Two new species of medusae (Cnidaria) from the coastal waters of the northern Beibu Gulf

1. Introduction

The Beibu Gulf is a semienclosed shallow bay in the northwestern part of the South China Sea that is connected to the South China Sea by its southern mouth and the Qiongzhou Strait on the eastern side. The spatial variation in water temperature and salinity in the Beibu Gulf is affected by the balance of seawater, freshwater inputs and water with a high salt content from the South China Sea and circulation in the gulf (Chen et al., 2008). Therefore, the Beibu Gulf is an important marine breeding area and high-quality fishery in China. Furthermore, the Beibu Gulf, which includes mangrove forests, coral reefs, seagrass beds and other typical marine ecosystems, is one of the most biodiverse marine areas in China (Chen et al., 2016).

A study on medusae in the Beibu Gulf was conducted by Xu (1965) along the Hainan Island and in the adjacent sea. In total, 52 species were identified, including 16 newly recorded species. Huang (1987) reported 64 species along the southern coast of Guangxi Zhuang Autonomous Region during six seasonal oceanographic cruises.

In the last two decades, the taxonomy and ecology of medusae in the Beibu Gulf have been well studied. Guo et al. (2008a) analyzed a total of 99 species of medusae, including six species of Anthomedusae that were new to science and three species newly recorded in China (Xu et al., 2008). Guo et al. (2008b) also studied the composition and distribution of planktonic medusae in summer and winter, identifying a total of 187 species. Later, Huang et al. (2010a) and Li et al. (2010) described two new species in the genera Eucheilota and Hydractinia along the Guangxi Zhuang Autonomous Region coast, and Lin et al. (2010) and Du et al. (2012) updated the number of medusae with five new species and three newly recorded species.

Based on previous studies (Xu, 1965; Huang, 1987; Guo et al., 2008a, b; Xu et al., 2008; Huang, 2010a, b; Li et al., 2010; Lin et al., 2010; Du et al., 2012) and recent records from the authors, there are 159 species of medusae in the Beibu Gulf. In this work, the species composition and seasonal variation of planktonic medusae in the coastal waters of the northern Beibu Gulf are listed. Two species, Helgicirrha apapillata Xu, Chen & Wang sp. nov. and Proboscidactyla pentacanalis Xu, Chen & Yang sp. nov., are reported as being new to science. Three species are newly recorded: Hydractinia vacuolata Xu & Huang, 2006, Proboscidactyla flavicirrata Brandnt, 1834 and Phialella macrogona Xu, Huang & Wang, 1985. All new species are described, photographed and illustrated in this paper.

2. Materials and methods

We analyzed planktonic medusae in samples collected from 29 stations in the coastal waters of the northern Beibu Gulf (21°16′00″–21°49′52″N, 108°13′23″–108°52′41″E) during four seasonal oceanographic cruises from October 2017 to August 2018 (Fig. 1). All planktonic samples were collected using a large-type zooplankton net (80 cm net mouth diameter, 0.505 mm mesh size) by vertical towing from the near bottom to the surface. The samples were preserved in seawater with 5% buffered formalin. The samples were then examined using stereoscopic and light microscopy, and taxonomic identification was performed using the literature specified in the reference section.

Figure  1.  Map of the study area showing the locations of the sampling stations.

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All drawings were made from preserved specimens using a camera lucida and a drawing apparatus and further processed with Adobe Photoshop CS6. Microphotographs were taken using either an Axiocam MRe5 (Zeiss) dissecting microscope or a Micaren DC200 camera mounted on an Olympus microscope. The specimens were deposited at the Third Institute of Oceanography, Ministry of Natural Resources.

3. Taxonomy

In total, 34 medusae species were identified, two of which are new to science. Three species are reported from the Beibu Gulf for the first time (Table 1).

Table  1.  List of medusae species in the coastal waters of the northern Beibu Gulf during four seasons

Species	Autumn	Winter	Spring	Summer
Phylum Cnidaria
Class Automedusa Lameare, 1920
Subclass Narcomedusae Hackel, 1879
Family Aeginidae Gegenbaur, 1857
Solmundella bitentaculata (Quoy & Gaimard, 1833)		+
Subclass Trachymedusae Hackel, 1866
Family Geryoniidae Eschscholtz, 1829
Liriope tetraphylla (Chamisso & Eysenhardt, 1821)	+++	+++	+
Family Petasidae Haeckel, 1879
Petasiella asymmetrica Uchida, 1947	+++
Class Hydroidomedus Claus, 1877
Subclass Anthomedusae Haeckel, 1879
Family Bougainvilliidae Lütken, 1850
Bougainvillia muscus (Allman, 1863)	+
Nubiella alvarinoae (Segura, 1980)			+
Family Clavidae McCrady, 1859
Turritopsis nutricula McCrady, 1857	++			+
Family Hydractiniidae L. Agassiz, 1862
Hydractinia apicata (Kramp, 1959)	+++	+
Hydractinia carnea (M. Sars, 1846)				+
Hydractinia vacuolata Xu & Huang, 2006*				+
Family Proboscidactylidae Hand & Hendrickson, 1950
Proboscidactyla flavicirrata Brandt, 1834*	+	+	+++
Proboscidactyla gemmifera (Fewkes, 1882)	++++
Proboscidactyla pentacanalis Xu, Chen & Yang sp. nov.**
Family Corymorphidae Allman, 1872
Euphysora apiciloculifera Xu & Huang, 2003		+
Euphysora brunnescentis Huang, 1999	+
Euphysora verrucosa Bouillon, 1978		+
Family Zancleidae Russell, 1953
Zanclea costata Gegenbaur, 1857				+
Subclass Leptomedusae Haeckel, 1866
Family Eirenidae Haeckel, 1879
Eirene brevigona Kramp, 1959			+
Eirene menoni Kramp, 1953	+
Helgicirrha apapillata Xu, Chen & Wang sp. nov.**				++
Helgicirrha malayensis (Stiasny, 1928)		+
Family Lovenellidae Russell, 1953
Eucheilota macrogona Zhang & Lin, 1984*	+
Eucheilota menoni Kramp, 1959				+
Eucheilota tropica Kramp, 1959	+
Eucheilota xiamenensis Xu, Huang & Guo, 2014				+
Family Phialellidae Russell, 1953
Phialella macrogona Xu, Huang & Wang, 1985			+
Family Campanulariidae Johnston, 1836
Clytia folleata (McCrady, 1859)		+		+++
Clytia hemisphaerica (Linnaeus, 1767)			++
Subclass Siphonophorae Eschscholtz, 1829
Family Agalmatidae Brandt, 1834
Nanomia bijuga (Delle Chiaje, 1841)		+
Family Diphyidae Quoy & Gaimard,1827
Diphyes chamissonis Huxley, 1859			+++
Lensia subtilis (Chun, 1886)				++++
Lensia subtiloides (Lens & Van Riemsdijk, 1908)	++++	+	+
Phylum Ctenophora
Class Tentaculata
to be continued

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Subclass Anthomedusae Haeckel, 1879

Order Filifera Kűhn, 1913

Family Proboscidactylidae Hand & Hendrickson, 1950

Genes Proboscidactyla Brandt, 1835

Proboscidactyla pentacanalis Xu, Chen & Yang sp. nov. (Fig. 2)

Figure  2.  Oral view of Proboscidactyla pentacanalis Xu, Chen & Yang sp. nov.

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Material examined: Holotype (TIO-GFT18017), one species collected from the coastal waters of the northern Beibu Gulf. 2017. Station: GFT24 (21°32′14″N, 108°28′30″E). Depth: 11 m. Collector: Lin Chang.

Diagnosis: Umbrella nearly hemispherical, jelly moderately thick, manubrium pentangular shaped, with 5 radial gastric lobes, mouth with 5 lips, often poorly marked; 5 primary radial canals, each branching into 2–3 canals, very long, approximately 12 terminal branch canals and as many tentacles, gonads on the manubrium and lateral wall of radial gastric lobes, with medusa buds arising from the forking of radial canals.

Description: Umbrella nearly hemispherical, 2.0 mm in height, 1.8 mm in width, jelly moderately thick, slightly thicker at apex, manubrium pentangular shaped, short with large base, with 5 radial gastric lobes, extending along proximal portions of radial canals, mouth with 5 lips, often poorly marked, gonads encircling the manubrium and extending onto the gastric lobes, with medusa buds arising from the forking of radial canals, 5 primary radial canals, each branching into 2–3 canals, very long, and finally all canals joining the solid endodermal marginal exumbrella core; 12 marginal tentacles, one at the foot of each terminal branch of the radial canals, tentacular bulbs large and hollow, nearly globular, their endoderm with dense pigmentation, marginal tentacles short and thick, covered with ring-like cnidocysts; alternating with the tentacles is exumbrella bear clusters of cnidocysts that are connected with the umbrella margin by a line; ocelli absent.

Distribution: The coastal waters of the northern Beibu Gulf.

Etymology: From the Latin pentacanalis, meaning penta-canals, the species name refers to an umbrella with 5 primary radial canals.

Remarks: This species has a manubrium presenting radial gastric lobes with branched radial canals, with clusters of cnidocysts on its exumbrella margin by a line. Usually without a circular canal, the marginal tentacles are hollow. These features place this medusa in the family Proboscidactylidae Hand & Hendrickson, 1950 and genus Proboscidactyla Brandt, 1835.

According to Schuchert (2020), the genus Proboscidactyla current consists of 10 valid species, i.e., Proboscidactyla abyssicola Uchida, 1948, P. circumsabella Hand, 1954, P. flavicirrata Brandt, 1835, P. menoni Pages, Bouillon & Gili, 1991, P. mutabilis (Browne, 1902), P. occidentalis (Fewkes, 1889), P. ornata (McCrady, 1859), P. stellata (Forbes, 1846), P. trifurcata Xu, Huang & Guo, 2019, P. tropica Browne, 1905; whereas five species are doubtful: P. brooksi (Mayer, 1910), P. furcata (Haeckel, 1879), P. pacifica (Maas, 1909), P. brevicirrata Haeckel, 1879, and P. conica Menon, 1932 (Bouillon et al., 2006).

This new species can be easily distinguished from the other species of Proboscidactyla by its 5 primary radial canals and medusa buds arising from the forking of the radial canals. It is similar to P. tropica Browne, 1905 and P. ornata (McCrady, 1859), which also have medusa buds. In addition, there are three other Proboscidactyla species that have been described with medusa buds: P. gemmifera (Fewkes, 1882), P. stolonifera (Maas, 1905), and P. varians Browne, 1905, all of which were synonymised with P. ornata (McCrady, 1859) by Hartlaub (1917).

However, Gershwin et al. (2010) suggests that the true P. ornata does not possess medusa buds and mistakes have probably been made in synonymizing other species that do possess buds with it. Mayer (1910) comments that the common P. ornata does not have medusa buds. In the life cycle of P. ornata in Naples described by Brinckmann and Vannucci (1965) and the life cycle of P. ornata described by Calder (1970), neither description mentioned medusa buds at any stage. Thus, the feature of the true P. ornata should be without medusa buds and gonads on the interradial side of the manubrium (Fig. 3a). The P. ornata recorded in the China seas should be referred to as P. gemmifera (Fewkes, 1882) (included the species in Table 1), of which each radial canal has a trifurcation and a single stolon arises from each corner of the manubrium, bearing several medusa buds (Fig. 3c). Until 2019, true P. ornata has not been found in the China seas, and this finding awaits further investigation.

Figure  3.  Comparison of four Proboscidactyla species. a. P. ornata (McCrady, 1859), mature specimens in which the radial canals have 12 terminal branches (redrawn after Mayer (1910)); b. P. varians Browne, 1905 (redrawn after Browne (1905)); c. P. gemmifera (Fewkes, 1882), showing unusually dark pigment in the tentacle bulbs (redrawn after Mayer (1910)); d. P. stolonifera (Maas, 1905) (redrawn after Mayer (1910)).

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Based on the above discussion, we consider P. gemmifera (Fewkes, 1882), P. stolonifera (Maas, 1905), and P. varians Browne, 1905a to be distinct from P. ornata (McCrady, 1859), and this updates the genus Proboscidactyla into 13 valid species from previous reports (Mayer, 1910; Kramp, 1961; Hand and Hendrickson, 1950; Uchida and Sugiur, 1975; Bouillon et al., 2006; Gershwin et al., 2010; Xu et al., 2014; Wang et al, 2019). Among all the Proboscidactyla species with medusa buds, P. tropica Browne, 1905 (Fig. 4), P. gemmifera (Fewkes, 1882) and P. stolonifera (Maas, 1905) (Fig. 3d) all have only 4 primary radial canals, while P. varians Browne, 1905 (Fig. 3b) has 6 primary radial canals. Therefore, the Beibu Gulf specimens with medusa buds bears one major structural difference from them, namely, 5 primary radial canals, and their branching pattern of the radial canals are different (more details are shown in the key).

Figure  4.  Proboscidactyla tropica Browne, 1905 (Gershwin et al., 2010). a. Lateral view; b. oral view; both images taken while specimen was alive.

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On the other hand, the immature medusae described by many authors can be distinguished from other species of Proboscidactyla with little or no certainty. The young medusae of P. stellata are predominantly hexamerous, although on occasion, a pentamerous type is found, while those of P. flavicirrata vary from tetramerous to hexamerous (Uchida and Okuda, 1941). Proboscidactyla mutabilis is also highly variable, and in the Californian form, mostly tetramerous medusa have been found and occasional pentamerous forms (Hand and Hendrickson, 1950). The medusae of P. ornata captured in Misaki over five years (1970–1975) were mostly young. Approximately 60% of the medusae presented 4 primary radial canals, while approximately 20% presented 5–7 canals and approximately 20% presented 8 canals (Uchida and Sugiura, 1975). However, the prevalence of 5 primary radial canals is not as extreme as formerly supposed. In no cases was branching of the radial canals or medusa buds that was found in immature medusae, which is in contrast to the characters of the Beibu Gulf specimens. Although the presently described medusa is approximately 2.0 mm and 1.8 mm wide and presents bifurcation of each primary radial canal, and medusa buds arising from the forking of radial canals, with five primary radial canals having five tentacles. These features differ from those of similar species in the genus Proboscidactyla. Therefore, we regarded this medusa of the Beibu Gulf as a new species (Figs 2a, b).

Key to the medusae of all known species in the genus Proboscidactyla

1. With 20 radial canals, some bifurcated; gonad extending along the proximal half of all radial canals; no tentacles .........……………………………P. abyssicola Uchida, 1948

– With 4–8 primary radial canals……………………………………2

2. With medusa buds………………..………………………...………...…..3

– Without medusa buds…………………………………..…………….….7

3. With only 4 primary radial canals…………………………..………….4

– With 5–6 primary radial canals…………………………..…………..….6

4. With a trifurcation per primary canal and the primary stem canal leading to a tentacle bulb; gonad just proximal to each trifurcation, each bearing about 3 medusa buds on the stolons; with 12 terminal branches, in correspondence with tentacles …...…...........................................................…P. tropica Browne, 1905

– With 3–5 branches per primary canal and the primary stem canal not leading to a tentacle bulb……………………………….5

5. With 2 side branches per primary canal, such that 3 terminal canals lead to a tentacle bulb and a single stolon arises from each corner of the manubrium, bearing several medusa buds……………………………………P. gemmifera (Fewkes, 1882)

– With twice bifurcated per primary canal, such that 4 terminal canals lead to a tentacle bulb and medusa buds arise from the second branch points………….… P. stolonifera (Maas, 1905)

6. With 5 primary radial canals, each branching into 2–3 canals, very long, approximately 12 terminal branch canals and as many tentacles, medusa buds arising from the forking of radial canals………............……P. pentacanalis Xu, Chen & Yang sp. nov.

– With 6 primary radial canals, each with 1 to 3 lateral branches, approximately 12–18 terminal branch canals and as many tentacles; medusa buds arising from near the stomach …………………………………………….. P. varians (Browne, 1902)

7. With more than 5 primary radial canals………………………….8

– With only 4 primary radial canals……………...…………...……..9

8. Normally with 6 primary radial canals, 24 terminal branches and as many tentacles, with adaxial basal cnidocyst cush ions……………………...……….……….P. stetlata (Forbes, 1846)

– Normally with 8 primary radial canals, 24–54 terminal branches and some number of tentacles, without adaxial basal cnidocyst cushions………….P. mutabilis (Browne, 1902)

9. Gonads at base of manubrium wall, extending along lateral wall of gastric lobes……..........................................……10

– Gonads restricted to manubrium wall………………………………….11

10. Manubrium with 8–16 radial gastric lobes; 4 primary radial canals, 60 terminal branches and as many tentacles, each with an adaxial cnidocyst cushion; gonads extending to sec ondary branches of radial canals…………………………..… ......................................P. menoni Pages, Bouillon & Gili, 1991

– Manubrium with 4 radial gastric lobes; 4 primary radial canals, 24 terminal branches and as many tentacles, each without an adaxial cnidocyst cushion; gonads extending slightly onto the proximal part of primary radial canals ………............................…….P. trifurcata Xu, Huang & Guo, 2019

11. Mouth lips simple, with crenate edges; 4 large masses of gon ads on the interradial side of the manubrium; 12–16 terminal branches and some number of tentacles………………………….

…………………...........................................P. ornata (McCrady, 1859)

– Mouth lips highly folded and hanging………………………..12

12. With 11–13 terminal branches per primary radial canal and some number of tentacles; 4 gonadial masses occupying in ternal positions, with each mass developed as a pair of thickened lobes upon the adradial sides of the quadratic manubrium with a thin sheet of gonadial tissue connecting the two lobes and covering the manubrium wall……………… ................................................P. flavicirrata Brandt, 1835

– With 8 terminal branches per primary radial canal and some number of tentacles………………………………………………13

13. With 24–32 tentacles; primary canal seems to run directly to the margin; gonads occurring in the interradial position as four paired masses of simple swollen lobes on the adradial side of the manubrium………..……P. circumsabella Hand, 1954

– With 40 tentacles; primary canal not running directly to the margin; gonads not fused across the radial margin of the manubrium and present as four interradial masses consist ing of paired adradial lobes connected at the interradial by thin sheets of gonadial tissue….P. occidentalis (Fewkes, 1889)

Subclass Leptomedusae Haeckel, 1866

Order Conida Broch, 1910

Family Eirenidae Haeckel, 1879

Helgicirrha apapillata Xu, Chen & Wang. sp. nov. (Fig. 5)

Figure  5.  Helgicirrha apapillata Xu, Chen & Wang. sp. nov. a–d. H. apapillata Xu, Chen & Wang, sp. nov. a. Lateral view; b. oral view; c–d. partial enlargement of the umbrella margin, showing the lateral cirri and all bulbs without adaxial excretory papillae; e. H. malayensis (Stiasny, 1928), showing all bulbs with adaxial excretory papillae (redrawn after Xu et al, 2014).

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Material examined: Holotype (TIO-GFT 18109), one specimen collected from the Beibu Gulf, northwestern part of the South China Sea. 2018. Station: GFT33 (21°35′10″N, 108°47′13″E). Depth: 14 m. Collector: Lin Chang.

Diagnosis: Umbrella nearly hemispherical, with thicker jelly at the apex; gastric peduncle very long, slightly extending beyond the velar opening; manubrium small, short, somewhat square in transverse section; mouth with 4 simple, long lips with crenulated margin; 4 radial canals and a circular canal; 4 gonads are linear shaped, extending from the peduncle base to near the bell margin, without medusa buds; up to 28 marginal, large tentacles and 1 rudimentary bulb between tentacles, all tentacles and rudimentary bulbs with pairs of lateral cirri and without adaxial excretory papillae; 2 statocysts between tentacles.

Description: Umbrella nearly hemispherical, 9.0 mm in height, 13.0 mm in width. With thicker jelly at the apex, thinning towards the umbrella margin; gastric peduncle very long, pyramidal base, slightly extending beyond the velar opening; manubrium small, short, somewhat square in transverse section; mouth with 4 simple, long lips with crenulated margin; 4 narrow radial canals, extending from the circular canal to the peduncle and connected to the manubrium; 4 linear subumbrella gonads extending from the peduncle base to near the bell margin; without medusa buds; up to 28 tentacles with elongated conical marginal bulbs and rudimentary bulbs between tentacles, all tentacles and rudimentary bulbs with pairs of lateral cirri, and all bulbs without adaxial excretory papillae; 2 statocysts between tentacles, each with a concretion; velum broad.

Distribution: The coastal waters of the northern Beibu Gulf.

Etymology: From the Latin apapillata, meaning without papilla. The species name refers to all tentacles and rudimentary bulbs without adaxial excretory papillae.

Remarks: The new species has a distinct gastric peduncle, with 1 pair of lateral cirri at the base of all tentacles, rudimentary bulbs and numerous closed statocysts. These features place this medusa in the family Eirenidae Haeckel, 1879 and the genus Helgicirrha Hartlaub, 1909.

The genus currently comprises 11 valid species, i.e., Helgicirrha brevistyla Xu & Huang, 1983, H. cari (Haeckel, 1864), H. cornelii Bouillon, 1984, H. danduensis (Bigelow, 1904), H. gemmifera Bouillon, 1984, H. irregularis Bouillon, Boero & Seghers, 1988, H. malayensis (Stiasny, 1928), H. medusifera (Bigelow, 1909), H. ovalis Huang, Xu, Lin & Guo, 2010, H. sinuatus Xu, Huang & Du, 2012, and H. weaveri Allwein, 1967 (Kramp, 1961, 1968; Xu and Huang, 1983; Bouillon,1984; Bouillon et al., 1988, 2006; Huang et al., 2010b; Du et al., 2012; Xu et al., 2014), and one species in doubt: H. schulzii Hartlaub, 1909, accepted as H. cari (Haeckel, 1864).

Schuchert (2017) concluded that H. schulzii Hartlaub, 1909 must be regarded as a synonym of H. cari (Haeckel, 1864) by comparing the COI (Cytochrome Oxidase I) sequence of a Mediterranean specimen of H. cari to the COI sequence of H. schulzii collected in the North Sea; the two sequences differed in only one nucleotide, indicating only intraspecific variation.

This new species is distinguished from other species of Helgicirrha by the following aspects: the gonads are linear, extending from the base of the peduncle to near the bell margin, without medusa buds; the gastric peduncle is long, slightly extending beyond the velar opening; and more than 25 marginal tentacles. Similar to H. malayensis (Stiasny, 1928), this species also has linear gonads, a very long gastric peduncle and more than 25 tentacles, but this new species differs from similar species as follows: (1) mouth lips shorter than manubrium; (2) up to 28 marginal tentacles, with rudimentary bulbs between tentacles; (3) all marginal tentacles and rudimentary bulbs without adaxial excretory papillae (Fig. 5d); and (4) all bulbs with 1 pair of lateral cirri.

Key to the medusae of all known species in the genus Helgicirrha

1. Gonads with medusa buds ……...................………………………… 2

– Gonads without medusa buds ………….……………………… 3

2. Gonads in distal 1/3 of radial canals; with 16–21 marginal tentacles; all with 1 or 2 pairs of lateral cirri ……..................... .....................................……H. medusifera (Bigelow, 1909)

– Gonads in middle portion of radial canals; with 4 marginal tentacles, each tentacle with 4 pairs of lateral cirri…… …………………………………………H. gemmifera Bouillon, 1984

3. Gonads linear, extending from the base of the peduncle to near the bell margin….................……………………………………4

– Gonads short, along middle or distal end of radial canals……9

4. With fewer than 25 tentacles……………………………………..5

– With more than 25 tentacles ……………………………..….… 6

5. Gonads undulate-shaped, with 16–18 tentacles without lateral cirri, and 80 rudimentary bulbs with 1 pair of lateral cirri …………………H. irregularis Bouillon, Boero & Seghers, 1988

– Gonads simple, with 14 tentacles and 56–84 rudimentary bulbs, all bulbs with lateral cirri……… H. weaveri Allwein, 1967

6. Peduncle short, never extending beyond the velar opening… 7

– Peduncle long, extending beyond the velar opening……....……8

7. Mouth lips longer than the manubrium; 50–60 tentacles without lateral cirri; approximately 100 smaller tentacles, each with 1 pair of lateral cirri….….…… H. cari (Haeckel, 1864)

– Mouth lips shorter than the manubrium; 28–54 tentacles with 2 pairs of lateral cirri; without smaller tentacles………. .………………..….…….…H. brevistyla Xu & Huang, 1983

8. Mouth lips longer than the manubrium; with 30–141 tentacles, each with 1 pair of lateral cirri; with 1–3 rudiment ary bulbs between tentacles, without lateral cirri; all bulbs with abaxial excretory papillae..…H. malayensis (Stiasny, 1928)

– Mouth lips shorter than the manubrium; with 28 tentacles and a rudimentary bulb between tentacles; all bulbs with 1 pair of lateral cirri and without abaxial excretory papillae ……………………………..…H. apapillata Xu, Chen & Wang, sp. nov.

9. Peduncle short, never extending beyond the velar opening……10

– Peduncle long, extending beyond the velar opening……….…11

10. Gonads oval-shaped in middle portion of radial canals; 8 tentacles with 3 pairs of lateral cirri; with 1–2 rudimentary bulbs between tentacles, each with 1 pair of lateral cirri and a black spot on its extreme tip…………..………………........................... ...............................H. ovalis Huang, Xu, Lin & Guo, 2010

– Gonads sausage-shaped, along the distal half of radial canals or slightly near the umbrella margin; 16–22 tentacles with 2–3 pairs of lateral cirri; with 3 rudimentary bulbs between tentacles, each with 1–3 pairs of lateral cirri and no black spot at the extreme tip………………………...…H. cornelli Bouillon, 1984

11. Gonads spindle-shaped, along distal 2/3 of radial canals; with 32 tentacles, the perradial is a little longer, each with 1 pair of lateral cirri; with 1–2 rudimentary bulbs between tentacles without lateral cirri; with 1 statocyst and each with 5 concretions………………………..…H. danduensis (Bigelow, 1904)

– Gonads sinuous-shaped, along distal 1/3 to 1/2 of radial canals; with 16–24 tentacles, each with 2 pairs of lateral cirri, with 3–5 rudimentary bulbs between tentacles, each with 1 pair of lateral cirri; with 3–4 statocysts between tentacles and each with 2–3 concretions … H. sinuatus Xu, Huang & Du, 2012

Acknowledgements

We are thankful for Jiaqi Huang (Xiamen University, China) for helping in medusae identification and the critical reading of the manuscript. We also thank the zooplankton research group in Third Institute of Oceanography, Ministry of Natural Resources, for providing useful comments on the manuscript.