This is a living fossil

The correct option is Latimeria.

Step-by-step Explanation:

1. Understanding "Living Fossils":
A "living fossil" is an extant (living) species that closely resembles ancient species known only from the fossil record. These organisms typically show very little morphological change over millions of years, and most of their close relatives are extinct.

2. Why Latimeria is the Correct Answer:
Latimeria is the only surviving genus of coelacanths, which are ancient lobe-finned fish. For a long time, coelacanths were believed to have gone extinct near the end of the Cretaceous period (about 66 million years ago) because no fossils of them were found in younger rock strata. However, in 1938, a live specimen of Latimeria chalumnae was discovered off the coast of South Africa. Because the living species is structurally and anatomically almost identical to its fossil ancestors that lived hundreds of millions of years ago, it is famously referred to as a living fossil.

3. Overview of the Other Options:
- Neoceratodus (Queensland lungfish) and Lepidosiren (South American lungfish) are ancient lungfish genera, but Latimeria is the iconic representative of the coelacanth lineage resurrected from presumed extinction.
- Lepidosteus (gars) represents a primitive group of ray-finned fish but is not the classic example associated with this specific question.