Freshwater Macroinvertebrates in Hong Kong

Ephemeroptera (Mayflies)

All mayfly species have aquatic larvae and short-lived terrestrial adults. The primitive characteristics of the group are an inability of the adult to fold their wings flat when at rest. Instead they are held straight above the body. Although mayfly adults are rather uniform in structure, larvae exhibit a wide variety of morphologies: the bodies of active swimmers are streamlined, while those that tend to cling to rocks are dorsoventrally flattened. Burrowing mayflies have cylindrical bodies with mandibular tusks and broad forelimbs for digging. Larval gills are filamentous or plate-like (more or less oval or heart-shaped), and may be arranged singly or doubly.

Here is a flow chart that uses 'key' features to identify mayflies to family level.

EphemeropteraFlowChart

This guide is intended as an aid to the identification of mayfly larvae in Hong Kong by comparison of their morphological differences under a dissecting microscope (50x). However there are several instars throughout larval stage, and the distinctive features might not be evident until the later stages. This website shows different sizes/instars of larvae of as many as species possible. Some individuals need to be dissected to show details of their mouthparts under a compound microscope (200x). Identification can be difficult because of loss of body parts (e.g. gills or legs are fragile), but mouthparts (on the head) tend to remain intact, and can be a good indicator for species identification.

An identification guide to Hong Kong mayflies:

Prosopistomatidae

The family comprises a single genus Prosopistoma. The total number of species globally is about 44.

Distribution (Global map): found in Africa, the Middle East, India, Oriental region and Australasian region.

*Features for ID*	*Scientific name*
Body size small, about 3mm long, oval shaped like a beetle Pronotum and mesonotum fused to form a hemispherical carapace, with gills I - VI concealed beneath it Three feathery cerci mostly retracted into body	Prosopistoma sinense

Ephemeridae

It presently includes 96 species in 7 genera and 2 subfamilies (Ephemerinae & Hexageniinae)

Distribution: these burrowing mayflies are almost cosmopolitan, but not yet found in Australia and the oceanic islands.

*Features for ID*	*Scientific name*
Frontal process concave anteriorly (bifurcate)
Mandibular tusks asymmetrical, right tusk reduced about 3/5 length of left tusk Length of frontal process longer than width
	Ephemera pictipennis
Mandibular tusks symmetrical, right tusk slightly shorter than left tusk
--> Length of frontal process subequal/shorter than width Pronotum yellow with dark margin anteriorly
	Ephemera spilosa
--> Length of frontal process subequal/longer than width Pronotum yellow without marking
	Ephemera serica
Frontal process rounded Mandibular tusks symmetrical and subequal in length
	Undescribed sp.

Baetidae

The most specious family of Ephemeroptera in Hong Kong. Globally, the number of known genera is more than 30 and the total number of species is probably around 900.

Distribution: cosmopolitan and widely distributed.

*Features for ID*	*Scientific name*
Double gills
Gills I - VI double Ventral gill lamellae rounded Hindwing pads absent
--> Terga II & V with conspicuous dark markings medially	Cloeon micki
--> Terga yellowish brown with a pair of pale spots; unique reddish brown markings on segments II - III and V - VI	Cloeon harveyi
--> Terga yellowish brown with a pair of pale spots but without conspicuous reddish brown marking	Cloeon nr. bengalense
Ventral gill lamellae asymmetrical & pointed Hindwing pads present or reduced Lateral spines present on posterior abdominal segments
--> Gills I - III with small dorsal flap, Gills IV - VII single --> Hindwing pads reduced	Procloeon incanum
--> Gills I - VI with dorsal flap, Gill VII single --> Hindwing pads well developed	Procloeon venustum
Single gills
Body dorso-ventrally flattened Femora with long dense setae dorsally Central filament greatly reduced to give a two-tailed impression
--> Single dorsal tubercles on posterior margin of terga I - II, but two on terga III - IX --> A finger-like coxal gill at the base of legs	Baetiella bispinosa
--> Single dorsal tubercles on posterior margin of terga I - III, but two on terga IV - IX --> No coxal gill	Baetiella trispinata
--> No dorsal tubercles on abdomen --> Hindtibae with 2 rows of setae along outer margin	Liebebiella vera
--> No dorsal tubercles on abdomen --> Femora & tibiae with 1 row of setae --> Central filament reduced to a couple of segments --> All tarsi with a long ventral subapical seta	Platybaetis bishopi
--> No dorsal tubercles on abdomen --> Femora & tibiae with 1 row of setae --> Central filament about a half length of cerci --> Tarsi without a long ventral subapical seta	Acentrella gnom (very rare)
--> No dorsal tubercles on abdomen --> Femora greatly enlarged with a remarkably short tibia	Undescribed sp.
Femora with sparse stout setae dorsally 3 caudal filaments (central filament may be slightly shortened)
--> Body dorso-ventrally flattened, no villiopore on femora, very long setae present on tibiae, pale coloration on tergum VIII
----> Claw with two rows of denticles ----> Presence of a row of long setae along tibiae & a transverse row of long setae across tibiae	Chopralla fusina
----> Claw without denticle ----> A row of long setae along tibiae, but without a transverse row across tibiae	Cloeodes longisetosus
--> Body cylindrical & elongated, frontal ridge between antennae, no villiopore on femora, segment II of labial palp with a distinctive distolateral lobe, paraprocts without a prolongation
----> 7 pairs of gills I - VII ----> Hingwing pads present ----> Abdominal terga II - IX with a pair of submedial oblique dashes & a pair of small dots in midregion	Labiobaetis atrebatinus orientalis (formerly L. morus)
----> 6 pairs of gills II - VII ----> Hindwing pads present ----> Terminal segment of maxillary palpus with a distinct notch in the mesoapical 1/3 portion	Labiobaetis mustus
----> 6 pairs of gills II - VII ----> Hindwing pads absent ----> Antennal scape with a distinct lobe at distolateral margin ----> Terminal segment of maxillary palpus with a distinctly concave inner margin near apex	Labiobaetis diffundus
--> Body cylindrical & elongated, frontal ridge between antennae, no villiopore on femora, no distolateral lobe on segment II of labial palp, paraprocts with a prolongation
----> Gills II - VII ----> Posterior margins of terga I - VII without triangular spines ----> Paraprocts with a pointed prolongation	Alainites acutulus
----> Gills I - VII ----> Posterior margins of terga II - X with triangular spines ----> Paraprocts with a tongue-like prolongation	Alainites lingulatus
--> Body dorso-ventrally flattened, no frontal ridge, dark markings on legs, villiopore present on fermora --> Inner margin of right mandibular incisor without a row of fine setae
----> Gills II - VII ----> Distinct darken markings on terga II - III, VII - VIII & pairs of dots medially on terga II - VIII ----> Labrum with a pair of submedial setae and about 4 to 5 setae on each side of midline	Baetis maculosus
----> Gills I - VII ----> Terga brown with pale markings: an impression of an inverted triangular mark on terga IV and a large pale area from posterior half of terga VIII to anterior half of tergum X ----> Posterior margin of terga with tiny spinules only ----> Labrum with a pair of submedial setae and about 3 to 4 setae on each side of midline ----> Labial segment II slightly longer than segment III	Baetis tatuensis
----> Gills I - VII ----> Terga yellow brown with a pair of faint spots and dashes ----> Antennal pedicles & scapes with stout long apical setae ----> Posterior margin of terga without triangular spines ----> Labrum with a pair of submedial setae and more setae (>6) on each side of midline ----> Maxillary palp much shorter than galealaciniae	Baetis illiesi
----> Gills I - VII ----> Terga yellow brown with a pair of faint spots and dashes; anterior half of tergum X paler ----> Antennal pedicles & scapes with small denticles only ----> Posterior margin of terga with triangular spines ----> Labrum with a pair of submedial setae and more setae (>6) on each side of midline ----> Maxillary palp reaches galealaciniae	Baetis qiweiae
----> Gills I - VII ----> Some robust setae situated medially on fermora ----> Labial segment II about 2 times as long as segment III	Tenuibaetis peudofrequentus(formerly Baetiella peudofrequentus)
--> Body cylindrical, no frontal ridge, no villiopore on femora --> Inner margin of right mandibular incisor fringed with a row of fine setae
----> Distinct markings - on mesonotum: a pale three-forked mark - on abdomen: generally dark brown, but pale on tergum IV and a large pale area from posterior half of tergum VIII to anterior half of tergum X ----> Hindwing pad absent	Nigrobaetis facetus
----> Abdomen plain without markings ----> Hindwing pads present ----> Paraglossae with distinct apicomedial projection & 3 rows of long setae apically	Nigrobaetis gracilentus

Heptageniidae

It is the second largest family after Baetidae in Hong Kong. Globally, there are more than 20 genera in over 500 described species.

Distribution: mainly in the Holoarctic, Oriental, and Afrotropical regions.

*Features for ID*		*Scientific name*
Central filament greatly reduced to give a 2-tailed impression
	--> Distinctive sub-triangular shape of head, anterior end wider --> Gill I enlarged greatly to form disc-like structure beneath abdomen --> Posterior margin of terga I - IX with a pair of tubercules submedially	Iron herklotsi
	--> Not as above; head more generally obvate, gill I not enlarged greatly --> Two pale markings on head anterio-submarginally	Epeorus sagittatus
Central filament not reduced, giving a 3-tailed impression
	--> Pronotum not expanded laterally as other heptageniids --> Gill I reduced, gills II - VII normal, oval shape --> No distinct markings on head or body
		Paegoniodes cupulatus
	--> Pronotum expanded laterally, wider than mesonotum
	--> Pale spots present on anterior margin of head
	--> 6 distinct pale spots on anterior margin of head --> Gills V & VI with a black apical process	Electrogena ngi
	--> 4 distinct pale spots on anterior margin of head --> Gills V & VI with a black apical process	Afronurus sinensis (formerly Cinygmina rubromaculata)
	--> 4 diffuse pale smudges on anterior margin of head --> No apical process on gills V & VI	Compsoneuria taipokauensis
	--> No pale spot on head --> Gills V & VI with a black apical process
		Afronurus dudgeoni (formerly Cinygmina dudgeoni)

Leptophlebiidae

There are more than 640 described species in 130 genera.

Distribution: an extremely diverse cosmopolitan group.

*Features for ID*		*Scientific name*
Gill I single, gills II-VII slender & deeply forked
	--> Abdominal sterna reduced, gills arise ventrally
		Isca purpurea
	--> Gills borne laterally as usual
	--> Gills forked from the basal 1/3 of their length --> Terminal edentate part of tarsal claw about 1/6 length of claw	Paraleptophlebia rostrata
	--> Gills forked from the basal 1/5 or 1/4 of their length --> Edentate part of tarsal claw about 1/4 to 1/3 length of claw	Habrophlebiodes gilliesi
Gill I present or absent, Gills II-VII with plate-like lamellae
	--> Gills II-VII ovate with fringed margin
		Thraulus bishopi
	--> Gill I single slender, Gills II-VII double lamellae terminated with 3 long filaments
	--> Maxilla without distinct projection on inner corner
	--> median plate-like much larger & longer than lateral ones	Choroterpes (Choroterpes) petersi
	--> all 3 filaments subequal in length --> sternum 9 with a shallow apical cleft in mature female	Choroterpes (Euthraulus) elliptica
	--> all 3 filaments subequal in length --> sternum 9 without a shallow apical cleft in mature female	Choroterpes (Euthraulus) trigonia (very rare)
	--> Maxilla with very long & distinct projection on inner corner
	--> Maxilla with very long & distinct projection on inner corner --> Gill tracheae with few branches	Choroterpes (Cryptopenella) facialis (very rare)

Caenidae

Only a single genus (Caenis) in the subfamily Caenidae in Hong Kong.

*Features for ID*	*Scientific name*
--> Anterolateral corner of mesonotum with a distinct process --> Dorsal surface of head, thoracic nota & forewing pads densely covered with rounded granules --> Operculate gills uniformly brown
	Caenis bicornis
--> Without any process at anterolateral corner of mesonotum
--> Dorsal surface of head, thoracic nota & forewing pads densely covered with rounded granules --> Entire dorsal surface of forefemora covered with wrinkles	Caenis aspera
--> Dorsal surface of head, thoracic nota & forewing pads densely covered with fine wrinkles and sparse tiny granules --> Basal half dorsal surface of forefemora smooth without distinct wrinkles	Caenis lubrica

Ephemerellidae

*Features for ID*	*Scientific name*
--> A robust appearance given by expanded mesonotum, enlarged femora, widened abdomen --> Gill III operculate, relatively large
	Torleya arenosa
--> Gills III - VII: III - VI similar in size, but VII smaller
	Serratella albostriata

Teloganodidae

Distribution: Afrotropical and Oriental regions. Only Teloganodes tristis is recorded in Hong Kong.

*Features for ID*	*Scientific name*
--> Central filament greatly reduced to give a two-tailed impression (cf. 3-tailed in Ephemerellidae) --> Gills II - V (gill II largest)	Teloganodes tristis

Isonychiidae

*Features for ID*	*Scientific name*
--> Coxal gill tufts present --> Conspicous double rows of long setae on inner side of femora & tibiae of forelegs --> Abdominal gills I-VII: large diffuse dark mark with small pale patch proximally	Isonychia kiangsiensis

References:

Tong, X. & Dudgeon, D. (2003) Two new species of Heptageniidae from China (Insecta, Ephemeroptera). Acta Zootaxonomia Sinica 28: 469-473.

Tong, X. & Dudgeon, D. (2002) Three new species of the genus Caenis (Ephemeroptera, Caenidae) from Hong Kong, China. Zoological Research 23: 232-238.

Tong, X. & Dudgeon, D. (2000) Ephemerellidae (Insecta: Ephemeroptera) from Hong Kong, China, with descriptions of two new species. Aquatic Insects 22: 197-207.

Dudgeon, D. (1996) Life histories, secondary production and microdistribution of heptageniid mayflies (Ephemeroptera) in a tropical forest stream. Journal of Zoology, London 240: 341-361.