Epiophlebia superstes, the Japanese relict dragonfly, is one of the four species of the genus Epiophlebia, belonging to the family Epiophlebiidae, which is itself the sole living representative of the epiproctan infraorder Epiophlebioptera.
Distribution and habitat
This species of dragonfly is native to Japan, distributing widely around the forested headwaters of rivers in its four main islands, serving as a freshwater indicator of ecosystem health. With the adults being adapted for flight in these cool habitats, and the larvae to exploit the stable environment and detritus based ecosystems of high elevation spring-fed seeps and streams.
Its flight period lasts about one month in length, but varies significantly through the diverse altitudes and latitudes of Japan, extending from late March in Kyushu to July in Hokkaido, for example, in the Kinki area, the flight period of E. superstes extends from the end of April to mid-June.
Phylogeny and evolutionary history
Epiophlebia superstes was originally considered to be part of the suborder Anisozygoptera along with the Himalayan Epiophlebia laidlawi, an intermediate clade between dragonflies and damselflies, mainly because their hind wings are very similar in size and shape to the forewings and held back over the body at rest, as in damselflies. Thanks to molecular data, it has been recognized that the genus Epiophlebia shares a more recent ancestor with dragonflies (having become separated from these in and around the uplifting of the Himalayas), and the group has accordingly been reclassified as Epiophlebioptera, an infraorder within dragonflies. The discovery of a third species, Epiophlebia sinensis, described from the Heilongjiang province in northeast China, has bridged the distribution of this genus between Nepal and Japan, with a fourth species, Epiophlebia diana, being claimed in Southern China but not universally accepted. This genus is representative of a dragonfly fauna which originated during the Jurassic period on the rising continent of Eurasia, being relicts of a once widespread group.
Description and keys for identification
Adults
Length in adult Epiophlebia superstes ranges from 45 mm to 53 mm. Its body is black, striped in bright yellow on both the thorax and abdomen.
They present a genae with lateral tubercles, their labrum widens distally, and the antennae are segmented with composed segments. Epiophlebia superstes presents an elongated and flattened pedicel, postfrons with transverse shield-like intraocellar ridge, antitandem lobes in the male occipital lobes, male epiproct with ventral and dorsal rami, male gonocoxae elongate and the 8th female abdominal segment with midventral apical spur.
The copulatory apparatus of Epiophlebia includes a pair of elongated and posteriorly directed hamuli with bloated studded hooked apices and a median process of abdominal sternum two, as well as a somewhat bottle shaped sperm vesicle that can be found at the 3rd abdominal sternum. The ovipositor of the females shares a lot of characteristics with zygopterans, with setae and sensilia which are in egg laying, assessing the suitability of the leave they are on and being responsible for the zigzag pattern of its egg disposition.
Some plesiomorphic character states are the following: labial end hook occasionally two-segmented (not as usual as one-segmented), well developed glossae and paraglossae, and a trilobate hypopharynx.
To distinguish E. superstes from the rest of its genre we have to observe the 6th abdominal segment, laterally beyond antecostal suture, and segments 7–10 and terminalia ferruginous, with dorsal pale spots of segments 8–10 obscure.
Wing features
The petiole of the hind wing is well-developed, the costal is widened at nodus, the pterostigmata are strongly convexed posteriorly, and the hind wings present one or two cell rows between the CuA and the wing margin. Epiophlebia also lacks a discal nodus, an often overlooked ventral membranous area along the discal brace, yet some wing flexibility is achieved by a slight flattening of the pleat at the discal brace, and although the costal nodus is hinge-like its flexibility is limited particularly in the forewings by a minimal nodal fissure. E. superstes can be divided up into two forms according to the type of formation of arculus found in the hind-wings, with one of the forms displaying clearly the process of passage from the Zygoptera to Anisoptera marked by the division of the discoidal cell into upper and lower cells, making the hind wings similar in shape and size to the forewings.