Ophioderma zibrowii, Stöhr & Weber & Boissin & Chenuil, 2020

Stöhr, Sabine, Weber, Alexandra Anh-Thu, Boissin, Emilie & Chenuil, Anne, 2020, Resolving the Ophioderma longicauda (Echinodermata: Ophiuroidea) cryptic species complex: five sisters, three of them new, European Journal of Taxonomy 600, pp. 1-37 : 28-32

Ophioderma zibrowii sp. nov.

urn:lsid:zoobank.org:act:7FB245FD-C8DF-402A-A7B1-FA7D048AFB04

Figs 11–12 ; Table 1

Diagnosis

Usually naked radial shields. Seven arm spines. Eight oral papillae. Colour pattern greenish brown to dark green variegated on dorsal and ventral disc, arms banded, with light and dark spots along distal dorsal plate edges, oral frame and ventral arms lighter. Largest known size 21 mm dd. Brooder.

Etymology

The species is named after Helmut Zibrowius for his important contributions in collecting material for this study. The existence of brooding Ophioderma in the Mediterranean Sea might still be unknown without his effort.

Material examined

Holotype

MEDITERRANEAN SEA • ♀ (brooding); southern Crete, Agios Pavlos ; May 2012; A. Weber leg.; preserved in 95% ethanol; SMNH-Type-9188.

Paratypes

MEDITERRANEAN SEA • 1 ♀ (brooding); same data as for holotype; SMNH-Type-9189 • 7 specimens; Greece, Symi Island , near Rhodes, Agios Georgios; 10 Aug. 2005; R. Graille leg.; preserved in 95% ethanol; SMNH-Type-9190 to 9196 .

Other material

MEDITERRANEAN SEA • 18 specimens (mitochondrial COI lineage L3, nuclear cluster C5); Greece, northwestern Crete, Elounda, Plaka Beach ; 2 Jul. 2008; Emilie Aegea leg.; preserved in 95% ethanol; SMNH-102712 , 113690 to 13697 , 11370 to 113704 , 113709 to 113712 • 21 specimens (mitochondrial COI lineage L3, nuclear cluster C5); Greece, Rhodes, Kallithea Bay ; 9 Sep. 2005; H. Zibrowius leg.; preserved in 95% ethanol; SMNH-99657 , 113982 , 113985 , 113987 to 113990 , 113992 to 114003 , 114005 , 114006 • 41 specimens (mitochondrial COI lineage L3, nuclear cluster C5); Greece, Crete; May 2012; A. Weber leg.; preserved in 95% ethanol; SMNH-147070 • 1 specimen (dd = 15.4 mm), dried dissociated ossicles and ossicles on two SEM stubs; same data as for preceding; SMNH-178455 .

Description

Holotype ( Fig. 11 )

Disc diameter 14.3 mm, one intact arm, all others removed for molecular analysis. Dorsal disc with dense cover of granules, radial shields naked, widely separated, visible part oval ( Fig. 11A ). Granules and scales crowd onto basal arms. Dorsal arm plates single on all joints, flat, overlapping, broadly fanshaped, twice as wide as long, with straight edges, wider distally than proximally ( Fig. 1D ). Up to seven conical, slightly pointed arm spines, about equal in length, half as long as arm joint, ventralmost spine thicker than others and blunt ( Fig. 7C ). Ventral disc covered by granules similar to dorsal disc. Adoral shields and oral plates covered by granules, oral shields naked ( Fig. 11B ). Seven to eight oral papillae, Lyman’s ossicle elongated, pointing into mouth slit, adoral shield spines two, block shaped, other papillae smaller, conical ( Fig. 11E ). Tooth papillae larger, conical, two in line with oral papillae. Oral shields triangular, twice as wide as long, straight distal edge, obtuse rounded proximal angle. Madreporite as wide as long. Adoral shield long, narrow, extending around the lateral edge of the oral shield, separating it from the arm. Adoral shields covered with granules, similar to disc granules. Proximal genital slits parallel to and as long as first and second joints. Distal genital slit parallel to and as long as fourth joint, at distance from disc edge. Bursae filled with brooded juveniles ( Fig. 11F ).

Dorsal disc slightly variegated dark brown-green with grey, dorsal arms greyish green with brown bands, each light and dark band about three joints wide, a series of larger white and smaller black spots along the distal edge of each dorsal arm plate ( Fig. 11A, D ). Ventral disc as dark as dorsal, oral frame and ventral arms lighter grey-green ( Fig. 11B ). Arm spines grey-green with white tips, except ventralmost spine, which is white ( Fig. 11 C–D). Oral papillae and tentacle scales white ( Fig. 11C, E ).

Paratypes

Disc diameter 9.7–13.5 mm.All have up to seven arm spines. Most paratypes have a green colour pattern similar to the holotype, one specimen is olive-brown. One paratype with granule-covered radial shields, all others naked. Oral papillae eight, in two specimens nine, but variable between jaws in an individual. Two specimens with two dorsal arm plates on 2–3 proximal joints on 1–3 arms. One specimen with 2–3 dorsal arm plates on proximal joints on three arms, on seven joints on one of those arms. One specimen has a parasitic snail ( Ersilia Monterosato, 1872 sp.) on one arm. All paratypes lack part of an arm, which was used for molecular analysis.

Non-paratypes (SMNH-147070)

Disc diameter 8.4–20.5 mm. Specimens smaller than 10 mm dd had six arm spines, all others seven. Most specimens have a green colour pattern similar to the holotype, several were dark olive with numerous white granules scattered across the disc. Out of the 42 specimens, a single one had granule-covered radial shields, all others with naked radial shields. Most of the specimens above 10 mm dd had at least two proximal arm joints on at least one arm with two dorsal arm plates, up to seven joints and several arms with double plates in one animal. The plates were usually of equal size or there was a hairline crack along the midline of the plate. Rarely, a third dorsal arm plate was present on one or two joints. Oral papillae eight, rarely nine, but variable between jaws in an individual and not correlated to size. These specimens were used for thermotolerance and regeneration experiments. These specimens were kept in an aquarium for a year where experiments of thermotolerance and regeneration were conducted. Therefore, most arms show signs of regeneration. One specimen had bright white distal arms but no sign of healed breaks. Maximum size recorded for O. zibrowii sp. nov. was 21 mm dd ( Weber et al. 2014).

Skeletal elements ( Fig. 12 )

Non-type specimen of 15.4 mm dd (SMNH-178455), completely dissociated. Radial shields elongated isosceles triangular, external surface with embossed oval of more finely meshed stereom in center of domed and thickened proximal half (only visible part in intact skeleton), row of eight pores curves around proximal dome ( Fig. 12A, C ). On inner side of radial shield, a large pore on distal half and a round patch with denser stereom, two low distal bulbs separated by a furrow ( Fig. 12B ). Dental plate consists of several pieces, sockets not penetrating the plate, bordered by low rim, tooth papillae sockets smaller, round, tooth sockets wide, oval ( Fig. 12D ). Adradial genital plate blade-like flat with bulbous distal end and large pore, distal pit with knob on one side, three ridges on other side ( Fig. 12 E–F). Abradial genital plate much smaller and scale-like flat, distally wider than proximally ( Fig. 12G ). Oral plates longer than high, middle part markedly lower than ends, abradial muscle fossa rounded triangular, not reaching upper edge ( Fig. 12H ). On adradial oral plate proximoventral part four oral papilla sockets and pores, at proximoventral edge four granule sockets and pores ( Fig. 12I ). Vertebrae typically zygospondylus, with large dorsal and small ventral muscle flanges, no growth rings obvious ( Fig. 12 J–K). Lateral arm plates compact, weakly curved around the arm, strongly convex distally, concave proximally, with ventral excavation for tube foot opening ( Fig. 12 L–M). Two spurs at proximal external edge and counterparts on internal distal edge of lateral arm plates. Internal lateral arm plate with vertical row of three pores just below the plate centre, distal to curved vertical ridge, fourth pore in tentacle opening edge, small ventral knob, protruding beyond plate edge. Spine articulations inset in the distal plate edge with one thickened lobe, separating muscle and nerve opening.

Remarks

The species determination rests mainly on the genetic analyses. We chose the predominant genetic group (C5) to describe a new species, but due to its short reproduction period (May–June, Weber et al. 2014) most specimens of this cluster happen to have been collected outside the brooding time. Since brooding is one of the key characters of this species, we felt that the holotype should be a brooding female. It is not ideal that the chosen animal has only a single intact arm remaining, but in a pentaradially symmetric animal one arm is sufficient and representative of the others.

Morphological differentiation from O. longicauda rests on the usually naked radial shields and the single, flat arm plates. Also, O. zibrowii sp. nov. usually lacks red pigments which are common in O. longicauda , whereas green pigments are common in O. zibrowii sp. nov. but absent in O. longicauda . In addition, O. zibrowii sp. nov. commonly has a series of white and black spots along the distal edge of the dorsal arm plates, which are shared with O. hybrida sp. nov. and O. guineense . The radial shields differ microscopically from those of O. longicauda in the clear demarcation of an embossed part with finer meshed stereom, representing the naked visible part of the radial shields in the intact animal. The major part of the radial shield is overlapped and covered by disc scales, obscuring its true shape. Possibly, the more elongated oral plates and higher lateral arm plates in O. zibrowii sp. nov. distinguish the species, but these small differences need to be studied with morphometric methods and larger samples.

Brooding females have been collected from Cyprus and Lebanon, but they belong to another genetic cluster (C6). Morphologically they cannot be distinguished at this time and we consider them to be allopatric populations within the same species. They are excluded from the concept of the new species O. zibrowii sp. nov., as new evidence may in the future lead to them being recognized as a different species.

Figures

Fig. 11. Ophioderma zibrowii sp. nov., holotype (SMNH-Type-9188), digital images. A. Dorsal aspect, note the naked radial shields. B. Ventral aspect. C. Ventral arm. D. Dorsal arm, note the entire plates. E. Jaw. F. Brooded juveniles in interradius (arrow). Abbreviations: DAP = dorsal arm plate; M = madreporite; OS = oral shield; RS = radial shield; VAP = ventral arm plate.

Fig. 12. SEM images of skeletal elements of Ophioderma zibrowii sp. nov., from non-type specimen of 15.4 mm disc diameter (SMNH-178455), Crete, Greece. A. Radial shield, external aspect, white arrows point to larger peripheral pores. B. Radial shield, internal aspect. C. Scale-free part magnified from Fig. 12A, note the absence of pores on the denser area (naked in intact animal, see Fig. 11A). D. Dental plate fragments. E. Adradial genital plate, lateral aspect. F. Distal end of Fig. 12E. G. Abradial genital plate. H. Oral plate, abradial face. I. Oral plate, adradial face, black arrows point to oral papillae sockets and pores. J. Arm vertebra, proximal face. K. Arm vertebra, distal face. L. Lateral arm plate, external face. M. Lateral arm plate, internal face. Abbreviations: dist = distal; dors = dorsal; prox = proximal; Sp = spurs; vent = ventral.

Fig. 1. Phylogenetic relationships and distribution of species of Ophioderma Müller & Troschel, 1840 in the Northeast and Tropical Atlantic Ocean and the Mediterranean Sea. A. Simplified phylogenetic relationships among species of Ophioderma described in this study, modified from Weber et al. (2019). Summary of reproductive strategy: S = broadcast spawner; B = brooder. Correspondence between species names, nuclear genetic clusters and COI mitochondrial lineages is summarized from Boissin et al. (2011) and Weber et al. (2019). C6 is tentatively assigned to O. zibrowii sp. nov. because it occurs far from the type locality and brooding species are expected to have low dispersal rates, leading to low gene flow between populations. B. Distribution of species of Ophioderma in the Northeast and Tropical Atlantic Ocean. C. Distribution of species of Ophioderma in the Mediterranean Sea.

Fig. 7. Ophioderma africana sp. nov., digital images. A–G. Holotype (SMNH-Type-7484). A. Dorsal aspect. B. Dorsal disc. C. Ventral aspect. D–E. Two dorsal arms, note multiple dorsal arm plates on both. F. Ventral arm. G. Mouth. H. Some paratypes (SMNH-Type-7487).