Styloniscus manuvaka, 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 : 30-33

Taxon classification Animalia Isopoda Styloniscidae

Styloniscus manuvaka sp. n. Figs 1A, 2, 3, 4

Styloniscus sp.; Wynne et al. 2014: 713, 714, fig. 2b.

Type material examined.

Chile, Rapa Nui: 1 ♂ holotype, 2 ♂♂, 2 ♀♀, 1 juv. paratypes (MNHN), Mahunga Hiva Hiva, Cave Q15-070, fern-moss garden (entrance zone), direct intuitive search, 10.VII.2009, leg. J.J. Wynne; 2 ♂♂, 1 ♀, 2 juvs. paratypes (MZUF), same location, 50 m from entrance, direct intuitive search (on decomposing tree branches; twilight zone), 6.VIII.2011, leg. J.J. Wynne; 1 ♀ paratype (MNHN), same data; 1 ♂, 1 ♀ paratypes (BPBM), Mahunga Hiva Hiva, Cave Q15-074, skylight entrance (1st entrance NE of main entrance; entrance zone), 3.VII.2009, leg. J.J. Wynne; 1 ♀ paratype (BPBM), Mahunga Hiva Hiva, Cave Q15-119, timed search at trap 4A, 5.VII.2009, leg. J.J. Wynne; 1 ♂ paratype (BPBM), same location, Zone 2 (approx. cave deep zone), trap, fish entrails 1, 6.VIII.2011, leg. J.J. Wynne; 1 ♀ paratype (BPBM), Mahunga Hiva Hiva, Cave Q15-071, Zone 2 (approx. cave deep zone), bait trap, fish entrails 1, 7.VIII.2011, leg. J.J. Wynne; 1 ♀ paratype (BPBM), Cave Q15-067, fern-moss garden (entrance zone), direct intuitive search, 4.XII.2008, leg J.J. Wynne.

Additional material examined.

French Polynesia, Bass Islands (Austral Islands), Rapa Iti Island: 4 ♂♂ (YPM), Pumarua-Maurua Ridge, Pumarua and some west, 500-620 m, from dead leaves of the bird’s nest fern, Asplenium nidus , 9.I.1980, leg. G. Paulay.

Description.

Maximum length: ♂ 4 mm, ♀ 4.2 mm. Dorsum brown with the usual yellow muscle spots (Fig. 1A). Body ovoid with pleon narrower than pereon (Figs 1A, 2A). Vertex and pereon distinctly granulated with granulations arranged on three rows on pereonite 1 and two rows on pereonites 2-7; pleon and telson smooth. Dorsal surface with scale-setae as in Fig. 2B. Cephalon (Fig. 2C, D) with obtuse middle lobe slightly protruding frontwards compared with rounded lateral lobes; eye consisting of three ommatidia in a triangle. Pleonites 3-5 reduced with small posterior points. Telson (Fig. 2E) with concave sides and truncate apex. Antennula (Fig. 2F) with second article shorter than first and third; third article with 6 long aesthetascs at apex. Antenna (Fig. 2G) with flagellum as long as fifth article of peduncle; flagellum cone-shaped, consisting of 5 articles with the second, third and fourth article bearing two aesthetascs each. Left mandible (Fig. 3A) with 2 penicils; right mandible (Fig. 3B) with 1 penicil. Maxillula (Fig. 3C) outer branch with 10 simple teeth and 2 long stalks; inner branch with 3 penicils. Maxilla (Fig. 3D) apically bilobate, inner lobe wider than outer lobe and bearing strong setae on its margin. Maxilliped (Fig. 3E) endite with a stout apical penicil; basal article of the palp with 2 setae. Pereopods 6 and 7 with a distinct water conducting system (Fig. 4B,C) on merus, carpus and propodus, and on basis, ischium and merus, respectively.

Male. Pereopod 1 (Fig. 4A) merus and carpus with a line of short scales on sternal margin. Pereopod 7 (Fig. 4C) ischium enlarged in the distal part, forming a flat rounded lobe with two short and stout setae on tergal margin, sternal margin almost straight; propodus with numerous long and thin setae on tergal margin. Genital papilla (Fig. 4D) with rounded and enlarged distal part. Pleopod 1 (Fig. 4D) exopodite triangular, as wide as long, with rounded posterior margin; endopodite with flagelliform distal segment, about twice as long as basal one and slightly enlarged at apex. Pleopod 2 (Fig. 4E) exopodite very short, rectangular, about twice wider than long; endopodite with distal segment about seven times longer than basal one, with tapering apical part slightly bent outwards, acute apex.

Etymology.

The species name is a combination of two Rapanui terms, manu and vaka. Manu is “bug” and vaka is “canoe” or “boat”; when combined this translates to "canoe bug." Based upon the identification of this species, and a collembolan ( Lepidocyrtus olena Christiansen & Bellinger, 1992) previously known from the Hawaiian Islands only, Wynne et al. (2014) suggested both of these animals may have been dispersed by the ancient Polynesians as they transported and transplanted cultivars (called "canoe plants"), such as banana, taro and sugar cane, throughout the South Pacific islands.

Remarks.

At present the genus Styloniscus includes about 45 species distributed in the tropics and the southern hemisphere ( Schmalfuss 2003; Nunomura 2007; Taiti 2014). The new species is characterized by the male pereopod 7 ischium enlarged in the distal part with a flat rounded lobe. A similar character is present also in a species from Omaio, North Island, New Zealand, identified by Vandel (1952) as Styloniscus otakensis (Chilton, 1901). The specimens redescribed and illustrated by Vandel certainly do not belong to Styloniscus otakensis according to the redescription of this species provided by Green (1971) on the basis of the type material studied by Chilton (1901) and on topotypic material (Dunedin, South Island). In fact, the male pereopod 7 ischium does not show any distinct lobe (compare fig. 31 in Green 1971 with fig. 37 in Vandel 1952), and the shapes of the male pleopod 1 exopodite and pleopod 2 endopodite are significantly different (compare figs 29 and 30 in Green 1971 with figs 38 and 39A in Vandel 1952). Thus, the specimens from Omaio must belong to a distinct species yet to be named. Styloniscus manuvaka sp. n. differs from Styloniscus otakensis sensu Vandel nec Chilton in having 6 instead of 5 aesthetascs at the apex of the antennula, 5 instead of 4 flagellar articles of the antenna, the male pereopod 7 ischium with two, instead of one, stout setae on the tergal margin, and the male pleopod 2 endopodite with a thicker distal part.

On Rapa Nui, Styloniscus manuvaka sp. n. is presently restricted to the cave environment, but is not troglomorphic (cave-adapted). This animal was detected within the fern-moss gardens (entrance zone) of three caves, but also occurred within the twilight and cave deep zones. This species was not detected during the surface sampling work conducted in 2009, nor has it been identified during previous invertebrate inventory work (e.g., Fuentes 1914, Olalquiaga 1946, Kuschel 1963, Campos and Peña 1973). The species also occurs on Rapa Iti, Bass Islands, where it is not restricted to the cave environment. This species is considered a Polynesian endemic and it might be present also on other Pacific islands.

Distribution.

Presently known from Rapa Nui and Rapa Iti.