Prosopistoma ocellatum, Shi, Weifang & Tong, Xiaoli, 2013

Shi, Weifang & Tong, Xiaoli, 2013, A new species of Prosopistoma (Ephemeroptera: Prosopistomatidae) from China with a key to Oriental species, Zootaxa 3718 (1), pp. 89-96 : 90-93

Prosopistoma ocellatum sp. n.

( Figs. 1–16 )

Material examined. Holotype (deposited in ethanol): 1 mature nymph, CHINA, Guangxi, Dayaoshan National Nature Reserve (24.13°N, 110.21°E), Jinxiu County, 15.xi.2011, leg. Weifang Shi.

Paratypes (deposited in ethanol unless otherwise stated): 1 mature nymph on slide and 11 mature nymphs, same data as holotype; 5 mature nymphs, same data as holotype but collected 8.iv.2012; 11 mature nymphs, China, Hainan, Diaoluoshan Nature Reserve (18.39°N, 109.55°E), 8.iv.2005, leg. Xiaoli Tong; 1 mature nymph, Diaoluoshan Nature Reserve, 30.xi.2011, leg. Weifang Shi.

Additional material (deposited in ethanol). 24 immature nymphs, Dayaoshan National Nature Reserve (24.13°N, 110.21°E), Jinxiu County, 15-vi-2011, and 5 immature nymphs, the same locality but collected on 8-iv- 2012, leg. Weifang Shi; 33 immature nymphs, Diaoluoshan Nature Reserve (18.39°N, 109.55°E), 8-iv-2005, leg. Xiaoli Tong.

Description. Mature nymph. Body length 3.5–4.2 mm, excluding caudal filaments. Head yellow dorsally with a V-shape brown marking encompassing median ocellus between antennae, head width approximately 2.1 times the length. Epicranial sutures evident, passing through anterior margin of lateral ocelli, and between compound eyes and antennal bases, continuing to lateral margin of head. Carapace general coloration dark brown, light yellowishbrown around edges of carapace along flange, and with 2 yellow eye-spot markings on each side of near the midline, two-thirds of the distance along the carapace from the base of the head ( Fig. 1 ). Cuticle of carapace finely punctated. Distal end of carapace concaving over exhalent notch (arrowed in Fig. 1 ).

Head. Antenna ( Fig. 4 ) 6-segmented, longer than distance from antennal base to anterior margin of head; segment I (scape) usually retracts into head capsule and invisible; segment III the longest, about 1.2–1.4 times the combined length of segments IV–VI. Labrum ( Fig. 5 ) narrow with surface punctated, approximately 3.0 times wider than long, anterior margin fringed with dense fine setae. Left and right mandibles similar. Outer canine of mandibles longer than inner canine with three apical teeth, outer tooth small and outer margin serrated near apex with 2–4 small short spines, inner tooth larger with margin serrated near apex with 4–6 small point spines; inner canine with two apical teeth, inner one a little larger, outer margin serrated near apex with 1–2 small spines, inner margin serrated near apex with 3–4 spines ( Figs 6–7 ). Three long serrated bristles arising from base of inner canine. A single stout feathered seta present lateromedially on each mandible ( Fig. 6 ). Maxillae ( Fig. 8 ) crowned by rigid canine and three subequal moveable dentisetae; three long feathered stout bristles arising near base of apical canine and dentisetae on galea-lacinia. A single unserrated bristle arising about two-thirds of way down the sclerotized section of galea-lacinia. Maxillary palpi 3-segmented, segment II the longest, length ratio of maxillary palp segments from basal one to apical: 2.5:3:1. Labium ( Fig. 9 ) typical of Prosopistomatidae and margin fringed with dense setae, consisting of fused prementum composed of fused glossae and paraglossae, recessed in greatly expanded postmentum; scale-like structures present along basal margin of postmentum. Labial palpi 3-segmented, length ratio of labial palpus segments from basal one to apical: 2.5:1.7:1.

Legs ( Figs10–11 ). Dorsal margin of fore femur with 6–10 simple, short setae; ventral margin of fore tibia with up to 10–11 pectinate setae ( Fig. 10 ). Mid and hind tibia each with one paired of stout distal setae, one pectinate seta, the other smooth seta ( Fig. 11 ). Ventral and basal half surface of all femora with dense scale-like structures ( Fig. 10 ); mid and hind femora with scale-like covering along the dorsal and ventral surface. All claws slender and smooth without denticles.

Abdomen. Abdominal gills as figures 12–15. Gill I with long lamellate upper portion, lower portion divided into ribbons, many of which branch dichotomously ( Fig. 12 ); gill II leaf-like and unbranched ( Fig. 13 ), covering the gills III–V ( Figs 14–15 ), gill VI tiny, unbranched. Posterolateral projections of abdominal segments VII–IX broad, apex pointed ( Fig. 1 ). The three caudal filaments short (typically retractile as see in all Prosopistomatidae nymphs).

Imago. Unknown.

Distribution. China (Guangxi and Hainan).

Etymology. Specific epithet from Latin ocellatus meaning eye-spot, referring to the color pattern of eye-spot on the mesonotum.

Remarks. Gillies (1954) suggested that the color pattern of mesonotum could be considered as good specific character for the identification of the different species at the nymphal stages even in the young nymphs (Gillies 1954). However, in Prosopistoma ocellatum sp. n. as in some Oriental species, e.g. P. palawana Peters, 1967 , P. indicum Peters, 1967 , P. lieftincki Peters, 1967 and P. olympus Sartori & Gattolliat, 2003 , the color patterns of the mesonotum vary with different stages and show clearly intraspecific variation: from yellowish brown ( Fig. 3 ) to dark brown ( Fig. 2 ) in early stages, the patterns of the carapace become dark brown with 2 pairs of eye-spot markings in the final stage ( Fig. 1 ). The color pattern seen in some of the younger instars ( Fig. 2 ) is very similar to that seen in P. s i n e n s e Tong & Dudgeon, 2000 with which it could be confused, but after checking detailed characters by dissecting and mounting on slides, the morphological characters were found to be the same as in the final nymphal stage of P. ocellatum sp. n. The new species can be easily distinguished from P. sinense Tong & Dudgeon and the other members of Prosopistoma by the following combination of characters: (1) antenna 6- segmented, segment III longest, about 1.2–1.4 times longer than the combined length of segments IV–VI; (2) three bristles at the basis of the inner canine; (3) 10–11 pectinate setae on ventral margin of fore tibiae, ventral and basal half surface of all femora with dense scale-like structures, and (4) color pattern of eye-spot on the mesonotum.

China is one of the most species-rich countries for the genus Prosopistoma , with five species of the genus up to now ( Fig. 16 ) (Tong & Dudgeon 2000; Zhou & Zheng 2004). Recently P. sinense Tong & Dudgeon and P. annamense Soldán & Braasch (formerly reported only from Vietnam and China) have been reported from Thailand (Tungpairojwong & Boonsoong 2011), which shows that the Chinese Prosopistoma species have a wider geographical distribution range.

Ecological notes. The new species was collected from riffle habitat in forest streams with moderate to fast current in Guangxi and Hainan. Both sampling sites are situated in the National Nature Reserves with undisturbed forests. The stream was around 2–4m width and 10–30cm depth with the cobble and gravel substrate ( Fig. 17 ). Three specimens (two young nymphs and one mature nymph) were examined for gut contents analysis under the dissecting microscope by dissecting and dispersing the stomach contents onto glass slides. The examination revealed only the presence of amorphous detritus-like elements without any remains of head capsules or claws in the gut contents of P. ocellatum . However, the mandibles have no molar region and well developed pointed apical incisors; the maxillae have a long rigid canine and moveable dentisetae ( Figs 6–8 ), which would imply that they have predacious habits. We are not sure at the moment if P. ocellatum is a carnivorous species or not because of the limited of examined individuals.

Figures

FIGURE 16. Distribution map of five known Chinese Prosopistoma species.

FIGURE 17. Habitat of P. ocellatum sp. n. in the Dayaoshan National Nature Reserve, Guangxi, China.

FIGURES 1 – 3. (1) Mature nymph of Prosopistoma ocellatum sp. n., dorsal view; (2 – 3) Color patterns of mesonotum in different immature nymphs of Prosopistoma ocellatum sp. n., dorsal view.

FIGURES 4 – 9. (4) antenna (excluding the scape), (5) labrum, (6) mandible, (7) details of canines, (8) maxilla, (9) labium.

FIGURES 10 – 15. (10) foreleg, (11) tibia of middle leg, (12 – 15) Gills I – IV.