Melicertissa antrichardsoni Uribe-Palomino & Gershwin

Uribe-Palomino, Julian, Pausina, Sarah & Gershwin, Lisa-ann, 2018, Two new species of Hydromedusae from Queensland, Australia (Hydrozoa, Leptothecata), ZooKeys 783, pp. 17-36 : 17-19

Melicertissa antrichardsoni Uribe-Palomino & Gershwin sp. n. Figures 2, 3, 4

Synonymy.

?Melicertiasa Haeckel, 1879 [incorrect spelling of Haeckel’s genus]: Munro 1940: 74. No figures or tables related to this specimen.

Type material.

Holotype: QM G335899, Male, BD ca. 2 mm, tentacles six well developed and two rudimentary (Figures 2A, B, C; 4B, C); Moreton Bay, Queensland, Australia, 27.38°S, 153.39°E, 1 m, (Study 1), coll. S. Pausina, 15 Feb 2011.

Paratypes: QM G335904, Lot of two specimens, both male, BD ca. 2 mm, SD ca. 1 mm, hemi-gonad: 0.8 mm × 0.3 mm, tentacular bulbs seven, one clearly missing, base ca. 0.6 mm diameter (Figure 3B), Moreton Bay, Queensland, Australia, 27.35°S, 153.17°E, 1 m, (Study 1), coll. S. Pausina, 3 Dec 2010.

QM G335903, very poor condition, BD ca. 2 mm (Not figured), Moreton Bay, Queensland, Australia, 27.38°S, 153.39°E, 1 m, (Study 1), coll. S. Pausina, 19 Apr 2011.

QM G335902, Male, BD ca. 2.4 mm, hemi-gonad: 0.8-0.9 mm x 0.3 mm, tentacle bulbs seven (five well developed, plus two small ones), base ca. 0.6 mm (Figure 4D), Moreton Bay, Queensland, Australia, 27.16°S, 153.22°E (Study 2, (CSIRO MB55)), 1-2 m, coll. CSIRO, 27 May 2011.

QM G335900, Male, flattened specimen, BD ca. 2 mm. (Not figured); Moreton Bay, Queensland, Australia, 27.28°S, 153.08°E, (Study 2), (CSIRO MB74), 1-2 m, coll. CSIRO, 19 Dec 2011.

QM G335901, Female, flattened specimen, eigth tentacles, BD ca. 2 mm (Figure 3A), Rous Channel, Moreton Bay, Queensland, Australia, 27.29°S, 153.34°E, 1-2 m, (Study 3); coll. CSIRO 8 Apr 2014.

Other material.

QM G335905, QM G335906, microscope slide nematocyst preparations, Moreton Bay, Queensland, Australia, 27°S, 153°E, coll. CSIRO, 19/3/2011-20/5/2013 (Figure 4E, F).

Diagnosis.

Melicertissa with pairs of small oval hemi-gonads near the base of each radial canal; with eight tentacles and approximately two cordyli and one statocyst between successive tentacles; with an extremely small body size at maturity (ca. 2 mm).

Description of holotype.

Umbrella isosceles trapezoid-shaped in lateral view, aborally flattened, with the margin curving inwards at the edges, possibly due to preservation (Figure 2A, C). Velum well developed, encircling the inner side of the umbrellar margin, ca. 1/3 radius (Figure 2A).

Tentacles eight, six fully developed and two incompletely developed; hollow; coiled; more or less evenly located around the bell margin (Figure 2 A–C). Tentacle bulbs voluminous, heart-shaped, short; approximately 0.3 mm across the base. Two ventral rows of nematocysts run parallel along the length of the tentacles (Figure 2B).

Cordyli club-shaped with a swollen end and slender stalk, almost half as long as the tentacle bulbs (Figure 2B), typically two between adjacent tentacles, ca. 200 μm long; with a nematocyst cap (Figure 4B, C).

Between adjacent cordyli typically lies another structure different in form, here interpreted as a statocyst. Compared to the tapered stalk of the cordylus, this structure is more evenly columnar or thimble-shaped with straight sides and a rounded distal end (Figure 2A, C). No cirri were observed associated with the tentacles or the umbrella margin.

Stomach amorphously round-ish, broad, nearly 1/2 BD in width (Figure 2A). Manubrium sculpted into eight vertical ridges, similar in appearance to a Greek column. Mouth shaped into eight smoothly rounded lobes with a simple margin (Figure 2A). In lateral view, the stomach occupies almost half the bell cavity, and the mouth nearly reaches the bell margin (Figure 2C).

Radial canals eight, relatively broad, straight-sided throughout length, clearly visible from the stomach to the ring canal (best illustrated in Figure 4D in paratype QM G335902).

Gonads in eight pairs of oval hemi-gonads straddling each radial canal adjacent to the stomach, occupying the proximal third of each radial canal (Figure 2A). Each hemi-gonad is voluminous with a smooth surface, interpreted to be male; approximately 230 μm long and half as wide.

Colour not noted in living specimen, but preserved specimen has a transparent bell with brown gonads, tentacle bulbs and stomach.

Type locality.

Moreton Bay, Queensland, Australia.

Variation from holotype.

One specimen (QM G335901) has lumpy gonads with obvious ova (Figure 3A), and is interpreted as a mature female. All other paratypes, which are nearly the same size, have smooth gonads and are interpreted as male.

Three of the specimens (two in lot QM G335904, and one in QM G335902) are each missing one tentacle bulb; these are not variants in merosity, but rather, they are octamerous with one bulb simply absent (Figure 3B). The holotype also has two tentacles in various stages of development, as one might expect following an injury (Figure 2A).

Colour.

Paratypes have a transparent and colourless bell and cordyli, pale yellowish gonads, and darkly pigmented tentacle bulbs. A black ocellus is found at the base of each tentacle and cordylus (Figure 4A).

Nematocysts.

Melicertissa antrichardsoni sp. n. has a cnidome of two size classes of oval cnidae on the tentacles (Figure 4E). There is only one size class of oval cnidae on the body (Figure 4F) and cordyli (Figure 4B, C).

On the tentacles, the larger size class is nearly 19 μm long by 10 μm wide, and bears a conspicuous barb on the free (= aboral) end of the undischarged shaft; we interpret this type as a stenotele. The smaller size class is approximately half the size of the larger, and bears a conspicuous v-shaped notch on the free (= aboral) end; we interpret this type as a microbasic p-mastigophore.

On the cordyli, nematocysts are scattered throughout the tip in a distal cap. The cordyli nematocysts are similar in shape but smaller in size (8 μm) than the small size class on the tentacles. However, we were unable to observe internal structures and were unable study them directly (Figure 4B, C).

Etymology.

The specific epithet, antrichardsoni , is given to honour Professor Anthony J. Richardson of CSIRO and the University of Queensland. Anthony has encouraged and supported the research of plankton from Moreton Bay and around Australia through the Australian Plankton Survey.

Environmental notes.

Melicertissa antrichardsoni has been found throughout the warmer months of the year from December to May, in salinities from 26-34 PSU and water temperatures from 18.84-26.5°C.

Systematic remarks.

Melicertissa antrichardsoni is the eighth species in the genus (Table 1). Its gonads make it entirely unique within the genus, as these organs in other species are linear and either tapering, sinuous, or foliaceous, whereas in M. antrichardsoni they are small and oval in tight pairs. Another distinguishing feature is that M. antrichardsoni is much smaller than its congeners, being less than 30% the size of the other smaller species, M. mayeri Kramp (1959) and M. platygastra Nair (1951).

Compared to the other species with eight tentacles, namely M. clavigera Haeckel (1879) and M. platygastra Nair (1951), there are ample differences to separate M. antrichardsoni . Firstly, the tentacle bulbs of M. clavigera and M. platygastra are both thick and conical, whereas those of M. antrichardsoni are so bulbous as to be heart-shaped. Secondly, the lips in M. platygastra are lanceolate while those of M. clavigera are said to be quadratic, whereas these structures in M. antrichardsoni sp. n. are more smoothly rounded as one might expect an eight leafed clover to look.

Finally, Melicertissa antrichardsoni would be unlikely to be confused with M. malayica Maas (1905), the only other species with gonads adjacent to the stomach: in the latter the gonads are slender and tapered, there are more than 160 tentacles, and the cordyli are irregular, whereas in the former the gonads are oval, there are eight tentacles, and the cordyli are quite regular.

One may wonder about the relationship between M. orientalis Kramp (1961b) and M. antrichardsoni , with both being apparently endemic to Queensland. Both species have heart-shaped tentacle bulbs and nematocyst-studded cordyli however, they are remarkably dissimilar in their tentacles, gonads, and distribution. For example, M. orientalis from tropical waters of the Great Barrier Reef has seventeen tentacles and the gonads are in wavy bands along the distal 2/5 of the radial canals, whereas M. antrichardsoni from coastal, shallow, sub-tropical waters of southeast Queensland has only half as many tentacles and the gonads are in paired ovals adjacent to the stomach.

With the specimens of M. antrichardsoni at only two millimetres in diameter, it is logical to ask whether they might be juveniles. However, this is unlikely as the female specimen (QM G335901) appears to have mature ova and is near the same size as the other specimens. Specimens have been found on numerous occasions throughout the summertime over a period of five years.

Curiously, Munro (1940) mentioned finding specimens of ‘Melicertiasa’ at an area of Moreton Bay locally known as Waterloo Bay, at a sampling station located halfway between Manly and Green Island (not to be confused with Manly in New South Wales or Green Island in the Great Barrier Reef). He gave no other indication as to the identity of his specimens, but we wonder whether these might be the same species as ours. Currently the only species of Melicertissa known from Australia are M. orientalis and M. antrichardsoni .

We recognise Melicertissa adriatica Neppi (1915) with some caution. Kramp (1961a) considered M. adriatica to be in the Laodiceidae (p. 143) but noted in the addendum (p. 444) that Picard referred this species to Octogonade mediterranea Zoja (1896) in the Mitrocomidae ( Kramp 1961a, p. 157). In a subsequent publication, Kramp (1961b) elaborated, noting: "Dr. J. Picard (Marseilles) has informed me in a letter that Melicertissa adriatica Neppi is identical with Octogonade mediterranea Zoja." However, Zoja’s original illustration of O. mediterranea gives no indication of cordyli, which appear to have been clearly described in M. adriatica by Neppi, who differentiated them from both tentacles and cirri: "Zwischen je zwei Tentakeln drei bis fünf Randkolben mit einem schwarzen Ocellus und noch zahlreichere Cirren." Octogonade has since been moved to the Tiaropsidae ( Boero et al. 1987) on the basis of having compound statocysts. Bouillon and Boero (2000) and Bouillon et al. (2004) upheld M. adriatica as a laodiceid (with three types of marginal appendages, namely tentacles, cordyli, and cirri), whereas Octogonade has two types of tentacles and neither cordyli or cirri. Schuchert (2016), however, considered M. adriatica to be a junior synonym of Octogonade . Here, we consider M. adriatica to be a laodiceid based on its possession of three types of marginal appendages, whereas Octogonade has only two.