Chironex yamaguchii

Description. Chirodropid medusae with smooth exumbrella (Fig. 2 A), maximum BH about 110 mm (average about 60 mm) and maximum IRW about 95 mm. Pedalia claw-like, each bearing up to nine tentacles, but usually only seven; proximal pedalial canal bend volcano-shaped sensu Fenner (1997) (Fig. 1 C). Extended trailing tentacles in life appearing flat and broad as in Chironex fleckeri; up to nine tentacles per pedalium with lavender-colored nematocyst bands. Upon contraction, or in preserved specimens, tentacles tending to be thicker and rounded, like sausage-links (Fig. 2 B). Manubrium cruciform with four narrow, lanceolate lips (Fig. 2 C); about 2 / 3 to 3 / 4 as long as bell height. Gastric phacellae V-shaped in each corner of stomach as in most other chirodropids (Fig. 2 A); gastric cirri simple and unbranched (Fig. 2 D). Gastric saccules (superior gonads) cock’s-comb shaped / grape-cluster-like and opaque in mature specimens (Fig. 2 E). Development of gonads following sequence described for Chironex fleckeri by Barnes (1966). Gastric saccules developing from small, smooth, kidney-shaped bulges at ceiling of subumbrella into large, grapecluster-like swellings by elongation and successive addition of numerous swellings until they occupy much of subumbrellar cavity. Perradial lappets smooth, broad, triangular, extending almost to subumbrellar edge of velarium (Fig. 2 F). Four perradial muscular brackets (frenulae) brace the right-angle connection from tip of rhopalial niche to 3 / 4 the distance between velarial turnover and its margin (Fig. 2 G). Each frenulum consisting of a single, thick gelatinous sheet (Fig. 2 G). Velarial canals numerous and highly branched, as in Chironex fleckeri (Fig. 2 H, 2 I). Each of the four rhopalia bearing a set of six eyes, with the two median possessing prominent lenses and the four lateral ones adjacent to the lens eyes being pigment pits and slits (Fig. 2 J). Statolith oval, transversally mounted at base of rhopalium (Fig. 2 J). As in other chirodropids, rhopalial niche ostium dome-shaped with a single upper covering scale (Fig. 2 K); rhopalial niche located in a triangular depression of exumbrella (Fig. 2 K). The cnidome of Chironex yamaguchii and its transformation throughout the course of development was described in detail based on specimens from Japan by Oba et al. (2004; as Chiropsalmus quadrigatus).

Diagnosis. Chironex yamaguchii, sp. nov., has a maximum bell height of about 110 mm (about 1 / 2 to 1 / 3 that of its congener Chironex fleckeri); up to nine tentacles per pedalium (versus up to 15 in Chironex fleckeri); proximal pedalial canal bend volcano-shaped (Fig. 1 B) (in contrast to the “ upswept corniculum ” in Chironex fleckeri; Fig. 1 B).

Remarks. Earlier misidentifications of Chironex yamaguchii can be attributed to Mayer’s (1910: 516 – 517) redescription of this species, under the name Chiropsalmus quadrigatus Haeckel, 1880, from the Philippines. Chiropsoides quadrigatus (Haeckel, 1880: 447, as Chiropsalmus quadrigatus) was described from Burma and is easily distinguishable from Chironex yamaguchii. Members of the genus Chiropsoides have laterally compressed pedalia and their gastric saccules are long, finger-shaped and smooth, whereas the pedalia in Chironex are claw-like and the gastric saccules in mature specimens are cock’s-comb shaped / grapecluster-like. Both Thiel (1928) and Stiasny (1937) noted the discrepancies between Mayer’s description of what he thought was Chiropsoides quadrigatus from the Philippines and Haeckel’s original description of the species from Burma. Stiasny (1937) nevertheless believed that the descriptions pertained to the same species. Rather than rectifying this taxonomic problem, he provided yet another redescription of Chiropsoides quadrigatus (as Chiropsalmus quadrigatus) by reconstructing the species from Haeckel’s (1880) and Mayer’s (1910) descriptions, as well as a specimen from the Maldive Archipelago. By doing so he perpetuated the confused identity of the chirodropids from the Philippines and, ultimately, from Japan. Our examinations of Mayer’s (1910) material at the National Museum of Natural History, Smithsonian Institution, revealed that the specimens belong to the genus Chironex, and they agree in their morphological characteristics with material examined from Japan. Specimens from the Philippines appear to be a developmental series displaying numerous stages in the maturation process from juvenile to adult in Chironex yamaguchii. Mayer (1910: 516, Fig. 331) depicted two stages in the development of Chironex yamaguchii, even though he did not explicitly state so. The oral view of the stomach shows the well-developed, cock’scomb shaped gonads typical of Chironex, whereas the side view of the animal depicts an immature specimen that has not yet fully developed. There is little doubt that what Mayer observed was a species of Chironex. Since Chironex was not described until some 45 years later (Southcott 1956), he did not recognize his mistake and believed that he had an opportunity to add to the arguably insufficient original description of Chiropsoides quadrigatus (see Gershwin 2006 b, for discussion). Morphological differences between Chironex fleckeri and Chironex yamaguchii are few, and the shape of the pedalial canal bend seems to be the most reliable character to distinguish the two. However, we believe that they represent different species, and geographic distance among the collection sites of Chironex fleckeri and Chironex yamaguchii lends additional credibility to this interpretation. In addition to morphological differences and allopatric distributions of Chironex fleckeri and Chironex yamaguchii, we observed a strong genetic differentiation among the two. We calculated uncorrected pairwise distances among mitochondrial COI sequences from the Ishigaki type material of Chironex yamaguchii (GenBank nos. FJ 665180 and FJ 665182) and an unvouchered specimen of Chironex fleckeri from Weipa, Queensland, Australia (GenBank no. FJ 665182). Both sequences of Chironex yamaguchii were identical, but differed from Chironex fleckeri by 16.7 %. In a medical thesis, Fenner (1997) identified close affinities between Chironex fleckeri and the deadly venomous chirodropid known from both Japanese and Philippine waters. Dr. Fenner’s familiarity with morphological characters of the latter was garnered through correspondence with Y. Araki and the first author of this manuscript, and his study of Mayer’s specimens. He also pointed out the distinguishing feature of the pedalial canal bend, but did not describe it as a new species. He noted many more fatalities related to jellyfish envenomations in the Indo-West Pacific. Future sampling will probably lead to additional records of Chironex species or probably even new, distinct species. In general, there appears to be a tendency for morphological conservativeness in Cubozoa and probably Medusozoa in general. Given these considerations, future studies may show that Philippine and Japanese specimens of Chironex yamaguchii represent two distinct species, but our current data do not support such an interpretation.

Etymology. The specific name honors Prof. Masashi Yamaguchi, who has contributed much to an understanding of Japanese cubozoans and the early life history of Chironex fleckeri.

Material examined. Holotype: USNM 1121554, female with fully developed gastric saccules and oocytes, 92 mm BH, 80 mm IRW, NT 6, Ishigaki Island, Ryukyu Archipelago, Okinawa Prefecture, Japan, 24 September 2007. Paratypes: USNM 1121555, female with fully developed gastric saccules but oocytes not fully developed, 90 mm BH, 85 mm IRW, NT 6, Ishigaki Island, Ryukyu Archipelago, Okinawa Prefecture, Japan, 24 September 2007; USNM 1121556, 70 mm BH, 60 mm IRW, NT 7, initially fixed in EtOH and subsequently transferred into formalin, gastric saccules fully developed, Okinawa Island, 26 º 20.9 ’ N 127 º 45 ’ E, 19 September 1988; QM G 317050, juvenile preserved in EtOH, 20 mm BH, 16 mm IRW, NT 5, Nakagusuku, Okinawa Island, 18 July 1992. Other material: Mayer’s Philippine lots USNM 27911 and 27915, Subig Bay, Luzon; USNM 27913, Cataingan Bay, Masbate; USNM 27914, Pujada Bay, Mindanao; USNM 27916, Panabutan Bay, Mindanao; USNM 27917 and 27918, Mansalay Bay, Mindoro; USNM 28691, Ulugan Bay, Palawan; USNM 28692 and 28696, Malcochim, Linapacan Strait, Palawan; USNM 28694 and 28697, Bolinao Bay, Luzon; USNM 28695 and 28701, San Miguel Bay, Luzon; USNM 28698, Tilik Bay, Lubang Island, Mindoro; USNM 28700, Hamilo Point, Luzon; USNM 38019 Taytay, Palawan [lots USNM 27912, 28693, 28699, and 38016 could not be located]; 232 unregistered specimens collected from 1978 to 1996 by Y. Araki, M. Yamaguchi, and the first author at Ginowan Marina, Ginowan Tropical Beach, Chatan Beach, and Motobu Port (Okinawa Island), and Sukuji Beach on Ishigaki Island; QM G 317051, Kana Beach, Ginoza, Okinawa Island. Type locality. Ishigaki Island, Ryukyu Archipelago, Okinawa Prefecture, Japan.