17Proc. Arthropod. Embryol. Soc. Jpn. 50, 17 (2016)Ⓒ 2016 Arthropodan Embryological Society of Japan
ISSN 1341–1527

Embryology of a “Living fossil” Beetle, Tenomerga mucida (Chevrolat,1829) (Archostemata, Cupedidae)*
Kazuki KOJIMA and Ryuichiro MACHIDA
Sugadaira Montane Research Center, University of Tsukuba, Sugadaira Kogen, Ueda, Nagano 386–2204, Japan
E-mail: s1521002@u.tsukuba.ac.jp (KK)

The order Coleoptera, the most species-rich lineage ofHolometabola, comprises about 40% of the described species
in Hexapoda. The order is divided into four suborders, i.e.,
Archostemata, Myxophaga, Adephaga and Polyphaga, but
their phylogenetic relationships have been variouslydiscussed. Archostemata, which include the oldest fossil
record of Coleoptera, have been often regarded as being thebasalmost lineage of the order from morphological andmolecular evidence (Friedrich et al., 2009; Bocak et al., 2014).
Thus, Archostemata are the most significant coleopteransubgroup in understanding Coleoptera, especially in thereconstruction of its groundplan and phylogeny. Althoughcomparative embryology is one of the most useful approaches
in phylogenetic discussions, no embryological study has been
conducted for Archostemata. In such background, we havestarted an embryological study, aiming at the reconstructionof groundplan and phylogeny of Coleoptera, using Tenomerga
mucida (Chevrolat, 1829) as material. In the present talk, wereport the outline of embryogenesis of T. mucida as well as
the embryological technique established.
We collected the rotten logs including T. mucida larvaeand brought back them to our laboratory to obtain adults.
Mating is of tail-to-tail type. Females laid eggs, 100 in average,
maximum ca. 130 per one female, on the surface of sliced
pieces of logs. Eggs are orange-brown in color and long-ovalshaped with about 1.5mm length and 0.4 mm width. A knoblike projection with micropyles or the micropylar projection isat the anterior pole of the egg. The micropylar projection
closely resembles those found in aquatic Adephaga (Komatsuand Kobayashi, 2012) and raphidiodean Neuroptera (Tsutsumiand Machida, 2006). Close resemblance in micropylar
structures between Coleoptera and Neuroptera should be
noteworthy, their affinity being strongly suggested in recent

molecular analyses (cf. Misof et al., 2014). We stained withDAPI and observed embryos under a fluorescencestereomicroscope and grasped the outline of T. mucida
embryonic development. It was revealed that T. mucida
embryo completely sinks deep into the yolk in the middle
stage of embryonic development. The complete immersion ofthe embryo into the yolk may be the first example inColeoptera. After the embryonic development of about 10days (under the room temperature), larvae hatched out fromnear the anterior pole of the egg. The first instar larva walked
around in the rearing case to seek for residence, and in several
days they burrowed among rotten logs.
References
Bocak, L., C. Barton, A. Crampton-Platt, D. Chesters, D. Ahrens andA. P. Vogler (2014) Building the Coleoptera tree-of-life for >8000
species: Composition of public DNA data and fit with Linnaeanclassification. Systematic Entomology, 39, 97–110.
Friedrich, F., B. D. Farrel and R. G. Beutel (2009) The thoracic
morphology of Archostemata and the relationships of the extant
suborders of Coleoptera (Hexapoda). Cladistics, 25, 1–37.
Komatsu, S. and Y. Kobayashi (2012) Embryonic development of awhirligig beetle，Dineutus mellyi, with special reference toexternal morphology (Insecta: Coleoptera，Gyrinidae). Journalof Morphology, 273, 541–560.
Misof, B., S. Liu, K. Meusemann and 98 other authors (2014)
Phylogenomics resolves the timing and pattern of insect
evolution. Science, 346, 763–767.
Tsutsumi, K. and R. Machida (2006) Embryonic development of asnakefly Inocellia japonica Okamoto: An outline (Insecta:Neuroptera, Raphidiodea). Proceeding of the Arthropodan
Embryological Society of Japan, 41, 37–45.

* Abstract of paper read at the 51st Annual Meeting of the Arthropodan Embryological Society of Japan, June 12–13, 2015 (Urabandai, Fukushima).