The marine animal called dugong which is vulnerable to extinction is a/an:

The dugong (Dugong dugon) is a seagrass‑dependent marine mammal, often called the “sea cow,” and is the sole living member of the family Dugongidae; it is therefore a mammal, not a fish, amphibian or shark [2]. Dugongs belong to the order Sirenia (the sirenians include manatees and dugongs), which are fully aquatic herbivorous mammals adapted to coastal tropical and subtropical waters [2]. The species is listed as vulnerable to extinction on the IUCN Red List and faces threats from hunting, habitat degradation (loss of seagrass), and fishing‑related mortality, confirming its conservation concern [3].

Sources

1. [1] https://www.cms.int/sites/default/files/document/Annex_7_EcologyConservation_of_the_Dugong_0.pdf
2. [2] https://www.fao.org/4/t0725e/t0725e31.pdf
3. [3] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 12: Animal Diversity of India > Dugong > p. 189