The five new Grallenia gobies were all discovered living on sandy bottom habitats. Prior to the formal description of these gobies, the genus Grallenia only had three recognized species. The first species, Grallenia lipi, was described in 2007. These gobies are hard to spot because all known Grallenia are tiny (less than 2.5cm/1 inch) and camouflage extremely well against the sandy/silty substrate.
G. rubrilineata is currently known from the Philippines, G. compta and G. dimorpha from Papua New Guinea, and G. lauensis and G. solomonensis from Fiji and the Solomon Islands. They share similar physical traits from one another and are differentiated by minor differences in coloration, scale pattern, dorsal fin-ray count, and/or dorsal fin shape.
Grallenia dimorpha, above, exhibits the greatest sexual dimorphism of the five new species, hence its etymology. Males (top photo) have squarish front dorsal fins with striped pigmentation running the entire length while females (bottom photo) have clear-colored fins with a triangular front dorsal.
Pictured above is a “family” of Grallenia rubrilineata: juvenile (left), female (center), and male (right). As can be seen, this species also has pronounced sexual dimorphism like G. dimorpha.
The new gobies are described in the Journal of the Ocean Science Foundation.