The 19th century was a golden age for ichthyological exploration. It signified an era of what seemed like an endless slew of new discoveries, where even the most iconic and noble of species we know today were without names. Taxonomists were still making sense of the creatures living beneath the waves, putting names to things living on coral reefs so bejewelled one could hardly imagine. Indeed, when it came to making sense of specimens back in those days, a little bit of imagination would often go a long way.
You see, despite the wealth of organisms pouring out of pristine oceans, many of these creatures were hardly seen alive or in situ. Camera technology was incipient, and photographs, though hardly useful at the time, were only common toward the later half of the 19th century. Natural history illustrations were a mainstay accompanying species descriptions, but with specimens often moribund or long dead before reaching the hands of a taxonomist, this too had its limitations.
One such example is Nemateleotris, a small genus with barely a handful of species, but all indubitably beautiful, and their distributions when combined stretching vastly across Indo-Pacific. Each species is spellbinding in its own unique way, and none of them unfamiliar to even the most novice of marine aquarists.
The genus was first erected by Henry Weed Fowler in 1938 for a small, but “exquisite little eleotrid” fish obtained from Sulawesi during the Albatross expeditions. Typical of the situation then, Fowler was unaware of its colouration in life, though he was sufficiently impressed by the specimen that he named it Nemateleotris magnifica. The prefix of his new genus is appropriate, and is from the Greek nemat meaning thread, in reference to the long filamentous first dorsal fin of his new species. The suffix is not, as the fish is not an eleotrid, but rather, a gobiid. Presumably, this suffix was given because of the unfused pelvic fins in Nemateleotris, an unusual condition for the Gobiidae but normal for Eleotridae.
Aquarists would be correct in recognising these fishes as gobies, but the more astute would have probably seen the following families and subfamilies used interchangeably, either in the literature, or in older field guides: the Ptereleotridae/nae, and the Microdesmidae/nae; the -dae suffix here denoting a family level rank, and the -nae suffix denoting subfamilial division. Today, most ichthyologists recognise only a single family (the Gobiidae) for the aforementioned fishes, with the ptereleotrines and the microdesmines used only as informal classifications, the former for the dartfishes, and the latter for the worm fishes. I spared you the ensuing taxonomic back and forth here, but if you’re curious about the history of these classifications, you’ll find a nice summary in the Introduction section of the paper linked at the end of this article.
Fast forward to 1973, and Fowler’s Nemateleotris has grown from a single species to a humble three, as a result of a revision of the genus by John (Jack) Ernest Randall and Gerald (Gerry) Robert Allen. I’m not sure why I referred to Jack and Gerry by their full names here, but I thought I’d give them the same treatment as I did when introducing Fowler at the start of this article. In their revision of Nemateleotris, Randall and Allen described Nemateleotris decora and Nemateleotris helfrichi. Two brand new species, each more beautiful than the last. Like magnifica, the Latin decora was given after the splendid appearance of their new species in life. This etymological indulgence ended with N. helfrichi, whose name was given not after how nice these fishes looked in life (seriously, we get it), but after Dr Philip Helfrich, the Associate Director of the Hawaii Institute of Marine Biology of the University of Hawaii and Director of the Enewetak Marine Biological Laboratory at the time. He was given this honour for being among the first to collect specimens of this new species.
Nemateleotris and its three species were left untouched for quite some time. Except for the constant back and forth at higher taxonomic classifications, the genus stood resolute for close to forty years with no new species discoveries. Silence. This was the crème de la crème of goby genera. Was this it? Only three (albeit gorgeous) species across the Indo-Pacific? If Nemateleotris was an exclusive nightclub, it would be the Berghain.
That is until 2013, when Randall and Allen Connell described Nemateleotris exquisita – and with it, the return of epithets emphasising their beauty. But a new Nemateleotris? In this economy? Turns out, Randall and Connell’s new species wasn’t entirely unknown. They recognised the Indian Ocean and Red Sea population of the widespread N. decora as distinct, which they named N. exquisita. This distinction was based on differences in colouration – yellower anterior body for N. exquisita (Indian Ocean) and pale grey for N. decora (Pacific Ocean). In addition to colouration differences, there were also purported differences in several morphometric features, such as the diameter of the eye and the length of the first dorsal fin.
These differences were never really all that compelling, considering exquisita-like examples of N. decora occur in the Pacific, and the reverse for the Indian Ocean. In the most recent review of the genus, I, along with Helen Larson, explored this contention. We find no compelling evidence separating N. exquisita from N. decora, and so subsume the former back into the latter. The synonymising of N. exquisita into N. decora provided impetus for a more thorough look at the genus, in particular, N. helfrichi.
Like Nemateleotris decora, N. helfrichi enjoys a rather expansive distribution across the Pacific Ocean. Its distribution loosely traces the boundaries of the Pacific Plate, reaching the Great Barrier Reef of northeastern Australia. The species was described from specimens collected all across the Pacific, with the type locality being Tahiti, in the French Polynesian Islands. Curiously, the species exhibits quite a distinct difference in colour pattern and maximum size across this range, with those in the French Polynesian Islands growing larger and having a very distinct black mark on its upper jaw. Those in the western and central Pacific Ocean are smaller and lack the black maxilla. They also differ in having a much yellower head and snout.
Curiously, these differences did not go unnoticed even in the original description of N. helfrichi. Presumably, Randall and Allen attributed these to interspecific variation. Well, Helen and I looked at every single specimen of N. helfrichi we could get our hands on in museum collections. Ironically, for a species so common in the aquarium trade and so widely recognisable, there are more specimens living in your home aquariums as pet fish than there are in the world’s museums! Unlike the nascent qualities separating “N. exquisita” from N. decora, the differences exhibited by the two N. helfrichi populations were compelling and robust. Both do not overlap in distribution, with the black jawed N. helfrichi sensu stricto restricted to French Polynesia and the Cook Islands, and the yellow-headed variety everywhere else.
And so meet Nemateleotris lavandula, the newest species of dartfish, and one that you’re probably already familiar with. You know as an inside joke I almost went with Nemateleotris splendida as a name but I decided against it. The species is unique in having pastel fins and a light lavender body, which it shares with N. helfrichi. The species name lavandula is also the genus of flowering plants bearing the same name.
In 2015 I wrote about these dartfishes, bringing attention to the N. helfrichi conundrum and this tale of two heads. It’s funny that 8 years later, I not only get to revise the taxonomy as part of my new career path as an ichthyologist, but also write about it again here on ReefBuilders. Funny how the world works. I’ll tell you what though. I doubt there’s any more Nemateleotris out there left to discover. I’m glad to be sharing a piece of this magnificent, decorated, exquisite (see what I did there?) genus with some great ichthyologists out there. And if you find the information in this article too condensed and you’d like to read the paper in its entirety, the paper is open access and available here.