Clypeaster brigitteae, Mooi & Noordenburg, 2021

Mooi, Rich & Noordenburg, Henk Van, 2021, A new species and comparative morphology of Philippine sea biscuits (Echinoidea Clypeaster), Zootaxa 4964 (1), pp. 1-36 : 9-18

Clypeaster brigitteae n. sp.

Figures 3–8 , tables 2–5, 11.

Diagnosis. Among all known extant taxa, very few Clypeaster species possess completely unique features (i.e. autapomorphies). Therefore, early workers used unique combinations of relatively conspicuous features to diagnose new species, and this is also the approach here. Nevertheless, among the Clypeaster species recorded from the Philippines, Clypeaster brigitteae n. sp. is unique with respect to certain characters, and these are marked with an asterisk in the following list of relevant characters:

Clypeaster with all petals widely open*; fewer than 9 respiratory pore pairs counted within a section 5 mm long along the length of single column in each petal; only 1 or 2 primary tubercles in poriferous zone between adjacent respiratory pore pairs*; interambulacral basicoronals separated from first pair of post-basicoronals by two plates from each adjacent ambulacrum; single occluded distal plate (very rarely two) in petal*; aboral primary tubercles not densely distributed (only about 50/cm 2)*; valves of ophicephalous large (largest of trio usually about 400 µm long).

Type and other material studied. A total of 12 specimens ( Table 2 ), consisting of a holotype ( CASIZ 234824 , Mactan Island , Cebu, Philippines) and 11 individually cataloged paratypes ( CASIZ 187409 , 187411 , 187450 , 234819–234823 , 234825–234827 , Balicasag Island , Bohol and Balut Island , Mindanao , Philippines), were available for study, obtained in a donation to the California Academy of Sciences by the second author in 2008–2009, or purchased with export permits by the first author through online dealers in the Philippines. See Table 2 for a complete list of all material of the new species studied, repository numbers, localities and depth, condition of each specimen as of this writing, and morphometrics for major features .

Etymology. The new species is named after the late spouse of the second author, Brigitte.

Description. This description relies primarily on the holotype, CASIZ 234824 ( Figs. 3 , 5C , 7 , 8 ). However, in order to maintain this specimen intact with nearly complete spination, other specimens were used in dissections and other preparations to obtain additional data and imagery (as noted in Table 2 and in the figure captions). Meristics and percentage calculations are from the holotype unless otherwise noted. Measurements from all specimens are given in Table 2 .

Holotype 93.8 mm TL (size range of type series 62.7–94.6 mm TL, Table 2 ), 85.1 mm TW, 25.2 mm TH. Ambitus relatively thick, rounded, approximately 8% TL thick through point at which oral surface begins to flatten ( Fig. 3 ). Aboral surface flat near ambitus, but rising close to perimeter to form slight dome ( Fig 3 ). Oral surface flat near ambitus, but deeply indented upwards in centre to form well-developed infundibulum ( Fig. 3 , and see below). Test broad (TW 90.7% TL), perimeter pentangular with broadly rounded vertices in ambulacra, very shallow indentations in paired interambulacra, slightly convex in posterior interambulacrum (V). Highest point of test at centre of apical system (madreporic plate), approximately 50% TL from anterior end. TH 26.9% TL, but variable among known specimens, see Table 2 ).

Apical system —Monobasal, pentangular (not star-shaped), 49.9% TL from ocular III to anterior edge of test, length ~6% TL, numerous hydropores scattered over slightly domed madreporic plate. Five gonopores, one in each interambulacrum, located at suture between madreporic plate and first adapical plates of interambulacral column ( Fig. 4A ).

Peristome —Circular to slightly pentangular, relatively small, about 6.6% TL. Anterior edge of peristome 48.1% TL from anterior edge of test. Peristome at top of deep infundibulum that extends 12.3 % TL (46.0% TH) upward from oral surface ( Figs. 3 , 5A ). Numerous irregular stereom spicules embedded in peristomial membrane, but none bearing spines ( Fig. 7H ).

Periproct —Small, length about 4.5% TL (92.0% TL from anterior ambitus, that is to say, posterior edge of the periproct situated approximately length of periproct from ambitus on oral surface). Adoral edge of periproct in con- tact with third and fourth post-basicoronals (interambulacral plates 4a and 5b), aboral edge with fourth and fifth (5a and 6b) ( Fig. 5B ). Periproctal membrane slightly sunken, covered in small plates (slightly larger near peristomial edge) surrounding small, central anal opening, plates bearing dense cover of miliary spines, triphyllous pedicellariae, and relatively small tridentate pedicellariae, but no primary spines ( Fig. 5C ).

Ambulacra —Petaloid adapically, petals broad, with pore pair columns continuously diverging or parallel distally, only slightly converging in some cases ( Figs. 3 , 4B, C ). Ambulacra widen near ambitus in oral view, approximately twice width of interambulacra at ambitus ( Figs. 5A, B ), most commonly with 8 to 10 plates in any given column (half-ambulacrum). Ambulacra with paired basicoronals, all in agreement with Lovén’s Rule (sensu David et al. 1996), ambulacral plates Ib, IIb, IIIa, IVb, Va about 2/3 length of other plate in pair ( Fig. 5B ). All ambulacral plates with densely arranged unipores scattered between spine tubercles, each unipore supporting single accessory tube foot.

Petals —Posterior paired petals (I and V) slightly longer than anterior paired petals (II and IV). Posterior paired petals longest relative to TL, petal V 60.0% length of corresponding test radius in planar view, but 32.5% TL; anterior paired petals next longest, petal IV 64.8% length of corresponding test radius, but 31.2% TL; anterior unpaired petal shortest, petal III 59.4% length of corresponding test radius, but 29.6% TL. Petal V width at widest point 19.0% TL, interporiferous zone 12.0% TL, distance between inner pores of distalmost respiratory pore pair in petal 14.2% TL (117.7% of maximum interporiferous zone width and a measure of the “openness” of the petal at its distal end, see Materials and Methods and Fig. 2 ); petal IV width 16.3% TL, interporiferous zone 11.2% TL, distance between inner pores of distalmost respiratory pore pair in petal 11.2% TL (100.0% of maximum interporiferous zone width and a measure of the “openness” of the petal at its distal end, see Materials and Methods and Fig. 2 ); petal III width 18.1% TL, interporiferous zone 11.8% TL (92.8% of maximum interporiferous zone width and a measure of the “openness” of the petal at its distal end, see Materials and Methods and Fig. 2 ). Respiratory tube foot pore pairs strongly conjugated, inner pore slightly elongate or almost circular, outer pore only slightly elongated ( Figs. 4B, C, D ). Column a of petal V with 42 pore pairs; of petal IV with 44; of petal III with 41. One or two (rarely three) primary tubercles situated along ridge between adjacent pore pairs. Plating within petals of typical clypeasterid architecture, with primary plate spanning entire distance from outer edge of petal to perradial suture, alternating with demiplate spanning just less than half that distance from outer edge of petal ( Figs. 4B, C, D ). One or two occluded plates present at tips of petals (e.g. Fig. 4D ).

Interambulacra —Narrower than ambulacra and straight on oral surface, slightly widening towards ambitus, but containing paired, zig-zag plates between petals right up to madreporic plate. Typically, five, occasionally six, post-basicoronal plates in each half-interambulacrum in oral interambulacra. Single, narrow basicoronal in each interambulacrum ( Fig. 5D ), typically but not always reaching ends of adjacent ambulacral basicoronals. Interambulacra disjunct, separated from first pair of interambulacral post-basicoronals by two adjacent oral ambulacral postbasicoronals ( Fig. 5B , 11 ). In some specimens, first interambulacral post-basicoronal in one column can be greatly reduced so that it is not contiguous with second post-basicoronal in corresponding column (see interambulacra 2 and 3 in Fig. 5B ), but it is not known if this is typical or unique, as it was decided not to prepare additional specimens to produce plate maps for other members of type series.

Tubercles —Of two main types, primary and miliary. Aboral miliary tuberculation homogeneous, primary tubercles relatively sparse, only about 50/cm 2. Oral tubercles slightly larger than those on aboral surface, particularly in interambulacra. Tubercles perforate, slightly crenulate, primaries with distinct, deeply sunken areole, miliaries with shallow areole, filling spaces between primaries and greatly outnumbering them (orally by at least 10 to 1, and approximately 20 to 1 on aboral surface). Abundant miliary tubercles on apical system ( Fig. 4A ) and periproctal membrane ( Fig. 5C ), primary tubercles lacking in those areas. No tubercles on peristomial membrane.

Food grooves —Unbranched, extending from edge of peristome, following perradial suture, shallowing and narrowing gradually, fading to merge with test surface just short of ambitus ( Fig. 5A ). Populated by specialized food groove miliary spines ( Figs. 7F, G ).

Internal structure —Strongly developed, with four or five peripheral, circumferentially arranged walls (sensu Mooi 1990; Mihaljević et al. 2011) in ambulacra, spanning space between floor and ceiling of test ( Figs. 6A, B ). Some reduced walls on inner side of channel that bears gut. Complicated masses of bars in interambulacra, continuing on proximal side of gut towards and beneath lantern ( Figs. 6A, B ). Minute, extremely thin, attenuated needles on both floor and ceiling of test ( Figs. 6D–F ), most strongly expressed in ambulacra. Some needles span entire space between floor and ceiling to join together to form thin columns or pillars ( Fig. 6F ).

Lantern —Of typical clypeasterine morphology ( Mooi 1989, 1990), not protrusible, with strongly developed outer wings separated from almost rudimentary inner wings by continuous, ring-like arrangement of supra-alveolar processes at summit of lantern ( Fig. 6G ). Epiphyses and rotules rudimentary, compasses absent, as typical in clypeasteroids ( Mooi 1989, 1990). Wings of each pyramid, particularly outer wings, strongly convoluted with subdivided walls connecting ambulacrally situated pyramidal muscle attachment surfaces to interambulacrally positioned symphysis between demi-pyramids underlying tooth slide ( Figs. 6G, H ). Tooth slide almost vertical, but biting surfaces of keeled tooth strongly angled relative to longitudinal axis of tooth to meet along nearly vertical axis from mouth through top of lantern. When in life position over peristome at top of infundibulum, entire lantern slightly canted forward so that supra-alveolar processes at anterior of lantern noticeably lower than at posterior ( Fig. 6C ). Lantern supports (auricles) of typical clypeasterid configuration ( Kier 1970; Mooi 1989, 1990), consisting of pairs of elongated, relatively thin, upright processes, one support for every pair contributed by adjacent ambulacral basicoronal ( Fig. 6B ).

Spines —Of two main types, primary ( Figs. 7A, B ) and miliary ( Figs. 7C–F ), corresponding to tubercle types described above, and as typical for other Clypeaster ( Telford et al. 1987) . Aboral primaries only about half length of oral primaries, much narrower, finer with about 75% number of longitudinal ribs ( Figs. 7A, B ). Core of spine sometimes hollow, sometimes with nearly solid meshwork ( Fig. 7A, B ). So-called “hyaline point” ( Serafy 1971) present at tips of undamaged, uneroded primaries on both aboral and oral surfaces ( Figs. 7A, B ). Miliary spines of variable length ( Figs. 7C–F ), rounded, blunt, slightly swollen distally but not crown-shaped, longest in interambulacral regions of oral surface, aboral interambulacral miliaries ( Fig. 7D ) about 80% length of oral interambulacral miliaries ( Fig. 7C ), aboral ambulacral miliaries shorter still, only 50% length of oral interambulacral miliaries ( Fig. 7E ). Miliary spines within food grooves short, only about half length of miliaries from adjacent oral ambulacra ( Fig. 7F ).

authors (CASIZ 232217).

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1 Known upper size limit, rounded up to the nearest 5 mm, based on examination of CASIZ, MNHN, and USNM specimens, and descriptions in the literature and of type series.

2 Approximate, range based on examination of CASIZ, MNHN, and USNM specimens, and descriptions in the literature and of type series .

3 Percentage based on approximate point at which test begins to inflect upwards towards the peristome – measured from the ambitus along oral interambulacrum 4.

4 In C. reticulatus , the margin is inflated relative to the rest of the distal part of the oral surface so that the distal ends of the petals are below the altitude of the margin.

5 Based on new observations and radiographs in Mihaljević et al. (2011). Structure described is only that distal to the path of the gut. Terminology adopted from Mooi (1989, 1990) and Mihaljević et al. (2011): bars = interambulacral, peripheral radiating buttresses (but not actually “radial” as used in Mihaljević et al. [2011]); walls = concentric, circumferential buttresses made of peripheral ambulacral pillars connected to form nearly solid partitions.

6 Number of ambulacral plates in each column adjacent to interradial suture between basicoronal and first post-basicoronal in posterior interambulacrum (interambulacrum 5). See also Figs. 5B , 11 .

Pedicellariae — Of three main types: triphyllous ( Fig. 8F ), tridentate ( Figs. 8C–E ), and ophicephalous ( Figs. 8A, B ). Following observations pertain to all specimens with well preserved complement of external appendages. Triphyllous widely distributed over entire test, extremely small and numerous, with long, flexible necconnect- ing three rounded valves to thin but robust stem, flexible neck about same length as stem, valves of usual shape for Clypeaster , with extremely short teeth on distal edges ( Fig. 8F ). Tridentates principally of two sizes, with three valves, those of smaller form ( Fig. 8C ) only slightly shorter than those of larger form ( Fig. 8E ). Smaller version scattered widely over oral surface, densely distributed (as many as 5/mm 2), particularly in infundibulum, much rarer aborally, nearly absent in aboral regions where ophicephalous pedicellariae most densely distributed. Larger tridentates tending to be more common near peristome and periproct. Only small version found on periproctal membrane. Valves of small form meet distally for about one third length of valve when pedicellaria closes, versus about one quarter in large form. Valves of both types with small proximal teeth along edges where valves meet, but with one, or more typically two longer distal teeth ( Figs. 8C–E ). Entire tridentate jaw connected to robust stem ( Fig. 8D ) by flexible neck about half as long as stem. Ophicephalous pedicellariae apparently absent on oral surface, but on aboral surface, extremely densely distributed (as many as 4/mm 2) all around peripheral portion of test inward from ambitus to point at which test slopes steeply upward towards apical system. Ophicephalous rare in this inner region, particularly proximal to apical system. Ophicephalous of typical Clypeaster morphology ( Figs. 8A, B ), with 3-valved jaw directly attached to top of vase-like stem ( Fig. 8B ), each valve connected to stereom meshwork in inner region of distal cup at top of stem by collagenous straps weaving between handles, inserting proximal to hinge of each valve. Handles always of three different lengths in single jaw, smallest nesting within medium-sized, then medium-sized within longest ( Fig. 8A ). Distal part of each valve with rounded, helmet-shaped head, inner surface of head with unbroken, oval ring of>30 prominent, sharp teeth, usually 4–6 additional teeth between head and top of hinge ( Fig. 8A ).

Tube feet —Of respiratory and accessory types, as typical for Clypeaster ( Mooi 1986) . Respiratory tube feet leaf-like, straddling conjugated respiratory tube foot pores in petals as described above, lacking spicules. Accessory tube feet varying in size and shape, distributed as typical for other Clypeaster ( Mooi 1986; Telford et al. 1987), tube feet extending from unipores distributed on all ambulacral plates, occasionally on interambulacrals in areas bordering the ambulacra as well, although not on interambulacral basicoronals ( Fig. 5D ). Smaller accessory tube feet in food grooves, small number of somewhat larger food groove tube feet just distal to slightly enlarged buccal tube feet as described for other species ( Mooi 1986). Spicules in tips of accessories (not known for buccals) like those of other Clypeaster , but elaborate, with two to three concentric rings of fenestrae, and peripheral projections pointing both proximally and distally ( Fig. 7I ).

Sphaeridia —Two per ambulacrum, one in each ambulacral basicoronal, located at outer edges of food groove near peristome just distal to buccal tube feet ( Fig. 5D ), consisting of solid sphere of imperforate stereom inside chamber entirely enclosed within surrounding ambulacral plate.

Colour. Unknown in living specimens. Aboral surface of dried specimens brown to purplish or grayish brown, oral surface slightly paler, approaching beige in interambulacra of some specimens, centres of some plates slightly darker, particularly aborally, so that major sutures and tube foot fields stand out in contrast ( Fig. 3 ).

Occurrence. Holotype collected by tangle net off Mactan Island , Cebu, Philippines, four paratypes from Mactan Island , four from Balicasag Island , Bohol, and three from Balut Island, Mindanao ( Fig. 1 , Table 1 ), at depths from 100 to 200 m.

Biology. C. brigitteae n. sp. has not been observed in its habitat, but gut and food groove contents suggest that it lives on soft bottoms with low particle size ranges. Food preferences are only partially known, because the gut contents are significantly broken up or pulverized, presumably by chewing action of the lantern ( Telford et al. 1987). Materials remaining in the food grooves suggest that the animal is a detritivore, with some preference for foraminiferans. However, as the specimens were primarily collected by tangle net, material normally gathered by the animals before capture could have been lost, and no quantitative assessments were possible. Low gonopore size suggests that the species possesses planktotrophic larvae (F. Armstrong and R. Mooi unpublished data concerning gonopore size in the genus).

Remarks. Clypeaster brigitteae n. sp. appears to fit some of the features listed by Mortensen (1948b) for the section (or subgenus) Stolonoclypus A. Agassiz, 1863 , given the well-developed bars and walls of the internal skeleton. However, even Mortensen (1948b: 88) was concerned that the “numerous species here enclosed in this section evidently do not form a natural group”. Mihaljević et al. (2011) were also unable to recover these so-called subgenera as monophyletic taxa, and this nomenclature is therefore abandoned, as indicated in Kroh & Mooi (2020).

C. brigitteae n. sp. is most easily distinguished from all other Clypeaster through the combination of several conspicuous features, such as low density of respiratory tube feet in the petals, all of which are also widely open, and low density of aboral primary spines (or tubercles on cleaned individuals). Of all known Atlantic species, only C. cyclopilus H.L. Clark, 1941 , C. euclastus H.L. Clark, 1941 , and C. ravenelii (A. Agassiz, 1869) have all petals even slightly similar to those of C. brigitteae n. sp. in terms of continuously diverging pore pair columns. However, these species all differ from C. brigitteae n. sp. in several other respects, including that the petals are very small in C. cyclopilus , the test is extremely flat in C. euclastus , and strongly pentangular with an inflated margin in C. ravenelii . Among Indo-Pacific forms, C. tumidus ( Tenison-Woods, 1878) has continuously diverging petals, but is found only in Australia, and has an extremely high, domed test.

Some characters used in previous descriptions of new taxa in the genus have proven unreliable in the distinction of C. brigitteae n. sp., and for this reason, they have not been emphasized in the present tabular comparisons of Philippine Clypeaster . For example, the hyaline point on primary spines used by Serafy (1971), needs to be reassessed for all taxa, because the primary spines of all the species examined herein have a hyaline point to some degree, except for oral spines of C. virescens and C. latissimus , in which spines are distally spatulate ( Table 5 ). This suggests that the degree to which this point is expressed is dependent on the condition of the spines, which are often worn or broken in museum material.

The presence or absence of stereom meshwork in the axial cavity of spines, a character also used in some keys ( Serafy 1971), is similarly not reliable because it is variably expressed within a given taxon. In several Philippine species, including C. brigitteae n. sp., even spines from a single specimen can have either a dense meshwork or a narrow, hollow axial cavity.

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Figures

FIGURE 1. Clypeaster brigitteae n. sp., maps showing location of Philippines, and of three localities from which specimens were collected (adapted from googleearth.com).A: Holotype CASIZ 234824; paratypes CASIZ 234822, 234823, 234826, 234827, Mactan Island, Cebu, Philippines. B: Paratypes CASIZ 234819 to 234821, 234825, Balicasag Island, Philippines. C: Paratypes CASIZ 187409, 187411, 187450, Balut Island, Mindanao, Philippines.

FIGURE 2. Measurements indicated as distances between caliper jaws set at indicated points on Clypeaster test. For aboral and oral views, anterior is towards top of page. Roman (ambulacra) and arabic (interambulacra) numerals on oral view indicate numbering established by Lovén (1874). Abbreviations as in the text (Material and Methods).

FIGURE 3. Clypeaster brigitteae n. sp., different views of holotype CASIZ 234824, Mactan Island, Cebu, Philippines, 93.8 mm TL.

FIGURE 4. Clypeaster brigitteae n. sp., paratype CASIZ 234821, Balicasag Island, Bohol, Philippines, 88.7 mm TL, photographs of aboral surface morphology of cleaned but not bleached specimen, painted with 50% glycerine in 95% ethanol. A: Detail of apical system. B: Petal in ambulacrum III. C: Petal in ambulacrum IV, specimen rotated to place distal part of petal and ambitus at top. D: Detail of distal portion of petal in ambulacrum IV.

FIGURE 5. Clypeaster brigitteae n. sp. A: paratype CASIZ 234827, Mactan Island, Cebu, Philippines, 73.0 mm TL, oral view of bleached test, ambulacrum III at top. B: Drawing of oral view of same specimen as in A, showing plate architecture (interambulacral plates shaded, peristome and periproct in solid black). C: Holotype CASIZ 234824, Mactan Island, Cebu, Philippines, 93.8 mm TL, detail of periproct. D: Paratype CASIZ 234823, Mactan Island, Cebu, Philippines, 94.6 mm TL, drawing of detail of peristomial region centred on ambulacrum II, with interambulacral basicoronals 1 and 2 (shaded), showing plate pattern (solid lines), position of food groove (fine, broken lines on either side of perradial suture), primary tuberculation (paired concentric circles, miliary tubercles omitted), accessory tube foot pores (small dots), buccal tube foot pores (larger, teardrop-shaped dots in ambulacrum near peristome), and positions of sphaeridia (shaded, dotted circles in ambulacrum near peristome).

FIGURE 6. Clypeaster brigitteae n. sp., photographs of internal structure and Aristotle’s lantern. A–E, G, and H show preparations from cleaned but not bleached specimen from paratype CASIZ 234826, Mactan Island, Cebu, Philippines, 70.1 mm TL, F shows bleached preparation from paratype CASIZ 234827, Mactan Island, Cebu, Philippines, 73.0 mm TL. A: Aboral view of specimen in which aboral surface was cut away, Aristotle’s lantern still in place. B: Aboral view of preparation in A, Aristotle’s lantern removed. C: Direct view of left side of preparation in A. D: Slightly oblique, left side view of preparation in B. Box indicates area shown in E. E: Magnified, oblique, left side view of inner surface of portion of interambulacrum 4 and ambulacrum V showing bars, walls, pillars and needles. F: Section through test along perradius showing pillars and needles. G: Slightly oblique, left side view of Aristotle’s lantern from preparation shown in A and C. H: Direct posterior view of Aristotle’s lantern shown in G.

FIGURE 7. Clypeaster brigitteae n. sp., spines and spicules, all from holotype CASIZ 234824, Mactan Island, Cebu, Philippines, 93.8 mm TL unless indicated otherwise.A: Bleached oral interambulacral primary spine with magnified tip and transverse section. B: Bleached aboral oral interambulacral primary spine with magnified tip and transverse section. C: Bleached oral interambulacral miliary spine. D: Bleached aboral interambulacral miliary spine. E: Bleached aboral ambulacral miliary spine. F: Bleached food groove miliary spine. G: Food groove in ambulacrum II just distal to peristome showing spination and tube feet. H: Bleached spicules from peristomial membrane of paratype CASIZ 234823, Mactan Island, Cebu, Philippines, 94.6 mm TL. I: Bleached spicule from tip of tube foot on oral surface.

FIGURE 8. Clypeaster brigitteae n. sp., bleached pedicellarial valves and stems from holotype CASIZ 234824, Mactan Island, Cebu, Philippines, 93.8 mm TL. A: Series of valves from same ophicephalous pedicellaria on aboral surface. B: Stem of ophicephalous pedicellaria on aboral surface. C: Valve of small tridentate pedicellaria from oral surface. D: Stem of of small tridentate pedicellaria from oral surface. E: Valve of large tridentate pedicellaria from oral surface. F: Valve, magnified view of valve, and stem of triphyllous pedicellaria from oral surface.

FIGURE 11. Drawings of oral surface showing plate architecture in posterior interambulacrum (interambulacrum 5) of all Clypeaster species recorded from the Philippines. Interambulacral plates shaded, peristome and periproct in solid black, posterior edge of test at bottom.