Morphology, Anatomy, and Physiological Aspects of Dytiscids

Abstract

Although the morphology of dytiscids is generally distinct from other aquatic insects, there is considerable variation within this highly diverse family. In the first part of this chapter I discuss the external morphology of adult and larval Dytiscidae, as well as highlight the morphological adaptations to the aquatic environment. In the second part of this chapter the internal anatomy and some physiological aspects, e.g., respiration and digestion, are discussed. The morphology of adult and larval Dytiscidae is very well documented, whereas pupae and the internal anatomy of all stages are neglected. Almost all taxonomic keys (e.g., Epler, The water beetles of Florida – an identification manual for the families Chrysomelidae, Curculionidae, Dryopidae, Dytiscidae, Elmidae, Gyrinidae, Haliplidae, Helophoridae, Hydraenidae, Hydrochidae, Hydrophilidae, Noteridae, Psephenidae, Ptilodactylidae and Scirtidae. Florida Department of Environmental Protection, Tallahassee, 2010; Arnett and Thomas, American beetles. Archostemata, Myxophaga, Adephaga, Polyphaga: Staphyliniformia, vol 1. CRC Press, Boca Raton, 2000; Larson et al., Predaceous diving beetles (Coleoptera: Dytiscidae) of the Nearctic region, with emphasis on the fauna of Canada and Alaska. NRC Research Press, Ottawa, 2000; Nilsson and Holmen, The aquatic Adephaga (Coleoptera) of Fennoscandia and Denmark. II. Dytiscidae. Brill, Leiden, 1995; Franciscolo, Coleoptera-Haliplidae, Hygrobiidae, Gyrinidae, Dytiscidae. Fauna d’Italia, vol. XIV. Edizioni Calderini, Bologna, 1979) give descriptions of the morphology of larvae and adults. Detailed information is also given in some textbooks (e.g., Balke 2005, 7.6. Dytiscidae Leach, 1915. In: Beutel RG, Leschen RAB (eds) Handbook of zoology. Volume IV. Arthropoda: Insecta. Part 38. Coleoptera, Beetles. Volume 1: Morphology and systematics (Archostemata, Adephaga, Myxophaga, Polyphaga partim.). Walter de Gruyter, Berlin/New York, 2005, Wesenberg-Lund, Biologie der Süsswasserinsekten. Springer, Berlin, p 682, 1943). Internal anatomy and physiological aspects are best documented in larger species (e.g., Dytiscus marginalis). Particularly, Korschelt (1923, 1924) (Bearbeitung einheimischer Tiere. Erste Monographie: Der Gelbrand Dytiscus marginalis L., vol 2, Engelmann, Leipzig, p 863, 1923, Bearbeitung einheimischer Tiere. Erste Monographie: Der Gelbrand Dytiscus marginalis L., vol 2, Engelmann, Leipzig, p 964, 1924) and his academic staff, as well as Blunck (1923) (Z Wiss Zool 100:459–492, 1912a; Z Wiss Zool 102:169–248, 1912b, Z Wiss Zool Leipzig 111:76–151, 1914, Z Wiss Zool Leipzig: 117(1):1–129, 1917, Z Wiss Zool Leipzig 121(2): 172–392, 1923) provide detailed documentation of their observations, experiments, and dissections that occurred almost 100 years ago. These documents still represent some of the best work on these subjects, however new techniques using advanced microscopic and laboratory methods could provide even great insights into the anatomy and physiology of this group of insects.

The dytiscus and the hydrophilus…both frequent the water of deep ponds, ditches or pools. With their legs flattened like oars and their very smooth bodies arched on the top, and shaped underneath like the keel of a ship, they are first class swimmers and divers. It is a pleasure to the eye to follow the graceful agility of their oars as they row quietly on the surface, or float under water

(Jean-Henri Fabre 2002)