Freyastera mortenseni ( Madsen, 1956 )

Freyastera mortenseni ( Madsen, 1956) View in CoL

Fig. 7 View Figure 7

Freyella mortenseni View in CoL : Madsen 1956: 29; Korovchinsky and Galkin 1984: 1213 (in key); Galkin and Korovchinsky 1984: 166; Mah in Clark and Mah 2001: 322.

Freyastera mortenseni View in CoL : McKnight 2006: 81; Zhang et al. 2019 (in key); Mah 2022: 15.

Material examined.

RSIOAST 0102 (Fig. 7 View Figure 7 ) ; IDSSE -EEB-HX 02 . (Suppl. material 1) .

Diagnosis.

Arms 6. Abactinal disk scattered with long, sharp spines. Abactinal arm plates with 1–5 (usually 2–4) spines of similar size and form with those on disk, not covered by membranous sheath. Abactinal arm plates and spines extend beyond genital area. Enlarged pedicellariae (about 0.5 mm in length) with curved valves present on oral spines, proximal adambulacral spines, abactinal surface of disk, and arm genital areas. Small pedicellariae (about 0.1 mm in length) cluster in transverse bands on abactinal arm beyond genital area. Proximal adambulacral plates with one subambulacral spine, one aboral spine, and one furrow spine in a diagonal row. Proximal subambulacral spines with truncate end. Oral plate with one actinostomal spine, one suboral spine, and one aboral furrow spine.

Distribution.

Southwest Pacific: Kermadec Trench; Northwest Pacific: Mariana Trench, Parece Vela basin. 5850–6200 m. Type locality: Kermadec Trench, 5850 m.

Remarks.

F. mortenseni is characterized by the presence of large pedicellariae on abactinal disk and arm genital area, as well as on oral spines and proximal adambulacral spines (Fig. 7 A, B, D View Figure 7 ). The adambulacral plate of the species carries one subambulacral spine and two aboral spines in an oblique row (Fig. 7 C View Figure 7 ). Beyond genital area, the large pedicellariae are absent; instead, small pedicellariae form transverse bands (Fig. 7 E, F View Figure 7 ). This species is morphologically and phylogenetically close to F. basketa (Fig. 12 View Figure 12 ), which also possesses large pedicellariae. The newly examined specimens extend the geographical and depth range of F. mortenseni , representing one of the deepest occurrences of Freyastera . F. mortenseni was also reported in the American Samoa region at 3770 m depth ( Mah 2022). However, based on the photos of the specimen investigated ( Mah 2022, Fig. 4 C View Figure 4 ), the large pedicellariae were not present on the oral spines. This specimen, with 1–4 (usually 2–3) sharp spinelets on abactinal plate, three adambulacral spines in a diagonal row, absence of large pedicellariae (based on photo and description), and presence of small pedicellariae on abactinal plates, is potentially a new species that is close to F. mortenseni and F. delicata .