Genus Ophiopyrgus Lyman, 1878

Fig. 3

Type species

Ophiopyrgus wyvillethomsoni Lyman, 1878 .

Examined species

Ophiopyrgus saccharatus Studer, 1882, O. wyvillethomsoni .

Oral GP

Absent.

Adradial GP

Ophiopyrgus saccharatus: rectangular, high, distally swollen, appears rounded axe-shaped in dorsal view, axe-head at abradial edge, adradial side straight, flat, large hole in distal dorsal part, articulates with RS at distal adradial point with round, finer meshed patch. As long as abGP, half as wide. Ophiopyrgus wyvillethomsoni: elongated, irregular, depression in distal abradial edge connects to abGP, flat distal end articulates with RS. Shorter than abGP, half as wide.

Abradial GP

Ophiopyrgus saccharatus: pear-shaped, stout, as long as but twice as wide as adGP, disto-dorsal depression connects to RS, adradial ventro-distal deep depression curves around adGP. Ophiopyrgus wyvillethomsoni: twice as wide as adGP, stout, distally wider than proximally, pear-shaped.

Oral shields

Externally, madreporite not distinguishable. Inner sides not examined.

Radial shield

Ophiopyrgus saccharatus: stout, articular notch in ventro-distal point articulates with adGP, central depression with hole, straight abradial distal edge connects to abGP. Ophiopyrgus wyvillethomsoni: articular structure a low knob/condyle in middle of distal end.

Remarks

The family Ophiopyrgidae contains several paedomorphic genera (Stöhr & Martynov 2016), including the type genus Ophiopyrgus, with a strongly juvenile appearance. Unusual among the studied species is that in O. saccharatus the abradial GP connects broadly to the radial shield, and apart from the oral shield, the abGPs are the only plates on the ventral disc. Externally, the radial shields resemble disc scales in shape and size. Ophiosparte gigas Koehler, 1922 was included in Ophiopyrgidae by molecular data (O’Hara et al. 2017), but its adGP is bar-like, distally inflated, and its abGP is cup-shaped, bearing comb papillae (Martynov 2010), and in combination with other characters, such as the superficial oral tentacle pore, oral papillae similar to Ophiura and the large number of tentacle scales, Ophiosparte is morphologically more similar to Ophiura than to any here analysed ophiopyrgid.