1. About homology of Haliplus Latreille, 1802 larvae postanal process and other structural features of Haliplidae Kirill V. MAKAROV 1) & Alexander A. PROKIN 2) 1) Zoology & Ecology Department, Moscow Pedagogical State University 2) Papanin Institute for Biology of Inland Waters, Russian Academy of Sciences

2. Haliplus larvae are characterized by long postanal process, often forked at the tip. This process was interpreted as: 1)partially fused urogomphi (Vondel, 2004, 2005, 2011 etc.; Beutel et al., 2011), 2) modified cerci (Jaboulet, 1960), 3) according to Seeger (1971), Spangler (1991) and Lawrence and Ślipiński (2013), abdominal segment X is expanded posteriorly forming a median process.

3. Handbook of Zoology, Pt. 38. p. 69 Jaboulet, 1960.: cq – cerque, s - soie

4. We have studied the structure of the terminal segment of the Haliplus s.str and Liaphlus spp. larvae on the series of sections 10 and 20  m, stained Mayer's haematoxylin. Authors are indebted to Nina N. Zhgareva (Institute for Biology of Inland Waters, Russian Academy of Sciences, Borok) and Dr. Vasily G. Dyadichko (Kovalevsky Institute of Biology of the Southern Seas, National Academy of Sciences of Ukraine, Odessa) for providing material. Photographs made with Zeiss AxioScope A1 and Nicon Eclipse 50i microscope with digital camera. Images were generated using Helicon Focus 5.3.14 software and enhanced using Photoshop® CS4.

5. Haliplus sp., L1 (extracted from egg in Nostoc colony) X 10

6. Haliplus L1 X segment

7. Peltodytes caesus – a few long processes

8. nomenclature of muscles after Kemner, 1913

9. Peltodytes caesus – normal direction of longitudinal axis in the abdominal segment X

10. Medial sections of Haliplus terminal segments with muscles

12. Abdominal muscles of Haliplus larva terminal segments (right body wall removed, sculpture not shown) M. dorsales interni mediales M. ventrales interni mediales M. urotergosternales interni M. tergosternales externi M. retractores ani dorsales M. retractores ani ventrales M. retractores bursarum analium

13. Abdominal muscles of Peltodytes larva terminal segments (right body wall removed, sculpture not shown) M. dorsales interni mediales M. ventrales interni mediales M. urotergosternales interni M. retractores ani dorsales M. retractores bursarum analium M. retractores ani ventrales M. tergosternales externi not shown (removed)

14. Muscles of abdominal segments in Haliplus consist of muscle bundles that do not form bands or layers. The complexity of the muscular system of Haliplidae is far inferior to that of the larvae of Dytiscidae (Speyer, 1922) and approaches to the minimum set of muscles, known for smallest larvae of Ptiliidae (Grebennikov, Beutel, 2002; Polilov, Beutel, 2009). Abdominal muscles of Ptinella tenella (Ptiliidae) larva terminal segments after Grebennikov & Beutel, 2002

15. Musculature of the abdominal segment X is represented by 3–4 bundles of muscles, which originate on the dorsal surface and are inserted at the edges of the anal area. Anal area of Haliplius, like other cuticle, is strongly sclerotized and represented by two lobes bearing paired apodemes. Paired distal muscles (homologs of dorsal retractor – M. retractores ani dorsales) attached to these apodemes, and also 2–3 pairs of proximal muscles, interpreted by us as ventral retractors (M. retractores ani ventrales, M. retractores bursarum analium). Musculature of abdominal segment X in Adephaga larvae is formed exclusively by longitudinal muscles – the retractors of the anus, anal camera, or eversible appendages (Kemner, 1913). Thus, it can be assumed that the longitudinal axis of abdominal segment X in Haliplus is heavily tilted, takes an almost vertical position and does not coincide with the axis of the postanal process, occupying the terminal position. Therefore, this postanal process should be considered as outgrowth of the dorsal surface of the segment X, not homologous to urogomphi or cerci. Probably, the reason of this reorganization of segment X – increasing of body surface connected with spiracular system features.

16. Tracheal system is apneustic for most part of larval development (spiracles are functional only in the 3rd instar). Thus, diffusion of oxygen across the cuticle is necessary and Haliplus and Peltodytes larvae increase body surface using different ways – 1) many small processes or 2) a few long processes. It was assumed by Seeger, 1971 that oxygen diffuses into the tracheal system directly in setigerous tubercles – “micro- tracheal” gills.

17. “micro-tracheal gills” after Seeger, 1971

18. Haliplus L1 abdomen X20

19. Haliplus L1 abdomen X40

20. Haliplus tubercles sections

21. Sagittal section of Haliplus segment X with paired trachea

22. Haliplus segment X with paired trachea

23. Haliplus segment X with trachea

24. Haliplus segment V with tracheal trunk and trachea to spiracle

25. Haliplus metanotum and segment I with spiracles

26. As a result, we have not found any tracheolae in micro-tracheal gills! Setigerous tubercles usually have a chamber connected with body cavity and a sensilla at the top. It is understandable slowly “dumped” diffusion of oxygen from big trunks to smaller, including tracheolae. Opposite direction of diffusion (proposed by Seeger, 1971) is possible, if exhausted air is removed from trunks. But it is not possible until spiracles become functional at the 3 rd instar. It can be proposed that Seeger’s “gills” with tracheolae (if they really exist) provide oxygen supply for hypoderma and sensillae. How do Haliplidae breathe? Is it possible to use metabolic oxygen from algae?

27. This study received financial support from the Ministry of Education and Science of the Russian Federation, project no 6.632.2014/K (K. Makarov) and Russian Foundation for Basic Research, project no. 15-04-02971 (A. Prokin). THANK YOU FOR THE ATTENTION!