Chone mollis

Chone cf. mollis (Bush, 1904) (Fig. 8) Metachone mollis Bush, 1904, 216, pt. 35, figs 19–20, 28. Chone mollis.— Hartman, 1942: 87, figs 141–143.— Hartman, 1944: 279.— Hartman, 1969: 673.— Banse, 1972: 469, fig. 3.— Tovar-Hernández, 2007: 539–543, fig. 10. Material examined. ICML-EMU-14018: TALUD X, St. 4, KD, 28º16'06"N 112º32'50"W, 09 February 2007, 587– 633 m, 1 specimen; ICML-EMU-14019: TALUD XIV, St. 20, BC, 28º46'29"N 112º45'40"W, 09 April 2011, 410 m, 13 specimens. Description of material examined (n: refer to the number of specimens measured). Trunk 8.3–9.2 mm long (n: 3), thorax 0.9–1.5 mm wide (n: 4), branchial crown 3.3–9.7 mm long (n: 2), nine pairs of radioles (n: 2), eight thoracic chaetigers (n: 6), 26–28 abdominal chaetigers (n: 5). Ratio of posterior peristomial ring collar length versus chaetiger 2 length, in lateral view: 2:1. Radiolar flanges broad. Radiolar tips as long as the space of 10 pinnules width. Anterior peristomial ring partially exposed between collar dorsal margins (Fig. 8B) and exposed ventrally, above collar margin, with a broad triangular base and slightly expanded laterally to triangular tip (Fig. 8C–E, pointed with arrows); collar ventral shield horse-shoe shaped, twice wider than long (Fig. 8A, C). Glandular ridge on chaetiger 2 narrow, homogeneous all around. Thoracic chaetigers with two rows of elongate, narrowly hooded chaetae (Fig. 8I); one anterior row with bayonet chaetae (Fig. 8I); two posterior rows of paleate chaetae with medium length mucros, broken in many chaetae (Fig. 8F–G). Thoracic acicular uncini (Fig. 8J) with main fang surmounted by five rows of teeth. Pre- and post-chaetal lobes well developed. Abdominal chaetigers with two transverse rows of elongate narrowly hooded chaetae. Abdominal uncini with breast rectangular, main fang surmounted by four regular rows of teeth, occupying 1/2 the length of main fang (Fig. 8H). Posterior segments with very elongated, narrowly hooded chaetae. Pygidium with rounded posterior margin. Remarks. Chone is composed of 20 species (Capa et al. 2021), plus one new species described below. The phylogenetic relationships within Chone were assessed by Tovar-Hernández (2008), using morphological characters obtained mostly from the study of type material and revising some features such as: dentition of thoracic uncini, shape of anterior and posterior abdominal uncini, and size of a pre-pygidial depression. The analysis revealed the existence of three genera previously assigned to Chone: Dialychone Claparède, 1870, Paradialychone Tovar-Hernández, 2008 and Chone sensu stricto. However, the recognition and placement of specimens in any of these three genera is still problematic due to their small size and because of details of uncini dentition (anterior and posterior abdominal chaetigers) and branchial crown structures (lips and pinnular appendages), that are often difficult to interpret (Capa et al. 2021). As a result, the position of some species within either Dialychone, Paradialychone or Chone based on morphology is uncertain (e.g., P. ambigua Capa & Murray, 2015) and a molecular approach to this group is needed. In the present study, two species of Chone are reported, one confer to C. mollis (Bush, 1904) and a new species described herein, from the Central Gulf of California. The specimens examined herein mostly fit the description of C. mollis provided by Tovar-Hernández (2007), except for the length of the mucros of thoracic notochaetae. In members of C. mollis mucros are minute, almost inconspicuous (hair-like), whereas in the specimens here reviewed, mucros are of medium length, but broken in many chaetae. Abiotic conditions. The specimens of C. cf. mollis were collected from 410–633 m deep, under the following environmental conditions. Temperature: 8.22–11.40°C; salinity: 34.62–34.90; dissolved oxygen: 0.20–1.94 ml O 2 /l; %MO: 0.94–7.70; sediments dominated by sand or silt (90.4 and 47.6%) (Table 1). Distribution. Central and northern Gulf of California, Mexico.