Corallium inutile, Nonaka & Muzik & Iwasaki, 2012

Nonaka, Masanori, Muzik, Katherine & Iwasaki, Nozomu, 2012, 3428, Zootaxa 3428, pp. 1-67 : 42-50

Paracorallium inutile ( Kishinouye, 1902) ( Figs. 35–42; Table 11)

Pleurocorallium inutile Kishinouye, 1902: 419 (in Japanese) Corallium inutile Kishinouye 1903a: 626 ; Kishinouye 1903b: 105 (in Japanese); Kishinouye 1904a: 28, pl. 5, figs. 1, 2; pl. 7,

fig. 7; pl. 8, fig. 18 (in Japanese); Kishinouye 1904b: 27, pl. 5, figs. 1, 2; pl. 7, fig. 7; pl. 8, fig. 18; Kuekenthal 1924: 48;

Bayer 1956: 76 (in key); Imahara 1996: 28 (in list). Paracorallium inutile Bayer & Cairns 2003: 224 ; Nonaka & Muzik 2010: 98, figs. 23–25.

Material examined: Neotype (designated herein), USNM 19935 , Tosa, Japan, erroneously labelled “ syntype ”, dry; sclerite preparation of USNM 19935 made by Yukimitsu Imahara.

Diagnosis. Main branches planar, but smaller branches ramify in all directions, often anastomosing, and netlike. Coenenchyme thin but firm and light red. Coenenchymal mounds small, 1.0– 1.5 mm in diameter, slightly elevated and distributed over all parts of the branches. Axis brittle, finely striated. Small but deep pits in axis underneath coenenchymal mounds. Axis white, slightly tinged with yellow. Five kinds of sclerites: 6-radiates, 7- radiates, double-clubs, rods and irregular forms. Double-clubs, mainly smooth, predominant in the coenenchyme; six- and 7-radiates few.

Description of the neotype:

Colony form: The dry specimen consists of only a part of a colony (the upper branches are missing) with a holdfast and a portion of substratum (limestone rock) still attached ( Fig. 35). The specimen is about 40 mm tall and 80 mm wide, branched almost in one plane without anastomoses. Branches are blunt and rounded at the tip, angle of branching is mostly 45 degrees ( Fig. 36), with branches arising from the main stem in a relatively zigzag manner. The base of the colony is about 18 mm in diameter, the main stem 10 mm, and thinnest branch tip is about 3 mm. Branch cross sections are rounded ( Fig.38). Symbiotic zoanthids are distributed on each side of the colony ( Fig. 37). Their dried vestiges are various sizes, 1.0–3.0 mm in diameter, and are distributed about 1–2 mm apart on the tips of the twigs, but more than 5 mm apart at the base.

Polyps: The coenenchyme covering each polyp cavity is not mounded but appears as shallow indentations 0.81–1.35 mm in diameter ( Fig. 37), visible only in undamaged areas, and distributed randomly (at roughly 3.0 mm intervals) all around the colony ( Fig. 36). Siphonozooids are invisible to the naked eye, 0.05–0.06 mm in diameter.

Axis: The surface of the axis is distinctly longitudinally grooved ( Fig. 39), at intervals of 0.22–0.39 mm, and covered with minute tubercles ornamented with thorny projections ( Fig. 40). A tiny pit is found on the axis at the position of each coenenchymal “mound” ( Figs. 38, 39).

Coenenchyme: The dried specimen is damaged and some parts of the coenenchyme (especially at the base) are missing ( Fig. 35). On the twigs, the coenenchyme is 0.19–0.27 mm thick ( Fig. 38). There are no warts on the coenenchyme.

Colour: The dry coenenchyme is pale ocherous white, the polyp mounds a little deeper in colour ( Figs. 35, 36), and the axis is white ( Fig. 38).

Sclerites: The coenenchymal “mound” contains mainly symmetric 6-radiates 0.033 –0.057 mm long and 0.030 –0.044 mm wide, double-clubs with a smooth surface 0.044 –0.061 mm long and 0.037 –0.054 mm wide, asymmetric 6-radiates 0.033 –0.056 mm long and 0.033 –0.048 mm wide, double-clubs with a rough surface 0.043 – 0.054 mm long and 0.036 –0.046 mm wide, and a few 7-radiates, rods, irregular forms ( Fig. 41A). The coenenchyme on the branch tips contains mostly double-clubs with a smooth surface 0.035 –0.065 mm long and 0.032 –0.053 mm wide, asymmetric 6-radiates 0.038 –0.052 mm long and 0.032 –0.047 mm wide, a few doubleclubs with a rough surface, and symmetric 6-radiates ( Fig. 41B); 8-radiates are very rare. The coenenchyme on the base of the colony contains mainly double-clubs with a smooth surface 0.044 –0.067 mm long and 0.040 –0.055 mm wide, some double-clubs with a rough surface 0.045 –0.063 mm long and 0.037 –0.049 mm wide, a few symmetric 6-radiates, asymmetric 6-radiates, rods, small 6-radiates and 7-radiates ( Fig. 41C). The statistical data for sclerites of this specimen are shown in Table 11.

The average size of double-clubs (both rough and smooth) is greatest at the base, and smallest in the coenenchyme over the retracted polyps. The size of the 6-radiates (both symmetric and asymmetric) is greatest in the basal region, while those on the branch tip and those in the coenenchymal “mounds” are similar in average size.

Relative abundance of sclerites ( Fig. 42; Table 11): There are 9 kinds of sclerites in the coenenchyme of the neotype. In the coenenchymal “mounds”, both symmetric 6-radiates and double-clubs with a smooth surface each represent 32% of the sclerites, and asymmetric 6-radiates 16%. The most abundant sclerites are double-clubs with a smooth surface, both at the branch tips (72%) and at the colony base (70%).

Double-clubs with a rough surface are few, comprising only about 10% of the sclerites in any region. Doubleclubs from the coenenchymal “mounds” are not abundant, composing 32% smooth and 9% rough. Both forms of 6- radiates are in almost the same ratio as both forms of double-clubs in coenenchymal “mounds”, but less abundant in other parts. Small 6-radiates, 7-radiates and rods are rare in the basal region. A few strangely-shaped sclerites from the coenenchymal “mounds” are apparently fused small sclerites.

Remarks: The neotype, established to define the species, is preserved in the collection of the Smithsonian Institution and is labeled “ syntype ”. Kishinouye (1902) did not designate any types when he described Pleurocorallium inutile nor did he mention this material, but it is the only known specimen of this species thought to be collected and identified by him. He described only the “distribution”, not a specific collection site, as Kochi Prefecture. USNM 19935 was collected from Tosa (the old name of Kochi), and therefore satisfies a requirement for a neotype designation.

The neotype has some morphological characteristics, such as thin coenenchyme, distribution of coenenchymal “mounds”, axis color and surface ornamentation, that are similar to the colony of C. inutile described by Kishinouye (1902, 1903a,b, and 1904a,b), but there are differences in the shapes of coenenchymal “mounds” and the anastomoses of the branches. Kishinouye reported that the main branches were planar and the smaller branches extended in all directions, often anastomosing. Our observations of the neotype reveal it to also be a planar colony, although without anastomoses ( Fig. 35), but the smaller branches are missing, so the colony shape remains unknown. According to Kishinouye (1904a,b), coenenchymal mounds were present as small elevations, 0.8–1.0 mm in diameter, whereas in USNM 19935 the coenenchymal “mounds” are 0.81–1.35 mm in diameter, but in the latter the coenenchyme has clearly shrunk, and measuring such structures is quite subjective. Although Kishinouye (1902, 1903a,b, 1904a) described a “brittle” axis, branches of the specimen are not particularly brittle, but seem the same as is found in specimens of any other species, so it is unclear to what he was referring. The most important character of this species appears to be the abundance of double-clubs with a smooth surface. Corallium konojoi also has some smooth double-clubs ( Fig. 33), but no other species of Coralliidae from Japan has this sclerite form in such abundance as P. inutile . The geographically distant species, C. borneense and P. thrinax (Bayer & Stefani, 1996) also have double-clubs with a smooth surface, but C. borneense has thicker coenenchyme with orange coloration, and in P. thrinax , the autozooid are distributed on the front side only ( Bayer 1996).

The specimen examined is encrusted by zoanthids. Kishinouye (1902, 1903a,b, 1904a,b) also reported that he always found a kind of sea anemone on the branches, which he identified as Palythoa sp. ( Kishinouye 1904b) . The presence of zoanthids may be an important identifying character for P. inutile . Reimer et al. (2008) described a new species of zoanthid living on the branches of P. japonicum as Corallizoanthus tsukaharai Reimer, 2008 , but the zoanthids living on P. inutile have not yet been identified. It is possible that the zoanthids are a different species and that they are host-specific.

Bayer & Cairns (2003) placed Corallium inutile in their new genus, Paracorallium , the diagnosis of which is “ Coralliidae with autozooids seated in deep pits…with prominently beaded margins especially near branch tips…”. In this study, we have found small pits occurring beneath all of the coenenchymal mounds of the neotype, but without beaded margins. Meanwhile, Uda et al. (2011) recently presented molecular evidence which seems to validate the separation of two genera, Corallium and Paracorallium , but without commenting on the presence of pits or beaded margins. For the time being, in this study we tentatively keep inutile in the genus Paracorallium , but consider it may be necessary to find a different generic character other than the presence or absence of beaded axial pits to distinguish it from Corallium .

Kishinouye described this species in English in 1903 as “ Corallium inutile n. sp. ”, probably leading Kuekenthal (1924) to record the species as “ Corallium inutile Kishinouye, 1903 ”, and Bayer & Cairns (2003) recorded it as “ Paracorallium inutile (Kishinouye, 1903) ”. However, Kishinouye had already named the species “ Pleurocorallium inutile ” in an earlier short paper published in Japanese in 1902, so the official date of the scientific name Paracorallium inutile is 1902.