Chlorocyphidae, Cowley, 1937

Orr, Albert G. W., 2024, A review of present knowledge of larvae of the Calopterygoidea (Zygoptera) of the Oriental realm, including keys to families and known genera, Zootaxa 5497 (2), pp. 209-243 : 228-230

Family Chlorocyphidae

The larvae of just six of the 16 recognised Oriental genera have been described and illustrated, representing in total just 15 out of 110 species present in the region. A few additional species of uncertain identity are represented by photographs posted on the internet, but none provides useful or reliable information, although they do give some indication of the range of additional morphological variation we might expect within the family.

The first account of a chorocyphid larvae was by Fraser (1919a) who described Libellago lineata (Burmeister) in considerable detail (as Micromerus lineatus ), providing a reasonably accurate illustration of the habitus and partial detail of the mask. He omitted the vestigial central gill (epiproct), and other details, but stated that the exuviae were very common and that the larvae cling to submerged roots, twigs and other debris in swift water and rarely to aquatic vegetation. He asserted “they are purely rectal breathers and if the larva be viewed in muddy water, strong currents of particles are seen issuing to and from the rectum”. The following year Laidlaw (1920) described the larva of Paracypha unimaculata (Selys) , (as Rhinocypha unimaculata ) concluding that it showed the affinity between Libellago and Rhinocypha (sensu lato), and correctly surmised that the African members of the family would have similar larvae. Fraser (1920) reached the same conclusion from the study of Rhinocypha ignipennis Selys , although his illustration of the habitus is very rough and lacks wing buds, which might be expected even in quite young larvae a few millimetres long, and he states that the specimen has no caudal gills or any evidence of them having been present, which is surely also an error as these structures are known develop very early (see Ng 2024c for a depiction of a very young larva of Heliocypha p. perforata Percheron ). Subsequently Fraser (1928) provided an excellent drawing of the mature habitus of this species and Heliocypha bisignata (Hagen) , as well as a new depiction of Libellago lineata , again unaccountably lacking the vestigial central gill which is shown in the other species, and commented further on the habits of the family: “Very sluggish in habits and cryptic in colouring, they are difficult creatures to find. They cling to roots or broken-up debris in slow-running streams or at the bottom of pools in swifter running ones. I have found the easiest way to take them is to dredge out a quantity of such debris and spread it on the foreshore exposed to the sun...”. Under these circumstances the larvae stir as they try to escape the heat and the drying plant matter and can be easily seen. They may exhibit thanatosis when originally scooped out, making them very hard to detect.

Chlorocyphid larvae are unmistakable by virtue of having two long spikes representing the lateral caudal gills, with a vestigial dorsal median gill (also termed epiproct) in the form of a short conical spine; all known species also have an unusual arrow-head shaped head with a prominent tubercle on the subocular lobe and a first antennal segment (scape) is at least 40% the total length of the antenna ( Figs 3, 7 ). The labrum of chlorocyphids is of an unusual form ( Fig. 39 ) with the anterior extremity folded under and forming with the upper posterior part an elongate, rounded boat-like cavity into which the tips of the mandibles fit. The lower section bears a ‘moustache’ consisting of a single row of long, thick setae (Orr et al. 2024). The palpal lobe of the mask ( Figs 40a, b, c ) is also unusual being deeply divided into upper and lower branches each with a shorter process originating about the midpoint. This was noted by Fraser (1919a). It has been suggested that the spur on the upper process is secondary, with the other branches representing a highly modified form of the three terminal processes normally found on the palpal lobe of other Calopterygoidea larvae (Orr et al. 2024). The prementum is moderately long and narrow with a modest median cleft that is frequently fused; the median lobe always has a clearly serrated margin ( Figs 6 , 40a ). All species examined bear two rows of pectinate setae on the underside of the tarsi ( Fig. 41 ) that require high magnification to resolve ( Kumar 1973, Kumar & Prasad 1977, Orr et al. 2024). Finally, all chlorocyphids examined bear a dense dorsal pile of long, very fine setae that entraps particles of detritus and silt and presumably aids in camouflage. This is only clearly visible in submerged living specimens, as even when wet-preserved the filaments collapse into a dense tangled mat covering the body surface as well as the caudal spikes (Orr et al. 2024). All these features may represent autapomorphies for the family.

Despite being the most speciose of all Oriental calopterygoids, with the highest number of recognised genera, the family is remarkable for the lack of inter-generic variation among its larvae. Apart from characters already mentioned, the body is squat, although a little more elongate in the comparatively large Paracypha unimaculata (figured by Kumar 1973, as Rhinocypha unimaculata ). Kumar & Prasad (1977c) use slight differences in the palpal lobe to discriminate between taxa, as well as differences in size, and the spines on the margins of the prementum which are unusually well developed in P. unimaculata . All species also have some spines on the gena below the eye, but these show some variation which may manifest at the intra-generic level, as is also the case with the relative length and shape of the prementum (Orr et al. 2024). Variation in the lateral caudal gills is a potentially difficult character, in that if lost early in development they may regenerate, but not to their normal extent (as evidenced by the depiction of a specimen with lateral gills of unequal lengths in P. unimaculata ( Kumar 1973)) and Fraser (1928) states that this phenomenon is common, stating “autonomy [sic = autotomy] of the caudal gills is accomplished with the greatest ease, so it is difficult to obtain one with all intact; probably these are more for defence than respiratory use, and they certainly carry on quite well without them”. Nevertheless where the structures are of equal length and consistent within a species they can probably be assumed to be intact.

Comparing four species representing the genera Aristocypha , Heliocypha , Sundacypha and Libellago Orr et al. (2024) concluded that the species studied could be separated readily based on characters such as the form of the caudal spikes, the subocular spines on the genae and the form of the prementum, relative antennal length and other small but consistent characters. However, taking into account these results with those of Kumar & Prasad (1977c), definitive generic differences could not always be established with confidence, even in the limited range of known species, with intra-generic variation blurring supposed distinctions. It appears that the caudal spikes are slightly broader and taper to a point more abruptly from near the apex in Aristocypha than Heliocypha but more species need to be examined to confirm this. The caudal spikes of known Libellago and Sundacypha are also distinctive. In one of the best depictions of chlorocyphid larvae Ishida (1996) illustrates unusually short, broad, somewhat foliate caudal spikes in Rhinocypha ogasawarensis Oguma and Rhinocypha uenoi Asahina , but this cannot be considered a generic character as R. ignipennis has normal, long lateral spikes ( Fraser 1928). However it must be noted that the generic classification of Rhinocypha and allied genera is unsettled ( Dijkstra et al. 2014), and this non-conformity may reflect a higher level phylogenetic difference between these taxa.

Despite these difficulties, over broad swathes of the Asian mainland assemblages of just four or five genera are likely to be encountered, and they may to some extent be differentiated at least to genus on size and other characters mentioned, as shown by Kumar & Prasad (1977c). However, it is unlikely that a comprehensive morphologybased regional key to chorocyphid genera will ever be possible. Perhaps the most promising way of determining chlorocyphid larvae over the whole region, short of breeding specimens to adulthood, is by molecular association with adults, but even this may fail at the specific level, at least when using the most widely available COI barcoding techniques (Orr et al. 2024).

Larva unknown: Calocypha (1 sp.), Cyrano (2 spp.), Disparocypha (1 sp.), Heterocypha (1 sp.), Indocypha (7 spp.), Melanocypha (1 sp.), Pachycypha (1 sp.), Rhinoneura (2 spp.), Sclerocypha (1 sp.), Watuwilla (1 sp.).

Figures

FIGURES 1–7. 1. Ventral view of abdomen of Euphaea sp. showing abdominal gills and saccoid gills (original drawing). 2. Head and antennae of Calopterygidae (Neurobasis chinensis) (original drawing). 3. Head and antennae of Chlorocyphidae (Heliocypha biseriata) (original drawing). 4. Antenna of Podolestes orientalis Selys, 1852, scape arrowed (from Choong & Orr 2010). 5. Mask of Calopterygidae (Calopteryx japonica Selys redrawn from Miyakawa 1983). 6. Mask of Chlorocyphidae (Libellago hyalina, from Orr et al. 2024). 7. Habitus of L. hyalina, with detail of right caudal spike (from Orr et al. 2024).

FIGURES 35–41. 35. Archineura incarnata, prementum (dorsal view, drawn from Yang et al. 2022). 36. Vestalis gracilis, prementum (dorsal view) and right antenna with supplementary antennomere between pedicel and scape (a) arrowed (redrawn from Rattanachan et al. 2022). 37. Vestalaria venusta: prementum (dorsal view) and right antenna (drawn from Wang et al. 2017). 38. Caliphaea angka: prementum (dorsal view) and right antenna (drawn from Yang et al. 2021). 39. Heliocypha biseriata, frontal view of labrum showing dorsal and ventral sections and ‘moustache’ of long, heavy setae on the latter (from Orr et al. 2024). 40. Heliocypha biseriata: details of labial palp in relation to prementum (a) dorsal view—base of movable hook dashed to reveal palpal lobe beneath and open base of premental median cleft arrowed, (b) frontal view, (c) inner view (from Orr et al. 2024). 41. Heliocypha biseriata, detail of fore tarsus with pectinate setae magnified (from Orr et al. 2024).