Melamphaes simus

Actinopterygii: The Actinopterygii, or ray-finned fishes, constitute a class or subclass of the bony fishes. The ray-finned fishes are so called because they possess lepidotrichia or "fin rays", their fins being webs of skin supported by bony or horny spines ("rays"), as opposed to the fleshy, lobed fins that characterize the class Sarcopterygii. In terms of numbers, actinopterygians are the dominant class of vertebrates, comprising nearly 99% of the over 30,000 species of fish. (Wikipedia)

Bathypelagic: The bathyal zone or bathypelagic – from Greek bathýs, deep – (also known as midnight zone) is the part of the pelagic zone that extends from a depth of 1000 to 4000 metres (3300 to 13000 feet) below the ocean surface. It lies between the mesopelagic above, and the abyssopelagic below. (Wikipedia)

Long: The ichthyolith is at least three times longer than it is wide.

Cavity: The ichthyolith has a central nerve cavity. This is a base keyword included whenever an ichthyolith has a cavity, even when the cavity is further categorized with an additional keyword.

Triangular: The base of the ichthyolith is the widest part.

Curved: The overall shape of the ichthyolith curves in one direction.