Sphaeriodiscus sp.

Mah, Christopher L., 2024, Two New Taxa of Goniasteridae (Asteroidea, Echinodermata) and Noteworthy Observations of Deep-Sea Asteroidea by the NOAA Ship Okeanos Explorer in the North and Tropical Atlantic, Zootaxa 5432 (4), pp. 461-508 : 495-497

Sphaeriodiscus sp.

FIGURE 15A–C

Description

Body pentagonal to weakly stellate (R/r=1.3), interradial arcs weakly curved to straight, body thick ( Fig. 15A–C ). Superomarginal plates large, forming distinct peripheral frame with penultimate superomarginal plates enlarged ( Fig. 15C ). Abactinal plates weakly tabulate, polygonal to hexagonal in outline.

Comments

Although some of the individuals ( Figure 15A–B ) do not show the distinctive enlarged penultimate superomarginals as figured in Clark & Downey (1992) several other characters suggest Sphaeriodiscus , possibly as variants of Sphaeriodiscus bourgeti . The abactinal surface shows identical shaped plates, weakly tabulate covered with granules as well as relatively few marginal plates in each interradius. Type specimens show a range of 6 to 8 per interradius, varying between approximately R=1.0 to 4.0 cm, with some specimens showing disproportionately enlarged and thickened penultimate superomarginal plates with the central two interradial plates relatively small by comparison. However as the specimens are larger, the acute disproportionate size range appears to normalize. This pattern of variation, which emphasizes enlargement of the penultimate superomarginals is observed in the east Atlantic goniasterid Peltaster placenta ( Tortonese, 1984) . The specimen observed herein also lacks secondary plates, i.e. numerous smaller plates approximately less than 10–20% of the diameter of the other plates among those on the abactinal surface, which Halpern (1970) used to diagnose Peltaster . Pacific Sphaeriodiscus also show relatively fewer marginal plates per interradius which seems consistent with the individuals observed here.

If these images ultimately demonstrate Sphaeriodiscus bourgeti from north of Terceira Island these would be a further range extension from off the NW African and Cape Verde Islands region.

Another potential character for identifying Sphaeriodiscus is color, which is in most cases not useful for deeperwater species which tend to be monochromatic and lacking distinctive patterns. In situ specimens identified as Sphaeriodiscus ammophilus from the North Pacific/Hawaiian region display a distinct orange present in each interradius, on the disc and extending to the proximalmost (i.e. central pair) superomarginal plates. This color pattern is also present in the specimens figured in Figure 15C from EX2205 from north of Terceira Island, suggesting similarity with the Pacific Sphaeriodiscus . Imagery of Peltaster placenta ( Mah 2020) from the tropical Atlantic, including the Gulf of Mexico shows this species as a yellow to tan color with no distinct pattern.

Further collection of these specimens is desirable.

Ecological Comments

Two observations of this species were recorded from north of Terceira Island at approximately 723–730 m, both times in close proximity to coral rubble with the oral surface, and the mouth positioned adjacent to dead coral skeletons with cup corals present in both instances ( Fig. 15B ). One image of the Hawaiian/Pacific Sphaeriodiscus ammophilus also shows seemingly deceased coral skeletons and rubble adjacent to a recent possible feeding ( Fig. 15C ). It is unclear however, if Sphaeriodiscus could be a predator of coral or a scavenger of tissue or other epizoic organisms on the skeleton’s surface.

Images Observed

North of Terceira Island, eastern North Atlantic, Portugal, 43.953658, -28.526545, 730 m ( Fig. 15A ) EX2205_IMG_20220720T135529Z_ROVHD.jpg

North of Terceira Island, eastern North Atlantic, Portugal, 43.95378, -28.526631, 723 m. ( Fig. 15B ) EX2205_IMG_20220720T140342Z_ROVHD.jpg

North of Terceira Island, eastern North Atlantic, Portugal, 43.953735, -28.528386, 567 m.

EX2205_IMG_20220720T163304Z_ROVHD.jpg

S. ammophilus, Kona coast, Hawaiian Islands, 19.80216672, -156.1261975, 392.7 m. Fig. 15C EX1504L3_IMG_20150830T010853Z_ROVHD_ASR.jpg

Figures

FIGURE 15. Sphaeriodiscus sp. A.–B. north of Terceira Island, 723–730 m. C. S. ammophilus, Kona coast, Hawaiian Islands 392 m