Tremaster 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 : 468

Tremaster sp. juv?

FIGURE 3A

Description

This specimen was weakly stellate (R/r=~1.46) with five rays, and broadly angular interradial regions, showed five distinct and open gonopores (indicated by arrows in Fig. 3A ), plates in ordered, transverse series between the carinal and marginal plate series, weakly developed plates with 1 to 4 spines per plate. Marginal periphery with a series of spines, pointed, evenly spaced.

Color of animal was white with dark grey disk.

Comments

This individual was identified as Tremaster based on the distinct, large gonopores present on the disc ( Fig. 3A ) in each interradius as well as the transversely arranged abactinal plates in each interradius. A distinct series of spines was also observed around the lateral edge.

However, it differs from other Atlantic in situ observations of Tremaster mirabilis in that it was more distinctly stellate (R/r=~1.2) with more triangular arms in contrast to other North Atlantic specimens with a nearly round outline (R/r= ~1.0) and arms indistinct from the disc.

The observed specimen was more flattened and weakly arched with a lower aspect ( Fig. 3A ) than other in situ observations of T. mirabilis . Color of this specimen was white, versus the more yellow/tan with dark highlights of other Atlantic T. mirabilis observed in situ ( Fig. 3B ). This specimen also displayed distinct transverse plate series relative to the carinal and adjacent plate series along the arm

Depth occurrence of this individual (1824 m) also differed from Tremaster mirabilis which has so far, been found in much shallower depths (<1060 m). No records of Tremaster are known from this region.

Plausibly, this specimen could be a smaller or juvenile specimen of Tremaster mirabilis . Scale was unavailable for this individual making a more precise size comparison problematic. Characters such as color and body shape could undergo distinct changes as the individual attains a larger size.

This individual could also be an undescribed asterinid taxon or a new species of Tremaster . Abactinal plates, while in transverse series, appeared much more linear and in narrow series, resembling Anseropoda rather than Tremaster . Known Anseropoda species, however, lack the distinct gonopores observed on this individual.

This observation is comparable with the deepest known occurrence for the Asterinidae that are from Antarctic and high-latitude settings, from between 2000–4000 m (3944 m, Mah 2023b). Most asterinid taxa are otherwise known from depth shallower than 500 m (A.M. Clark 1993).

Image Observed

Kai Ridge, North Atlantic, 38.755736, -30.46133, 1824.0 m.

EX2205_IMG_20220729T135649Z_ROVHD.jpg

Figures

FIGURE 3. Tremaster (Asterinidae) A. Tremaster sp. Kai Ridge, 1824 m. Arrows indicating gonopores. B. Tremaster mirabilis, Puerto Rico.