The callionymid fish genus Protogrammus is represented by two closely related species living on soft bottoms at 70-300 m, with extremely restricted, but disjunct distributions: Protogrammus sousai from seamounts near Madeira in the northeastern Atlantic, and P. antipodus from the Loyalty Islands (New Caledonia) in the southwestern Pacific. Obviously, these are relict distributions of a formerly more widespread group. Does anyone know similar cases of closely related species with disjunct ranges in the northeastern Atlantic and southwestern Pacific?
Exactly the same relict distribution is, as far as I know, not known in the Mollusca.
There are three species of Right whale with a somewhat similar distribution. Eubalaena glacialis is a North Atlantic species and there exists a separate species of Right whale, Eubalaena australis, inhabits the South Pacific. The third, Eubalaena japonica, ranges through the North Pacific.
I'm familiar, and did some (published) research, but about rather recent case(s), which I thought were associated with the opening, over 100 years ago, of the Suez Canal.
There is a couple of sof coral genera with Caribean and Indian-WPacific species, in the recent years Azorian and/or Mediterranean species have been described or reported linking the genus distribution EAtlantic - Indian-WPacific.
See in my list of publications:
López-González PJ & JM Gili (2008) A new species of Nidalia Gray, 1835 from Mid-Atlantic seamounts (Octocorallia, Alcyonacea, Nidaliidae). Helgoland Marine Research, 62: 389-392.
PJ López-González, J Grinyó & JM Gili (2012) Rediscovery of Cereopsis studeri Koch, 1891, a forgotten Mediterranean soft coral species, and its inclusion in the genus Nidalia Gray, 1835 (Octocorallia, Alcyonacea, Nidaliidae) Marine Biology Research, 8: 594-604.
and another paper published online last week:
Pablo J. López-González, Jordi Grinyó & Josep-Maria Gili (2014 online version) Chironephthya mediterranea n. sp. (Octocorallia, Alcyonacea, Nidaliidae), the first species of the genus discovered in the Mediterranean Sea. Marine Biodiversity, DOI 10.1007/s12526-014-0269-5
Though this subject field is beyond my knowledge, but I think you would find similar cases in middle or far east regions.
The morids Lepidion schmidti and probably L. guentheri have a similar distribution
Bañón, R., J.C. Arronte, S. Vázquez-Dorado, J.L. del Río & A. de Carlos. 2013. DNA barcoding of the genus Lepidion (Gadiformes: Moridae) with recognition of Lepidion eques as a junior synonym of Lepidion lepidion. Molecular Ecology Resources, 13: 189–199
Protogrammus may be a case of a highly unusual, exceptionally disjunct distribution. Alternatively, it might be a case of a very rare genus that has yet to be recorded in most places where it lives. GBIF finds just nine records of known specimens, some of which look to be duplicates, suggesting a global total of only a half-dozen confirmed records. More extensive sampling on seamounts, and a search of existing collections for specimens that have been dismissed as something far more abundant, could produce a very different picture.
I'd want a lot more data before drawing any biogeographic conclusions.
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