The disk is round, slightly inflated, and flexible. The disk diameter measures 7.6 mm. The primary plates are distinguishable as larger round plates among smaller round imbricating scales. There is a distinct border between the dorsal and ventral disk, and the ventral scales are smaller, visible from above in the interradii. The border bears a fringe of low conical spines that continue across the arm base. Several of the spines lateral of the arm base bear a similarity to an ‘arm comb’. The radial shields measure about one-tenth of the disk diameter, and are oval, being twice as long as they are wide, and are widely separated by several overlapping disk scales.

The dorsal arm plates are fan-shaped from the fourth segment, and are twice as wide as long, with a convex distal edge, and an acute proximal angle, with the following plates contiguous. The first two dorsal arm plates are reduced to short overlapping bands across the arm, but do not form a wedge between the radial shields. The third plate is half as long as the following plates. There are up to five equal, smooth arm spines that are slightly longer than an arm segment. They are erect on a pronounced articulation ridge.

The ventral scales strongly overlap, and in bulging parts almost stand vertically on edge, with their full size visible only at the bursal edge. The jaws bear 1-2 slender pointed apical papillae, block-like teeth that are twice as wide as the apical papillae, and four flat, pointed oral papillae along each lateral jaw edge, which distally increase in width. The second tentacle pore is inside the mouth slit, and bears two low wide scales; one on the oral plate, and a smaller one on the adoral shield. The adoral shields are flaring, extending around the lateral angles of the oral shield. The oral shield is pentagonal, with strongly convex distal and lateral edges, whilst the proximal edges are slightly concave, and are shorter than one-eight of the disk diameter. There are two flat tentacle scales on all the pores, parallel to each other with a straight inner and convex outer edge. A slightly shorter one arises from the lateral plate, and a longer one arises from the ventral plate. The ventral arm plate is pentagonal, wider distally than proximally, and slightly wider than it is long. The adjacent plates are contiguous, and there is a concave notch in distal edge. The lateral edges are concave, and the proximal angle is obtuse. The bursal slit extends from the oral frame to the disk edge, and there are no genital papillae. The colour of specimens preserved in alcohol is cream.

(Stohr & Segonzac, 2005)

Blake Ridge cold seep off South Carolina (32°29.62'N, 76°11.47W), 2, 155 m, among Bathymodiolid mussels (Stohr & Segonzac, 2005).

Holotype for Ophienigma spinilimbatum Stohr & Segonzac, 2005
Catalog Number: USNM 1026303
Collection: Smithsonian Institution, National Museum of Natural History, Department of Invertebrate Zoology
Preparation: Dry
Collector(s): C. Van Dover
Year Collected: 2001
Locality: Blake Ridge, at cold seep site, South Carolina, United States, North Atlantic Ocean
Depth (m): 2155 to 2155
Vessel: Alvin DSR/V

Paratype for Ophienigma spinilimbatum Stohr & Segonzac, 2005
Catalog Number: USNM 1026304
Collection: Smithsonian Institution, National Museum of Natural History, Department of Invertebrate Zoology
Preparation: Alcohol (Ethanol)
Collector(s): C. Van Dover
Year Collected: 2001
Locality: Blake Ridge, at cold seep site, South Carolina, United States, North Atlantic Ocean
Depth (m): 2155 to 2155
Vessel: Alvin DSR/V

Depth range based on 4 specimens in 1 taxon.
Water temperature and chemistry ranges based on 4 samples.

Environmental ranges
  Depth range (m): 2155 - 3050
  Temperature range (°C): 2.889 - 4.250
  Nitrate (umol/L): 18.415 - 24.434
  Salinity (PPS): 34.944 - 34.979
  Oxygen (ml/l): 5.035 - 6.021
  Phosphate (umol/l): 1.225 - 1.485
  Silicate (umol/l): 15.157 - 34.435

Graphical representation

Depth range (m): 2155 - 3050

Temperature range (°C): 2.889 - 4.250

Nitrate (umol/L): 18.415 - 24.434

Salinity (PPS): 34.944 - 34.979

Oxygen (ml/l): 5.035 - 6.021

Phosphate (umol/l): 1.225 - 1.485

Silicate (umol/l): 15.157 - 34.435
 
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