Pleurocorallium cf. pusillum ( Kishinouye, 1903c )

Nonaka, Masanori & Hayashibara, Takeshi, 2021, A Report on Coralliidae (Cnidaria: Octocorallia) Specimens Collected from the Emperor Seamounts with Descriptions of Three New Species, Species Diversity 26, pp. 297-342 : 304-306

publication ID	https://doi.org/ 10.12782/specdiv.26.297
publication LSID	lsid:zoobank.org:pub:1E87A39C-02DE-4710-BFEF-E5C2FBCD54FB
persistent identifier	https://treatment.plazi.org/id/CC5187C7-FFC9-FF8A-FF4A-FEF3FADAFEE8
treatment provided by	Felipe
scientific name	Pleurocorallium cf. pusillum ( Kishinouye, 1903c )
status

Treatment

Pleurocorallium cf. pusillum ( Kishinouye, 1903c) View in CoL ( Figs 3–13 View Fig ; Tables 2, 3)

Corallium pusillum Kishinouye, 1903c: 372 View in CoL (in Japanese); Kishinouye 1904: 29, pl. 5, figs 3, 4, pl. 7, fig. 4 (in Japanese); Kishinouye 1905: 27–28, pl. 5, figs 3, 4, pl. 7, fig. 4; Kukenthal 1924: 50; Bayer 1956: 76 (in key); Imahara 1996: 28 (in list); Nonaka and Muzik 2010: 95–96, figs 17–19; Tu et al. 2012: 5 (in key); Nonaka et al. 2012: 5 (in key); Nonaka and Muzik 2012: 79 (in key), table 1.

Pleurocorallium pusillum: Tu et al. 2015b: 181 View in CoL (in list); Tu et al. 2016: 1036 (in key), table II; Nonaka and Muzik 2016: 16 (in list).

Material examined. NSMT-Co 1717, Kanmu Seamount, 350–800 m, 31 May 2009; NSMT-Co 1718, Kanmu Seamount, 350–800 m, 22 May 2009; NSMT-Co 1719, Kanmu Seamount, 350–750 m, 27 April 2009; NSMT- Co 1720, Kanmu Seamount, 550–610 m, 25 March 2009; NSMT-Co 1721, Kanmu Seamount, 550–610 m, 25 March 2009; NSMT-Co 1722, Koko Seamount, 404–591 m, 2 September 2009; NSMT-Co 1723, Kanmu Seamount, 563– 595 m, 16 September 2010; NSMT-Co 1724, Koko Seamount, 446–523 m, 18 May 2010; NSMT-Co 1725, Koko Seamount, 372 m, 25 May 2010; NSMT-Co 1726, Koko Seamount, 415–427 m, 28 May 2010; NSMT-Co 1727, Koko Seamount, 336–410 m, 16 June 2011 ( Table 1).

Diagnosis. Colony is in one plane with a few anastomoses. Branching in an asymmetrically dichotomous manner, at acute to right angles. Contracted autozooids making hemispherical mounds, distributed on only one side of the colony, about 1.5 mm in diameter and 0.6 mm in height, sometimes forming clusters of over four or five on the twigs. Coenenchyme is about 0.3 mm thick, with small but distinct warts. Almost orange in color, and yellowish on branchlets. Some commensal polychaete burrows with I or T-shaped openings are found on the surface. Axis is stout, no pits underneath autozooids, surface with longitudinally grooved, white in color. Tentacles contain small (about 0.05 mm long) 8-radiates and rods, coenenchyme contains mainly doubleclubs, 6-radiates, 8-radiates and multi-radiates. 8-radiates are about 0.09 mm long.

Description of the 11 specimens examined. Colony form. The specimens include large branches (NSMT-Co 1718, NSMT-Co 1719, NSMT-Co 1722, NSMT-Co 1723, Fig. 4A), and small fragments (NSMT-Co 1717, NSMT-Co 1720, NSMT-Co 1721, NSMT-Co 1724, NSMT-Co 1725, NSMT-Co 1726, NSMT-Co 1727, Figs 3A View Fig , 6A View Fig ). The colonies branch in one plane in an asymmetrically dichotomous manner, with a few anastomoses (NSMT-Co 1724; Fig. 6B View Fig ). Angles of branching are acute to right. Almost all colonies are wider than tall, curving backward (opposite the side with autozooids). The branchlets are thick and rounded. The thickest part is more than 4 mm in diameter, and the thinnest is about 2 mm in diameter. The cross sections of main branches are rounded.

Polyps. The autozooids are retracted into the coenenchyme, making hemispherical mounds. These mounds are distributed on only one side of the colony ( Fig. 3B, C View Fig ) and sometimes make clusters of over four or five ( Figs 3B View Fig , 4B). They are denser on the branchlets than on the base of the colony ( Fig. 4A). They are 1.46–1.69 mm in diameter and 0.47–0.78 mm high ( Table 2). Siphonozooids are invisible to the naked eye ( Fig. 7 View Fig ), forming minute pits 0.05–0.12 mm in diameter ( Table 2), distributed randomly on the both sides ( Fig. 7 View Fig ).

Axis. The surface of the axis is faintly longitudinally grooved ( Fig. 5B View Fig ), at 0.23–0.38 mm intervals ( Table 2). Removal of autozooid mounds in order to collect the sclerites from the tentacles and the autozooids confirmed that there are no rounded pits on the surface of the axis at the position of the autozooids.

Coenenchyme. The coenenchyme is 0.27–0.35 mm thick ( Table 2) and the longitudinal axial grooves are not visible through it ( Figs 5B View Fig , 7 View Fig ). There are small and inconspicuous warts 0.18–0.30 mm in diameter ( Table 2) distributed mainly on the sides of autozooids ( Fig. 7A View Fig ). Some commensal polychaete burrows with I or T-shaped openings are found on the surface of the autozooids ( Figs 4B, 5A View Fig )

Color. The dry coenenchyme is red to orange and yellowish on branchlets ( Figs 3–7 View Fig ). The axis is white ( Fig. 5B View Fig ).

Sclerites. The tentacles contain mainly small symmetric 8-radiates (ranging from 13–69%; 0.046 –0.065 mm long, 0.027 –0.042 mm wide), multi-radiates (12–39%; 0.047 – 0.056 mm long, 0.026 –0.034 mm wide) and a few rods, asymmetric 6-radiates, 7-radiates and asymmetric 8-radiates ( Figs 8–13 View Fig View Fig View Fig View Fig View Fig View Fig ; Table 3).

The autozooid mounds contain mainly symmetric 8-radiates (21–47%; 0.061 –0.092 mm long, 0.038 –0.060 mm width), asymmetric 6-radiates (12–32%; 0.062 –0.070 mm long, 0.051 –0.061 mm wide) and double-clubs with a rough surface (16–38%; 0.061 –0.075 mm long, 0.049 –0.061 mm wide). A few 7-radiates and asymmetric 8-radiates are present ( Figs 8–13 View Fig View Fig View Fig View Fig View Fig View Fig ; Table 3).

The branch tips contained mainly double-clubs with a rough surface (19–66%; 0.062 –0.075 mm long, 0.053 – 0.060 mm wide), asymmetric 6-radiates (20–51%; 0.061 – 0.069 mm long, 0.050 –0.057 mm wide) and symmetric 8-radiates (18–45%; 0.072 –0.094 mm long, 0.047 –0.056 mm wide), and a few 7-radiates and asymmetric 8-radiates ( Figs 8–13 View Fig View Fig View Fig View Fig View Fig View Fig ; Table 3).

The coenenchyme on the base of the colony also contains mainly double-clubs with a rough surface (11–67%; 0.057 – 0.070 mm long, 0.049 –0.060 mm wide), asymmetric 6-radiates (10–54%; 0.056 –0.070 mm long, 0.044 –0.055 mm wide), and symmetric 8-radiates (11–40%; 0.070 –0.092 mm long, 0.044 –0.057 mm wide). There are also a few 7-radiates and asymmetric 8-radiates ( Figs 8–13 View Fig View Fig View Fig View Fig View Fig View Fig ; Table 3). in the basal coenenchyme.

The average size of the symmetric 8-radiates is similar from all three parts (autozooid mounds, branchlets and base) of the colonies (Table 3).

Remarks. Some species belonging to genus Pleurocorallium , such as P. borneense ( Bayer, 1950) , P. carusrubrum ( Tu, Dai, and Jeng, 2012) , P. clavatum Tu, Dai, and Jeng, 2016 , P. konojoi (Kishinouye, 1903) , P. niveum ( Bayer, 1956) , P. norfolkicum Tu, Dai, and Jeng, 2016 , P. porcellanum , P. pusillum (Kishinouye, 1903) , P. occultum ( Tu, Altuna, and Jeng, 2015) are also known to have autozooid-clusters as well as the present specimens. Of these nine species, P. borneense , P. carusrubrum , P. pusillum and P. occultum are having orange or reddish coenenchyme. However, the autozooids of P. borneense are distributed on all side of the branch ( Bayer 1950). Pleurocorallium carusrubrum has smaller autozooids (about 0.4 mm in diameter), axis in crimson red, and almost no 8-radiate sclerite in its coenenchyme ( Tu et al. 2012). And P. occultum is an Atlantic species. Therefore, the characters of these three species don’t fit the present 11 specimens in this study.

In contrast, many characters of the present specimens fit the features of the original description of P. pusillum ( Kishinouye 1903c, 1904, 1905), such as color of coenenchyme (“orange color, gradually changing to pale yellow at the terminal branches”) and axis (“white and striated”), distribution of autozooid clusters (“making small groups here and there”), diameter of autozooids (“about 1.5 mm in diameter”), presence of commensal polychaetes in burrows in the coenenchyme. Kishinouye (1905) reported “spicules of C. pusillum are the largest” in the Japanese Coralliidae he had ever studied at that time. Nonaka et al. (2012) measured the sizes of the sclerites of the Coralliidae specimens studied by Kishinouye preserved in the Smithsonian Institution, reporting that the largest sclerite was about 0.06–0.07 mm long [cross shape of P. gotoense ( Nonaka, Muzik, and Iwasaki, 2012) , or 6-radiate shape of P. konojoi ]. In this study, large 8-radiate sclerites are about 0.07–0.09mm long. P. pusillum was first described by Kishinouye (1903c), but the original specimen collected from around Izu-Ohshima Island (depth unknown) has been lost, and no further specimens have been found since then. Therefore, the identifications are tentative, and specimens of this study are reported as P. cf. pusillum .

The most abundant sclerites are symmetric 8-radiates and double-clubs in most of the specimens, such as NSMT-Co 1717 ( Fig. 9 View Fig ). However, in 4 specimens (NSMT-Co 1722, NSMT-Co 1723, NSMT-Co 1724 and NSMT-Co 1726) asymmetric 6-radiates are most abundant ( Fig. 11 View Fig ). However, the size of autozooids ( Table 2) and sclerites (Table 3) are very uniform, and the other characters are also similar. Therefore, we conclude that the differences in % composition of sclerites can be attributed to intraspecific variation.

The photograph of a specimen of Corallium secundum in Tu et al. (2012: figure 4) showed very similar colony shape cies in 1904 (e.g. Nonaka and Muzik 2016). However, a onepage description in Japanese with this scientific name (Kisinouye 1903c) was found, and thus, the year of publication of the specific name pusillum is corrected in this paper.