Hawaiioscia rapui, Taiti, Stefano & Wynne, J. Judson, 2015

Taiti, Stefano & Wynne, J. Judson, 2015, The terrestrial Isopoda (Crustacea, Oniscidea) of Rapa Nui (Easter Island), with descriptions of two new species, ZooKeys 515, pp. 27-49 : 33-36

Taxon classification Animalia Isopoda Philosciidae

Hawaiioscia rapui sp. n. Figs 1B, 5, 6, 7

Hawaiioscia sp.; Wynne et al. 2014: 714, 716, fig. 2a.

Type material examined.

Chile, Rapa Nui: 1 ♂ holotype, 2 ♀♀ paratypes (MNHN), Mahunga Hiva Hiva, Cave Q15-034, pitfall trap 5A (twilight zone) 12.VII.2009, leg. J.J. Wynne; 1 ♀ paratype (MZUF), 1 ♀ paratype (BPBM), same data, pitfall trap 7A (approx. deep zone); 1 ♂ Paratype (MZUF), Mahunga Hiva Hiva, Cave Q15-076/078, pitfall trap 2C (light zone), 4.VII.2009, leg. J.J. Wynne.

Description.

Maximum length: ♂ and ♀ 7.5 mm. Dorsum light brown with the usual muscle spots (Fig. 1B). Body flat, ovoidal, with pleon narrower than pereon, outline as in Fig. 5A. Dorsal body surface finely granulated with small triangular scale-setae (Fig. 5B). Pereonites with no sulcus marginalis, gland pores absent. Noduli laterales (Fig. 5C, G) clearly visible, inserted on a small tubercle and disposed as follows: two on the cephalic vertex, one per side on pereonites 1-6 with that on the fourth pereonite much more distant from the lateral margin of the segment, and two per side on pereonite 7. Cephalon (Fig. 5 D–F) with short triangular lateral lobes not protruding frontwards compared with the obtuse middle lobe; frontal and supra-antennal lines absent; eyes small, consisting of eight ommatidia. Pleon epimera reduced but with distinct posterior points (Fig. 5A,H). Telson (Fig. 5H) triangular, about twice as wide as long, with broadly rounded apex. Antennula (Fig. 5I) of 3 articles, second article slightly shorter than first and third; third article bearing two rows of 7 and 2 aesthetascs each, and 2 apical aesthetascs. Antenna (Fig. 6A) long and thin, reaching back rear margin of pereonite 6; flagellum as long as fifth peduncular article, first flagellar article distinctly longer than second and third, with two rows of 4 to 6 aesthetascs on each second and third article. Mandibles (Fig. 6B,C) with molar penicil semidichotomized, i.e. consisting of 3-4 setae on a common stem; left mandible with 2+1 and right mandible with 1+1 free penicils. Maxillula (Fig. 6D) outer branch with 5+6 teeth, all simple; inner branch with two stout subequal penicils. Maxilla (Fig. 6E) apically setose and bilobate with outer lobe wider than inner one. Maxilliped (Fig. 6F) endite apically setose and bearing a large penicil at medial corner, proximal article of palp bearing 2 strong setae. Pereopods with elongated articles and flagelliform dactylar and ungual setae (Fig. 7A). Pleopodal exopodites with no trace of respiratory structures. Uropod (Fig. 5H) protopod with a /\-shaped groove on outer margin; insertion of endopodite slightly proximal to that of exopodite.

Male. Pereopod 1 carpus with a brush of trifid spines on sternal margin (Fig. 7A). Pereopod 7 (Fig. 7B) with no peculiar modifications, ischium with sternal margin straight. Pleopod 1 (Fig. 7C) exopodite cordiform, with a broadly rounded apex; endopodite with thickset distal part, straight with rounded apex. Pleopod 2 (Fig. 7D) with exopodite triangular, shorter than endopodite and bearing 5 setae on ouer margin. Pleopods 3-5 exopodite as in Fig. 7 E–G.

Etymology.

The new species is named after Sergio Rapu Haoa, a humanitarian who has furthered cultural and archeological knowledge of Rapa Nui. Sergio was Rapa Nui’s first governor of Rapanui descent and the first director and curator of Museo Antropológico P. Sebastián Englert on Rapa Nui. He is also a world-renowned Rapa Nui archaeologist and purveyor of Rapa Nui culture. He graciously provided logistical support to the second author and his research teams while on Rapa Nui.

Remarks.

Prior to discovering this new species, the genus Hawaiioscia consisted of four troglomorphic species restricted to lava tube caves on the Hawaiian Islands (Schultz 1973; Taiti and Howarth 1997): Hawaiioscia parvituberculata Schultz, 1973 from Maui, Hawaiioscia microphthalma Taiti & Howarth, 1997 from O‘ahu, Hawaiioscia paeninsulae Taiti & Howarth, 1997 from Moloka‘i, and Hawaiioscia rotundata Taiti & Howarth, 1997 from Kaua‘i. No epigean species in this genus were previously known. The new species shows all the characters of the genus Hawaiioscia with the sole exception of the molar penicil of the mandible which is semidichotomized instead of simple as in all the others species from Hawai‘i. Considering that all the most important characters (number and position of noduli laterales, maxillular teeth, penicil on maxillipedal endite, uropod and shape of male pleopod 1) are shared with all the other Hawaiioscia species, we include the new species in this genus.

Specimens from this new species were collected from both within the entrance zone of one cave and the twilight zone of another cave. It is important to note, this species does not have troglomorphic characteristics, such as body depigmentation or eye reduction as do other congeners within Hawaiioscia . However, as with Styloniscus manuvaka sp. n., this new species was not detected during the surface sampling effort, nor has it been previously identified by earlier entomological surveys of the island. Thus, we believe this animal to be restricted to cave environment on Rapa Nui.

Distribution.

Presently endemic to Rapa Nui.