Olindias deigo, Toshino, Sho, Tanimoto, Miyako & Minemizu, Ryo, 2019
Toshino, Sho, Tanimoto, Miyako & Minemizu, Ryo, 2019, Olindias deigo sp. nov., a new species (Hydrozoa, Trachylinae, Limnomedusae) from the Ryukyu Archipelago, southern Japan, ZooKeys 900, pp. 1-21: 4-11
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New Japanese name.
Holotype: NSMT-Co1690. Ada, Kunigami, Okinawa Prefecture, Ryukyu Archipelago, southern Japan; 26°43'29.0"N, 128°19'7.0"E; March 11, 2018; collector: Shuhei Odoriba. Paratypes: NSMT-Co1691. Same locality as holotype, March 16, 2018, collector: Shuhei Odoriba. NSMT-Co1692. Motobu, Okinawa Prefecture, Ryukyu Archipelago, southern Japan; 26°40'18.0"N, 127°52'49.0"E; April 19, 2015; collector: Shinichi Arakawa.
Mature medusae with transparent, dome-like exumbrella ( Figs 3A View Figure 3 , 4A View Figure 4 ). Umbrella height about 40 mm and umbrella diameter about 80 mm (Table 2 View Table ). Exumbrella smooth, lacking nematocyst warts ( Fig. 3B View Figure 3 ). Four radial canals elongate from four corners of stomach ( Figs 3B, C View Figure 3 , 4B View Figure 4 ). Folded gonads attached along entire length of four radial canals ( Fig. 5A View Figure 5 ). Immature gonads light red to orange ( Figs 3D View Figure 3 , 4C View Figure 4 ) while mature gonads are milky-white in color. Manubrium long, length about 50% of umbrella height, with quadrate base, light red to orange in color, folded ( Fig. 5B, C View Figure 5 ). Mouth quadrate to rhomboid ( Fig. 5C View Figure 5 ). Oral rips complexly folded ( Fig. 5C View Figure 5 ). White fibrous structures scattered in mesoglea of exumbrella ( Fig. 5D View Figure 5 ). Different length of black bands elongated from umbrella margin to the apex of exumbrella ( Fig. 5F View Figure 5 ). Centripetal canals about 80 to 100, long and short alternately aligned ( Fig. 5D View Figure 5 ). Long canals reached apex of the umbrella while short ones were half or quarter length that of long canals terminating in tentacles. Some canals connected or branched ( Fig. 5D View Figure 5 ). Tentacles and marginal clubs aligned on the umbrella margin ( Figs 3D View Figure 3 , 5E View Figure 5 ). Primary tentacles about 80 to 140, thin, short with distal adhesive pads and cnidocysts in transverse clasps. Color of exumbrella tentacles and primary tentacles pale black with purple and glowing green tips and with black base ( Fig. 3D View Figure 3 ). Number of secondary tentacles about 50, thick, no adhesive pads, cnidocysts in rings, deep-brown in color ( Fig. 3D View Figure 3 ). Contracted secondary tentacle short, coil-like while elongate ones reaching 2 m in length. Exumbrella tentacles about 30 to 60, developing on tip of black bands ( Fig. 5F View Figure 5 ). Shape and color similar to those of primary tentacles ( Fig. 3D View Figure 3 ). Number of marginal clubs about 170 to 240, rounded, short, whitish in color ( Fig. 3D View Figure 3 ). Statocysts were not found in fixed mature medusae.
Fertilization and polyp formation. Spawning occurred in dark conditions. Thousands of fertilized eggs were collected from the bottom of the tank in the early morning (from 8 to 9 am); diameter of blastocysts ~100 µm ( Fig. 6A View Figure 6 ). Blastocysts developed into planulae within two days. Planulae had a pear-shaped body, 70 µm in diameter and 130 µm in length ( Fig. 6B View Figure 6 ); they developed into polyps within 20 days.
The polyps form small colonies by elongation of the stolon, developing into a network ( Fig. 6 C–F View Figure 6 ). The hydrorhizae were cylindrical with small egg-shaped or cylindrical hydranths developing on the stolon. The hydranths had an ovoid body, 0.7 mm in length ( Fig. 6E View Figure 6 ). The body was divided in two parts, gastric region (0.3 mm in diameter and 0.5 mm in length) and hypostome (0.2 mm in diameter and 0.2 mm in length). Tentacle single, filiform, 1.7 mm in length ( Fig. 6E, F View Figure 6 ). The hydroid, usually brownish or yellowish, became orange or pink owing to the consumption of Artemia nauplii. Tentacle and hypostome transparent.
Budding and development of young medusa. Budding of young medusae was observed after 8 months of polyp formation. Medusa bud formation occurred on stolon ( Fig. 7A View Figure 7 ) at temperatures below 20 °C. The shape of the buds was ovoid and 0.3 mm in diameter ( Fig. 7A View Figure 7 ). Two days after onset of budding, four radial canals and a circular canal appeared, but were obscure ( Fig. 7B View Figure 7 ). Eight days after onset of budding, rudiments of tentacles developed from the bud ( Fig. 7C View Figure 7 ). Fourteen days after onset of budding, the buds enlarged (0.8 mm in diameter) and green fluorescence was observed on the tentacles ( Fig. 7D View Figure 7 ). Fifteen days after onset of budding, the medusa buds detached.
Newly detached medusae had a spherical umbrella translucent in color ( Fig. 8 A–C View Figure 8 ). Umbrella height about 1.6 mm and diameter about 1.5 mm. Exumbrella with tiny nematocysts along entire exumbrella ( Fig. 8D View Figure 8 ). Four simple radial canals from four corners of the stomach ( Fig. 8B, D View Figure 8 ). Statocysts four, enclosed in mesoglea, adjacent to primary tentacles ( Fig. 8E View Figure 8 ). Manubrium long, about 50% that of umbrella height ( Fig. 8F View Figure 8 ). Marginal tentacles of two types ( Fig. 8C, G, H View Figure 8 ). Primary tentacles four, short (about 1 to 2 times that of umbrella diameter) bearing nematocyst clusters on the tips ( Fig. 8G View Figure 8 ). Secondary tentacles two, long (about 5 times that of umbrella diameter) bearing 10 to 20 nematocyst batteries ( Fig. 8H View Figure 8 ). The medusae attached using the tip of the primary tentacles, but adhesive pad was not observed ( Fig. 8G View Figure 8 ). Green fluorescence was observed at the base of tentacles and four corners of the stomach ( Fig. 8 D–F View Figure 8 ).
Ninety-day-old medusae were about 10 mm in diameter ( Fig. 9A View Figure 9 ). Umbrella bowl-shaped. Primary and secondary tentacles about 40 and 20, respectively. About 20 centripetal canals were observed. Medusae aged 120-day-old were about 15 mm in diameter ( Fig. 9B View Figure 9 ). White fibrous structures appeared around radial canals. Manubrium elongated and mouth rips developed. Number of primary and secondary tentacles and radial canals not increased much. Medusae aged 150-day-old were about 20 mm in diameter ( Fig. 9C View Figure 9 ). Primary and secondary tentacles about 60 and 20, respectively. About 20 centripetal canals observed. Exumbrella tentacles developed near umbrella margin, but were not observed on the apex of exumbrella. Medusae aged 200-day-old were about 40 mm in diameter ( Fig. 9D View Figure 9 ). Primary and secondary tentacles about 80 and 40, respectively. About 60 centripetal canals were observed. Gonad developed. Exumbrella tentacles developed near the margin of umbrella and the middle part of exumbrella. Medusae aged 240-day-old were about 60 mm in diameter ( Fig. 9E View Figure 9 ). Primary and secondary tentacles about 120 and 40, respectively. About 60 centripetal canals observed. Gonad developed and matured. Spawning observed ( Fig. 9E View Figure 9 ).
Cnidome. Two different nematocyst types were identified and measured in the adult medusae, young medusae, and mature polyps (Table 3 View Table ). Adult medusae had two nematocyst types. Two sizes of macrobasic b-mastigophores ( Fig. 10A, B View Figure 10 ) and microbasic euryteles ( Fig. 10C, D View Figure 10 ) were found on primary, secondary, and exumbrella tentacles. Young medusae had two nematocyst types. Macrobasic b-mastigophores ( Fig. 10E, F View Figure 10 ) were found only on tentacles while two sizes of microbasic euryteles ( Fig. 10 G–J View Figure 10 ) were found on primary, secondary, and exumbrella tentacles. The mature polyps had one nematocyst type, microbasic euryteles ( Fig. 10K, L View Figure 10 ).
In the resulting maximum likelihood tree ( Fig. 11 View Figure 11 ), four major monophyletic clades were formed in the genus Olindias : 1) O. formosus ; 2) Olindias muelleri Haeckel, 1879; 3) O. sambaquiensis ; 4) Olindias tenuis (Fewkes, 1882); and 5) a fifth group ( O. deigo ). The monophyly of O. deigo was evident in the 16S phylogenetic tree with high bootstrap values (99%), strongly supporting the validity of the new species. The Kimura 2-parameter distance between O. deigo and O. formosus was 0.03, below the distance 0.06-0.11 between olindiids (Table 4 View Table ). Interspecific distance 0.000-0.002 between O. formosus from Iwate Prefecture, eastern Japan and O. formosus from Oita and Miyazaki prefectures, western Japan. Therefore, K2P divergence factor between 0.03-0.11 could be a threshold for discriminating olindiid species.
Habitat and ecology.
Medusae of O. deigo appeared in shallow waters (from 3 to 10 m) during winter and spring in a range of subtropical temperature localities in the Ryukyu Archipelago, southern Japan. The medusae rested on the sandy bottom or in areas with a good slope and movement of water during the daytime while they drifted and swam by extending their tentacles during the night. Thus, the species seems to be nocturnal in behavior. Stinging events attributable to O. deigo have not been reported thus far.
A comparison of key features of the species in the genus Olindias is presented in Table 5 View Table . All species of Olindias have four radial canals and numerous centripetal canals; numerous tentacles of two kinds: primary ones issuing above the umbrella margin, with distal adhesive pads and cnidocysts in transverse clasps and secondary ones on the umbrella margin, no adhesive pads, cnidocyst in rings; gonads with papilliform processes, on radial canals; numerous marginal clubs, statocyst usually in pairs at base of primary tentacles ( Bouillon et al. 2006). Olindias deigo can be distinguished from other Olindiidae species by the number and color of tentacles in adult medusae. Many more primary tentacles than secondary tentacles in O. deigo , O. formosus , and O. singularis , while fewer primary tentacles than secondary tentacles in O. malayensis , O. muelleri , O. sambaquiensis , and O. tenuis (Table 5 View Table ). Several exumbrella tentacles present in O. deigo and O. formosus while lacking in others. Exumbrella tentacles of O. deigo many more than those of O. formosus (84 vs 30-60, respectively). The primary tentacles were colorful (black, purple, and glow green) in O. deigo and O. formosus , while they were red and yellow in O. malayensis , O. muelleri , O. sambaquiensis , and O. tenuis (no data for O. singularis and Olindias sp.) (Table 5 View Table ).
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