Ophioderma longicauda ( Bruzelius, 1805 )

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 : 8-11

Ophioderma longicauda ( Bruzelius, 1805)

Figs 2–3 ; Table 1

Asterias longicauda Bruzelius, 1805: 28–29 .

Ophioderma longicauda – Müller & Troschel 1842: 86.

Diagnosis

Multiple tumid proximal dorsal arm plates, up to 10 (usually fewer) arm spines, up to eight oral papillae (counting from and including Lyman’s ossicle but excluding tooth papillae, see Fig. 2F ). Dorsal disc uniformly dark reddish brown or olive, dorsal arms uniformly dark or weakly banded, ventral disc as dark as dorsal disc, ventral arms and oral frame lighter coloured. Disc diameter up to 30 mm.

Material examined

Neotype (here designated)

MEDITERRANEAN SEA • ♀; France, Marseille , E of Isle Maïre; depth 6–8 m; 7 Aug. 2004; H. Zibrowius leg.; under stones; scuba diving, hand collecting; preserved in 95% ethanol; SMNH- Type-8729.

Other material

MEDITERRANEAN SEA • 37 specimens (each specimen in separate plastic bag, numbered); same data as for neotype; SMNH- 102357 • 62 specimens (not used for DNA sequencing); France, E of Marseille, Port d’Alon ; depth 3–15 m; 26 May 2006; H. Zibrowius leg.; under stones; scuba diving; preserved in ethanol; SMNH- 81012 • 1 specimen (dd = 12 mm), dry ossicles; same data as for preceding; SMNH- 112871 • ossicles on SEM stub (from SMNH- 112871 ); same data as for preceding; SMNH- 133258 • 1 specimen (dd = 15.5 mm, mitochondrial COI lineage L1, nuclear cluster C3), dry ossicles, ossicles on 2 SEM stubs; same data as for preceding; SMNH- 160226 • 4 specimens; Tunisia, Tabarka ; 36°57.27′ N, 8°45.48′ E; Jul. 2013; A. Weber leg.; hand collecting; preserved in 95% ethanol; SMNH- 147063 to 147066 • 13 specimens (mitochondrial COI lineage L 1, nuclear cluster C 3); Greece, Crete; May 2012 (kept in aquarium, killed Mar. 2013); A. Weber leg.; preserved in 95% ethanol; SMNH- 147069 .

Description

Neotype ( Fig. 2 )

Disc diameter 22.5 mm; five arms, one cut for molecular analysis, one regenerating close to disc (recognizable by abrupt change in arm width; Fig. 2A, D ), two regenerating close to tip. Dorsal disc, including all radial shields, completely covered by small round granules ( Fig. 2A ). Disc scales and granules crowd onto proximal arms, covering first few joints completely, following three joints laterally ( Fig. 2 C–D). Proximal dorsal arm plates thick, robust, slightly tumid, several pieces of variable size placed irregularly on each arm joint, fewer pieces distalwards and on regenerating parts ( Fig. 2C ). Entire dorsal plates on distal arm rounded fan-shaped, distal edge wider than proximal, twice as wide as long. Small granules, similar to disc granules, between arm plates along the arm ( Fig. 2 C–D). Arm joints about three times as wide as long proximally. Two to seven flat, blunt arm spines at ventral to ventro-lateral distal edge of lateral arm plate (from first spine-bearing joint under disc to proximal free ones), half as long as joint. Ventralmost spine longer and wider than others ( Fig. 2B, E ). Small scales at dorsolateral distal edge of lateral arm plate on some arms, few tiny scales and some granules on others. Scattered granules along spine articulations/bases of spines.

Ventral disc covered with granules similar to dorsal disc ( Fig. 2B, E ). Bursal slits divided into short proximal part, reaching from oral shield to second arm joint, and distal part reaching from fourth joint to disc edge ( Fig. 2B , E–F). One interradius cut open. No juveniles in bursae; gonads small, with few oocytes, light brown. Adoral shields covered by granules, larger than on disc, conical ( Fig. 2F ). Adoral shield long, narrow, extending around the lateral edge of the oral shield, separating it from the arm. Four oral shields, rounded triangular, almost twice as wide as long, with obtuse proximal angle, convex distal edge, obtuse lateral angles, small central compression. Madreporite irregularly oval, almost as long as wide, larger central depression. Large, rectangular teeth. On either side of jaw a line of eight papillae: Lyman’s ossicle large, 2.5–3 times as wide as high, angled upwards, first adoral shield spine rounded bicuspid, as wide as long, second adoral shield spine indistinguishable from other five conical, pointed lateral papillae (including infradental papilla) at oral plate edge, two tooth papillae at jaw tips in line with oral papillae, larger than oral papillae ( Fig. 2F ). First ventral tooth in median position above tooth papillae, rectangular with straight edges. Second oral tentacle pore hidden in oral slit.

Granules from adoral shields continue laterally along the first arm joints, decreasing in size, meeting the granules from dorsal disc at arm base, becoming indistinguishable from them ( Fig. 2E ). First ventral arm plate smaller than following plates, proximally convex, distally narrowing to a point, touching second plate. Second and following proximal ventral arm plate axe-head shaped pentagonal, thick to slightly tumid, distal edge variable concave, straight or convex, proximal edge with angle, lateral edges excavated concave. Lateral excavations decrease in depth along arm. Two oval shaped tentacle scales, superimposed on the ventralmost spine, articulating to the lateral arm plate, fitting into excavation in lateral edge of ventral arm plate.

Dark brown colour on dorsal disc and arms, ventral disc dark, ventral arms and oral frame light brown to cream ( Fig. 2 A–B).

Skeletal elements ( Fig. 3 )

Non-type specimen of 15.5 mm dd (SMNH- 160226), morphologically similar to neotype, e.g., radial shields covered by granules. Several dorsal arm plates per joint on at least seven proximal arm joints, on many more on some arms. Radial shields isosceles triangular with strongly concave abradial edge and distal abradial process, external distal half domed with slightly finer mesh stereom and scattered small pores (the domed part is not covered by scales but with granules in the intact animal, all other areas are covered by scales). Two larger pores on distal part, adjacent to rough patch, and circle of medium-sized pores bordering domed part ( Fig. 3A, C ). Internally, radial shield with distal groove and two weakly domed bulbs, two pores in center of proximal half ( Fig. 3B ). Dental plates as varying numbers of pieces, sockets for teeth and apical tooth papillae not penetrating, bordered by low ridges ( Fig. 3D ). At the ventralmost edge of the dental plate, a row of small pores, probably granule articulations, followed by a row of three small round articulations for tooth papillae, the median one slightly higher than the lateral ones, followed by a row of two or a single larger round articulation and from then on single wide slit-like tooth articulations. Adradial genital plate blade-like flat with bulbous distal end and large pore, distal pit with knob on one side, three knob-like ridges on other side ( Fig. 3 E–F, N–O). Abradial genital plate much smaller and scale-like flat, distally wider than proximally ( Fig. 3G ). Oral plates longer than high, only slightly lower in central part than at proximal end, with large adradial muscle fossa with finer mesh stereom than remaining ossicle ( Fig. 3H ), conspicuous s-curved suture line crosses foot basin ( Fig. 3I ). Row of five small pores and depressions near lower edge of adradial proximal oral plate as articulations of oral papillae; four pores at proximal ventral edge of oral plate as articulations of granules ( Fig. 3I ). Adradial distal muscle fossa ventrally wide, tapering dorsalwards, almost vertical, shorter than height of oral plate. Large basin of first tube foot. Vertebrae typically zygospondylus, with large dorsal and small ventral muscle flanges, faint growth rings ( Fig. 3 J–K). Lateral arm plates compact, weakly curved around the arm, strongly convex distally, concave proximally, with ventral excavation for tube foot opening ( Fig. 3 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, slightly bent, flat vertical proximal ridge and ventral small protruding knob. Spine articulations inset in the distal plate edge with one thickened lobe, separating muscle and nerve opening.

Non-type specimen of 12 mm dd (SMNH-133258), adradial genital plate in lateral view with large distal pore and distal knob ( Fig. 3 N–O). Radial shield with irregular edges and abradial edge not concave, other characters similar to larger specimen ( Fig. 3P ).

Remarks

In southern France, at Marseille, only one genetic cluster of O. longicauda exists according to our analyses and it is safe to assume that the whole population belongs to the same species. The specimen chosen as neotype is a female for the purpose of comparison with brooders. It was selected from the samples used in Boissin et al. (2011). As one of the larger specimens in our collection, it was chosen to demonstrate the superior size of this species compared to the brooders. The species reaches a size of up to 30 mm dd ( Stöhr et al. 2009) in the western population, but these large specimens are rare and none was included in the molecular studies. Most are well below 20 mm dd and the eastern population seems to stay slightly smaller with a maximum of 25 mm dd found ( Weber et al. 2014). Internal ossicles were taken from a smaller specimen because this is the most common and easily available size in all studied species. It is important to compare individuals of similar size, since most characters are size dependent.

The highest number of arm spines recorded for O. longicauda is 10 and this character is only weakly correlated to size ( Stöhr et al. 2009). The radial shields are covered by granules in the majority of examined specimens of O. longicauda in the western population ( Stöhr et al. 2009) and in all examined specimens of this species in the eastern population ( Weber et al. 2014), which makes this character fairly reliable to differentiate O. longicauda from sympatric O. zibrowii sp. nov., although specimens with covered radial shields have been found in the latter. The radial shields are a key character to distinguish these two species. In the intact animal, scales cover most of the radial shield, except for the domed distal area that becomes visible only after the radial shield has been isolated by dissociation of the skeleton in bleach. Granules are attached to all scales and to the unscaled part in O. longicauda . Each small pore in this area probably indicates the position of a granule. They may be nerve openings but little is known about these. The shape of the radial shield is variable between individuals but the granule articulations are the same. The domed distal part is finer meshed than the remaining areas; in O. longicauda it is not as well defined as in O. zibrowii sp. nov., and it is oval instead of round as in O. africana sp. nov. The large number and thickness of the dorsal arm plates are another character that distinguishes O. longicauda from all other species, but in small specimens, there is a single plate on each arm joint. For further differentiation between species, see below.

Figures

Fig. 2. Ophioderma longicauda (Bruzelius, 1805), neotype (SMNH-Type-8729), digital images. A. Dorsal disc and arm bases, arrow points to regenerating part. B. Ventral disc and basal arms. C. Basal dorsal arm, note the multiple dorsal plates. D. Regenerating arm, dorsal plates already more than one. E. Ventral arm base. F. Jaws. Abbreviations: 2°AdShSp = second adoral shield spine; AdShSp = adoral shield spine; DAP = dorsal arm plate; IPa = infradental papilla; LOPa = oral papillae; LyOS = Lyman’s ossicle; M = madreporite; OS = oral shield; TPa = tooth papillae; VAP = ventral arm plate.

Fig. 3. SEM images of skeletal elements of Ophioderma longicauda (Bruzelius, 1805). A–M. Non-type specimen of 15.5 mm disc diameter (SMNH-160226). A. Radial shield, external aspect. B. Radial shield, internal aspect. C. Scale-free area of Fig. 3A magnified, white arrowheads point to granule sockets and pores, white arrows point to large peripheral pores. D. Dental plate fragments, arrows point to granule pores. E. Adradial genital plate. F. Articulation knobs of Fig. 3E. G. Abradial genital plate. H. Oral plate, abradial face. I. Oral plate, adradial face, black arrows point to oral papillae sockets and pores, white arrows point to granule socket pores. J. Arm vertebra, proximal face. K. Arm vertebra, distal face. L. Lateral arm plate, external face. M. Lateral arm plate, internal face. – N–P. Non-type specimen of 12 mm disc diameter (SMNH-133258). N. Adradial genital plate, lateral view. O. Adradial genital plate, distal end. P. Radial shield, internal aspect, note the different shape from Fig. 3A–B. Abbreviations: dist = distal; dors = dorsal; prox = proximal; S = suture line; Sp = spurs; vent = ventral.