Paracorallium japonicum (Kishinouye, 1903)

Nonaka, Masanori, Muzik, Katherine & Iwasaki, Nozomu, 2012, 3428, Zootaxa 3428, pp. 1-67 : 51-62

Paracorallium japonicum (Kishinouye, 1903) ( Figs. 43–57; Tables 12, 13)

Corallium japonicum Kishinouye, 1903a: 623 ; Kishinouye 1903b: 103 (in Japanese); Kishinouye 1904a: 22, pl. 1, figs. 1, 2; pl. 2; pl. 4, fig. 3; pl. 7, fig. 1; pl. 8, figs. 1–6 (in Japanese); Kishinouye 1904b: 21, pl. 1, figs. 1, 2; pl. 2; pl. 4, fig. 3; pl. 7, fig. 1; pl. 8, figs. 1–6; Kuekenthal 1924: 50; Bayer 1956: 76 (in key); Grigg 1984: 59; Harper 1988?: 64; Imahara 1996: 28 (in list).

Paracorallium japonicum Bayer & Cairns 2003: 224 ; Nonaka et al. 2006: 1823, figs. 3–5; Nonaka & Muzik 2010: 99–100, figs. 26–29.

Material examined: Neotype (designated herein) USNM 19931 , Tosa, Japan; USNM 19932 , Tosa , Japan. Both of the dry samples were identified and donated by Kishinouye , and both are erroneously labeled “ syntype.” Diagnosis. Colony abundantly branched in one plane. Short , prickly branchlets grow on the “front” of the colony and on the sides of the branches. Coenenchyme thin, and generally dark red with growing tips pinkish to white. Coenenchymal mounds small, about 0.7 mm in diameter, are only slightly elevated. They are distributed in four or five rows, generally on one surface only. Axis longitudinally grooved, normally dark red with a white center and having a small pit underneath each polyp mounds. In cross section, the axis of the main stem is round or oval, but that of the branch tip is Y or X-shaped. Five kinds of sclerites occur: 6-, 7-, 8-radiates, crosses and rods. Eightradiates about 0.05 mm long are numerous, other sclerites are smaller and fewer.

Description of the neotype:

Colony form: The specimen has a holdfast and appears to be almost complete (only some branch tips are missing). It is about 140 mm tall and 70 mm wide, branched irregularly almost in one plane, and the angles of branching are mostly at 30–90 degrees ( Fig. 43). Branches are tapered and sharp at the tip. The diameter at the base of the colony is about 25 mm, the main stem and the thickest branch are 10 mm, (not including the coenenchymal mounds), and the thinnest branch tip is 4 mm. Branch cross sections are rounded, but twig tips are irregular.

Polyps: The specimen is preserved dry with damaged coenenchyme. Originally retracted into the coenenchyme, making hemispherical coenenchymal mounds, the autozooid tissue has now completely disintegrated. Coenenchymal mounds appear to be distributed on one side (the “front”) of the colony (occasionally straying on to the back surface) ( Fig. 44). They are only slightly elevated, 0.16–0.54 mm in height and 0.55–1.03 mm in diameter, with an indistinct 8-lobed summit. The mounds are arranged 1.32–3.29 mm apart (center to center).

The siphonozooids appear as very small pits 0.03–0.05 mm in diameter ( Fig. 45), observable only on undamaged surfaces and distributed sparsely and randomly.

Axis: The surface of the axis is longitudinally grooved ( Fig. 46) at intervals of 0.19–0.31 mm, and covered with minute tubercles ornamented with thorny projections ( Fig. 47). There are shallow, rounded pits, approximately 0.4 mm in diameter and without beaded margins, at the position of each coenenchymal mound ( Fig. 46).

Coenenchyme: The coenenchyme is so abraded (0.04–0.06 mm thick) that the longitudinal axial grooves and axial sculpture are clearly visible through it in many areas. There are fine warts (0.10–0.13 mm in diameter) distributed evenly on undamaged areas of coenenchyme.

Colour: The dried coenenchyme and the coenenchymal mounds are pale brick-red to orange ( Figs. 44, 45). The axis is dark red ( Fig. 43), with a whitish central core.

Sclerites: The coenenchymal mounds contain mainly 8-radiates 0.038 –0.060 mm long and 0.022 –0.040 mm wide, some rods 0.030 –0.045 mm long and 0.014 –0.028 mm wide, symmetric 6-radiates 0.034 –0.048 mm long and 0.023 –0.035 mm wide, and a few 7-radiates, crosses and multi-radiates ( Fig. 48A). The coenenchyme on the branch tip contains mostly 8-radiates 0.039 –0.058 mm long and 0.024 –0.038 mm wide, some symmetric 6-radiates 0.036 –0.058 mm long and 0.029 –0.036 mm wide, 7-radiates 0.038 –0.052 mm long and 0.024 –0.038 mm wide, and a few asymmetric 6-radiates, rods, crosses and multi-radiates ( Fig. 48B). The coenenchyme on the base of the colony also contains abundant 8-radiates, which are 0.043 –0.057 mm long and 0.029 – 0.028 mm wide, along with a few symmetric 6-radiates 7-radiates and crosses ( Fig. 48C). The statistical data for sclerites of this specimen are shown in Table 12.

The 8-radiates, which are the most abundant form, are of similar size in all the three regions sampled ( ANOVA, p>0.05).

Relative abundance of sclerites ( Fig. 49; Table 12): There are 7 kinds of sclerites in the coenenchyme of the neotype. In the coenenchymal mounds, 8-radiates represent 49% of the sclerites, rods 26%, and symmetric 6- radiates 13%. In the branch tip, 8-radiates represent 58% of the sclerites, and symmetric 6-radiates 17%, and in the base, 8-radiates are also the most abundant at 71%.

Description of specimen USNM 19932

Colony form: This specimen is an incomplete colony (missing at least two main branches) but it has a holdfast ( Fig. 50). The specimen is about 100 mm tall and 55 mm wide, but the original colony would have been wider. Branching is almost in one plane without anastomoses. The branches taper to a sharp tip, and the angle of branching is acute. The diameter at the base of the colony is about 30 mm, the main stem is 10 mm, the thickest branch is also 8–10 mm, and the thinnest branch tip is 2–3 mm. Branch cross sections are rounded, but irregularly flattened at the twig tip ( Fig. 52).

Polyps: The specimen is dry and the coenenchyme is damaged. Originally retracted into the coenenchyme, making hemispherical coenenchymal mounds, the autozooid tissue has now completely disintegrated. The coenenchymal mounds appear to be distributed on one side of the colony, especially at the branch tip ( Fig. 51). They are only slightly elevated, 0.12–0.32 mm in height and 0.44–1.09 mm in diameter, indistinctly 8-lobed on their summit ( Fig. 52), and are distributed 0.81–4.34 mm apart (center to center). Siphonozooids appear as very small pits which are only observable on undamaged surfaces. They are 0.04–0.07 mm in diameter, not visible to the naked eye, and distributed randomly.

Axis: The surface of the axis is longitudinally grooved at intervals of 0.21–0.33 mm ( Fig. 51), and covered with minute tubercles ornamented with thorny projections ( Fig. 54). These appear to be projecting parts of partially embedded radiate sclerites. At the tip of a branch underneath each coenenchymal mound, there is an indistinct, shallow, rounded pit, about 0.4 mm wide and 0.5 mm long without a beaded margin, ( Fig. 53). The axis at the tip of a branchlet is spatula shaped ( Fig. 52).

Coenenchyme: In many parts this is so thin (approximately 0.07 mm in dry condition) that the axial sculpture is exposed, and the longitudinal grooves are easily detected ( Fig. 51). There are fine warts (0.13–0.16 mm in diameter), distributed evenly (0.19–0.31 mm apart) on the undamaged parts of coenenchyme.

Colour: The branch coenenchyme and the coenenchymal mounds are pale brick-red to orange. The axis is dark red with a whitish central core.

Sclerites: The coenenchymal mounds contain predominantly 8-radiates 0.040 –0.059 mm long and 0.025 – 0.038 mm wide, some multi-radiates 0.040 –0.046 mm long and 0.032 –0.040 mm wide, rods 0.033 –0.045 mm long and 0.017 –0.039 mm wide, and a few symmetric 6-radiates, 7-radiates and crosses ( Fig. 55A). The coenenchyme on the branch tip contains abundant 8-radiates 0.035 –0.058 mm long and 0.024 –0.037 mm wide, some 7-radiates 0.033 –0.050 mm long and 0.023 –0.035 mm wide, a few asymmetric 6-radiates, and some rods, crosses and multiradiates ( Fig. 55B). The coenenchyme on the base of the colony also contains abundant 8-radiates, which are 0.037 –0.058 mm long and 0.023 –0.041 mm wide, and a few symmetric 6-radiates, 7-radiates and crosses ( Fig. 55C). The statistical data for sclerites of this specimen are shown in Table 13.

The most abundant sclerites, the 8-radiates, are similar in size in the three regions sampled and do not significantly differ in their length ( ANOVA, p>0.05). They are the largest sclerites of all.

Relative abundance of sclerites ( Fig. 56; Table 13): There are 6 kinds of sclerites in the coenenchyme of specimen USNM 19932 . Unlike the neotype, asymmetric 6-radiates are not present. In the coenenchymal mounds, 8-radiates represent 74% of the sclerites, multi-radiates 14%, and rods 13%. In the branch tip, 8-radiates represent 70% of the sclerites, and 7-radiates 10%. In the base, 8-radiates are also the most abundant form, present as 65%, while crosses represent 20% of the total .

The most abundant sclerites are 8-radiates, composing over 65% of all sclerites. Small rods are few in the branch tips, but are quite numerous in the coenenchymal mounds, multi-radiates are few and found only in the coenenchymal mounds and the branch tip, and 6-, 7-radiates and crosses are few.

Remarks: The average composition of the basal sclerites in these two specimens ( USNM 19931 and USNM 19932) is significantly different from all other species examined in this study ( Table 3; Chi-square test). The two specimens have almost the same colony shape and colour ( Figs. 43, 50), size, shape and distribution of coenenchymal mounds ( Figs. 44, 51), axis surface sculpture ( Figs. 46, 47, 53, 54) and surface ornamentation of sclerites ( Figs. 48, 55). Moreover, the sizes of the 8-radiates in the two specimens overlap ( Fig. 57). These characteristics were first described by Kishinouye (1903b, 1904a,b), so we therefore conclude they are the same species, P. japonicum . Compositions of basal sclerites are not significantly different from each other (Chi-square test, p>0.05), but there is some variation in percent composition of the different types of sclerites in the other colony regions ( Figs. 49, 56), which may be attributed to mere variation. Kishinouye (1903b, 1904a,b) described only three kinds of sclerites, abundant 8-radiates, and rare crosses and rods. We also observed abundant 8-radiates, but found more kinds of rare sclerites, 6- and 7-radiates in our specimens ( Figs. 49, 56).

Kishinouye (1903a) did not designate any types for this species, and he described only the general distribution off the southwestern coast of Kyushu, and off Tosa, not a specific locality. The Smithsonian specimens, which were not mentioned in his publication, were collected from Tosa, meaning Kochi, and were each subsequently labelled as “ syntype ”, but not by Kishinouye. These are the only specimens of Paracorallium japonicum known to exist that were collected and identified by Kishinouye. The more complete colony, USNM 19931, is designated here to be the neotype and fixes the characters of the species. The special character, the dark red axis, occurs in only three species: C. ducale , C. reginae and P. japonicum . However double club sclerites are present in former two species but absent in P. japonicum .

As mentioned above, both of these specimens have axial pits beneath the coenenchymal mounds, but without beaded margins. Therefore, as they do not exactly fit the diagnosis for the genus Paracorallium , we have kept them in this genus only provisionally.