DOI: 10.15468/uam4xe
title: Larval Morhology Of Hydrotarsus Falkenström: Generic Characteristics, Description Of H. Compunctus (Wollaston), And Analysis Of Relationships With Other Members Of The Tribe Hydroporini (Coleoptera: Dytiscidae, Hydroporinae)

description: This dataset contains the digitized treatments in Plazi based on the original journal article Alarie, Yves, Bilton, David T. (2001): Larval Morhology Of Hydrotarsus Falkenström: Generic Characteristics, Description Of H. Compunctus (Wollaston), And Analysis Of Relationships With Other Members Of The Tribe Hydroporini (Coleoptera: Dytiscidae, Hydroporinae). The Coleopterists Bulletin 55 (3): 341-350, DOI: 10.1649/0010-065X(2001)055[0341:LMOHFM]2.0.CO;2, URL: http://dx.doi.org/10.1649/0010-065x(2001)055[0341:lmohfm]2.0.co;2AbstractDescription of larval instars of the madicolous species Hydrotarsus compunctus (Wollaston 1865) is presented including a detailed chaetotaxic and porotaxic analysis of the cephalic capsule, head appendages, legs, last abdominal segment and urogomphi. Compared to other genera of the tribe Hydroporini, Hydrotarsus Falkenström (1938) is postulated to be more closely related phylogenetically to Sanfilippodytes Franciscolo and Hydroporus Clairville based on the following combination of characters: (i) absence of the primary seta MX 5, (ii) absence of a constriction at level of occipital suture, (iii) presence of a maxillary cardo, (iv) insertion of the primary seta MX 1 on the maxillary cardo, (v) presence of spiracles on mesothorax and abdominal segments 1–7, and (vi) presence of the primary seta TR2.The hydroporine genus Hydrotarsus Falkenström (1938) is a highly endemic Macaronesian genus comprised of only three species: H. compunctus (Wollaston 1865) and H. pilosus Guignot (1949), two Canarian endemics, and H. lundbladi Falkenström (1938) known only from Madeira (Machado 1987; Balke and Hendrich 1989; Balke et al. 1990). All three species are specialist madicoles [i.e., found in habitats with a constantly seeping film of water over bedrock (Malmqvist et al. 1995)], which probably explains why they have rarely been collected by entomologists working on the Atlantic islands. Balke and Hendrich (1989) and Balke et al. (1990) discuss the habitats of the three species, and suggest that they are semi­terrestrial, being found on damp rocks, particularly those with growths of Marchantia polymorpha and other bryophytes, around small springs.Within the Hydroporinae, Hydrotarsus belongs to the tribe Hydroporini Sharp which includes approximately 36 genera Worldwide (Pederzani 1995; Nilsson and Roughley 1997). Like members of Necterosoma Mac Leay and Sternopriscus Sharp, species of Hydrotarsus characterize by presence of pentamerous pro­ and mesotarsi (compared to pseudotetramerous in all other Hydroporinae i.e., with tarsomere 4 clearly visible and not locked by lobes of tarsomere 3). Franciscolo (1979) suggested a more basal placement of those genera within Hydroporinae based on that character state.Many of the derived features of adult Hydrotarsus are almost certainly associated with the switch from rheophilic to madicolous life, which occurred in the ancestral lineage. The loss of swimming hairs seen in these beetles is an obvious adaptation for crawling on wet rockfaces, and is paralleled in fully terrestrial species of dytiscid. A similar argument may apply to the unusual structure of the fore and mid tarsi, one of the features which has been used to argue a phylogenetically isolated position for this genus. The Madeiran endemic, H. lundbladi, has, uniquely amongst the Dytiscidae, expanded hind tarsal segments in males. This feature has probably evolved as a result of sexual selection, since the hind legs of these madicolous dytiscids are freed from the functional constraint of working as swimming organs, and can instead be modified to assist in grasping females during mating.Nothing is known about the larval morphology of members of the genus Hydrotarsus. Accordingly, the recent discovery of larvae of H. compunctus is interesting not only because it provides an opportunity to describe for the first time their larvae but also to discuss the relative position of Hydrotarsus within the tribe Hydroporini.Our article focuses on the comparative morphology of larvae of the genus Hydrotarsus with an emphasis on chaetotaxy and porotaxy. It has the following three goals: i) description of the second and third instar of H. compunctus; ii) identification of genus level larval characters; and iii) comparison of the genus Hydrotarsus with other genera of Hydroporini for which the larvae have been described.