Staurodiscus gotoi ( Uchida, 1927 )

Peter Schuchert, 2017, Systematic notes on some leptomedusa species with a description of Neotima galeai n. spec. (Hydrozoa, Cnidaria), Revue suisse de Zoologie 124 (2), pp. 351-375 : 357-358

Staurodiscus gotoi ( Uchida, 1927)

Staurodiscoides gotoi Uchida, 1927: 165 , figs 1-2.

Staurodiscus gotoi . – Kramp, 1961: 147. ‒ Kramp, 1965: 56. – Kramp, 1968: 70, fig. 183. ‒ Xu & Zhang, 1974: 20, fig. 9. – Bouillon, 1984: 65. – Bouillon & Barnett, 1999: 87, fig. 85. ‒ Xu et al., 2014: 577, fig. 455.

Material examined: MHNG-INVE-33467,> 30 specimens of various developmental stages; New Zealand, Hauraki Gulf, Devonport, Narrow Neck Beach , 36.8123°S 174.8025°E, 0 m; collection date 26.07.2002; DNA isolate 126, 16S sequence FJ550472 , COI MF000510 , 18S sequence FJ550535 , 28S sequence FJ550391 ; for photos of living specimens see Table 1.

Diagnosis ( NZ material): Umbrella somewhat higher than hemisphere, diameter 5-8 mm, jelly thick, at apex about half the bell height. Manubrium moderately long, cruciform in section, four simple lips. Four radial canals and circular canal rather broad. Radial canals in proximal half thick and on both sides with 2-4 lateral outgrowths, outgrowths thick, not strictly opposite, covered by gonad tissue, longer ones curved towards bell margin but not connected to circular canal. Bell margin with four large perradial bulbs tapering into long tentacles. Interradial tentacle bulbs present, in fully mature animals tapering into tentacles but these shorter than the perradial ones. All tentacle bulbs with a black abaxial ocellus. Occasionally some additional, very small adradial bulbs. Between perradial- and interradial bulbs usually three cordyli. Cordyli relatively large, hollow, cylindrical gastrodermal cells, with a few nematocysts at the tip. Some of the cordyli also with an ocellus near their origin.

Polyps unknown.

Variation: Young medusae have only two tentacles and very small lateral outgrowths of the radial canals. Xu & Zhang (1974) depicted an animal with 16 tentacles.

Distribution: Japan, China, Papua New Guinea, Indonesia, North Island of New Zealand ( Kramp, 1965; Bouillon, 1984; Bouillon & Barnett, 1999). Type locality: Japan, Shizuoka Prefecture, Shimizu Bay.

Remarks: The identification of this material as St. gotoi was largely influenced by Bouillon & Barnett (1999) who used also material provided by the author. There are nevertheless some differences of the New Zealand medusae to those of Japan and China: there are fewer cordyli (24-26 versus up to 88), the bell diameters are smaller (4-8 versus up to 15), the interradial tentacles are often small or absent, the mesogloea is much thicker, and the lateral outhgrowths are limited to the proximal half of the tentacles. It is assumed that these are population differences. Additionally, it was noted that the mesogloea shrinks in formalin-preserved animals. A later transfer into 70% ethanol makes the mesogloea disappear completely, resulting in a condition where the lateral outgrowths cf. the radial canals reach the bell margin. It is possible that some published illustrations of Staurodiscus species are actually based on such material with a shrunken bell.

Figures

Fig. 6. Staurodiscus gotoi subadult, schematic composite drawing made after photographs of living specimens and preserved specimens. Diameter of bell approximately 6 mm (A) Lateral view. (B) Oral view. (C) Circular canal with tentacle-less bulb and a cordylus shown in optical section.