Ophioderma guineense Greeff 1882

Ophioderma guineense Greeff, 1882

Figs 4–6; Table 1

Ophioderma guineense Greef, 1882: 156.

Ophioderma longicauda var. guineense – Koehler 1914: 173.

Ophioderma longicauda guineense – Madsen 1970: 225, fig. 43.

“ Ophioderma appressa ?” – Koehler 1914: 175; Madsen 1970: 228.

Diagnosis

Predominantly single flat dorsal arm plates, up to 13 arm spines, nine oral papillae (counting from and including Lyman’s ossicle but excluding tooth papillae). Colouration in alcohol variable, dorsal disc brown with white spots and dark rings, arms banded dark and light brown to grey, ventral disc, arms and oral frame cream to light grey, dark and white spots along distal edge of dorsal arm plates. Disc diameter of largest paralectotype 29 mm.

Material examined

Lectotype (here designated)

TROPICAL ATLANTIC OCEAN • West Africa, Gulf of Guinea, Islands Sao Tomé and Rolas; cliffs at low tide; ZMH E8315.

Paralectotypes (here designated)

TROPICAL ATLANTIC OCEAN • 6 specimens (2 specimens at hand, 4 specimens examined on photographs); same data as for lectotype; ZMH E1686.

Other material

TROPICAL ATLANTIC OCEAN • 11 specimens (photographed specimens in separate bags labelled as #1–3, mitochondrial lineage L6, nuclear cluster C 1); Senegal, Dakar, Grand Thiouriba; depth 38 m; 6 Sep. 2007; H. Zibrowius leg.; from heavily fouled piece of fishing net; scuba diving, hand collected; preserved in 95% ethanol; SMNH- 95511 • 1 specimen (dd = 11.7 mm), dried arm pieces, dried ossicles, ossicles mounted on two SEM stubs; same data as for preceding; SMHN-178429 • 3 specimens (labelled as O. longicauda var. guineense); Equatorial Guinea, Gulf of Guinea, Annobón; depth 18–30 m; Discovery exped. (stn 283); dried; NHMD- 225525.

Description

Lectotype (Fig. 4 A–D)

Disc diameter 28.5 mm, radial shields widely separated, sunken in, concealed by granules. Scales and granules crowd onto proximal arms, obscuring dorsal plates laterally, granules rubbed off in some places. Dorsal arm plates entire almost on whole arm (single cracked plates on mid-arms), not tumid, three times as wide as long, contiguous (Fig. 3C). Three to 13 arm spines (from first spine bearing joint under disc to proximal free ones), flattened, slightly pointed, slightly longer than half arm-joint length, ventralmost spine longer and wider than others. Ventral arm plates wider than long, with convex distal edge, overlapping, except the proximalmost 3–4 which are separated by pores. Two oval scale-like tentacle scales, superimposed on the ventralmost spine.

Ventral disc covered by granules similar to dorsal disc (Fig. 4D). Lyman’s ossicle elongated, reaching into the mouth slit, not obvious, adoral shield spines on some jaw edges block-like, on others as lateral papillae and not obvious, in total nine oral papillae per jaw edge. Two tooth papillae at jaw tips in line with oral papillae, slightly larger than oral papillae. Teeth rectangular with straight edges. Oral shields rounded triangular with obtuse proximal angle and straight distal edge, slightly wider than long. Madreporite larger than other oral shields, depressed. 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 in size.

Colour pattern with tiny dark spots on the dark grey-brown dorsal disc, dark and white spots on the distal edge of the dorsal arm plates, cream ventral side (Fig. 4 A–C).

Paralectotypes (Fig. 4 E–H)

Disc diameter 26 and 29 mm, both with up to 13 arm spines, 9–10 oral papillae. Radial shields concealed by granules, but in parts of the disc, the granules have been rubbed off (Fig. 4E, G). Proximal dorsal arm plates entire. In the largest syntype, colour faded light brown dorsally, cream with some dark brown ventrally, arms with faint dark bands. There are irregular dark rings on the pale brown dorsal disc of the smallest syntype examined (Fig. 4G). In these specimens, there are dark brown and white spots along the distal edge of the dorsal arm plates. Among the paralectotypes examined only from photographs, one is dark brown on dorsal disc and arms, and the dark colour extends onto the ventral disc, fading towards the oral frame. The other specimens have a faded brown dorsal colour and light ventral discs and arms. Some of these show faint spots on distal edges of the dorsal arm plates.

The amplification of nuclear markers from the syntypes was not successful, most likely due to the long storage time and unknown initial preservation method of the specimens, which might have caused the DNA to deteriorate.

Specimen from Senegal (SMNH-95511#1, Fig. 5 A–D)

Disc diameter 15 mm, up to nine arm spines proximally, dorsal arm plates flat, entire along whole arm, radial shields covered by granules. Disc scales with granules crowding onto arm base, covering first dorsal arm plate except for a mid-distal portion, second plate also covered by scales and granules laterally. Dorsal arm plates overlapping, twice as wide as long, rounded fan-shaped, distal edge wider than proximal, not tumid. Ventral disc covered by similar granules as dorsal disc. Jaws with nine lateral papillae. Two larger tooth papillae at jaw tips in line with oral papillae, rectangular teeth with straight edges. Oral shields triangular, almost as long as wide. Adoral shield long, narrow, extending around the lateral edge of the oral shield, separating it from the arm. Adoral shields covered with granules similar in size to disc granules. Proximal genital slits small, extending from oral shield to proximal edge of second ventral arm plate. Distal genital slits at disc edge, next to fifth arm joint.

Disc dark brown dorsally, large white patches in centre. All over with small irregular white dots with black margins (ring-like). Disc light green ventrally. Oral shields with darker green centres. Arms dorsally dark brown, with lighter and darker bands, ventrally cream white with faint darker bands. Dorsal arm plates with small black spots along distal edge.

Variation in other Senegalese specimens

Size range 8–13 mm dd. The specimens vary in colour pattern. One specimen has large white patches over the area around the radial shields, on an otherwise dark disc. Some animals have a light brown disc with minute, irregular white spots with black borders (SMNH-95511#2, Fig. 5 E–F) or a greyish green disc with black rings (SMNH-95511#3, Fig. 5 G–I). Dorsal arms banded light and dark, distal edge of dorsal arm plates with small dark and white spots. The ventral disc is always much lighter than the dorsal disc, often cream with a hint of darker colour, sometimes green. The oral shields are completely creamy white in some specimens. Ventral arms are cream. Some specimens with only up to eight oral papillae. Skeletal elements (Fig. 6)

From specimen with 11.7 mm dd (SMHN-178429). Radial shield at widest part about as wide as long, isosceles triangular with abradial projection and convex radial edge, externally with domed center with finer mesh stereom (the domed part is not covered by scales but with granules in the intact animal, all other areas are covered by scales), a circle of pores around domed part, two large pores on the proximal end (Fig. 6A, C). Internally, radial shield with large pore in center of distal half, adjacent to rough patch, distally two knobs, radial one larger, separated by a furrow (Fig. 6B). Dental plates as varying numbers of pieces, sockets for teeth and apical tooth papillae not penetrating, bordered by low ridges, tooth papillae sockets small round, tooth sockets wider oval (Fig. 6D). 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. 6 E–F). Abradial genital plate much smaller and scale-like flat, distally wider than proximally (Fig. 6G). Oral plates longer than high, middle part markedly lower than ends, abradial muscle fossa rounded triangular with depression in upper half, not reaching upper edge (Fig. 6H). On adradial oral plate proximoventral part four oral papilla sockets and pores, at proximoventral edge four indistinct granule sockets and pores (Fig. 6I). Vertebrae zygospondylous, with large wing-like muscle fossae (Fig. 6 J–K). Lateral arm plates compact, weakly curved around the arm, strongly convex distally, concave proximally, with ventral excavation for tube foot opening (Fig. 6L, 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, fourth pore in tentacle opening edge, bent vertical proximal ridge and 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

Ophioderma guineense was until now considered conspecific with O. longicauda. It differs from O. longicauda in having mainly single and flat dorsal arm plates and a higher number of arm spines (Table 1). A previously unrecognized differentiating character is the light colouration of the ventral side of O. guineense, in contrast to the dark colour of O. longicauda, and the spots on the distal edge of the dorsal arm plates, which are absent in O. longicauda. Considering the small morphological differences between the genetic clades in the species complex of O. longicauda, we propose to treat O. guineense as a valid species and we consider the recently collected specimens of genetic cluster C1 as conspecific due to their colouration and mostly single dorsal arm plates. The specimens of NHMD-225525 also concur with this assignment. As lectotype, we selected a specimen that concurs well with the original description (Fig. 4 A–C): Greef (1882) described the colouration of his specimens as on the dorsal disc blackish or dark brown, ventrally light green, the arms dorsally black with grey white rings, ventrally grey yellow, which fits with the material from Senegal (Fig. 5). There are irregular dark rings on the pale brown dorsal disc of the smallest paralectotype examined (Fig. 4G) and tiny dark spots on the dark grey-brown dorsal disc of the lectotype (Fig. 4A), both have cream ventral discs and arms (Fig. 4B, H). The largest of the examined paralectotypes has a faded brown dorsal disc and also some dark brown pigmentation remaining on the ventral disc (Fig. 4 E–F); one of the specimens seen only on photographs has a dark dorsal disc and dark pigment on the ventral disc, quite similar to O. africana sp. nov. (see below, Fig. 7). Based on colour pattern, there may be a possibility that the type specimens are conspecific with O. africana sp. nov. However, in addition to differences in colour, multiple dorsal arm plates are more common in O. africana sp. nov. than in O. guineense, which has led us to assign the Senegal specimens to O. guineense.

Colour pattern tends to vary in most species of Ophioderma (Hendler et al. 1995) but O. guineense differs notably from all species observed by this study from Mediterranean and East Atlantic localities (over 800 specimens in the collection of SMNH). These may be similar in dorsal colour with uniformly brown or mottled dorsal discs, sometimes with white spots, but they always have a dark ventral disc and lighter coloured, but never white, arms and oral frames (Stöhr et al. 2009). Red pigments seem more common in O. longicauda than green, and the ventral arms are often either reddish or green in the Mediterranean species, with the disc being brown or olive.

No embryos have been found in specimens of O. guineense and this species is most likely a broadcast spawner.