Thursday, June 7, 2018

[Ichthyology • 2018] Plectranthias ahiahiata • A New Species of Perchlet (Serranidae, Anthiadinae) from A Mesophotic Ecosystem at Rapa Nui (Easter Island)


Plectranthias ahiahiata
Shepherd, Phelps, Pinheiro, Pérez-Matus & Rocha, 2018


Abstract
A new species of the perchlet genus Plectranthias is herein described from a single specimen found at Rapa Nui (Easter Island) in the South Pacific. Plectranthias ahiahiata sp. n. was collected at a depth of 83 m in a mesophotic coral ecosystem at Rapa Nui. The main difference between Plectranthias ahiahiata and other members of the genus is higher fin-ray counts (X, 18 dorsal; 18 pectoral) and its distinctive coloration. Compared to the three other known eastern South Pacific species, P. ahiahiata has more dorsal-fin rays, more pectoral-fin rays, fewer tubed lateral-line scales, fewer gill rakers, a longer head relative to SL, a very short first dorsal spine relative to SL, and a short third anal spine relative to SL. Plectranthias ahiahiata is distinguished from western Pacific species, by having more dorsal- and pectoral-fin rays. The closest relative based on genetic divergence (with 12.3% uncorrected divergence in the mitochondrial COI gene) is Plectranthias winniensis, a widely distributed species, suggesting important links between Rapa Nui and western Pacific islands. This new species adds to the high endemism of the Rapa Nui ichthyofauna, and is further evidence of the importance of mesophotic reefs as unique communities.

Keywords: endemism, ichthyology, reef fish, South Pacific, taxonomy


Figure 1. Plectranthias ahiahiata sp. n., holotype shortly after death, 39.95 mm SL
(photograph: Luiz A. Rocha).

Plectranthias ahiahiata sp. n.
  Sunset perchlet

Type locality: Hanga Piko, Rapa Nui (Easter Island), Chile.
  
Diagnosis: Plectranthias ahiahiata differs from all of its congeners by the following combination of characters: dorsal rays X, 18; pectoral rays 18; longest dorsal spine the fourth; LL continuous and complete with 31 tubed scales; circumpeduncular scales 16; head length 43.3% SL; first dorsal spine 4.5% SL; third anal spine 13.7% SL; gill rakers 6+11; and in coloration: overall orange-red in color, with predominantly yellow snout, dorsal, pelvic and anal fins, a brilliant red spot outlined in white on the caudal peduncle, and four white spots on each side, following the contour of the lateral line.


Etymology: Plectranthias ahiahiata is given a Rapa Nui name; the phrase ahiahi-ata means “the last moments of light before nightfall.” The species was given this name because the colors of the fish remind us of the beautiful Rapa Nui sunsets. To be treated as a noun in apposition.

Distribution and habitat: Plectranthias ahiahiata is currently only known to occur at Rapa Nui (Easter Island). This fish was collected with hand nets at a depth of 83 m in a rocky patch reef surrounded by a large sandy area, and transported to the surface alive in a perforated plastic jar.


 Bart Shepherd, Tyler Phelps, Hudson T. Pinheiro, Alejandro Pérez-Matus and Luiz A. Rocha. 2018. Plectranthias ahiahiata, A New Species of Perchlet from A Mesophotic Ecosystem at Rapa Nui (Easter Island) (Teleostei, Serranidae, Anthiadinae). ZooKeys. 762: 105-116. DOI:  10.3897/zookeys.762.24618

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