Paracymus Thomson 1867
Creators: name: Minoshima, Yûsuke N.
name: Watanabe, Kohei
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Hydrophilidae
Paracymus

description: Genus Paracymus Thomson, 1867
Diagnosis of larva. Surface of head capsule smooth. Nasale with three to four distinct teeth (Figs 2C, 4A, 5B). Both epistomal lobes projecting anteriorly, slightly asymmetrical, rounded or angulate (Figs 2C, 4A, 5B). Epistomal lobe bearing a few cuticular spines; gFR2 composed of two or three setae (Fig. 2C). Frontal lines lyriform, not convergent at base; coronal line absent (Fig. 2A). Sensilla PA26–28 not closely grouped; PA27 between PA26 and PA28 (Fig. 2B). Antenna, maxilla and labium not bearing long cuticular hairs (Figs 3A, 4B, 6A). Antennomere 1 longer than second (Figs 3A, 4B, 6A). Antennal SE1 long, as long as antennomere 3 (Figs 3A, 4B, 6A). Mandibles symmetrical, with two or three inner teeth (Figs 3B, 4C, 6B). Ligula present, as a small tubercle or long (Figs 3D, 4E, 6D). Prosternal sclerite divided into two plates (Fig. 5E). Mesonotal sclerites closely placed (Fig. 5F). Leg five segmented, short (Fig. 5H). Abdominal segments more or less lobed laterally and with transverse rows of tubercles dorsally and laterally (Fig. 1C, D, F–I). Spiracular atrium developed, without acrocercus and prostylus (Fig. 5I). Tracheal gills absent (Fig. 1C, D).
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) and a more or less developed ligula is present (Fig. 4E; 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).
description: Published as part of Minoshima, Yûsuke N. & Watanabe, Kohei, 2024, Morphology of the egg-case and larva of Paracymus aeneus (Germar) (Coleoptera: Hydrophilidae), pp. 200-214 in Zootaxa 5541 (2) on page 202, DOI: 10.11646/zootaxa.5541.2.5, http://zenodo.org/record/14240956