Ophiacantha vivipara Ljungman, 1871

Brogger, Martin I. & O'Hara, Timothy D., 2015, Revision of some ophiuroid records (Echinodermata: Ophiuroidea) from Argentina, Zootaxa 3972 (3), pp. 432-440 : 432-435

Ophiacantha vivipara Ljungman, 1871

( Fig. 1 )

Ophiacantha vivipara Ljungman, 1871: 471 .— Lyman, 1878: 149.— Lyman, 1882: 185 –186, pl. 46(7–9).— Studer, 1882: 23 – 24.— Koehler, 1907: 321 –323 (in part).— Koehler, 1908: 276.— Koehler, 1914: 96.— Koehler, 1922: 12 –13.— Mortensen, 1936: 246 –248, fig. 5a, pl. 7(2).— Bernasconi, 1965: 151 –152.— Castillo-Alarcón, 1968: 45 –47, fig. R, pl. 1(4,6).— Bernasconi, 1973: 331 –332.— Bernasconi & d'Agostino, 1977: 107 –109, pl. 10(3,4).— Lucchi, 1985: 133 –134, fig. 49–50. Ophiacantha ingrata .— Bernasconi & d'Agostino, 1975b: 19 –21, pl. 1(3 –4).— Bernasconi & d'Agostino, 1978: 217 [Non Ophiomitrella ingrata Koehler, 1908 ].

? Ophiacantha vivipara .— Tommasi et al., 1988: 6.

Material examined. Argentina. Isla de los Estados (between Cabo San Juan and Punta Fallows), 54° 45.677´S, 63° 49.114´W, 54 m, 1934, identified by Bernasconi & d'Agostino (1977) ( MACN 21956, n=3). East of Isla de los Estados, 54° 47´S, 63° 35´W, 144 m, 1933 ( MACN 22277, 13). 38° 31´S, 55° 42´W, 109 m, 1938, identified by Bernasconi & d'Agostino (1977) ( MACN 23346, 3). 39° 28´S, 57° 2´W, 90 m, 1941, identified by Bernasconi & d'Agostino (1977) ( MACN 25122, 5). 12 miles east from Punta Médanos Lighthouse, 39° 30´S – 40° 11´S, 109 m, 1924, identified by Bernasconi & d'Agostino (1977) ( MACN 14423, 15). Océano Atlántico Sur, 54° 52´S, 37° 28´W ( MACN 28128, 3). M2: stn E9, off Mar del Plata, 38° 50.91´S, 55° 34.585´W, 140 m, 2009 ( MACN, 15). Walther Herwig: stn 277, 40 ° 54´S, 56° 49´W, 300 m, identified by Bernasconi (1973) ( MACN 27263, 1). South Georgia. Grytviken, 54° 16.905´S, 36° 30.394´W, 0 m, 1933, identified by Bernasconi & d'Agostino (1975b) as Ophiacantha ingrata ( MACN 26927, 12). Puerto Larsen, 25–27 m, 1929, identified by Bernasconi & d'Agostino (1975b) as Ophiacantha ingrata ( MACN 18768, 1). Bahía Antartica, 35–36 m, 1929, identified by Bernasconi & d'Agostino (1975b) as Ophiacantha ingrata ( MACN 18760, 21). Islas Orcadas: stn 18, Georgias del Sur, 54° 21´S, 36° 1´W, 106 m, 1975, identified by Bernasconi & d'Agostino (1978) as Ophiacantha ingrata ( MACN 28139, 4). South Sandwich Is. Islas Orcadas: stn 21, Sandwich del Sur, 57° 47´S, 26° 26´W, 105 m, 1975, identified by Bernasconi & d'Agostino (1978) as Ophiacantha ingrata ( MACN 28127, 2). South Shetland Is. 61° 26´S, 56° 25´W, 1975 ( MACN 34933, 25).

Distribution. Malvinas / Falkland Islands, South Georgia, Patagonia to Uruguay (north to 37°S), Chile (north to 50°S), Brazil? Macquarie Ridge, 0–1100 m.

Remarks. Bernasconi & d'Agostino (1975b, 1978) record a series of specimens from South Georgia and South Sandwich Islands under the name “ Ophiacantha ingrata ( Koehler, 1923) ”. This is an invalid name, as Koehler did not describe a species under this name in 1923, but included photographs of both five and six-armed specimens under the previously described Ophioripa ingrata Koehler, 1908 . The five-armed individuals ( Koehler 1923, pl. 14, fig 5–6) have the characteristic small rounded granules and thick blunt arm spines found on the holotype of O. ingrata , which has been subsequently transferred to the genus Ophiomitrella (see O’Hara 1990). Bernasconi & d'Agostino (1975b) are possibly correct in identifying as a separate species the small (<6 mm d.d.) six-armed specimen photographed by Koehler (1923, pl. 14, fig 5–6), with its even covering of small conical spinelets, but they are in error to re-use the specific epithet ( ingrata ) in a separate genus ( Ophiacantha ) and then attribute this name to Koehler (1923) (who actually considered both photographs to represent the same species).

Bernasconi & d'Agostino (1975b) noted the similarity of their material to the widespread species Ophiacantha vivipara , distinguishing the two species by the number of arm spines, 7–8 in “ O. ingrata ” and 10–12 in similar sized (16 mm d.d.) O. vivipara . In their synonymy of “ ingrata ”, they included a photo of a six-armed specimen from Marguerite Bay, Antarctica attributed to O. vivipara by Koehler (1912, pl. 11, fig. 2). Koehler (1912) also included a photograph of a similar looking five-armed individual (pl. 11, fig. 1). Mortensen (1936) interpreted these photographs differently. He considered the six-armed specimen to represent O. vivipara and described the five armed form as a separate variety O. vivipara var pentactis which he also distinguished on the basis of reproduction (the presence of males in pentactis ) and biogeography (no five armed specimens occur on the Patagonian Shelf), but not arm spine number. Ophiacantha pentactis was subsequently raised to species rank by Madsen (1955). Fell (1961) found no difference in arm spine number (11–12) or disc spines between his six- and five-armed specimens from the Ross Sea.

The true identity of Ophiacantha vivipara is complicated by the uncertainty over the type locality. Ljungman (1871) recorded it from Altata off the Pacific coast of Mexico, however, this locality has been rejected by a series of authors and the presumed locality is now considered to be the Malvinas / Falkland Islands ( Bell 1908; Fell 1961).

There have been two molecular studies that have shed light on the phylogenetic relationships within the Ophiacantha vivipara complex. Martin-Ledo et al. (2013) found several distinct phylogenetic clades from around Shag Rock near South Georgia that they identify as O. vivipara , O. pentactis , the five-armed O. densispina Mortensen, 1936 , a new five-armed species O. wolfarntzi , and an undescribed five-armed species (sp. 1). O’Hara et al. (2013, 2014) found three clades within O. vivipara and several others which were similar to the five-armed O. rosea Lyman, 1878 . The three clades of “ vivipara ” had separate distributions: ‘A’ was predominantly circum- Antarctic, ‘B’ was subantarctic and ‘C’ occurred mainly around southern Australia and New Zealand. Clade A included both five and six-armed individuals, the others only six-armed forms. A direct comparison of the COI sequences (O’Hara unpublished data) has revealed that clade A is the same as the clade identified by Martin-Ledo et al. (2013) as O. pentactis and B as O. vivipara .

In summary, there are at least three clades with six-armed forms (as well as numerous clades with only fivearmed individuals) within this complex. One clade (clade B of O’Hara et al. 2013 and the vivipara of Martin-Ledo et al. 2013) is known to occur on the Patagonian Shelf, South Georgia and the Macquarie Ridge. Presumably this clade is the one that also occurs further north along the Argentinean coast to Uruguay and in the fjords of southern Chile (although this should be checked with genetic data). It may also occur on other subantarctic islands. The second clade (clade A of O’Hara et al. 2013 and pentactis of Martin-Ledo et al. 2013) is circumpolar Antarctic as well as occurring around South Georgia ( Martin-Ledo et al. 2013), South Orkney and Bouvet Islands, and on the southern Macquarie Ridge (O’Hara et al. 2013). It appears to include both five and six-armed individuals, although this should be confirmed with a study using faster evolving genetic loci than COI which is known to be unable to discriminate some echinoderm species pairs ( Williams 2000). The third clade (clade C of O’Hara et al. 2013) occurs on seamounts around southern Australia and New Zealand and along the northern Macquarie Ridge. A plausible hypothesis is that these clades represent O. vivipara , O. pentactis and an undescribed Ophiacantha species respectively. Thus many of the records from Antarctica previously considered O. vivipara (e.g. Bell 1908; Koehler 1912, 1922; Fell 1961; Madsen 1967; McKnight 1967b) are six-armed O. pentactis specimens, and records from Australia and New Zealand ( O’Hara et al. 2008) are an undescribed species.

The identity of specimens found in other regions remains unclear. No genetic sequences are currently available from specimens collected around Crozet, Marion, Kerguelen or Heard Islands. Specimens from around Kerguelen are frequently seven armed and may be “ vivipara ” (although the name Ophiacantha kerguelensis Studer, 1876 is available if specimens from this remote location form a distinct clade). Northern records, such as those found off Brazil (Tommasi 1970; Tommasi et al., 1988), need to be critically compared with the six-armed Ophiacantha anomala Sars, 1871 from the North Atlantic.

To test whether arm number or maximum arm spine number varied between the two western hemisphere clades as suggested by Mortensen (1936) and Bernasconi & d'Agostino (1975b), we compared the abundant material in the MACN from two regions: a) the Patagonian Shelf off Argentina and Uruguay (33–55°S) and b) the South Sandwich and South Shetland Islands (57–62°S). The first group (n=59) presumably representing “ vivipara ” and the second “ pentactis ” (n=26). Specimens from South Georgia were excluded from the analysis as this locality may represent a zone of overlap of the two species. We performed ANCOVA (Analysis of Covariance) analyses with region as the categorical variable and disc diameter as the co-variant, as both arm and arm-spine number are potentially related to animal size. We rejected the null hypothesis (no difference between groups, p=0.000) for both arm number and arm spine number ( Fig. 1 A & B). Animals from the Patagonian Shelf (“ vivipara ”) had 6–7 (rarely 8) arms while those from further south (“ pentactis ”) had 5–6. Patagonian Shelf specimens tended to have more arm spines at any given disc diameter, however, the maximum arm spine number (n=11) was the same for both forms. In summary, there is no simple dichotomous character to distinguish 6-armed specimens of the two forms. This makes the identity of specimens from South Georgia problematic, as 26 of the 27 specimens examined from there had 6 arms (the last 7). However, many had relatively few arm spines at small to medium disc diameters and so appear to fit the profile of “ pentactis ” rather than “ vivipara ” ( Fig. 1 C), although the data is not conclusive and needs to be confirmed with a molecular study.

Consequently the final identity of Bernasconi & d'Agostino “ ingrata ” specimens remains uncertain as both O. vivipara and O. pentactis are possibly present at South Georgia. However, “ Ophiacantha ingrata ” (as distinct from Ophiomitrella ingrata ) can be removed from the list of species known from the region.

Figures

FIGURE 1. Graphs of Analysis of Covariance of arm number (A) and arm spine number (B, C) of MACN specimens of “ Ophiacantha vivipara ” from the Patagonian Shelf (n = 59), South Georgia (n = 26, fig. 1 C only) and South Shetland / Sandwich Islands (n = 26). All analyses were significant, i. e. arm number and arm spine number differed between populations when disc diameter was incorporated as a covariate.