Hyalopomatus biformis XIV

Hyalopomatus biformis (Hartman, 1960) (Fig. 37) Vermiliopsis biformis (Hartman, 1960): 164, plate 18, figs 1–3.— Hartman, 1969: 777–778, figs 1–7. Hyalopomatus biformis.— Zibrowius, 1971: 1374 (transferred to the genus Hyalopomatus).— Bastida-Zavala, 2008: 21, fig. 5E–H. Material examined. ICML-EMU-14051: TALUD XIV, St. 7, BC, 28º15'05"N 112º39'20"W, 07 April 2011, 195 m, 1 specimen. Description of material examined. Tube white and opaque, with a longitudinal ridge, anterior collar-like shallow rings (without wide flaring peristomes) and a terminal pointed peak (Fig. 37A). Small specimen, 8 mm long, 0.3 mm wide. Branchial crown 3 mm long plus operculum (0.4 mm) with 10 pairs of radioles. Peduncle broader than other radioles. Opercular stalk annulated (Fig. 37B–D). Operculum soft, transparent, semi-globular (pear-shaped), with an anterior end cap that can be visible when seen in different angle, as well as a transverse whitish line under light microscopy (Fig. 37B–D). Pseudoperculum absent. Thorax with six chaetigerous segments, five of which uncinigerous. Number of abdominal segments unknown (parts of tube attached to body). Small bundle of collar chaetae of two types: limbate and fin-and-blade with distal blade separated from basal fin by a short gap. Remarks. Hyalopomatus contains 17 nominal species worldwide (one declared incertae sedis), mainly from bathyal and abyssal depths (ten Hove & Kupriyanova 2009; Kupriyanova & Flaxman 2024). Among these species, only two occur in North America: H. biformis (Hartman, 1960) originally described from the Santa Catalina Basin, Southern California, USA, in 1,280 m depth, and H. mironovi Kupriyanova, 1993, a species described from the Kurile-Kamchatka Trench in 5,110 m depth and reported by Bastida-Zavala (2008) to California (USA). Tube, operculum and opercular stalk of the specimen here examined match with those of H. biformis described by Hartman (1960), a species with a sinuous tube with a basal part longitudinally ridged, with a high, dorsal keel. The tube of the specimen here reported is incomplete, lacks the basal part, but a longitudinal keel run from the anterior end to the last preserved section. In addition, it has some collar-like shallow rings anteriorly. This constitutes the first record of H. biformis for Mexico. Abiotic conditions. The specimen of H.biformis was collected in 195 m deep, under the following environmental conditions. Temperature: 12.7°C; salinity: 34.99; dissolved oxygen: 2.9 ml O 2 /l; %MO: 2.9; sediments dominated by sand (88.6%) (Table 1). Distribution. Northern Gulf of California, Mexico. Genus Hydroides Gunnerus, 1768