Coelopleurus exquisitus, Coppard, Simon E. & Schultz, Heinke A. G., 2006

Coppard, Simon E. & Schultz, Heinke A. G., 2006, A new species of Coelopleurus (Echinodermata: Echinoidea: Arbaciidae) from New Caledonia, Zootaxa 1281, pp. 1-19 : 4-12

Coelopleurus exquisitus sp. nov.

Figs. 1–5 , table 1a.

Diagnosis: Long, highly curved primary spines that are banded red and pale­green for three quarters of their length distally (see Figs 1 A–C and 3D–F). For the basal quarter of their length the spines blend from pale­green to lavender mid­way through the spine’s collar. The collar measures 18 % of the ambital primary spine’s length and has a prominent longitudinal dorsal ridge. Smaller longitudinal ridges are present on both the collar’s dorsal ( Fig. 3 G) and ventral ( Fig. 3 H) surface with granules between dorsal ridges. Secondary spines ( Fig. 3 K) are either cream or olive green blending into red distally and tapering to a point. The test has large, straight edged, naked median interambulacral regions ( Figs. 1 A and C, 2A and F; 3C) that start from the genital plates, and comprise 65 % of the width of the interambulacra measured at the ambitus. These naked median regions are purple in contrast to the test’s olive/light brown epithelium, with each median region having a pinkish/lavender undulating line that continues to the lower element of the fifth plate from above. The peristome is large ( Figs. 1 B and 2B), measuring 56 % of the test’s horizontal diameter. The auricles are robust, with moderately high processes ( Fig. 2 E). The aboral ophicephalous pedicellariae have stalks that are not distinctly swollen or ‘fleshy’ ( Fig. 3 L). The distal and proximal regions of the ophicephalous valves are equal in length and are slightly constricted above the adductor muscle insertion points ( Fig. 4 H and I).

Holotype: EcEh 1281, MNHN­Paris­Echinoderms, N. O. “Vauban” MUSORSTOM 4, St. DW181 350 m, 18°57’S 163°22’E, New Caledonia, C. Vadon Coll. 18th September, 1985.

Paratypes: fifteen specimens; fourteen specimens in MNHN­Paris­Echinoderms (EcEh 1282), N. O. “Vauban” MUSORSTOM 4, St. DW181 350 m, 18°57’S 163°22’E, New Caledonia, C. Vadon Coll. 18th September, 1985. One specimen in the Natural History Museum, London, registration number (NHM 2006.599).

Other material: Five specimens (unregistered) MNHN­Paris­Echinoderms, N. O. “Jean­Charcot” BIOCAL, St. DW50 240–260 m, 23° 07’ South, 167° 54’ East, New Caledonia, Guille and Menau Collection, 31th August 1985; Registration No. J20052 Sydney Museum collection,, Coreolus Expedition, 23° 06’ South, 167° 05’ East, South of Isles of Pines, New Caledonia, at a depth of 520 m.

Etymology: After the exquisite coloured markings on the test and spines.

Description: The test is subcircular ( Figs. 1 A, 2A and E) (not distinctly pentagonal as in C. maillardi see tables 1a and 1b) with a horizontal diameter of 32.5 mm (holotype) and is moderately inflated adapically with a vertical diameter of 17.8 mm. The ambulacra are slightly raised aborally ( Fig. 2 C) while the interambulacra are correspondingly slightly sunken ( Fig. 2 D). The base colour of the epithelium of the test is olive/light brown ( Fig. 1 A), these regions being white on the denuded test (see Fig. 2 A–E). The apical system is small (9.0 mm) and dicyclic (see Figs. 2 A and 3A) with all ocular plates exsert. The genital plates are proportionally large, with ophicephalous pedicellariae on their inner edge ( Fig. 3A ). The attachment points for the ophicephalous pedicellariae are small granules on the denuded test ( Fig. 2 A). The genital plates and ocular plates are brightly coloured. The points of the ocular and genital plates are pink with a lavender central region in contrast to the orange terminal plates of the outer series of the interambulacra and the olive/light brown (white on naked test) of the ambulacra. The genital pores are small and are encompassed on the genital plates by a purple U­shaped region that forms the top of the purple naked region of each interambulacrum.

The periproct on the holotype measures 4.8 mm (approximately 15 % of the test’s horizontal diameter) and has four equally sized, valve­like, triangular plates. These are cream in colour, and fill the periproct ( Fig. 3A ).

The ambulacra are slightly inflated, the adradial edges undulating ( Fig. 3 B) as the ambulacra expand towards the ambitus and decreasing in size towards the peristome. Plating on the ambulacra is formed of typical arbaciid triads (compound plates formed of three plates), each triad possessing a large primary tubercle with an imperforate mamelon, the areole forming a raised platform on the plate, with two series of primary tubercles in each ambulacrum. The uppermost ambulacral plates bear a primary tubercle only on one side (i.e. in one series). On the plate immediately beneath the ambitus the primary tubercles on the ambulacra and interambulacra are of equal size ( Fig. 2 C and D). Adapically the areoles are confluent, but from the compound plate directly above the ambitus to the peristome there is a narrow median region which has a series of secondary tubercles, interspaced with miliary tubercles ( Fig. 3 B). These increase in number adorally. There are no secondary or miliary tubercles in the pore­zones above the ambitus, while miliary tubercles are present in the pore­zones beneath the ambitus. The ambulacra are olive/light brown ( Fig. 1 A), while on the naked test the ambulacra are white with orange median lines ( Figs. 2 C and 3B), which begin from the fourth primary tubercle and bisect the median region continuing to the apex of the test adorally.

The interambulacra are broader than the ambulacra at the ambitus ( Figs. 3 B and C) with a ratio of 1.5:1.0. The interambulacra are characterized by large naked median regions ( Figs. 2 D and 3C). These are purple and sharply defined both in colour (bordered by olive lines with red dots on the adradial edge of the lower corner of each plate) and by small straight edged adradial ridges. This naked region comprises 65 % of the width of the interambulacra measured at the ambitus. A pinkish/lavender undulating line proceeds down the centre of each naked median region, which increases in the width of the undulation towards the ambitus. The purple colouration starts from the genital plates and is clearly defined to the sixth plate from above ( Fig. 3 C). The purple colour faintly continues beyond the naked region towards the peristome, but not in the midline between the two series of tubercles beneath the ambitus ( Fig. 3 C). There are no primary tubercles in the naked median regions on the first four plates adapically. One or two secondary tubercles are present on the adambital and lower adradial edges of the fourth plates. On the fifth plate there are several secondary tubercles and a small primary tubercle, which lacks a large areole. The sixth plate (at or just below the ambitus depending on which series is being observed) has a large primary tubercle, equal in size and structure to those in the same region on the ambulacra. There are 6–7 primary tubercles in each of two main series of primary tubercles, which gradually decrease in size towards the peristome. The median region between these two series is relatively narrow with a single series of secondary tubercles and miliary tubercles on either side. Three distinctive red ‘dots’ are present in the suture line between the central elements of plates 5 and 6 in one series and plate 5 in the second series ( Fig. 3 C). These correspond to the positions of three red secondary spines. An outer series of tubercles extends from the peristome to the apical disc, which become increasingly oblique and reduced in number adapically. Such tubercles on the naked test appear white in the upper element of each compound plate and red in the lower element appearing as red patches in olive lines that border the naked median regions. These red tubercles increase in number with a single tubercle in the lower corner of plate 1, 2 in the lower corner of plate 2, with a maximum of three in an oblique series in the lower corner of plate 3.

The peristome is subcircular ( Fig. 2 B and E) and on the holotype measures 17.4 mm in diameter, 56 % of the test horizontal diameter. The peristomial membrane is dark brown with five pairs of buccal tube feet ( Fig. 1 B). Each pair being distinctly separated from the next and closely surrounded by large numbers of ophicephalous pedicellariae. A few scattered ophicephalous pedicellariae occur across the peristomial membrane, which is otherwise naked. The buccal notches are shallow but distinct while the gill­tags proceed to the midpoint of the fourth ambulacral primary tubercle ( Fig. 2 B). The auricles have moderately high processes and are robust in appearance ( Fig. 2 E).

Primary spines occur in three forms (see Figs. 3 D­J). The most adapical large primary spines (the first large tubercles on the ambulacra) are moderately curved and almost cylindrical except for the laterally compressed ridge, which proceeds up one third of the spine’s dorsal length ( Fig. 3 F). These spines are banded red and pale­green for three quarters of their length distally. For the basal quarter of their length the spines blend from pale­green to lavender. This colouration occurs on all sides of the spine. The collar of the spine does not distinctly end, as ridges and furrows occur along the spine’s total length and are clearly visible when seen in cross­section ( Fig. 4 B). Granules occur between the ridges, most noticeably proximally, but also along the spine’s length both dorsally and ventrally. The tips of these spines are slightly rounded, but without an obvious hyalinecap. The spines are subcircular when viewed in cross­section with distinct ridges and furrows, which proceed longitudinally down the spine’s length. The internal structure ( Fig. 4 B) consists of a small central cavity (which comprises 27 % of the spine’s diameter), a large region of dense stereom and an outer dermis. The central cavity is comprised of an axial cavity, which is filled with loosely reticulated stereom and 12–14 radiating solid wedges. These project into and through the dense stereom. The dermis is thin and rough in texture, but non­verticillate.

The second form of primary spine start on the fifth ambulacral tubercle and the second interambulacral tubercle beneath the naked median region and continue down to the apex of the test. These primary aboral spines are highly curved ( Fig. 3 D and E), and flattened both laterally and ventrally above the collar. On their upper surface these spines have the same colouration as the adapical primaries, however, on their underside the spines are typically white ( Fig. 1 B), with occasionally a faint impression of the pattern observed on the dorsal surface. The longest primary spines in this species are of this form and on the holotype the longest spine measures 76.2 mm (2.3 times the test’s horizontal diameter) but does not have the tip present. The collar is well defined and typically measures 18 % of the spine’s total length with distinct longitudinal furrows and ridges on the underside ( Fig. 3 H), and granules and a few ridges on the dorsal surface ( Fig. 3 G). In cross­section the spines are triangular with a convex ventral surface. Their internal structure consists of a small central cavity, which comprises 23 % of the spine’s horizontal diameter, a large, dense region of stereom and a relatively thick epidermis. The central zone is composed of an axial cavity, which is filled with loosely reticulated stereom and 12–14 radiating solid wedges. These project into the dense stereom region. The epidermis is smooth continuing from the spine’s tip to the spine’s collar.

The third form of primary spine is present on the oral surface. They are short (typically not longer than 15 mm) and dorso­ventrally flattened ( Figs. 3 I and J; 4C). On their dorsal surface they are light green with a central ridge ( Figs. 3 I and 4C), while their ventral surface ( Fig. 3 J) is white and smooth. The collar is well defined, measuring 18 % of the spine’s length, with distinct ridges dorsally and ventrally. These spines are almost diamond­shaped when viewed in cross­section ( Fig. 4 C). Their internal structure is similar to the ambital spines but compressed dorso­ventrally. However, the axial cavity is proportionally larger (33 % of the spine’s diameter), filled with loosely reticulated stereom and has short radiating solid wedges which typically number from 12–14. The dense stereom is well developed and continues between the dorsal and ventral solid wedges. The epidermis is thick and smooth and continues down the spine’s length to the collar.

Secondary spines ( Fig. 3 K and 4D) are slender and pointed (not club­shaped) either red proximally blending into green distally or cream with longitudinal ridges. These spines are circular in cross­section with a large central cavity (relative to the primary spines) measuring 55 % of the spine’s diameter, which consists of a small axial cavity filled with loosely reticulated stereom and 12–14 solid wedges. The region of dense stereom is proportionally smaller than in the primary spines, while the epidermis is rough (but nonverticillate) and thin. Miliary spines are similar in colour to secondary spines but lack the longitudinal ridges.

Ophicephalous pedicellariae ( Figs. 3 L and 4E, H and I) are abundant all over the test surface. These are particularly noticeable around the periproct ( Fig. 3A ) and along the adradial edges of the ambulacra. The stalks of the ophicephalous pedicellariae are relatively long (typically 1.5 mm), the skin of the stalk being only very slightly swollen proximally ( Figs. 3 L and 4E). The neck of each pedicellaria is short but is not distinctly swollen, indicating the absence of glandular tissue in this region. The distal and proximal regions are of approximately equal length, with peripheral teeth present both along the edges of the valves and along the edges of the apophyses ( Figs. 4 H and I). These interlock when the valves are closed. The distal regions are constricted, the degree of constriction varying from being very constricted ( Fig. 4 H) to moderately constricted ( Fig. 4 I) on a single sea urchin. Both specimens illustrated ( Figs. 4 H and I) were removed from the aboral surface of the holotype. Ophicephalous pedicellariae are also abundant on the oral surface. These are particularly noticeable around the peristome, the valves of which are only slightly constricted. All ophicephalous pedicellariae in this species exhibit very developed proximal handles, which increase grasping pressure ( Mortensen, 1935) and are typical of this class of pedicellaria.

The tridentate pedicellariae have long narrow valves ( Figs. 3 M, 4F and J) which meet for their entire length. Peripheral teeth are present along the edges of the valves, which interlock. The neck of each pedicellaria is narrow and relatively short, and is attached to a relatively long (approximately 1.5 mm) and narrow stalk. Tridentate pedicellariae are abundant on the aboral surface particularly around the adapical region of the ambulacra, and are typical of the genus.

Triphyllous pedicellariae are less numerous than the other two classes in this species, and have a small head supported by a relative long, broad neck on a proportionally (in relation to the size of the valves) long stalk ( Figs. 3 N and 4G). The valves are broad and spoon­shaped with small peripheral teeth along the edges of the valves which interlock when the head of the pedicellaria is closed. This form of pedicellaria is distributed all over the test in small numbers but provide no species­specific characters.

Figures

FIGURE 1. MNHN EcEh 1281, holotype: A, aboral view; B, oral view; C, lateral view.

FIGURE 2. MNHN EcEh 1282, paratype: A, aboral view; B, oral view; C, lateral view of an ambulacrum; D, lateral view of an interambulacrum; E, oral view showing auricle.

FIGURE 3. A, (holotype) apical system; B, ambulacrum (paratype); C, interambulacrum (paratype), D & E, ambital primary spines; F, adapical primary spine; G & H, ambital primary spine’s collar (G, dorsal view; H, ventral view); I – J, oral spines (I, dorsal, J, ventral); K, secondary spine; L, ophicephalous pedicellaria; M, tridentate pedicellaria; N, triphyllous pedicellaria.

FIGURE 4. Scanning electron micrographs: A, transverse section mid­way through a primary ambital spine; B, transverse section mid­way through a primary adapical spine; C, transverse section mid­way through a primary oral spine; D, transverse section mid­way through a secondary spine; E, ophicephalous pedicellaria; F, tridentate pedicellaria; G, triphyllous pedicellaria; H & I, individual valves from ophicephalous pedicellariae; J, individual valve from a tridentate pedicellaria; K, individual valve from a triphyllous pedicellaria.

FIGURE 5. Comparison of mean (± SD) peristome widths (as % of test’s horizontal diameter) between species of Coelopleurus.