Gronella Barnard & Karaman 1991
Creators: name: Kilgallen, N. M.
name: Lowry, J. K.
Publisher: name: Zenodo
Year: 2014
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Amphipoda
Lysianassidae
Gronella

description: Gronella Barnard & Karaman, 1991
Gronella Barnard & Karaman, 1991: 489.
Type species. Anonyx groenlandica Hansen, 1888, original designation.
Included species. Gronella includes two species: G. groenlandica (Hansen, 1888); G. lobata (Chevreux, 1907).
Diagnostic description. Antenna 1 flagellum article 1 lacking robust seta on distal margin; accessory flagellum forming cap. Antenna 2 flagellum articles 3–5 slender, with strong brush setae on the anterior margin. Mandibular incisor curved; molar with reduced column and convex triturating surface (button); palp attached midway. Maxilla 1 ST-7 cuspidate along distomedial margin; ST-D slender, apically cuspidate. Maxilliped outer plate with apical robust setae. Gnathopod 1 subchelate; coxa large, slightly shorter than coxa 2, tapering; carpus shorter than propodus; propodus palm acute or transverse, straight. Pereopod 4 coxa with well developed posteroventral lobe. Uropod 2 inner ramus constricted. Uropod 3 rami with plumose setae in male, absent in female. Telson moderately cleft.
Remarks. Gronella appears to be the sister taxon of Tryphosa. The only clear distinction between these genera is that Gronella has a tapering gnathopod 1 coxa, the setal-teeth of maxilla 1 are less cuspidate and apparently in females the rami of uropod 3 do not develop plumose setae. Gronella is also a sister taxon to Tryphosella which has a tapering first coxa and also a cap on the accessory flagellum. The main difference between these genera is the constricted inner ramus on uropod 2 that occurs in Gronella but not in Tryphosella. The other apparent difference is the structure of the maxilla 1 setal-teeth, most noticeable in ST-7 which is serrate along the entire curved medial margin in Tryphosella (see Lowry & Stoddart 2011), but serrate distally in Gronella groenlandica, with a smooth, straight medial margin. Tryphosa nana has setal-teeth more similar to species of Tryphosella.
Two species, Tryphosella propinqua (Chevreux, 1926) from deep water off Portugal and Tryphosella spitzbergensis (Chevreux, 1926) from the Norwegian Arctic, may also belong to Gronella. Neither the seta-teeth of maxilla 1 nor the rami of uropod 2 have ever been illustrated or described for T. propinqua so that the critical characters which determine its generic status are not known and it cannot be definitely placed in either Gronella or Tryphosella. Chevreux (1926) shows a cap on the accessory flagellum and a broadly tapering gnathopod 1 coxa in T. spitzbergensis. Stephensen (1935) shows a multi-articulated accessory flagellum and a narrowly tapering gnathopod 1 coxa. Neither author illustrated or described uropod 2. Stephensen (1935) was unsure of his identification and his material may well be a different species. Chevreux (1926) indicates the similarity of T. spitzbergensis to Tryphosella schneideri Stephensen, 1921, which does not have a constricted inner ramus on uropod 2. Until this character is known the species cannot be definitely placed in either Gronella or Tryphosella.
Distribution. Arctic, northwest boreal Atlantic.
description: Published as part of Kilgallen, N. M. & Lowry, J. K., 2014, The Tryphosa group (Crustacea: Amphipoda: Lysianassoidea: Lysianassidae: Tryphosinae), pp. 501-545 in Zootaxa 3768 (5) on page 507, DOI: 10.11646/zootaxa.3768.5.1, http://zenodo.org/record/4909684