Pseudarachna Sars 1897

• Main Author: Merrin, Kelly L.
• Format: Other/Unknown Material
• Language: unknown
• Published: Zenodo 2006
• Subjects: Biodiversity; Taxonomy; Animalia; Arthropoda; Malacostraca; Isopoda; Munnopsidae; Pseudarachna; North Atlantic
• Online Access: https://doi.org/10.5281/zenodo.6257034; http://treatment.plazi.org/id/03BCAA724D49BA54FEC7FCFC4914B2A5

Pseudarachna Sars, 1897 Mesostenus Sars, 1864: partim: 9 (preoccupied). Pseudarachna . — Sars, 1897: 142.— Nierstrasz & Schuurmans-Stekhoven, 1930: 129.— Kussakin, 2003: 261. Not Pseudarachna . — Schultz, 1976: 13. Type species: Mesostenus hirsutus Sars, 1864; by monotypy. Diagnosis Cephalic frons enlarged, broad, semi-circular, without defined ridge around antennae; cephalon anterior flanges absent. Pereonites 1–4 not short or compact, dorsal spines present, apical setae present. Pereonite 2 largest; pereonites 5–7, lateral margins not narrow, natasome not reduced. Pleon anterolateral margins rounded, without spine. Antennae positioned widely apart; antenna 1 small, article 1 with lateral flange; antenna 2 article 1 with no anterolateral spine. Mandible lacinia mobilis, spine row and palp all absent; mandibular fossa angular, sub-horizontal across mandible. Pereopod 2 elongate, robust; ischium compact, wider than other articles; pereopods 5 and 6 ischium superior margin with plumose setae; carpus paddle shaped; carpus and propodus with marginal plumose setae; pereopod 7 more ambulatory, with setation similar to that of pereopods 5 and 6; dactyli of natatory pereopods flattened, slightly broadened. Pleopod 4 exopod with more than 1 plumose seta. Pleon triangular, domed in centre. Operculum partially vaulted, with small medial keel. Pleopod 5 simple lobe. Uropods flat, uniramous. Remarks Pseudarachna has many unique apomorphies, the most notable being the enlarged, semi-circular shaped cephalic frons, the widely spaced antennae, the small antenna 1, enlarged pereonite 2 and a robust and enlarged pereopod 2 with a wide, compact ischium. Pseudarachna is easily distinguished by these characters from other closely related genera such as Ilyarachna Sars, 1870 and Echinozone Sars, 1897. Males are not known for this genus, and thus there is no data specific on sexual dimorphism. Distribution In the North Atlantic, from western Ireland to Denmark (Wolff 1962) at depths between 50–478 metres (Svavarsson et al . 1993); ...