Anacaena Thomson, 1859

Minoshima, Yusuke N., Kamite, Yuuki & Fikacek, Martin, 2023, The genus Anacaena Thomson from the Ryukyu Archipelago of Japan (Coleoptera, Hydrophilidae), Deutsche Entomologische Zeitschrift 70 (1), pp. 143-157 : 143

Genus Anacaena Thomson, 1859

Anacaena Thomson, 1859: 18 [Type species: Hydrophilus globulus Paykull, 1798 by original designation.]. For detail synonymy, see Hansen (1999).

Differential diagnosis.

Within the hydrophilid species on the Ryukyu Archipelago, Anacaena is the most similar to Chaetarthria Stephens, 1835 ( Chaetarthriini , Chaetarthriinae ) and Paracymus Thomson, 1867 ( Laccobiini , Hydrophilinae ) by the small-sized, oval, and convex body. Chaetarthria has a fringe of setae on the first abdominal ventrite, whereas Anacaena does not have the fringe; in addition, the known distributions of both genera do not overlap: Chaetarthria is known from Sakishima Islands in the Southern Ryukyus ( Inahata and Minoshima 2019; Watanabe 2019), Anacaena from Amami Islands and Okinawa Islands in the Central Ryukyus. Paracymus has a longitudinal median carina on the prosternum, whereas Anacaena does not have a carina ( Matsui and Nakane 1985; Short and Fikáček 2013). Moreover, Paracymus differs considerably from Anacaena , e.g., by the shape of eyes, labrum, maxilla, mentum, mesoventrite, and metafemur ( Komarek and Beutel 2007).

Ryukyu species of Anacaena are easily distinguishable from the other Japanese Anacaena , A. asahinai Satô, 1982 by the shape of the pubescent area of the metafemur: Ryukyu species have a horizontal hairline (Fig. 3J-M ) on the metafemoral area, whereas an oblique hairline is present in A. asahinai .

Characters of taxonomic importance.

Anacaena species of the Ryukyu Archipelago are morphologically similar to each other as well as to the species from adjacent areas. As in other species of Anacaena , the morphology of the aedeagus is the most reliable character set to delimit species; the shape of all structures of aedeagus is useful for identification, but the apparent shape of this part can be affected by preparation when the manubrium is curved dorsally. Shape and colour or maxillary palpomeres are used as diagnostic characters; apical infuscation is easily recognisable but may vary within species (Fig. 3A-D ). Colouration of the pronotum and elytra, i.e., the width of yellowish margin of the pronotum, and the ground colour of elytra, are useful despite their slight intraspecific variation. Pubescence on the metafemur (Fig. 3J-M ) cannot separate the species on the Ryukyu Archipelago, but it is a significant character to delimit Ryukyu species from other similar species distributed in Southeast Asia.

Figures

Figure 3. A-E. Maxillary palpus; A. Anacaena kumejimana, paratype; B-D. A. okinawana, paratypes; B. from Okinawa-jima I., C, D. from Aka-jima I. (Kerama Is.); E. A. torikaii, holotype; F-I. Mentum; F. A. kumejimana, paratype; G, H. A. okinawana, paratypes; G. from Okinawa-jima I.; H. from Aka-jima I. (Kerama Is.); I. A. torikaii, holotype; J-M. Hind femora, indicating femoral pubescence but borderline of pubescence often not clear at base; J. A. kumejimana, paratype; K, L. A. okinawana, paratypes; K. from Okinawa-jima I.; L. from Aka-jima I. (Kerama I.); M. A. torikaii, holotype.