Aurelia mozambica Brown & Gibbons, 2021

Brown, Michael, Scorrano, Simonetta, Kuplik, Zafrir, Kuyper, Drikus, Ras, Verena, Thibault, Delphine & Engelbrecht, Adriaan, 2021, A new macromedusa from the coast of Mozambique: Aurelia mozambica sp. nov (Scyphozoa: Ulmaridae), Zootaxa 4933 (2), pp. 263-276 : 269-274

Aurelia mozambica Brown & Gibbons sp. nov.

Figures 5 , 6 and 7 ; Tables 2 and 3 .

Material examined: Five specimens collected by Dr D Thibault from a bottom trawl net fished to a depth of 38 m on 10/03/2018 at 18º 58’ 12” S, 36º 47’ 60” E; Nine specimens, and an additional 19 tissue specimens for molecular characterisation, collected by Dr D Thibault from a bottom trawl fished to a depth of 25 m on 16/03/2018 at 13º 42’ 36” S, 40º 36’ 0” E. Three specimens deposited to Iziko South African Museum: SAMC-A091379 , A091380 and A091381 .

Diagnosis: Characterised by 16 velar lobes (f19); shorter, very folded oral arms; deep (0.10 BD), broad (0.20 BD), manubrium base (f2, f6); frequently anastomosing canal network with a higher number (10–17) of canal origins and lilac gonads.

Holotype: Specimen number SAMC-A091379 Iziko South African Museum , collected by Dr D. Thibault from a bottom trawl on 16/03/2018 at 13º 42’ 36” S, 40º 36’ 0” E. Bell shape approximately circular ( Figure 6 ), flat, thickening to centre; opaque, 47 mm in diameter (Table 1). Bell margin with 16 velar lobes, broad (1.70 mm), narrow (0.35 mm); with eight equally spaced rhopalia ( Figure 7 ). Rhopalium with a rounded, triangular hood dorsally, formed by the bell margin; bending downwards from the statocyst, away from the exumbrella. Rhopalium with two ocelli (diameter 0.07 mm), one directed dorsally ( Figure 7 A ), one ventrally ( Figure 7 B ). Numerous (70–80 per octant) short, narrow white tentacles at bell margin. Tentacles have a thickened base (0.30 mm width, 2.00 mm length) which narrows into a filament (0.07 mm width, 5.00 mm length). Four undivided oral arms, each less than half width of umbrella diameter in length (mean length 20 mm, mean width 3 mm at midpoint); lancet-shaped and pale in colour. Manubrium broad (20 mm width) and deep (8 mm). Mean proximal gastric cavity distance 8 mm, distal gastric cavity distance 24 mm. Each of the four gastric cavities leads to four perradial canals, nine interradial canals, and two adradial canals: adradial canals do not anastomose, but perradial canals anastomose three times (on average) and interradial canals anastomose 15 times (on average). Sub-genital pore within gastric tissue not centred. Mesoglea around sub-genital pore thickened, 1 mm. Gonads lilac in preserved specimens.

Variations: (Paratypes: Specimen numbers: SAMC A091380 and A091381 Iziko South African Museum, collected by Dr D Thibault from a bottom trawl on 16/03/2018 at 13º 42’ 36” S, 40º 36’ 0” E). Bell diameter 39 mm to 160 mm. Numerous small white tentacles slightly above the bell margin, 60–70 per octant in number. Each gastrogenital sinus leading to two unbranched adradial canals, 2–4 perradial canals and 4–6 interradial canals. Perradial and interradial canals anastomose within the distal half of the exumbrella. Oral arm is very folded and with a length of 1.1–1.5 bell radius (r) in mature specimens and manubrium is firm and broad (width: r/2–r/3). Bell shape and thickness not allometrically linked; specimens below 45 mm in bell diameter did not exhibit the classic bell shape or thickness profile and some had not fully developed oral arms (Supplementary Table 3 ).

Cnidome: The cnidome includes three types of nematocyst: rhopaloids, a-isorhizas and polyspiras ( Figure 8 ). Table 2 shows the measurements of these and Figure 5 shows the relative abundances of each nematocyst within the two tissue types. There was no significant difference in the relative abundances of the different nematocysts between the bell and oral arm tissues. Paired t -tests also showed a significant difference in the size of a-isorhizas and polyspiras between the two types of tissue (df = 19, t = 2.303, p = 0.016 and df = 19, t = 1.792, p = 0.045 respectively), but there was no significant difference in the size of rhopaloids (df = 19, t = -0.856, p = 0.201). The findings differ from Russell (1970) who found atrichous haplonemes and microbasic heterotrichous euryteles in Aurelia aurita samples. However, they are in agreement with Calder (1977), who found a-isorhizas and euryteles in A. aurita samples as well as polyspiras in the polyp stage although notably Calder (1977) did not find polyspiras in the ephyrae stage of A. aurita .

Distribution: Shallow water along the coast of Mozambique, collected off the mouth of the Zambezi River (18º 58’ 12” S, 36º 47’ 60” E) and south of the Lurio River (13º 42’ 36” S, 40º 36’ 0” E)

Etymology: ‘ mozambica’ referring to the area in which the specimens were collected, Mozambique.

Remarks: This species contrasts with other species of Aurelia in a number of ways: it differs from Aurelia coerulea in bell shape, number of interradial canals and number of anastomoses; from Aurelia relicta in manubrium depth, manubrium breadth and number of anastomoses on interradial canals; and from Aurelia solida in oral arm length, manubrium breadth and number of anastomoses on interradial canals ( Table 3 ). This species also shows clear differences from the type of Aurelia maldivensis , which was described by Bigelow (1904), as having a simple cruciform mouth surrounded by very elongated lips hanging below the bell as a curtain, resembling those of an immature Cyanea . Bigelow (1904) also noted its violet colour and eight velar lobes, each with a very slight depression in the centre. Table 4 shows the differences between this species and other species that have been recorded in the region.

While it is conventional to designate neotypes for a species in the absence of a holotype, rather than erect a new species (for reasons of stability), we do not believe that the material recovered here can be assigned to Aurelia colpota . Our arguments are twofold. Firstly, Aurelia colpota was collected “in der Südsee unter d. 35 ° südl. Breite und dem 33 4 Grade westlicher Länge in der Nähe der Süd-spitz von Africa gefangen” ( Brandt, 1838). Jarms and Morandini (2019) appear to have interpreted this as 3° 34’ W, which is in water with a depth of ~4 200 m and at a location that is over 2 000 km from the west coast of South Africa. Not only is this very far from the mouth of Zambezi River in Mozambique, but it is also situated in a very different environment. South Africa has a rich marine biodiversity ( Gibbons et al., 1999; Griffiths et al., 2010), and pronounced biogeographic provincialism, especially for taxa that show an alteration between a benthic and pelagic life-history phase (e.g. Gibbons et al., 2010), as species of Aurelia do. Indeed, Ras et al. (2020) have recently shown that two species of the scyphozoan Chrysaora can be found around South Africa, despite having a slightly overlapping distribution; one with a centre of distribution along the south coast ( C. agulhensis ) and one along the west coast ( C. fulgida ). Given that the environments of the south and west coasts are not as distinct as those of the west and north-east coasts, we consider it highly unlikely that A. colpota and A. mozambica sp. nov. are the same.

Lutké (1835) documents the voyages of the Russian vessels Senyavin and Moller over the period 1826–1829, in which Dr KH Mertens participated. Mertens contributed to this volume, reporting on the observations of “L’académicien Docteur Brandt”. In the account, Mertens makes mention of all the medusae recovered, including Aurelia limbata and Aurelia hyalina but not Aurelia colpota , which further supports Brandt’s own concerns about its identity as articulated in 1838 ( Brandt, 1838). A number of authors have subsequently reported on specimens of Aurelia aurita var colpota , either without description (as Goette, 1886), or with a description that is almost as unconvincing as the type (e.g. Stiasny, 1919). Colour is notoriously unreliable as a diagnostic feature ( Holst, 2012), and specimens of Aurelia colpota appear to vary from lilac, through rose to yellow ( Brandt, 1838; Maas, 1903; Stiasny, 1919). While the number of radial canals arising from the genital sinus is repeatedly reported as five, this feature is shared by many species in the genus (e.g. Mayer, 1910). But one of the key features that sets Aurelia colpota apart from others is the “deeply incised” nature of the oral arms ( Brandt, 1838; Stiasny, 1919), a feature that is missing from the present material.

Interestingly, Vanhöffen (1888) considered that the species of Aurelia recorded off Zanzibar was probably Aurelia colpota , but he noted that he had no evidence to support this assumption, adding rather that the species of the genus Aurelia which “have hitherto been distinguished are not sufficiently specified”.

The use of a few, traditional, morphological features to distinguish between species of Aurelia has largely proven to be inconclusive ( Dawson & Jacobs, 2001), but the application of quantitative morphometric analyses can provide some resolution ( Scorrano et al., 2017). Our findings here echo and build upon those of Dawson (2003) and Scorrano et al. (2017) in finding distinguishing characteristics that can statistically differentiate species of Aurelia ( Table 3 ); or at least those specimens included here with comparable information.

Multiple COI trees generated in PAUP* and MEGA X all confirm the monophyly of the Mozambican clade of Aurelia with a minimum bootstrap support of 96%. This suggests that these Aurelia are distinct from the balance of species within the genus. Ortman (2010) showed that when analysing COI fragments using the K2P method, mean genetic divergence within species of Discomedusae never exceeds 5.8%, this finding was echoed by Gómez Daglio & Dawson (2017). Although reference to this work by Scorrano et al (2017), indicated that this pointed towards a suitable barcoding threshold for species delimitation being 6%, the article by Gómez Daglio & Dawson (2017) suggests a more nuanced approach to barcoding thresholds and further highlights the value of the phylogenetic approach to molecular species delimitation. When viewed in combination with the phylogenies generated for the genus, the results of the K2P pairwise analysis, which showed a mean intragroup divergence of 4.8% and mean intergroup divergences ranging from 15–22% within the genus Aurelia , further indicate that the Mozambican Aurelia are distinct at the species level.

Figures

FIGURE 5. Relative abundances (percentage of total count ± SE) of nematocyst types found in oral arm and bell margin tissues of Aurelia mozambica sp. nov. shaded area indicates bell tissue and unshaded are indicates oral arm tissue.

FIGURE 6. a) A whole specimen of Aurelia mozambica sp. nov. on the deck of the RV Dr Fridtjof Nansen. Specimen diameter ~15 cm b) Holotype, specimen number SAMC-A091379, Iziko South African Museum. Specimen diameter ~ 4.7cm. Both pictures have been edited to increase contrast in order to make features clearer.

FIGURE 7. Superior ocellus of the rhopalium of Aurelia mozambica sp. nov. (A), inferior ocellus facing away from the exumbrella (B).

FIGURE 8. Nematocysts of Aurelia mozambica sp. nov: Rhopaloid (A), a-Isorhiza (B) and Polyspira (C).