Myrmecina ryukyuensis

Myrmecina ryukyuensis is found on the floor of broadleaf forests where it nests under stones (Japanese Ant Image Database).

Identification
Terayama (1996) - Similar to Myrmecina sauteri from Taiwan. However it is easily distinguished from the latter by the straight anterior margin and rounded anterolateral corners of first gastral tergite in dorsal view (concave anterior margin and acutely produced anterolateral corners in the sauteri type specimen).

Distribution based on Regional Taxon Lists
Palaearctic Region: Japan.

Nomenclature

 *  ryukyuensis. Myrmecina ryukyuensis Terayama, 1996: 29, figs. 69-71 (w.) JAPAN.

Taxonomic Notes
Although the species is distributed in the Nansei Islands, specimens from the Sakishima Group are slightly different from those collected on Amai-oshima I. and Okinawa I., in having smaller body size, less intense sculpturation, and smaller eyes. These differences need to be assessed as to whether they indicate infraspecific variation or the presence of several species (Japanese Ant Image Database).

Worker
Holotype. HL 0.60 mm; HW 0.59 mm; SL 0.40 mm; CI 98; SI 78; WL 0.65 mm; PL 0.18 mm; PH 0.20 mm; DPW0.18 mm; TL2.4mm.

Head almost as long as wide, with shallowly concave posterior margin in frontal view; frons rnicroreticulate with reticulate rugae; genae microreticulate. Mandibles with acute apical and preapical teeth following 6 small blunt teeth. Anterior margin of clypeus with a small median lobe and a pair of lateral angles. Antennae with 12 segments; scape microreticulate, 0.75x head length. Eyes small, smaller than the 10th antennal segment, and each consisting of 6 facets.

Dorsum of alitrunk weakly rnicroreticulate, with relatively irregular longitudinal rugae; lateral faces of pronotum with 6 rugae; anterolateral corners of propodeum with small blunt teeth; propodeal teeth slightly longer than its basal width. Petiole wider than long in lateral view; disc slightly wider than long in dorsal view. Subpetiolar process low, anteroventoral corner acutely produced. Postpetiole 1.2x as wide as long in dorsal view.

Gaster very weakly rnicroreticulate and subopaque; anterior border of 1st gastral tergite straight, anterolateral borders rounded in dorsal view.

Body blackish brown; mandibles, antennae, legs and tip of gaster yellowish brown.

Variation. The specimens from the Sakishima Is. Are distinguished from the type series (Okinawa and Amarni materials) by the smaller size (HL 0.52-0.55 mm, HW 0.52-0.55 mm), lighter coloration of body, and weaker and more irregular rugae on head and dorsum of alitrunk in worker. The differences of body size are more distinct in females; HL 0.68 mm and HW 0.70 mm in Okinawa material, while HL 0.58 mm and HW 0.60 mm in Sakishima material. However, I regard these morphological differences as a geographic variation within a single species. Much information will be needed to finally determine the exact taxonomical status of those populations.

Type Material
Holotype. Worker, Shuri, Okinawa-jima, Okinawa Pref., 6.X.1988, M. Terayarna leg. Paratypes. 1 worker, same data as holotype; 1 female, 1 worker, Chibana, Okinawa-jima, Okinawa Pref., 29.XII.1989, M. Terayama leg.; 1 worker, same locality, 20.V.1982, H. Takamine leg.; 1 worker, Okinawa-jima, Okinawa Pref., 30.III.1983, H. Takantine leg.; 2 workers, Sumiyo-son, Amami-oshima, Kagoshima Pref., 21.III.1980, M. Terayama leg.

References based on Global Ant Biodiversity Informatics

 * Shimono A., and S. Yamane. 2003. Ant species diversity on Okinoerabu-jima, the Ryukyus, southern Japan. For the Establishment of Remote Islands Study (Kagoshima Univ.) 3: 11-29.
 * Terayama M. 1996. Taxonomic studies on the Japanese Formicidae, part 2. Seven genera of Ponerinae, Cerapachyinae and Myrmicinae. Nature & Human Activities 1: 9-32.
 * Terayama M., S. Kubota, and K. Eguchi. 2014. Encyclopedia of Japanese ants. Asakura Shoten: Tokyo, 278 pp.
 * Yamane S. 2016. How many species of Ants in Amami Islands? (in Japanese). Part 2, chapter 1 in How many species of Ants in Amami Islands? Pp. 92-132.
 * Yamane S., S. Ikudome, and M. Terayama. 1999. Identification guide to the Aculeata of the Nansei Islands, Japan. Sapporo: Hokkaido University Press, xii + 831 pp. pp, 138-317.
 * Yamane S.; Ikudome, S.; Terayama, M. 1999. Identification guide to the Aculeata of the Nansei Islands, Japan. Sapporo: Hokkaido University Press, xii + 831 pp. pp138-317.