystems. Biofilms can be beneficial (e.g., in wastewater treatment) or harmful (e.g., causing infections).

2. Mantle: This refers to the layer of the Earth that lies beneath the crust and above the core. It's primarily composed of solid rock but behaves in a viscous, plastic way over geological timescales. This is where plate tectonics occurs.

3. Mantle (Biology): Some animals have a mantle, which is a fold of tissue that covers the visceral mass. For example, cephalopods like octopuses and squids have a mantle that forms a cavity around their gills and helps them move by jet propulsion.

4. Biomaterial: This refers to any material that is derived from living organisms or biological sources. Biomaterials are used in a wide range of applications, including medical implants, tissue engineering, and drug delivery.

If you can provide more context about where you encountered the term "biomantle", I might be able to give you a more precise answer.