Holopus mikihe, Donovan, Stephen K. & Pawson, David L., 2008

Donovan, Stephen K. & Pawson, David L., 2008, A new species of the sessile crinoid Holopus d’Orbigny from the tropical western Atlantic, with comments on holopodid ecology (Echinodermata: Crinoidea: Holopodidae), Zootaxa 1717, pp. 31-38 : 33-36

publication ID	https://doi.org/ 10.5281/zenodo.274172
DOI	https://doi.org/10.5281/zenodo.6230944
persistent identifier	https://treatment.plazi.org/id/EC51B653-551F-FFA9-6083-FDF2FD0F702A
treatment provided by	Plazi
scientific name	Holopus mikihe
status	sp. nov.

Treatment

Holopus mikihe View in CoL new species

Figures 1 View FIGURE 1 , 2 View FIGURE 2 , 3 View FIGURE 3 E

Holopus rangii d’Orbigny. View in CoL - Donovan, 1992, fig. 1.2; Améziane et al., 1999, table 8, USNM 41507. Non: Holopus rangii d’Orbigny, 1837 View in CoL .

Diagnosis: Holopus with dorsal cup unsculptured apart from faint radial ridges and with proximal secundibrachials bearing strong midaboral tubercles on the external surface.

Material examined: Holotype: USNM E41507, in alcohol. The only specimen known.

Locality: Off Gouldings Key, New Providence, Bahamas, 24º 59' 59" N, 77º 34' 34" W. Dive #JSL-II- 1501, 758 m, 20 Oct 1987.

Description: Stemless crinoid cemented at base to hard substrate ( Figure 3 View FIGURE 3 E), although holotype, about 33 mm high, broken off above attachment area. Walls of dorsal cup thick; broken section 8.6 mm in maximum diameter, but maximum diameter of body cavity only 3.2 mm. Dorsal cup tall (slightly less than 50 % total height of crinoid), pentagonal in cross-section with angles in mid-radius, narrowest just above attachment and widest at oral surface, not perfectly pentagonal conical, but skewed slightly to one side ( Figures 1 View FIGURE 1 , 2 View FIGURE 2 A, B). No plate sutures apparent within cup. Radial facets wide, in contact, scalloped; scalloping apparent on surface of cup as faint stacked growth (?) lines. External coloration purple.

Arms branch once at IBr1. Ten arms, uniserial, consisting of circa 30 brachials ( Figure 2 View FIGURE 2 C–F). Arms divided into a bivium of two shorter arms and trivium of three longer arms. Arms enrolled and in close contact; sutures between arms crenulated, giving the crown the appearance of a clenched, ten-fingered fist. Arms strongly tapered towards the distal end and geniculated at about IIBr8-9, after which arms become much narrower ( Figure 2 View FIGURE 2 C, F). The primaxillary (IBr1) is large, broad, pentagonal in external view, swollen on aboral surface and with two low tubercles towards the center corresponding to the base of faint, low ridges that continue distally. Proximal facet broad with a central, oval axial canal and a broad, V-shaped adoral groove; distal facets equal in size. Proximal secundibrachials wedge-shaped and with large raised midaboral tubercles on each. Adoral groove central, parallel to long axis of arm and with lateral branches extending to pinnule facets. Cover plates small, polygonal.

All brachials except IBr1 pinnulate. Pinnules situated on alternate sides of arms on adjacent brachials, curling adorally when enrolled ( Figure 2 View FIGURE 2 C, F), and composed of broad, low ossicles.

Mouth bordered by five triangular oral plates. Anal pyramid located to left of removed arm, that is, this arm represents the C ray. Thus, B-C-D is the trivium and E-A the bivium.

Ecology: Like its congener H. rangii , H. mikihe lives attached to a hard rock substratum ( Figure 3 View FIGURE 3 E), in this case an almost vertical rock face a few meters above the sediment-covered seabed. Apparently, the single specimen was not observed in the open position.

Etymology: The trivial name of this species, mikihe , is derived from the first two letters of the surnames of colleagues who were involved in the 1983–1989 echinoderm research on the Johnson-Sea-Link I and II. The first syllable, “mi-”, is from John E. Miller. The second syllable, “-ki-”, is from Porter M. Kier. The third syllable, “-he”, is from Gordon Hendler.

Remarks: Although based on a single specimen, the distinctive morphology is sufficient to warrant recognition of a new species. Of the three known species of Holopus , H. rangii (tropical western Atlantic; see, for example, Springer, 1924, pls 1–3; Rasmussen, 1978, fig. 562.1a, d; Grimmer & Holland, 1990, fig. 1; Donovan, 1992, fig. 1.1) and H. alidis (southwest tropical Pacific; see Bourseau et al., 1991, pl. 12, figs 1–5) are much closer to each other in gross morphology than either is to H. mikihe , despite their wide geographic separation. Indeed, the strongly spinose arms of H. mikihe are distinct from those of all known holopodids ( Heinzeller et al., 1996, pp. 82–83). Such a strongly spinose crown is more reminiscent of some Paleozoic crinoids, although there are other post-Paleozoic exceptions (such as Simms, 1989, pl. 13, fig. 1).

As noted above, we regard previous instances where H. rangii and H. mikihe were ‘lumped’ together to be no more than that. In addition to the obvious morphological differences, H. mikihe comes from a greater water depth than any other Holopus . David et al. (2006) distinguished three western Atlantic subspecies of the sea lily genus Endoxocrinus , partly on the basis of their bathymetric separation. Holopus mikihe is considered to be most closely related to H. rangii , as both species lack an abrupt bend of the arms, a feature of H. alidis and Cyathidium spp. ( Heinzeller et al., 1996, fig. 4).