Anisops Spinola, 1837

Nieser, Nico, 2004, Guide To Aquatic Heteroptera Of Singapore And Peninsular Malaysia Iii. Pleidae And Notonectidae, Raffles Bulletin of Zoology 52 (1), pp. 79-96 : 83-84

Anisops Spinola, 1837

Remarks. – This genus has been revised by Brooks (1951) who provides a key to species for males. Since then many species have been added including one described from Melaka ( Leong, 1963). In addition the distributional areas of many species are much greater than was suggested by Brooks.

There are 11 species actually known from the Malay Peninsula. They are remarkable for having haemoglobin cells anteriorly in their abdomen ( Bare, 1928). In these haemoglobin cells they store the reserve oxygen during a dive ( Miller, 1964). The amount of air they take with them under water on the outside of the body can be regulated and so that they can obtain neutral buoyancy which makes them belong to the few really planktonic insects. They usually live in ponds or pools, including virtually stagnant parts of streams, with few or no fish. However, some fish ponds may occasionally be infested with Anisops and other Notonectidae , preying on the fry. Some species which live in farmponds are widely distributed, e.g. A. bouvieri , A. breddini and A. kuroiwae .

Definite identification is usually possible only for males, which have several distinguishing secondary sexual characteristics. The front tarsi are one-segmented in males but two-segmented in females ( Figs. 9, 10 ). In Malayan species, the most important identification characteristics are to be found on the head of the male, notably the length and place of origin of the rostral prongs is diagnostic ( Figs. 12- 17 ). The tylus, may be swollen or posses a median groove ( Fig. 18 ) and the shape of the cephalic projection ( Fig. 2 ), is diagnostic of several Malayan species. Other important identification characters include the fore leg of the male, notably the stridulatory comb ( Fig. 9 ). The number and shape of the teeth in the stridulatory comb are very important for specific identification in some species. The apex of the comb is towards the posterior (i. e. the concave, flexor) margin of the tibia. In addition the shape of the forefemur, especially wether its apex is narrow or broad, and the general shape of the tibia; the number and position of spines on the tibia and the presence or absence of small spines on the tarsus are important characters. Other characters used in keys are various ratios. Important is the ratio between the synthlipsis and the anterior width of the vertex, which is the width between the eyes anteriorly in dorsal view ( Fig. 2 ). Except for tylus which was introduced by Truxal (1953) most of the above terminology was introduced or redefined by Brooks (1951). The colour of Anisops is, apart from a few exceptions, rather uniform and tends to fade in specimens killed or stored in alcohol. So it is usually ignored in the treatment of the genus below.

KEY TO MALES OF ANISOPS SPECIES IN WEST MALAYSIA AND SINGAPORE

1. Interocular space anteriorly produced into a cephalic projection ( Figs. 2 , 13, 15 ) ..................................................................... 2

– Interocular space anteriorly not produced into a cephalic projection ................................................................................ 4

2. Cephalic projection in dorsal view rounded at apex, in lateral view extending in front of eye less than half the total length of the frons ( Fig. 15 ) .................................................................. 3

– Cephalic projection in dorsal view more or less acuminate at apex, in lateral view extending in front of eye half or more the total length of the frons ( Fig. 13 ) .......................... A. bouvieri

3. In frontal view, frons diverging ventrally and with a lateral carina over its entire length ( Fig. 19 ) ................................ A.kuroiwae

– In frontal view frons narrowest halfway between the eyes, with a weak carina in its dorsal part only ( Fig. 20 ) ..... A. nasutus

4. In dorsal view eyes holoptic in posterior half ( Figs. 25, 26 ) ................................................................................... A. breddini

– In dorsal view eyes not holoptic ........................................... 5

5. Tylus medially excavate ( Fig. 18 ) ............................. A. niveus

– Tylus flat or somewhat swollen, not medially excavate ........ 6

6. Rostral prong shorter than third rostral segment ( Fig. 16 ), originating in its proximal third ............................................ 7

– Rostral prong longer than third rostral segment, originating in its distal third ( Fig. 17 ); length up to 5.6 mm .... A. lansburyi

7. Synthlipsis one fifth or less the anterior width of vertex, length up to 4.8 mm ........................................................... A. exiguus

– Synthlipsis about one third or more the anterior width of vertex, length over 5.0 mm ............................................................... 8

8. Length over 6.6 mm .............................................................. 9

– Length up to 6.5 mm ........................................................... 10

9. Length 8.5 mm or more; tylus swollen, with a pair of tufts of bristles which reach the base of the labrum ( Fig. 12 ) ................................................................................ A. barbatus

– Length up to 8.3 mm; tylus flat or slightly swollen, without tufts of bristles ............................................................ A. occipitalis

10. Along the median longitudinal axis the head is less than one half the length of the pronotum; tylus and frons not carinate, in lateral view frons extending in front of the eyes; stridulatory comb on foretibia with about 22 teeth 14 apical ones distinctly longer than the 8 basal ones which are differently orientated ( Fig. 22 ) ............................................................ A.nigrolineatus

– Along median longitudinal axis the head is more than one half the length of the pronotum; tylus and adjacent part of the frons carinate, in lateral view dorsal half of frons not extending in front of eyes ( Fig. 14 ); stridulatory comb of about 25 to 32 teeth which decrease in width from base to apex ( Fig. 23 ) ................................................................................ A. tahitiensis

Figures

Figs. 9-10. Fore leg of Anisops kuroiwae. 9 male, 10 female; s= stridulatory comb.

Figs. 12-17. Anisops male, head in lateral view. 12 A. barbatus; 13 A. bouvieri; 14 A.tahitiensis; 15 A.kuroiwae; 16 A. exiguus; 17 A. lansburyi. p = rostral prong; t = tylus.

Figs. 18-20. Anisops male, head in frontal view; 19-20 rostrum removed. 18 A. niveus; 19 A. kuroiwae; 20 A. nasutus. t = tylus.

Fig. 2. Anisops kuroiwae, dorsal view of male, length 6.4 mm. a = anterior width of vertex; c = cephalic projection; s = synthlipsis

Figs. 25-26. Anisops breddini, male, anterior part of body in dorsal view. 25 brachypterous form; 26 macropterous form. p = ciliated pit at base of hemielytral commissure.

Figs. 21-23. Anisops, male, stridular comb. 21 A. lansburyi; 22 A. nigrolineatus; 23 A. tahitiensis.