Paracymus Thomson, 1867

Genus Paracymus Thomson, 1867 View in CoL

Diagnosis of larva. Surface of head capsule smooth. Nasale with three to four distinct teeth ( Figs 2C View FIGURE 2 , 4A View FIGURE 4 , 5B View FIGURE 5 ). Both epistomal lobes projecting anteriorly, slightly asymmetrical, rounded or angulate ( Figs 2C View FIGURE 2 , 4A View FIGURE 4 , 5B View FIGURE 5 ). Epistomal lobe bearing a few cuticular spines; gFR2 composed of two or three setae ( Fig. 2C View FIGURE 2 ). Frontal lines lyriform, not convergent at base; coronal line absent ( Fig. 2A View FIGURE 2 ). Sensilla PA26–28 not closely grouped; PA27 between PA26 and PA28 ( Fig. 2B View FIGURE 2 ). Antenna, maxilla and labium not bearing long cuticular hairs ( Figs 3A View FIGURE 3 , 4B View FIGURE 4 , 6A View FIGURE 6 ). Antennomere 1 longer than second ( Figs 3A View FIGURE 3 , 4B View FIGURE 4 , 6A View FIGURE 6 ). Antennal SE1 long, as long as antennomere 3 ( Figs 3A View FIGURE 3 , 4B View FIGURE 4 , 6A View FIGURE 6 ). Mandibles symmetrical, with two or three inner teeth ( Figs 3B View FIGURE 3 , 4C View FIGURE 4 , 6B View FIGURE 6 ). Ligula present, as a small tubercle or long ( Figs 3D View FIGURE 3 , 4E View FIGURE 4 , 6D View FIGURE 6 ). Prosternal sclerite divided into two plates ( Fig. 5E View FIGURE 5 ). Mesonotal sclerites closely placed ( Fig. 5F View FIGURE 5 ). Leg five segmented, short ( Fig. 5H View FIGURE 5 ). Abdominal segments more or less lobed laterally and with transverse rows of tubercles dorsally and laterally ( Fig. 1C, D, F–I View FIGURE 1 ). Spiracular atrium developed, without acrocercus and prostylus ( Fig. 5I View FIGURE 5 ). Tracheal gills absent ( Fig. 1C, D View FIGURE 1 ).

Remarks. The tribe Laccobiini comprises two lineages: the Laccobius -group and the Paracymus -group. Paracymus belongs to the latter, and its larvae exhibit greater similarity with the genera of the Paracymus -group than with the Laccobius -group. The Paracymus -group comprises five genera, Afrotormus Hansen, 1999 , Paracymus , Scoliopsis Orchymont, 1919 , Tormus Sharp, 1884 and Tritonus Mulsant, 1844 , with the larval morphology of three of these genera ( Paracymus , Tormus and Tritonus ) having been described ( Archangelsky 1997, 1999; Short & Fikáček 2013; Fikáček et al. 2013, 2017; this study).

Larvae of the Laccobius -group genera have a piercing-sucking type (sensu Rodriguez et al. (2020)) morphology of the mandible and the epistomal lobe, which are considered adaptations to a benthic lifestyle in aquatic habitats ( Rodriguez et al. 2020). In contrast, larvae of the Paracymus -group genera have more ‘typical’ features within Hydrophilidae .Among the larvae of the Paracymus -group, the New Zealand endemic terrestrial genus Tormus is the most morphologically similar to Paracymus , as indicated by previous phylogenetic studies revealing a sister group relationship ( Short & Fikáček 2013; Toussaint et al. 2016; Toussaint & Short 2018). Fikáček et al. (2013) discussed the morphological similarity and evolutionary implications of Tormus and Paracymus larvae based on their general morphology. The most notable differences between the larvae are that Tormus bears numerous long cuticular hairs on the mouthparts (excluding the mandibles) and lacks a developed ligula ( Fikáček et al. 2013), whereas such long cuticular hairs are absent ( Fig. 6 View FIGURE 6 ) and a more or less developed ligula is present ( Fig. 4E View FIGURE 4 ; Archangelsky 1997, 1999) in Paracymus . Larvae of the Afrotropical genus Tritonus also share characters with those of Paracymus , but Tritonus is differentiated by having V-shaped frontal lines, the presence of a coronal line, the position of PA26–28 (forming a group), a small antennal sensorium SE1, and an undivided prosternum ( Fikáček et al. 2017).