New records of Pegantha spp. (Hydrozoa: Narcomedusae) off Northern Brazil

Abstract

Specimens of Pegantha laevis H.B. Bigelow, 1909 and Pegantha triloba Haeckel, 1879 were found in oceanic waters off the northern Brazilian coast. The former species is clearly distinct due to the thickness and shape of peripheral channels, while the latter is recognized mainly due to the exumbrellar furrows and long otoporpae. This study represents the first actual record of P. laevis inside the Brazilian Economic Exclusive zone, since previous reports were far away from the coast, and clarifies the presence of P. triloba off Brazil.

Key-Words.
Jellyfish; Cnidaria; Hydrozoa; Taxonomy; Biodiversity; South Atlantic

INTRODUCTION

Holoplanktonic hydromedusae of the family Solmarisidae Haeckel, 1879 is distinguished from other Narcomedusae mainly by the absence of manubrial pouches, thus the periphery of manubrium is circular and unbroken at the same level as the tentacles rise. Two genera are recognized in the family: i) Pegantha Haeckel, 1879, with a peripheral canal system and otoporpae, and gonads forming lobes on the margin of manubrium wall; and ii) Solmaris Haeckel, 1879, without peripheral canal system and otoporpae and with simple annular gonads (Bouillon & Boero, 2000; Bouillon, et al. 2004, 2006).

Currently there are five valid species of Pegantha, in addition to many doubtful names regarded as “taxon inquirendum” or possible synonymies (Schuchert, 2015). All valid species are widely distributed, mostly in epipelagic oceanic waters (Kramp, 1957, 1961; Bouillon, 1999). At southwestern Atlantic all the five species have been found (Bouillon, 1999), among which Pegantha laevis H.B. Bigelow, 1909 was recorded off Argentina and in oceanic waters > 1,300 km offshore the Brazilian coast (Kramp, 1957; Genzano et al., 2008). Pegantha trilobaHaeckel, 1879 was recorded at Fernando de Noronha archipelago (Vanhöffen, 1913) and offshore North of Brazil (Ranson, 1949; Kramp, 1959b), but its occurrence has been overlooked by Oliveira et al. (2016) in the census of Cnidaria from South America, and thus its distribution became uncertain. Hydromedusae are important predators in marine zooplankton and information on its distribution is essential for understanding species diversity, biogeographic patterns and marine ecosystem functioning. In this study, we report the occurrence of both species on North Brazilian shelf and offshore waters, extending northwards the known distribution of P. laevis in the western Atlantic and clarifying the presence of P. triloba in Brazilian waters.

MATERIALS AND METHODS

One specimen of Pegantha laevis and eight specimens of Pegantha triloba were found in superficial plankton samples collected in oceanic waters off the northern coast of Brazil (Table 1) with a David-Hempel catamaran (Hydro-Bios, Kiel, Germany) equipped with two superposed nets, each with a rectangular mouth and 500 μm mesh size. Sub-superficial temperature and salinity was measured with a Seabird SBE 25 Sealogger CTD profiler. Specimens were deposited in the Museu de Oceanografia Prof. Petrônio Alves Coelho from Universidade Federal de Pernambuco. All applicable international, national, and/or institutional guidelines for the care and use of animals were followed by the authors.

Table 1
Pegantha laevis and Pegantha triloba occurrences off northern Brazil. T = temperature; S = salinity.

	Location	Number of specimens	T(°C)	S	Bottom depth (m)
P. laevis	0.0013°N, 38.0073°W	1	27.9	36.2	4,426
P. triloba	3.9963°N, 38.0042°W	7	28.1	36	4,208
	5.9126°N, 49.7035°W	1	27.6	36.2	3,592

RESULTS AND DISCUSSION

The single Pegantha laevis medusa found was 9 mm in bell diameter. Umbrella flattened with completely smooth surface (Fig. 1A). The specimen was damaged and ca. 1/5 of the margin was missing, and about 16 square marginal lappets were estimated. Peripheral canals quadrate, very broad mainly in the sides which represent 1/3-1/4 of the total lappet width and do not tapering (Fig. 1B). Only remnants of short otoporpae present, with nearly the same length of the peripheral canal width. Gonads absent.

Figure 1
Pegantha laevis medusa from North Brazil. (A) Aboral view. (B) Detail of marginal lappet and peripheral channel.

A total of eight individuals of Pegantha triloba were analyzed, ranging from 1.5 to 4.6 mm in bell diameter (Fig. 2A). Seven medusae presented eight marginal lappets and one medusa had nine lappets. Peripheral canals thin, more or less triangular with rounded or pointed margins (Fig. 2B). Typically, three long otoporpae in the smaller medusae and five in the two larger ones, reaching almost the middle of the central disk and tapering upwards; exumbrella with furrows from the base of the tentacles to almost the apex, leaving the central disk smooth (Figs. 2A, B). The largest specimen presented gonads with three lobes (Figs. 2B, D), except one of the gonads with a single lobe.

Figure 2
Pegantha triloba medusae from North Brazil. (A and B) Oral view. (C) Detail of marginal lappet and otoporpae. (D) Aboral view showing furrows and ridges on exumbrella. (E) Detail of tri-lobed gonads. Arrows indicate some otoporpae.

Species of the genus Pegantha are mostly characterized by the width and/or shape of the peripheral canals, the size of the otoporpae and the presence/absence of exumbrellar furrows (Kramp, 1957, 1959b, 1961, 1965, 1968; Pagès et al., 1992; Bouillon, 1999; Bouillon et al., 2004). The number of gonadal lobes has also been used by earlier researchers (e.g.,Haeckel 1879), but this has been long shown to be highly variable and not accurate to distinguish species (e.g.,Bigelow, 1909; Kramp, 1961).

Pegantha triloba is easily distinguished from the remaining species by the exumbrella with furrows. This character, along with the long otoporpae and relatively thin peripheral canal system (Fig. 2B), confirm the present identification (e.g.,Bigelow, 1909; Kramp, 1957, 1959b, 1961; Bouillon, 1999). Bigelow (1909) described the otoporpae reaching the level of the base of the tentacles, however latter authors indicate the otoporpae may be considerably longer than the lappet, reaching the apex of the exumbrella (Kramp, 1957) likewise the present material (Fig. 2D). The observed medusae have 8-9 marginal lappets and tentacles, less than the 12-16 typically reported for this species. This may be attributed to the small size of our specimens (Xu & Wu, 1998), in spite the fact that one of them already had gonads. Although medusae as small as 5-7 mm have 12-14 lappets (Kramp, 1957), our specimens are smaller (1.5 to 4.6 mm) and in accordance with the medusa reported by Bigelow (1909) (with 2.5 mm in diameter and 7 lappets). The smaller number of otoporpae (3-5 per lappet) observed in the present specimens is also probably related to the small size of the medusae sampled here (see Bigelow, 1909: 88).

Among Pegantha species with smooth exumbrella, P. laevis differs from Pegantha clara R.P. Bigelow, 1909 and Pegantha rubiginosa (Kölliker, 1853) in the thickness of the peripheral canals. Pegantha martagonHaeckel, 1879 has also thick peripheral canals, however those from P. laevis are even thicker, being almost as wide as the space between them (Kramp, 1957; Fig. 1B). Also, the peripheral canals of P. martagon taper towards the margin (Bigelow, 1909; Kramp, 1957, 1961), while the same is not true for P. laevis (Fig. 1B). These differences in the peripheral canal system are robust and may help even the identification of badly preserved specimens (Kramp, 1957). In addition, P. martagon has a vaulted umbrella, while in P. laevis the umbrella is flatter and lenticular (Bouillon, 1999).

Although P. laevis is not a common species (Kramp, 1959b, 1968), it is widely distributed in tropical, temperate and even Antarctic (temperatures down to 0.2°C; Navas-Pereira & Vannucci, 1990) regions of the three large oceans, but mostly in the Atlantic and Pacific (Fig. 3). Its known distribution is somewhat skewed southwards, with current records not surpassing 50°N, but reaching nearly 70°S (Fig. 3). In South Atlantic waters, the occurrence of this species was recorded off the African and Argentinean coast and in the center of the Atlantic at tropical, temperate and polar latitudes (Fig. 3). Recently, Oliveira et al. (2016) considered this medusa as integrating the Brazilian fauna based on Kramp’s (1957) record at 31.27°S, 29.94°W (number 4 in Fig. 3). However, this location is > 1,300 km offshore, in the center of Atlantic Ocean (Fig. 3), and far outside the economic exclusive zone and Brazilian waters. Thus, the present study represents the first actual record of this species off Brazil.

Figure 3
Global distribution of the narcomedusa Pegantha laevis based on this study and literature records. The dashed line shows the 250 m isobath, roughly corresponding to the shelf break (generated using Ocean Data View software; Schlitzer, 2007). Data Source: 1 = this study; 2 = Bigelow, 1909; 3 = Kramp, 1955; 4 = Kramp, 1957; 5 = Kramp, 1959a; 6 = Kramp, 1959b; 7 = Kramp, 1965; 8 = Fagetti, 1973; 9 = Bouillon et al., 1986; Bouillon, 1978; 10 = Navas-Pereira & Vannucci, 1990; 11 = Pagès et al., 1992; 12 = Buecher et al., 2005; 13 = León et al., 2005; 14 = Ayón et al., 2008; 15 = Genzano et al., 2008; 16 = Rodriguez, 2012; 17 = Gasca & Browne, 2017.

Pegantha triloba is widely distributed in oceanic waters of the Atlantic, Indian and Pacific Oceans, mainly in warm latitudes between ca. 30°N and 30°S (Fig. 4). Outside this latitudinal range, P. triloba has been recorded at northwest of South Georgia (48°S), in the Mediterranean and in the Southern Ocean, a single record on each locality (respectively numbers 5, 4 and 35 in Fig. 4). The two latter records may be misidentifications (Kramp, 1959b, 1965). In the South Atlantic, the species was recorded off the African coast and in several oceanic localities between Africa and South America (Fig. 4). Although there were some previous records of this species on Brazilian waters (Ranson, 1949; Kramp, 1959b), these occurrences were overlooked in a recent review (Oliveira et al., 2016), perhaps because they were reported only as “Atlantic” or “Equatorial Atlantic”. Thus, this study highlights the presence of P. triloba in oceanic waters offshore northern Brazilian coast. While specimens collected in this study were in the subsurface, this species has extensive vertical distribution from surface to strata as deep as 5,000 m (Bigelow, 1909; Kramp, 1959b, 1965).

Figure 4
Global distribution of the narcomedusa Pegantha triloba based on this study and literature records. The dashed line shows the 250 m isobath, roughly corresponding to the shelf break (generated using Ocean Data View software; Schlitzer, 2007). Data Source: 1 = this study; 2 = Haeckel, 1879; 3 = Bigelow, 1909; 4 = Vanhöffen, 1913; 5 = Kramp, 1948a; 6 = Kramp, 1948b apud Kramp, 1961; 7 = Ranson, 1949; 8 = Kramp, 1957; 9 = Kramp, 1959b; 10 = Bouillon et al., 1988; 11 = Bouillon et al., 1986; 12 = Chang, 2008; 13 = Du et al., 2012; 14 = Kramp, 1965; 15 = Larson, 1982; 16 = Loman-Ramos et al., 2007; 17 = Ayón et al., 2008; 18 = Baldrich & López, 2010; 19 = Navas-Pereira & Vannucci, 1990; 20 = Navas-Pereira & Vannucci, 1991; 21 = Pagès, 1992; 22 = Pagès et al., 1992; 23 = Segura-Puertas, 1984; 24 = Segura-Puertas, 1991; 25 = Suárez-Morales et al., 2002; 26 = Vannucci & Navas, 1973; 27 = Xu & Wu, 1998; 28 = Suárez-Morales et al., 1999; 29 = Segura-Puertas, 1992; 30 = Bleeker & Van Der Spoel, 1988; 31 = Chaparro & Peralta, 2013; 32 = Repelin, 1965; 33 = Chaparro, 2007; 34 = Muñoz-Pozo, 2015; 35 = Vanhöffen, 1912 apud Kramp, 1961; 36 = Fernández-Álamo, 2002.

Holoplanktonic animals such as Pegantha species usually present a wide distribution in the oceans, being dispersed by large-scale processes such as global circulation (Boltovskoy et al., 2003). Furthermore, many Narcomedusae early life stages are parasitic (Xu & Wu, 1998; Osborn, 2000), and movement and migration of their hosts can also contribute to the wide distribution of P. laevis and P. triloba (Figs. 3, 4).

The waters off the northern Brazilian coast are amongst the least studied regarding zooplankton in general (Lopes, 2007) and medusae in particular (Oliveira et al., 2016), leaving a gap in the understanding of species diversity and biogeographical patterns. Particularly considering the Amazon River plume as a potential barrier for marine organisms (e.g.,Rocha, 2003), and the potential high diversity of this understudied tropical and highly productive ecosystem. These aspects emphasize the need of comprehensive surveys in the area and faunistic studies such as the present one.

ACKNOWLEDGEMENTS

We thank the support of Brazilian National Institute of Science and Technology for Tropical Marine Environments - INCT AmbTropic (CNPq/FAPESB grants 565054/2010-4 and 8936/2011), Brazilian Research Network on Global Climate Change - Rede CLIMA (FINEP grant 01.13.0353-00) and European Integrated CARBOCHANGE (FP7 264879). Everton Giachini Tosetto was supported by CNPq (grant 140897/2017-8). And also to all the boarded scientific team of Camadas Finas III and Amadeus II research project.

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Publication Dates

• Publication in this collection
  14 Nov 2018
• Date of issue
  2018

History

• Received
  09 June 2018
• Accepted
  19 Sept 2018