Pilot whales: how many species are there?

Grzimeks encyclopedia from 1969 [1] contains a small section on pilot whales saying that the exact number of species is uncertain. Nevertheless, three species are mentioned according to geography: the common or North Atlantic pilot whale (Globicephala melaena), the Indic Ocean pilot whale (Globicephala macrorhyncha), and the Pacific Ocean pilot whale (Globicephala sieboldii).

The World Cetacea Database notes the species status of the latter (Globicephala sieboldii, GRAY, 1864) as taxonomically unaccepted [2].

Globicephala melaena and Globicephala macrorhyncha survived taxonomic evaluations and are commonly known as long-finned pilot whale and short-finned pilot whale. Note that the scientific name Globicephala melaena changed to Globicephala melas and Globicephala macrorhyncha changed to Globicephala macrorhynchus. Who said that a binomial term uniquely identifies a species?

The genus name Globicephala (“round head”) in different languages
Dutch: grienden
English: pilot whale
French: baleines-pilote (also: globicéphale)
German: Grindwal
Italian: globicephala
Portuguese: baleia-piloto
Spanish: ballena piloto

The Dutch and German names are derived from the Faroese language, in which the word grind means whale hunt.

By the way, pilot whales are dolphins, belonging to the Delphinidae family in the order Cetacea. Why not call them pilot dolphins?

References and much more
[1] Grzimeks Tierleben • Elfter Band • Säugetiere 2, page 503.
[2] Worl Cetacea Database: Globicephala sieboldii Gray, 1846.
[3] NOAA > Marine Mammals: Long-finned Pilot Whale (Globicephala melas).
[4] NOAA > Marine Mammals: Short-finned Pilot Whale (Globicephala macrorhynchus).