An unknown mineral sample cannot be scratched by glass but can be scratched by a steel file. For identification purposes, how is the mineral's hardness described?

Centriole.centrioles are present in animal cells but are usually absent in plant cells.

Although i don't know what is the simulated system, starfish are predators that eat mostly  microalgae,  snails, sponges, bivalves, mussels and other small marine animals. removing starfish from any system would definitely increase this animals that they prey.