Ampheraster alaminos Downey 1971

Mah, Christopher L., 2020, New species, occurrence records and observations of predation by deep-sea Asteroidea (Echinodermata) from the North Atlantic by NOAA ship Okeanos Explorer, Zootaxa 4766 (2), pp. 201-260 : 206-210

Ampheraster alaminos Downey 1971

Figure 2 A–D, 3A–C

Upon first examination, in situ video and the examined specimen (USNM 1550644) displayed several characters which were thought to distinguish it as separate from Ampheraster alaminos Downey. Examination of in situ imagery of other individuals and the collected specimen showed that this species shows variation with regard to the degree of its coelomic inflation and outward skeletal expression. Variation between the swollen specimen ( Fig. 2A ) and the dried holotype also became evident ( Fig. 2B ) also became apparent. As the specimen dried, many of the tissue based characters, which were mainly based on the tissue-covered spines came to be identical with those on the holotype, which is dry. These original description have never mentioned character differences owing to varying preservation artifacts.

It should be noted that the R/ r for this species in Clark and Downey (1992: 408) is only for the holotype and does not account for the full range of known variation. Downey’s (1971) original measurements show R/ r ranging from 1:7 to 1:11, which are more consistent with measurements of the specimen herein.

Ecological Observation

The Blake Ridge observation shows an individual of this species hunched over what appears to be an indeterminate stalk, possibly from a cnidarian or sponge. It is unclear what the star was feeding upon.

The collected specimen did not show any specific feeding behavior, but a significant amount of sediment was present within the folds of its partially extended pyloric stomach.

In situ observations show this species in motion over a fine, loosely consolidated muddy surface ( Fig. 3C ) with tube feet fully extended, and the body held well above the the surface. Movement in this species may depend on gliding rather than a strict, traditional crawling over the surface.

Endoparasitic Gall Examination of the specimen revealed the presence of an endoparasitic gall within one of the specimen arms which was not evident from the in situ image. The gall was round, kidney-shaped and was attached to the ambulacral column. Dissection of the gall did not reveal any apparent limbs or apparent diagnostic features. Pedicellasterids have not previously been documented as hosts for endoparasites. Other deep-water forcipulate asteroids with parasites have included eulimid gastropods, such as Asterophila rathunasteri in Rathbunaster californicus (Warén A. & Lewis 1994) and parasitic barnacles, such as the Acrothoracica (e.g. Stone & Moyse 1985). The apparent absence of legs and other segmented limbs suggests eulimid. Further dissection was not attempted to avoid further damaging the specimen.

Occurrence: Gulf of Mexico: Off the coast of South Carolina, NW of Florida Keys, Straits of Florida, Florida Escarpment, Blake Plateau off the coast of South Carolina, South of Mississippi Delta, off the Texas coast, Cuba, off the coast of Puerto Rico. 256–3365 m

Wet vs. Dry Characters

Newly collected material using ROV and video observation provide new insight into the morphology and biology of this poorly known species. The holotype and all of the material that formed the basis for Downey’s (1971) description of Ampheraster alaminos were collected by trawl and all of it was preserved dry ( Ahearn 1995). In situ observations ( Fig. 3A,B ) showed arms on the collected specimen (USNM 1550644) were strongly inflated relative to the dry specimens. It is possible that this swollen condition facilitates gas exchange across the thin body surface, as spines and pedicellariae are projected outwards.

Abactinal, especially the carinal series, inferomarginal, and furrow spines were among the most dissimilar characters observed on the in situ specimen versus the dry. The ensacculate inferomarginal spines were nearly twice the width of the dry spines and were rounded with blunt tips. Furrow spines possessed a tissue sheath, which were slightly longer than the spine tip. Upon closer examination, the holotype and other specimens showed some tissue residue, but none which appeared evident. Pedicellariae across the abactinal surface were also covered by tissue along their base.

Description

Body strongly stellate, R/r=11.4, interradial arcs acute.Arms six, deciduous, cylindrical in cross-section, gradually tapering with blunt tips.

Abactinal skeleton reticulate, overlain by tissue covering body surface, including spines and skeleton. Spines, pedicellariae ensacculate. Skeleton reticulate but forming closely arranged mesh with irregularly shaped polygonal openings but papulae not evident from specimen nor from in situ observation. Disk skeleton thickened around periphery, one to three spines, ensacculate, present on disk surface, especially laterally. Smaller, individual spines present on disk central surface. Tissue covering abactinal and lateral surfaces of arms, forming discrete segmented tissue corresponding with transverse plates.

Skeleton forming reticulate structure along disk, prominent carinal row along arms with transverse ribs forming evenly distributed quadrate spaces along each arm. Individual plates imbricate, polylobate in shape, mostly quadrilobate forming single series. Carinal plates each with single sharp spine, enveloped within an ensacculate sheath which obscures the skeletal structure while tissue is hydrated. Blake Ridge in situ observation shows one individual with an additional series of irregular spines present along the adradial regions along the arms.

Pedicellariae abundant, forming dense covering over body surface. Three pedicellariae types. Most abundant pedicellariae small wrench-shaped with blunt, valves evenly distributed teeth. Straight unguiculate pedicellariae also present on disk, actinal plates between oral and adambulacral plates. Smaller, straight pedicellariae present on adambulacral plates in furrow.

Superomarginals widely spaced, spines short, but each covered in tissue sheath. Inferomarginal spines single, large prominent in series, covered in thick tissue sheath. Inferomarginal plates adjacent to adambulacral plates with no actinal plates.

Furrow spines primarily one per plate, each with well-developed tissue covering.

Two spines per oral plate on the plate apex, with the furrow side spine with eight to ten wrench-like pedicellariae around the base.

Color in life ranges from white with light orange highlights to white.

Images Observed

Blake Ridge, North Atlantic, 32.0124, -75.26125, 3372 m

EX1806_IMG_20180615T174109Z_ROVHD.jpg

EX1806_IMG_20180615T174148Z_ROVHD.jpg

North West Florida Escarpment, 27.70906, -85.74808, 2977 m.

EX1803_IMG_20180427T154746Z_ROVHD.jpg

Material Examined

USNM 1550644 North of Vega Baja, Puerto Rico, 18.8456, -66.3943, 3032 m, Coll. D. Wagner, with ROV Deep Discoverer aboard NOAA Ship Okeanos Explorer. 1 wet spec. 6 arms. R=5.7 r=0.5. EX1811_IMG_ 20181111T 180247 Z_ROVHD.jpg

Figures

FIGURE 2. Ampheraster alaminos comparison. A. and C. USNM 1550644 wet specimen, abactinal surface. Scale-=1.0 cm, and furrow spines. Scale=5.0 mm. B. and D. Holotype, USNM E11397, abactinal surface, scale=1.0 cm, and furrow spines. Scale=5.0 mm.

FIGURE 3. Ampheraster alaminos and Pedicellaster sp. feeding. A. In situ observation of USNM 1550644. B. In situ observation of A. alaminos from Blake Ridge, 3372 m. R=5.7 cm. C. Ampheraster alaminos moving along substrate, North West Florida Escarpment, 2977 m. D. In situ observation of Pedicellaster sp. feeding on sibogolinid worm tubes. WR488 site, 2167 m.