Ophiocoma marmorata Marktanner-Turneretscher, 1887

Stöhr, Sabine, Boissin, Emilie & Hoareau, Thierry B., 2013, Taxonomic revision and phylogeny of the Ophiocoma brevipes group (Echinodermata, Ophiuroidea), with description of a new subgenus (Breviturma) and a new species, European Journal of Taxonomy 68, pp. 1-26 : 20-23

Ophiocoma marmorata Marktanner-Turneretscher, 1887

Ophiocoma marmorata Marktanner-Turneretscher, 1887: 303 , pl. 12 figs 16, 17.

non Ophiocoma dentata – Devaney 1970: 17.

Material examined

NHMW 3. Zool. Abt. Nr. 10.466

Collection Eichhorn 2873, 0- 7°N, 23- 25°W (= Tropical Atlantic). Lot of 5 spms, wrongly registered as “ syntypes ”. One very obviously belongs to another species and was not examined more closely. Examined, photographed and data transmitted by A. Kroh, Vienna. Each spm is treated separately below.

Description

Holotype NHMW 10.466 a

8.7 mm dd, dorsally light orange colour pattern with darker spots on arms, ventrally cream coloured, spines white, not annulated, arm spine sequence (2)3, 3, 3, 3(4), 4, 4, 4, 3(4), 4, 3(4), 4(3), 3(4), 4(3), 3, 4, 3 (numbers vary between arms and alternate between segments), oral shield longer than wide. Granule density about 80 mm-2. Holotype status inferred from original description.

NHMW 10.466b

6.3 mm dd, cream colour dorsal and ventral, no pattern, coarser granules than holotype, arm spine sequence 3, 3, 3(4), 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4. Granule density 60 mm-2.

NHMW 10466c

6.1 mm dd, cream colour dorsal and ventral, no pattern, coarser granules than holotype, arm spine sequence 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4. Granule density 48 mm-2.

NHMW 10.466d

5.2 mm dd, cream colour dorsal and ventral, no pattern, coarser granules than holotype, arm spine sequence 3, 3, 4, 4, 4, 4(5), 4(5), 4, 4, 4, 4, 4, 4, 4, 4. Granule density 60 mm-2.

Remarks

The original description of O. marmorata mentions only a single specimen of 9 mm dd (Marktanner- Turneretscher 1887), which should be regarded as the holotype. The remaining three specimens cannot be regarded as type material since they are not mentioned in the description. The locality of O. marmorata is most likely incorrect as it lies in the middle of the Atlantic Ocean at great depth. Ophiocoma is a shallow water tropical genus, rarely reported below 100 m depth. Taking into account that the determination of coordinates, in particular longitude, was difficult and often inaccurate in the 19 th century, we think it possible that the correct locality may be the Saint Peter and Saint Paul Archipelago, which is situated at 0.9°N, 29°W, assuming that the data are based on the Greenwich Meridian. Instead, the Ferro Meridian may have been used, which would put the locality at 40°40’- 42°40’W today, even closer to Brazil. The specimens were bought by director Eichhorn of Graz ( Austria) from the trader Hugo Schilling in Hamburg in 1882, together with several other echinoderms, and transferred to the natural history museum in Vienna (A. Kroh, pers. comm.).

The alternating spine sequence of the holotype of O. marmorata may be interpreted as an unusual variation, if we accept that it is conspecific with the three smaller specimens in the lot. This character is typical for species in the scolopendrina group though and therefore the holotype of O. marmorata may belong to one of the species in that group, possibly O. echinata (Lamarck, 1816) or O. wendtii Müller & Troschel, 1842 , which are the only two species of that group known from the Atlantic Ocean. The smaller specimens, however, may belong to a different species, possibly O. pumila Lütken, 1856 , a member of the pumila group, which has a spine sequence similar to the smaller O. marmorata (NHMW 10.466b-d) and is known from the Atlantic. Devaney (1970) does not seem to have examined O. marmorata and did not know about the existence of five spines on one of the specimens in the lot. He also did not consider the significance of geographic distribution when he suggested that O. marmorata (an Atlantic species) may be conspecific with O. dentata (an Indo-Pacific species). Although the fifth arm spines in the small O. marmorata are in exactly the same position, arm segments 6 and 7, as in O. krohi sp. nov., the granules in these small specimens are high and pointed, different from those found in the species of Breviturma subgen. nov. Granules like that are known from the pumila group. The holotype of O. marmorata has low round granules, which also supports that it is a different species from the three smaller specimens.

The taxonomic status of O. marmorata could not be completely resolved by this study and requires further investigation, but we strongly doubt that it is conspecific with O. dentata . We propose that the synonymy of O. dentata includes only O. ternispina , O. insularia and O. variegata .

Remarks on species delimitations

Prior to Devaney’s (1970) work, the three species previously recognized in the brevipes group were considered mere variations of a single species. Devaney (1970) was able to separate them by spine sequence, colour pattern and arm width. In addition to the annulated colour pattern of the arm spines, spine numbers seem to be a critical character to distinguish between O. dentata and O. doederleini . According to Devaney (1970), O. dentata has five arm spines only at disc diameters above 20 mm and spine numbers decrease to three on the middle arm (beyond segment 17 at 13-14 mm dd, beyond segment 25 at 24 mm dd), whereas four spines are found on far more distal arm segments in O. doederleini of similar disc sizes (to segment 32-38 at 13-14 mm dd, to segment 55 at 24 mm dd). In light of our findings ( Table 1 ) we cannot exclude though that the specimens regarded as O. dentata by Devaney actually included individuals of O. krohi sp. nov.. All of his data must therefore be treated with caution. The type of O. dentata (18-19 mm dd) has up to four spines on the proximal arm segments, decreasing to three from segment 13, which contradicts Devaney’s (1970) observations. Our largest specimen of O. dentata has two occurrences of five spines among all ten sides of the arms, and three spines from segment 16.

In the type material of O. brevipes , spine numbers appear to be uncorrelated with disc size; five spines are present from the fourth, fifth or sixth segment and for a variable number of segments before the number drops to four and finally three again on the distalmost part of the arm. The smallest type, at 12 mm dd, shows 12 segments with five spines, whereas the largest, at 17-18 mm dd shows only six segments with five spines; in both animals there are five spines from the sixth segment. Similarly, spine numbers vary between specimens on the types of the three nominal species currently regarded as conspecific with O. dentata . In O. krohi sp. nov., the smallest specimen has five spines on two segments, while the largest one has only up to four spines. These variations are common in the genus Ophiocoma as was observed already by Devaney (1970). We also found significant differences in granule density among species as shown in Fig. 7 (Kruskal-Wallis test, K=8.9055, d.f.=3, P =0.0306). Likewise, granule sizes and/or densities may be subject to growth changes as suggested by the inverse correlation observed between the granule density and the disc diameter in O. krohi sp. nov. (Spearman test, R =-0.8012, P =0.0006). The smallest O. krohi sp. nov. had 152 granules/mm 2, whereas the largest one had only 64-96 granules/ mm 2. Small O. dentata have three times higher granule densities as large ones, which suggests that granule numbers do not increase with growth. Somewhat contradictory are the data for O. brevipes , where specimens from La Réunion have greater granule densities than similar size specimens from Madagascar.

We decided to examine a rarely used character, granule density, that has occasionally been mentioned in species descriptions and revisions, but never been used in a systematic way to differentiate Ophiocoma species. Devaney (1970) used granule densities as a character in his key to the species of the scolopendrina group, but only for few of the species. Granule densities were compared between light images and SEM images of the same animal and the small observed differences can probably be attributed to uneven distribution of the granules on the disc, rather than to a real difference in accuracy between these methods. Our method of counting granules on digital images resulted in considerably higher numbers than what has been published before. However, published values are not always related to size and as we see in our results, the largest specimens have larger and fewer granules. It is also possible that counts on images are more accurate than counts under the dissecting microscope. In any case, since we used the same method for all specimens, the differences between them are valid and important.

Devaney (1970) examined arm span on the 10 th free segment, “composed of the length of the longest arm spines on each side of a segment, the breadth of the dorsal arm plate and the breadth of the lateral arm plates” (cited from Devaney 1970), and found larger arm spans in O. doederleini than in O. dentata . However, his values overlap and vary uncorrelated to size, and we consider this a weak character that is difficult to assess.

Figures

Fig. 7. Granule densities in relation to disc diameter of the examined nominal species of Ophiocoma, from Table 1.