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12 Fig. 1. libanica sp. n., holotype specimen NI 3a, Fig. 2. Chresmoda libanica sp. n., holotype specimen NI 3a, photograph of general habitus. drawing of general habitus, scale bar represents 5 mm.

0.2 mm wide, bearing about 20 long and sharp spines long. The prothoracic femora are straight and elongate, (Fig. 10), probably corresponding to maxillary palpi. 10.7 mm long, 0.45 mm wide, bearing a short anterior These structures are better preserved in specimens NI 1 process and a series of small apical spines. The protho- and NI 2 than in NI 3. A short two- or three-segmented racic tibiae have a curved base, very short, 2.5 mm long, labial palpus is visible in NI 3, with no visible setae, 0.4 mm wide, representing the 23% of femoral length. about 1.0 mm long; mandibles visible in NI 3, 0.7 mm There is a row of small spines at tibial apex. The whole long and 0.5 mm wide, bearing a row of small obtuse prothoracic tarsus is 10.0 mm long, first tarsomere 3.0 teeth and several short but sharp spines (Figs 3–4). The mm long, second tarsomere about 2.5 mm long, third eyes are visible in NI 3, large elliptic, about 1.2 mm long about 1.0 mm long. The more distal segmentation of and 0.8 mm wide, 0.8 mm apart. The antennae are not visible, probably not preserved. The thorax is rather rounded but with a strong posterior concavity in ventral view, 4.0 mm long, 5.4 mm wide (NI 3), 2.5 mm long, 4.0 mm wide (NI 1), 2.5 mm long, 4.8 mm wide (NI 2), with no visible wing sheaths. The legs are very long and narrow, covered with very small hairs arranged in rows (visible in NI 2). The pairs of coxae are widely separated, 2.5 mm apart (NI 3), all similar, those of the same side of thorax being very close to each other, rounded and large, 0.8 mm wide and long. The trochanters are small and short, all similar, 0.5 mm

Fig. 3. Chresmoda libanica sp. n., holotype specimen NI 3a, photograph of head and thorax, arrow indicates right mandible Fig. 4. Chresmoda libanica sp. n., holotype specimen NI 3a, with an apical short spine. drawing of ventral view of the body. Scale bar represents 5 mm.

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16 Fig. 5. Chresmoda libanica sp. n., holotype specimen NI 3a, photograph of ovipositor. this last point. Interestingly, Martínez-Delclòs (1991) demonstrated that adult males of C. aquatica and C. obscura were apterous, suggesting that also the adult females of C. libanica could have been apterous. The presence of unique, highly specialized tarsi in C. obscura, C. aquatica, C. libanica sp. n., and probably C. orientalis strongly supports the hypothesis that these were living on the water surface, using the water superficial tension to “skate” on surface like extant Ger- Fig. 6. Chresmoda libanica sp. n., holotype specimen NI 3a, ridae and Veliidae, as already proposed by Martínez- drawing of ovipositor, scale bar represents 1 mm. Delclós (1991). Baudoin (1980) tried to establish that Chresmoda obscura could not live on water surface, (Baudoin 1980: 2). The oblique apices of the tarsomeres using the water superficial tension, through a comparison probably acted as a blocking system in order to avoid the with the extant . He supposed that the Chres- complete distortion of the legs (see Figs 7–8, 13). Simi- moda were too large to float like Gerridae. But nobody larly, some Gerridae such as Potamobates thomasi Hun- knew in 1980 that at least some Chresmoda spp. could gerford, have no specialized setae but their have highly specialized legs and tarsi. Numerous extant two-segmented tarsi are curved (Andersen, 1982: Fig. Gerridae bear highly specialized setae that help them to 438). float by increasing their surface in contact with water sur- Nevertheless, the probably did not use face (Andersen, 1982). Chresmoda aquatica and Chres- their legs for skating in the same way as modern Gerridae moda libanica sp. n. have no specialized setae on their and Veliidae do. These insects have short to very short legs but their exceptionally high number of tarsomeres fore legs, useless in skating, and they mainly use their (about 40 in C. libanica sp. n., about twelve in C. obscura median and partly hind legs for this purpose. The fore, and C. aquatica) probably helped to increase, thanks to mid and hind legs of the Chresmodidae have nearly the the curvature of the tarsi, the length of that part of the leg same lengths and structures, and so probably similar func- in contact with the water surface, and consequently to tions in skating. increase the vertical component of the superficial tension C. aquatica, Saurophthiroides mongolicus, and the Chresmodidae from Araripe (Lower of Brazil) probably lived in lacustrine palaeoenvironments. The Solnhofen lithographic limestone was a marine deposit, but it has yielded numerous fossils of terrestrial origin. The Nammoura “fish beds” are also of marine origin

Fig. 8. Chresmoda libanica sp. n., holotype specimen NI 3a, Fig. 7. Chresmoda libanica sp. n., holotype specimen NI 3a, drawing of left median tibia and tarsi, scale bar represents 3 photograph of left median tarsus, arrows indicate tarsomeres. mm.

148 Fig. 10. Chresmoda libanica sp. n., paratype specimen NI 2b, photograph of maxillary palpi, arrow indicates some of the long and sharp spines of a palpus.

less, two of the three known specimens of C. libanica sp. n. are well-preserved nymphal exuviae, which are very delicate remains that do not support long transport. This Fig. 9. Chresmoda libanica sp. n., paratype specimen NI 2b, suggests that these nymphs were living in the sea or very photograph of general habitus. close to it. C. libanica sp. n. was probably carnivorous since it (Schram et al., 1999), but with “a considerable influx of shows well-developed maxillary palpis, as in C. aquatica, terrestrial organic debris” (Krassilov and Bacchia, 2000: bearing numerous strong and sharp spines and it has 798). Thus both C. obscura and C. libanica sp. n. could strong mandibles. It would probably eat small insects have been marine or freshwater insects. trapped by the water surface tension, or planktonic or The long ovipositor with indentations of C. libanica sp. nektonic when they came to the surface, maybe n., already observed in C. aquatica by Martínez-Delclós the larvae of the abundant fauna of Crustaceae (Schram et (1991: Fig. 6.6.7), can be related to an endophytic egg- al., 1999). Nothing was known until now concerning the laying in floating plants, for example palustrine or marine mouthparts and the alimentation of the Chresmodidae. algae. Six to eight different plant taxa of this kind were Baudoin (1980: 116) proposed that the Chresmodidae present in the outcrop of Nammoura (Makhoul, pers. were herbivorous, and thus they would have nothing to obs.). Nammouria gracilis Krassilov, 2000 is an aquatic eat if they had been surface skaters. From our point of fern with floating leaf segments described from Nam- view, this argument is not valid because of the existence moura (Krassilov and Bacchia, 2000). Thus, the sug- of freshwater and marine floating plants in the gested endophytic egg-laying of C. libanica sp. n. does Cretaceous. Furthermore, the present discovery allows us not exclude a freshwater origin for this . Neverthe- to reject Baudoin’s argument.

Fig. 11. Chresmoda libanica sp. n., paratype specimen NI 1b, Fig. 12. Chresmoda libanica sp. n., paratype specimen NI 1, photograph of general habitus. photograph of cerci and ovipositor.

149 Fig. 13. Chresmoda libanica sp. n., paratype specimen NI 1, photograph of right median tarsus, arrows indicate oblique apices of tarsomeres.

The legs of the Chresmodidae bearing numerous tarso- meres constitute a highly specialized, unique feature among the Hexapoda. Interestingly, the two basal tarso- meres are of “normal size”. Distal tarsomeres are very short and seem to result from a multiple subdivision of the 2–3 normal ones. The most apical tarsomeres are “drop-like” shaped, looking like antennomeres rather than tarsomeres. Nevertheless, the intermediate tarsomeres Fig. 14. Chresmoda libanica sp. n., apices of tibiae. A. Para- have retained the same oblique joints as the two basal type specimen NI 1b, median leg. B. Holotype specimen NI 3, ones. Lastly, these legs lack apical claws. These tarsi have left median and left hind legs, scale bar represents 1 mm. the general shape of antennae. We can hypothesize the occurrence of a mutation, maybe homeotic or affecting , if not all the Lower Cretaceous. These bugs some genes that participate to the leg development, did not “replace” and did not cause the extinction of the resulting in the transformation of the distal part of the Chresmodidae, at least in freshwater environments. The legs into “antennae”. Such mutations have been artifi- oldest known marine water strider is from the Middle cially induced in Drosophila sp. (holometabolous Eocene of Italy (Andersen et al., 1994). Thus, it is still Diptera) (Struhl, 1981, among other authors). It is impos- not possible to demonstrate the existence of marine water sible to establish the mechanisms that precisely explain striders during the Upper Cretaceous that would have the phenomenon in fossil Chresmodidae, but the major “replaced” the alleged marine Chresmodidae. The extinc- leg mutation that affected the Chresmodidae is a unique tion of this curious Mesozoic group is still unexplained. phenomenon among the Hexapoda. The reduction of the ACKNOWLEDGEMENTS. This study was a contribution from number of tarsomeres is much more frequent in the the Scientific Projects PGC 2001-0173 and PGC 2001-0185 insects. The number of tarsomeres increased from the (Spain), and Project CEDRE between France and Lebanon 02 E older, Upper , Chresmoda obscura to the Lower F12 / L11 “Les entomofaunes crétacés du Liban: apport à la Cretaceous C. aquatica, and the most recent, Upper Cre- reconstitution des paléoclimats et Paléoenvironnements”. taceous, C. libanica, just as if, after the occurrence of a REFERENCES major fundamental mutation in the Jurassic lineage of the Chresmodidae, less important mutations of the same type ANDERSEN N.M. 1982: The semiaquatic bugs (Hemiptera: Gerro- had resulted in more and more numerous tarsomeres in morpha): phylogeny, adaptations, biogeography and classifi- the most recent taxa of the group. It would be interesting cation. Entomonograph. Scandinavian Science Press, to study the mutations transforming legs into antennae in Klampenborg, Denmark, 3: 445 pp. extant Orthoptera or Phasmida, potential closest relatives ANDERSEN N.M. 1999: The evolution of marine insects: phyloge- to the Chresmodidae. netics, ecological, and geographical aspects of species diver- sity in marine water striders. Ecography 22: 98–111. Chresmoda libanica sp. n. is the most recent represen- ANDERSEN N.M., FARMA A. MINELLI A. & PICCOLI G. 1994: A tative of the Chresmodidae, which probably became fossil Halobates from the Mediterranean and the origin of sea extinct during the Upper Cretaceous. The oldest aquatic skaters (Gerridae). Zool. J. Linn. Soc. 112: 479–489. insects attributed to the families Mesoveliidae and BAUDOIN R. 1980: Sur les Gerris des miroirs d'eau actuels et les Veliidae are 120 Myr old. The same minimal age can be Chresmoda des lagunes post-récifales portlandiennes de Soln- hypothesized for the Gerridae, as sister group of the hofen. Annls Sci. Natur., Zool.-Biol. Anim. 2: 111–116. Veliidae (Andersen, 1999). The recent discovery of a rep- CARPENTER F.M. 1992: Superclass Hexapoda. In: Moore R.C. & resentative of the Gerridae in the Upper Albian French Kaesler R.L. (eds): Treatise on Invertebrate Paleontology. The Geological Society of America and the University of amber confirms the presence of Gerridae and Veliidae in 3/4 the Lower Cretaceous (Perrichot et al., submitted). Thus Kansas, Boulder, Colorado, (R), Arthropoda 4, : xxii + 655 pp. the Chresmodidae and the freshwater surface skater bugs ESAKI T. 1949: The occurrence of the Mesozoic insect Chres- were contemporaneous during at least the Albian and moda in the Far East. Insecta Matsumurana 17: 4–5.

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