Freyastera mortenseni ( Madsen 1956 )

Mah, Christopher L., 2022, New Genera, Species and Occurrences of Deep-Sea Asteroidea (Valvatacea, Forcipulatacea, Echinodermata) collected from the North Pacific Ocean by the CAPSTONE Expedition, Zootaxa 5164 (1), pp. 1-75 : 15-17

Freyastera mortenseni ( Madsen 1956)

FIGURE 4A–F

Madsen 1956: 29; Clark & Mah 2000: 322; McKnight 2006: 81

Diagnosis. Abactinal surface covered by polygonal plates each with 5–9 spinelets. Proximal arm region with 4–6 plate count across arm width, each with 1–5 spinelets. Adambulacral plates with single furrow spine, 2 subambulacral spines (narrowing to 1 distally).

Comments. Freyastera mortenseni is identified based on the arrangement of the adambulacral spines, a single furrow spine and two subambulacral spines in an oblique row as well as the pedicellariae on the abactinal surface and the pedicellariae morphology. Scanning electron micrographs were consistent with those illustrated by Madsen (1956). McKnight (2006) moved Freyella mortenseni Madsen 1956 to Freyastera based on its six rays. The specimen described herein is consistent with the slender ambulacral and adambulacral ossicles which are synapomorphies of Freyastera (Mah 1996) .

Freyastera is in need of revision with many Freyella species showing six rays and similar morphology. It is possible that further refinement within Freyastera might affect the identity of this species (e.g. as a synonym of another species).

Occurrence: American Samoa region, Kermadec Trench (New Zealand). 3770 –6160 m.

Description. Body stellate, arms elongate (R/r>25.0), proximal abactinal cover distended becoming flattened and transparent, allowing ambulacrals to be visible, along remainder of arm ( Fig. 4A, C ). Interradial arcs acute but distinct concavity ( Fig. 4A–B ). Basal arm width at disk contact narrow becoming wider due to abactinal dissension along proximal region.

Abactinal surface covered by abutted flattened to weakly convex plates, thin and translucent, polygonal to irregularly rounded plates. Each plate with one to four, mostly two or three sharp spinelets. Remainder of plate surface covered by 10 to 40 pedicellariae, approximately 10–15 present along a 1.0 mm line. Larger single spines present centrally on disk with smaller, spines present on disk periphery, arm plates. Madreporite raised above plane of disk ( Fig. 4A ), surrounded by 10 to 20 sharp spines projecting around lateral edge, 2 to 8 on madreporite surface. Spination and pedicellariae present only on abactinal plates with lateral, more ventrally facing surface spineless and smooth.

Basal adambulacral plates in contact interradially in unfused syzygy ( Fig. 4C ). Adambulacral plates vertebraeshaped. Each adambulacral with three total spines forming lateral series. Adambulacral spines all covered with a sheath covered in abundant pedicellariae. Two spines projecting dorsolaterally with one spine projecting ventrally ( Fig. 4F ). Of the two dorsolateral projecting spines, the uppermost is most elongate, approximately 1.0 cm in length, with adjacent spine and that of the downward directed spine, approximately half the length. Dorsolateral projecting adambulacral spines correspond to tube feet along arm ( Fig. 4F ).

Pedicellariae composed of three-part “forcipulate” wrench-like valves, articulated near base ( Fig. 4D ). Valve tips with 10 shank-like teeth of two lengths in different rows flanked on each corner by large, pronounced fang-like points. Three to four shank-like teeth along lateral edges of each valve ( Fig. 4E ).

Oral spines, two each plate, projecting into mouth, one suboral spine on oral plate surface ( Fig. 4C ). Thus, each interradius with four spines projecting into mouth, two per paired oral plate. As with adambulacral/lateral spines all spines in the oral region with thick sheath with embedded pedicellariae. Tube foot grooves shallow.

Color in life was a very light orange to pink weakening to white distally along the arms ( Fig. 4B ). Specimen was sitting on manganese-encrusted boulder.

Material Examined: USNM 1453620 Utu Seamount, American Samoan region, South Pacific Ocean. -12.65, - 167.27, 3770 m, Coll. NOAA ship Okeanos Explorer with ROV D2, EX 1702. EX 1702_IMG_20170221 T 005042Z_ ROVHD.jpg orange, 1 wet spec. R > 10.0, r=0.4

Figures

FIGURE 4. Freyastera mortenseni (Madsen, 1956). Scale bar=3.0 mm. A. Whole body-top/lateral view. B. In situ abactinal view showing disk. C. Oral view showing mouth spines. D. Pedicellariae with articulated valves. Scale bar=20 µm E. Individual valve showing teeth on tip. F. Oral view showing tube foot groove as well as lateral and furrow spines.