Cassiopea cf. maremetens, Gershwin, Zeidler & Davie, 2010

Keable, Stephen J. & Ahyong, Shane T., 2016, First Records of the Invasive “ Upside-down Jellyfish ”, Cassiopea (Cnidaria: Scyphozoa: Rhizostomeae: Cassiopeidae), from Coastal Lakes of New South Wales, Australia, Records of the Australian Museum 68 (1), pp. 23-30 : 26-28

Cassiopea cf. maremetens

Gershwin, Zeidler & Davie, 2010

Figs 2 E–H, 3C, 4E,F

Material examined. AM G.18137, 1 specimen, in channel splitting Godwin Island approximately one third distance from southern shore, Breckenridge Channel, Wallis Lake, New South Wales, Australia, 32°11'45"S 152°29'56"E , R. Pearce , 15 August 2014 . AM G.18138, 1 specimen, collection data as for G.18137 . AM G.18139, 11 specimens, collection data as for G.18137 . AM G.18143–18155, single specimens; AM G.18156, 13 specimens, Pipers Creek , behind Smugglers Cove Caravan Park, Wallis Lake, New South Wales, Australia, 32°12'00"S 152°30'39"E , R. Pearce , 18 September 2014 . AM G.18181–18183, 4 specimens, inlet on south east side of Mather Island , Wallis Lake, New South Wales, Australia, 32°11'26"S 152°29'36"E, S. J. Keable & A. D. Hegedus, 28 April 2015 . AM G.18184, 1 specimen, Pipers Creek within Smugglers Cove Caravan Park, Wallis Lake, New South Wales, Australia, 32°11'58"S 152°30'39"E, S. J. Keable & A. Murray, 30 April 2015 . Bell diameter 35 mm ( AM G.18182) to 210 mm ( AM G.18139) .

Comparative material of C. maremetens . QM G6645 , 3 paratypes (110–130 mm), Mud Island, Moreton Bay , Queensland, C. Wallace, 8 April 1972 .

Remarks. The Wallis Lake specimens appear to be closest to C. maremetens Gershwin, Zeidler & Davie, 2010 , from Queensland ( Figs 2 I–L, 3D) (type locality, Lake Magellan, southwest of Caloundra, 26°49'42"S 153°06'48.6"E), with which they agree in most respects including exumbrella conformation, branching pattern of the oral tentacles and the numbers of rhopalia (19–21) ( Gershwin et al., 2010). The material from Wallis Lake ( Fig. 2G ) agrees with type material of C. maremetens (QM G6645; Fig. 2K ), and most noticeably differs from the Lake Illawarra specimens ( Fig. 2C ), in having alternating (i.e., non-opposing) rather than pinnate lateral branches along the length of the oral arms and lacking a distinct subequal bifurcation just distal to the midpoint of the primary arm. They differ, however, from both C. maremetens sensu stricto and C. ndrosia in the presence of numerous, large, conspicuous vesicles along the length of these arms (compare Fig. 2H and Fig. 2D [ C. ndrosia, Lake Illawarra ] and Fig. 2L [ C. maremetens ]). The vesicles are variably leaf shaped (generally slightly broader in the distal half, maximum width approximately one-third length), and generally as wide as the lateral arm branches. The presence of the numerous large vesicles on the oral arms is the most significant distinction between the Wallis Lake specimens and C. maremetens sensu stricto, which has few or no vesicles. Gershwin et al. (2010), however, noted they could not adequately assess the significance of the presence or absence of vesicles in their material, whether a polymorphism or indicative of an additional unrecognized species. Just as Gershwin et al. (2010) observed no correlation between body size and presence of vesicles on the oral arms in C. maremetens , the vesicles in the Wallis Lake specimens are similarly numerous across the size range.

Significantly, our Wallis Lake specimens also differ from the description of C. maremetens in the lappet shape and arrangement ( Fig. 3 C–D). Ocelli are present in the Wallis Lake specimens, absent in C. maremetens . The margin of the parameres in the Wallis Lake specimens are sinuous, resulting in 4–5 low, rounded lobes ( Fig. 3C ). In contrast, the lappets of C. maremetens are reported as square and deeply incised, with four per paramere ( Gershwin et al., 2010). Close examination of paratypes of C. maremetens , however, revealed the squared, apparently deep incisions are bridged by transparent exumbrella membrane ( Fig. 3D ). Thus, instead of being deeply incised, the outline of the lappets of C. maremetens (at least in the paratypes examined) is actually essentially sinuous and indistinctly lobate, much like that of C. ndrosia . The lappets in the Wallis Lake material differ from C. maremetens in having a more strongly sinuous margin with more numerous lobes per paramere. The differences in lappet shape and vesicle complement in comparison to C. maremetens suggest that the Wallis Lake specimens may represent a separate, possibly undescribed species. Pending further study, however, we tentatively identify our material as C. cf. maremetens to highlight its similarity to C. maremetens . Cassiopea maremetens sensu stricto is presently known from Bentinck Island, Gulf of Carpentaria, Queensland (c. 17°03'34"S 139°29'09"E) to Moreton Bay on the Queensland east coast (27°48'S 153°24'E). Reports of C. andromeda from Southport, Queensland (27°58'S 153°25'E), just south of Moreton Bay, may also represent C. maremetens ( Gershwin et al., 2010) .

The original collector of Cassiopea cf. maremetens from Wallis Lake first observed these jellyfish “in their hundreds” in Pipers Creek in 2009. The 2014 outbreak in the vicinity of Godwin Island (reported as “in large numbers within a small area”), documented here with specimens, was noticed on or near 2 August 2014 although specimens were not collected until 15 August 2014. Specimens of C. cf. maremetens were obtained again from the same location in Pipers Creek in September 2014.

Subsequent fieldwork in Wallis Lake in April 2015 confirmed the continued presence of C. cf. maremetens in Pipers Creek ( Fig. 4B ) and at a third locality within the lake adjacent to the shore at Mather Island ( Fig. 4C ). A 75 m transect line was placed randomly along the shoreline in both these locations and Cassiopea within 1 m of the shore along this distance were counted. Five randomly selected individuals from each transect were also measured for bell diameter.At Pipers Creek, 30 individuals were present along the transect, the bell diameter of the individuals measured ranged from 120 to 210 mm ( Fig. 4D ) with a mean of 170 mm. At Mather Island 24 individuals were present along the transect, those measured ranged in size from 40–70 mm with a mean of 53 mm. Distribution of Cassiopea appeared patchy. Outside the transects, dense aggregations were observed ( Fig. 4E,F ) with up to 35 per square metre at Mather Island. A water temperature of 21.5°C and a salinity of 28.7 parts per thousand was recorded during the Mather Island transect and a salinity of 12.1 parts per thousand at Pipers Creek. Cassiopea were observed lying with the aboral surface resting on very soft sediment in depths of 10–100 cm.

Figures

Figure 2. (A–D) Cassiopea ndrosia, bd 80 mm, Lake Illawarra, AM G.18075. (E–H) Cassiopea cf. maremetens, bd 80 mm, Wallis Lake, AM G.18155.(I–L) Cassiopea maremetens, bd 110 mm, Moreton Bay, paratype, QM G.6645.A, E, I, aboral surface;B, F, J, oral surface; C, G, K, aboral view of oral arm; D, H, L, oral view of oral arm.

Figure 3. Lappets, oral view.(A) Cassiopea ndrosia, Lake Illawarra, bd 80 mm,AM G.18075.(B) Cassiopea ndrosia, bd 100 mm, Hayman Island, AM G. 13568. (C) Cassiopea cf. maremetens, bd 90 mm, Wallis Lake, AM G.18156. (D) Cassiopea maremetens, paratype, bd 110 mm, Moreton Bay, QM G6645. Scale = 5.0 mm.

Figure 4. (A) Collection site for Cassiopea ndrosia from Lake Illawarra, canal through “Jetties By The Lake Lifestyle Village” looking toward lake.(B) Collection site for Cassiopea cf. maremetens from Pipers Creek, Wallis Lake, looking toward lake.(C) collection site for Cassiopea cf. maremetens from inlet on south east side of Mather Island, Wallis Lake, looking toward lake.(D) field measurement of bell diameter of c.210 mm for Cassiopea cf. maremetens from Pipers Creek, Wallis Lake. (E–F) Aggregation of Cassiopea cf. maremetens at inlet on southeast side of Mather Island, Wallis Lake from above and below water surface, respectively.