Massinium japonicum, Yamana & Ota & Kohtsuka & Yoshizaki, 2020

Yamana, Yusuke, Ota, Yuzo, Kohtsuka, Hisanori & Yoshizaki, Kazumi, 2020, A New Species of Massinium (Echinodermata: Holothuroidea: Dendrochirotida: Phyllophoridae: Semperiellinae) from Western Japan, Species Diversity 25, pp. 227-236 : 230-235

publication ID	https://doi.org/ 10.12782/specdiv.25.227
publication LSID	lsid:zoobank.org:pub:723551AC-EDF9-45B6-A45D-4D5912196130
persistent identifier	https://treatment.plazi.org/id/03938D32-FF8C-FFC7-FECB-C1E77B3B1E01
treatment provided by	Felipe
scientific name	Massinium japonicum
status	sp. nov.

Treatment

Family Phyllophoridae Östergren, 1907 View in CoL Subfamily Semperiellinae Heding and Panning, 1954 Genus Massinium Samyn and Thandar, 2003 Massinium japonicum sp. nov.

[New Japanese name: Nippon-hana-namako] ( Figs 2–5 View Fig View Fig View Fig View Fig )

Material examined. Holotype, WMNH-INV-2017-127 ( TOT, anesthetized, length 63 mm, width 22 mm) ( Fig. 2C View Fig ) . Paratypes: 6 specimens, WMNH-INV-2014-124 ( WAK, anesthetized, length 70 mm, width 20 mm) ( Fig. 2D–G View Fig ); WMNH-INV-2015-50 ( OKA, contract, length 22 mm, width 15 mm); WMNH-INV-2015-2432 ( KUM, contract, length 44 mm, width 21 mm) ( Fig. 2B View Fig ); WMNH- INV-2017-121 ( TOT, contract, length 63 mm, width 22 mm); WMNH-INV-2017-132 ( TOT, contract, length 20 mm, width 10 mm) ( Fig. 2A View Fig ); WMNH-INV-2017-133 ( TOT, contract, length 26 mm, width 12 mm) . Other materials: 14 specimens, WMNH-INV-2017-118–120; 122–126; 128–131 ( TOT), WMNH-INV-2016-221; 223 ( KUM).

Diagnosis. Tentacles 20, arranged in double circles (10+10), comprising five pairs of large tentacles in outer circle and five pairs of small tentacles in inner circle. Calcareous ring elongate, tubular, with both radial and interradial plates fragmented into a mosaic of small pieces and prolonged posteriorly, with posterior prolongations distally linked to prolongations of neighboring plates forming a loop. Ossicles of body wall comprising only rosettes. Tentacles also with only oval rosettes 20–40 µm long, rods and tables absent from both body wall and tentacles.

Description. Length up to 70 mm; body fusiform, curved, with both ends tapered, turned slightly upwards ( Fig. 2 View Fig ); body wall thick, soft. Live coloration basically Sienna with dark gray blotches, preserved coloration paler, not seriously affected by fixation/preservation. Tentacles 20, in double circles (10+10), comprising five pairs of large tentacles in outer circle and five pairs of small tentacles in inner circle. In life, tentacle bases, oral periphery, and introvert dark-salmon and gray, tentacle trunk and tip transparent. A row of thin short villi-like projections (pharyngeal villi) surround the pharyngeal opening. Pedicels (tube feet) retractile, uniformly covering the body except for the midinterradial areas, forming two longitudinal rows along each radius in introvert region and becoming gradually smaller anteriorly and posteriorly. Color of pedicels same or slightly paler than that of the general body wall. Anal papillae 10 bordering five anal teeth in radii.

Calcareous ring elongate, tubular, with both radial and interradial plates fragmented into a mosaic of small pieces and prolonged posteriorly, with the posterior prolongations distally linked to prolongations of neighboring plates ( Fig. 3 View Fig ). Polian vesicle usually single, as long as or slight longer than the calcareous ring, sometimes 1 or 2 short additional ones exist together, mid-ventral in position, stone canal single ending with a pinecone-shaped madreporite, mid-dorsal ( Table 1). Gonad situated in mid-body, in two clumps, one on each side of dorsal mesentery, most tubules branched. Gonad lacking ossicles.

Ossicles of body wall comprise thickened, mostly circular, flattened, open to almost closed rosettes ( Figs 4E, F View Fig , 5E, F View Fig ), some with central perforation ( Fig. 4E View Fig ). Tentacle ossicles comprise usually thickened, oval, open rosettes, 20–40 µm but without rods or tables of any form ( Figs 4A View Fig , 5A View Fig ; Table 2). Perioral and introvert skin comprise large, regular tables and small, regular, open rosettes ( Figs 4B, D View Fig , 5B, D View Fig ; Table 2). Regular tables with oval disc perforated by four large central holes and other smaller, marginal ones, and a two-pillared, low spire terminating in usually a single cross-beam and bito quadri-partite apex with 2–6 teeth, irregular tables multilocular, with numerous small perforations, and rarely intermediate ones with a closed rosette-shaped disc ( Fig. 4D View Fig ); spire sometimes absent ( Fig. 5D View Fig ). Introvert tables often concentrated in areas adjacent to tentacle bases. Pharyngeal villi with small open rosettes ( Figs 4C View Fig , 5C View Fig ; Table 2).

Pedicels with circular endplate and rod-like supporting ossicles encircling the endplate ( Figs 4G View Fig , 5G View Fig ; Table 2), and the usual body-wall rosettes. Endplates usually very circular with numerous minute holes increasing or decreasing marginally with margins sometime thickened and inwardly curled; some individuals with poorly calcified endplate that sometime comprising several, overlapping plate. Supporting rods surrounding end plate usually curved with two or more terminal holes. In a fully-grown pedicel, most supporting rods present not as independent ossicles, but adhere to the periphery or rim of the endplate.

Anal papillae exhibiting mostly large supporting rods in distal part and rosettes proximally ( Figs 4H View Fig , 5H View Fig ; Table 2). Skin around anus without deposits.

Distribution. Western Japan along the shore of Seto Inland Sea, Ariake Sea and Sea of Japan, 0–20 m depth.

Etymology. The specific name japonicum indicates that this species of Massinium was first described from the Japanese waters.