Netrostoma nuda, Gershwin, Lisa-Ann & Zeidler, Wolfgang, 2008

Gershwin, Lisa-Ann & Zeidler, Wolfgang, 2008, Two new jellyfishes (Cnidaria: Scyphozoa) from tropical Australian waters, Zootaxa 1764, pp. 41-52 : 46-50

Netrostoma nuda , sp. nov.

Figures 2 , 3

Netrostoma coerulescens . -? Stiasny, 1931: 36, Wilson Islet, Capricorn Group, QLD. -? Stiasny, 1926: 251, Funafuti Island north of Australia. - Kramp, 1965: 265, Tongue Reef, QLD.

? Netrostoma sp. - Laboute and Magnier, 1979: 74, fig. 29 (caption confused with fig. 26), New Caledonia. “Sugar Bowl Jelly” - Brown, 1973: 14.

Holotype: QM G325000, Palm Cove, Cairns, QLD, coll. L. Gershwin, 1 February 2005; ca. 15cm absolute BD, female.

Paratypes: MTQ G55271, no data, from James Cook University Teaching Collection; ca. 118mm BD. MTQ G55272 (JHB J916), Bathurst Head, Princess Charlotte Bay, York Peninsula, QLD, coll. H.W. Cummings, 22 December 1961; ca. 132mm BD, with 2 small associated fish. MTQ G55273 (JHB J924), Palm Beach, Cairns, QLD, 10 January 1962; ca. 74mm BD. SAM H958 (RVS A516), north side of Tongue Reef, Cairns, QLD, at surface, coll. T. Purcell, 30 January 1960; ca. 115mm BD, previously identified by P. Kramp as N. coerulescens . AM G16003, Palm Cove, Cairns, QLD, south side of stinger net, coll. J. Seymour, 18 January 1999; ca. 93mm BD. QM G317065, Coral Sea, E. of MacGillivray Reef, 1–2m below surface, coll. Lyle Vail, 13 February 2000; ca. 120mm BD. QM G317066, same data as QM G317065; 1 specimen ca. 100mm BD, plus fragments from 2 others. QM G306742, Casuarina Beach, W. side of Lizard Island, GBR, QLD, 14.40.8’S, 145.26.6E, coll. JNA Hooper & PA Tomkins, 7 March 1996, over soft coral beds, sand base; 2 specimens, ca. 15cm BD. QM G324996 – G324999, same collection data as holotype; ca. 10–12cm absolute BD. SAM H1584, same collection data as holotype; 9 specimens in 6 jars, ca. 10–15cm absolute BD.

Type locality: Palm Cove, Cairns district, North Queensland.

Diagnosis. Netrostoma with a single large, round protruding knob at apex of umbrella; with 7 rounded velar lappets, 2 pointed smaller rhopaliar lappets per octant; lacking exumbrellar papillae and appendages between the mouths.

Description of holotype. Exumbrella smooth, lacking papillae or warts; ornamented only with a single, large, round apical knob ( Figures 2 A, 3A &B); subumbrella with approximately 10 gelatinous radial ridges per octant, extending from peripheral edge of gastro-gonadal region approximately halfway to margin. Peripheral region of bell inverted.

Lappets 9 per octant, of two types: rhopalial lappets small, pointed, with simple blind projection of radial canal network; remaining 7 (velar) lappets rounded, large, each with one or more short blind spikes projecting distally from top of radial canal loop.

Oral arms 8, about as long as bell radius; bi-forked, with numerous progressively shorter branches along adaxial side of arm; branches further branched, dendritic, with feather-like mouths; lacking appendages between mouths ( Figure 2 B).

Radial canals: Rhopaliar canals 8, of even thickness; inter-rhopaliar canals 3 per octant (total of 32 canals projecting from gastro-gondal region); completely anastomosed in outer 1/3 of bell, with “squares” proximally, becoming “rectangles” peripherally; with many blind diverticula, especially in proximal region where main canals have not yet anastomosed, with diverticula from network pointing laterally toward main canals.

Rhopalia 8, 4 perradial and 4 interradial, within heart-shaped niches, “pointed” end of heart being the opening between adjacent lappets, with “bilobed” end enveloping a short radial canal projection; niches closed entirely on exumbrellar side, with short subumbrellar protective membrane, such that rhopalium directly exposed to water flow on subumbrellar side.

Oral plate with numerous long, stiff, hollow, cylindrical, gelatinous appendages ( Figure 2 B) arising at branch-points of oral canal network. Body open to outside only at 4 small interradial funnels; gastric and genital systems continuous. Gonads 4, interradial, U-shaped to amorphous, entirely enclosed.

Color in life translucent hazy bluish-white throughout, lacking spots, streaks, or other pigment ( Figure 3 B); preserved mostly transparent with translucent canals and oral arms, gonads yellowish.

Variation. Paratype MTQ G55273, presumably a sub-adult based on size, with only 5–6 velar lappets per octant, which are fused; it also has only 2–3 radial canals per octant between main canals, and gonads appear mature, but we can only identify three with confidence. The remaining paratypes all have a damaged apical knob; despite this fact, there can be no mistake that it is without papillae. One possible explanation for the damage may be found in the collection label with specimen MTQ G55272, which noted “part showing above water while swimming.” As mesoglea dries quickly when exposed to air, perhaps this, or compaction during preservation, attributed to the damage.

Observations on live animals. Netrostoma nuda drifts along near the surface, with the knob bobbing above or just below the surface of the water; in some specimens the knob is damaged, possibly as a result of desiccation from being held above the water too long. Occasionally the species comes inshore in large numbers, giving a mild but annoying sting to swimmers. The largest medusa we have observed was well over 30cm bell diameter; the knob is conspicuous at all sizes (range 10–30+ cm).

Distribution. Previous records of Netrostoma spp. in Australian waters deserve some comment. The first was by Stiasny (1926), as N. coerulescens , from Funafuti Island north of Australia. However, this may have actually been N. nuda , since it lacked oral-arm appendages, but no mention was made of the apical structure. Stiasny (1931) later recorded the same species from Wilson Islet, Capricorn Group, QLD, though it is unclear what species he actually had. He commented that the oral appendages were only small, indicating that they did occur on the oral arms as well as the oral disk, but made no comment as to the exumbrellar ornamentation. He further commented that the species was rare in Australia. Subsequently, Kramp (1965) reported N. coerulescens from Tongue Reef, QLD. However, we have examined Kramp’s specimen (SAM H958 = RVS A516) and it is clearly N. nuda , lacking any form of oral arm appendages between the mouths, having seven velar lappets per octant, and a squashed but papilla-free apical knob. Curiously, N. nuda is quite common in North Queensland waters, being well represented in Australian collections. We have yet to see Australian specimens that correspond to the description of any other species of Netrostoma . The only other reference that we are aware of, which appears to be for this species, is in a field guide for New Caledonia ( Laboute & Magnier 1979); thus extending the range of N. nuda .

Remarks. Stiasny (1921) and Kramp (1961) both separated the genera of Cepheidae based on the number of radial canals per octant, with Netrostoma having three, Cephea having more than three. Unlike the four other species of Netrostoma , N. nuda does not have warts or papillae on the exumbrella. Rather, it has only a single large central knob, much like the knob on the lid of a saucepan. Although Kramp (1961) defined the genus Netrostoma as having large warts on the central dome, N. nuda clearly must be assigned to this genus based on its radial canal arrangement, namely three per octant between main canals. It seems most sensible to broaden the genus Netrostoma to include taxa lacking exumbrellar warts or papillae, rather than to propose a new genus for this taxon.

Netrostoma nuda differs from its congeners not only in lacking exumbrellar papillae, but also in other characters as follows: from N. dumokuroa ( A. Agassiz & Mayer 1899) in having prominent lappets, whereas in the latter the lappets are nine per octant and inconspicuous; from N. coerulescens Maas (1903) and N. setouchianum ( Kishinouye 1902) in lacking appendages between the mouths; and from N. typhlodendrium Schultze (1898) in having only seven velar lappets per octant, rather than eight. Furthermore, in the sensory niches in N. nuda , the protective web on the subumbrellar side is very shallow, such that the niche is open and rhopalium itself is directly exposed to water flow, whereas the protective web appears to be more distally placed, thus the sensory niche more closed, in N. dumokuroa ( Agassiz and Mayer 1899, Pl. 12, fig. 39). The radial canals in N. dumokuroa are described and figured as having four wider than the rest, whereas in N. nuda all eight main canals leading to the rhopalia are of equal width, but thicker than the remaining 24 canals. N. dumokuroa and N. setouchiana are said to have the genital sacs completely separated from the gastric sacs ( Agassiz & Mayer 1899; Mayer 1910); however, in N. nuda bubbles injected through the subgenital pores could be freely shifted throughout the gastric and genital cavities simply by rotation of the specimen, indicating no separation. In addition, one paratype (MTQ G55271) has numerous eggs lodged in the radial canals of the lappets, further evidence that the gastric and genital systems are connected in this species.

Revised Diagnosis for the genus Netrostoma . Cepheidae with three inter-rhopaliar canals in each octant; exumbrella with large warts on central dome or with a single large central knob; with or without stiff appendages on mouth-arms and arm-disk.

Figures

FIGURE 2. Netrostoma nuda, sp. nov., holotype. A, Exumbrellar view; note large central knob and lack of papillae. B, Subumbrellar view; note presence of thick appendages on oral plate, but lack of appendages between the mouths.

FIGURE 3. Netrostoma nuda, sp. nov. A, Paratype specimen MTQ G 55271. B, Holotype, in life.