European Journal of Taxonomy 107: 1-23

http://dx.doi.org/10.5852/ejt.2014.107

This work is licensed under a Creative Commons Attribution 3.0 License.

ISSN 2118-9773

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2014 • Gambill M. & Jarms G.

Research article

um:lsid:zoobank.org:pub:33E50E3C-53D8-49DB-84F8-0A6AABC0A2A7

Can Aurelia (Cnidaria, Scyphozoa) species be differentiated

by comparing their scyphistomae and ephyrae?

Maria GAMBILL 1 & Gerhard JARMS 2

institute of Hydrobiology and Fisheries Science, University of Hamburg, Olbersweg 24,

22767 Hamburg, Germany.

Email: [email protected] (corresponding author)

2 Zoological Institute and Museum, University of Hamburg, Martin-Luther-King Platz 3,

20146 Hamburg, Germany.

1 um:lsid:zoobank.org:author:43164A98-3AF4-4DB7-8AAF-C2464BlABC22

2 um:lsid:zoobank.org:author:76C2ADDC-93D8-4A13-BC4F-36F44727CC25

Abstract. Debate exists regarding the number of species of the moon jellyfish (genus Aurelia ), a

common member of the planktonic community of the coastal shelf seas around the world. Three Aurelia

congeners (A. aurita , A. labiata and A. limbata ) are currently considered to exist but recent genetic

analyses suggested that this is an oversimplification. We analyzed the morphological characteristics

of scyphistomae, morphological characteristics of ephyrae and differences in the time span of the

strobilation process of Aurelia congeners from 17, 7 and 6 different source populations, respectively, of

known species. Morphological characteristics of scyphistomae were similar among the 17 populations

but those of ephyrae, such as the shape and form of lappets, were effective discriminators in the 6

cases examined. We recommend identifying species based on differences in 1) the morphological

characteristics of scyphistomae and ephyrae (and not only medusae), 2) the genetics of individuals, and

3) the geographical occurrence of the population. This study adds to the growing body of knowledge

on scyphozoan scyphistomae and ephyrae, stages of the metagenic life cycle of scyphozoans that have

received relatively little study compared to medusae.

Keywords. Polyps, jellyfish, strobilation, nomenclature, morphology.

Gambill M. & Jarms G. 2014. Cm Aurelia (Cnidaria, Scyphozoa) species be differentiated by comparing their

scyphistomae and ephyrae? European Journal of Taxonomy 107: 1-23. http://dx.doi.org/10.5852/eit.2Q14.107

Introduction

The perceived increased frequency of blooms of jellyfish in the world’s ocean (Mills 2001; Purcell

et al. 2007; Purcell 2012; Condon et al. 2012, 2013; Lee et al. 2013) has intensified research efforts to

understand the population dynamics of gelatinous plankton, with the majority of research having been

conducted on the conspiculous medusoid life stages (Lucas et al. 2012). Medusae in the genus Aurelia

Lamarck, 1816 have been reported to occur in the world’s oceans from 70° N to 40° S where they are

most commonly found along continental shelves or close to large islands (Mayer 1910; Kramp 1961;

Russell 1970; Miyake et al. 2002; Schroth et al. 2002). Despite >100 years of research on Aurelia, the

European Journal of Taxonomy 107: 1-23 (2014)

taxonomy of the genus is still unclear. The genus was originally described as ‘ Aurellia\ which was

changed to ‘ Aurelia ’ by Rees (1957). It had three species: A. aurita (Linne, 1758), the Pacific A. labiata

Chamisso & Eysenhardt, 1820 and A. maldivensis Bigelow, 1904 from the Indian Ocean (Linne 1758;

Chamisso & Eysenhardt 1820; Bigelow 1904). Debate existed on whether A. labiata and/or A. limbata

Brandt, 1838 were valid members of the genus (Brandt 1838). Kramp (1961) described six different

species of Aurelia, whereas Russell (1970) declared that only A. aurita and A. limbata were valid species.

Gershwin (2001) provided a new description of A. labiata and reported it to be endemic to coastal

areas of the Eastern Pacific. Although three species (A. aurita , A. labiata and A. limbata) are currently

morphologically considered to comprise the genus (Wrobel & Mills 1998; Gershwin 2001; Miyake et al.

2002; Albert 2005; Widmer 2005), genetic analyses have suggested a more complex situation, including

five cryptic species of Aurelia in the North Pacific and up to nine species worldwide (Dawson & Jacobs

2001; Dawson & Martin 2001; Schroth et al. 2002; Dawson 2003; Dawson et al. 2005).

The vast majority of studies using morphology to distinguish species of Aurelia has examined medusae,

while only five studies (Uchida & Nagao 1963; Gershwin 2001; Straehler-Pohl 2009; Straehler-Pohl &

Jarms 2010; Straehler-Pohl et al. 2011) have considered the morphology of scyphistomae and ephyrae.

It is known that scyphistoma populations of scyphozoan jellyfish can be distinguished not only by

using morphological features but also by analyzing asexual propagation as well as the timing and

intermittency of strobilation (e.g., Condon 2001; Lucas 2001; Ma & Purcell 2005; Willcox et al. 2007;

Adler & Jarms 2009; Straehler-Pohl 2009; Holst 2012a). Documenting the morphological characteristics

of scyphistomae and ephyrae can not only (potentially) help clarify the taxonomic status of the genus

Aurelia , but advancing our knowledge on the strobilation of Aurelia scyphistomae is also an important

step towards understanding the bloom dynamics of members of this genus (Lucas 2001; Purcell 2007;

Purcell et al. 2012).

We examined aspects of the morphology of scyphistomae and ephyrae and the strobilation dynamics

of Aurelia populations collected from 17 locations around the world. Populations were from three

species and we tested whether the same species assignments would be made using morphological

measurements of scyphistomae and ephyrae. We also measured characteristics of strobilation (duration,

number of ephyrae per scyphistoma), contrasting Pacific from Atlantic populations. We performed these

comparisons not only to help clarify the taxonomic status of the genus but also to gain knowledge of

basic features of scyphistomae and their reproductive dynamics in the laboratory.

Material and methods

Cultures

We compared the morphology of scyphistomae and ephyrae from populations of Aurelia collected at

17 locations in the North and Baltic Seas as well as the Atlantic and Pacific Oceans (Table 1). A priori

species identifications were: populations 1 to 14 = A. aurita , populations 15 and 16 = A. labiata , and

culture 17 = A. limbata. Species-level identifications were made a priori based on the morphology of

medusae. Scyphistomae were kept in culture for more than 5 years. Scyphistomae and ephyrae were

cultured using natural seawater at temperatures (SANYO incubators MIR 553 and MIR 253) and

salinities (ATAGO S7Mill refractometer) that represented their local conditions (Table 1).

Scyphistomae were kept in 150-ml glass bowls in darkness and ephyrae were maintained in aerated,

500-ml flasks in daylight with the photoperiods occurring between May 5 th and September 23 rd 2009 in

Hamburg, Germany, and room temperature (18 to 21°C). Based on previous work, we tried to induce

strobilation by first decreasing the temperature and then raising it again to the initial temperature (Holst

2008, Holst 2012a). In 14 cultures (all except cultures 6 and 14 because strobilation was happening

already on a regular basis) temperature was set from 15°C to 10°C and back to 15°C after 7 days. In

GAMBILL M. & JARMS G., Comparison of different life stages of the genus Aurelia

Table 1 . Origin, salinity and incubation temperature of 17 different cultures of Aurelia sp. Strobilation

was induced by temperature drop and, if required, additional potassium iodine (KI).

Culture

Proposed

species

(a priori)

Origin

Location

long /lat

Salinity

Temperature (°C)

(psu)

Scyphistomae

Strobilation

Ephyrae

North Sea

Sylt,

Germany

N 55°02’32” E 8°24’40”

10-15

Room temp

(18-22°C)

North Sea

Helgoland,

Germany

N 54°10’50” E 7°52’50”

10-15

10 (KI)

Room temp

(18-22°C)

Northeast

Atlantic

Hebrides,

Scotland

N 57°36’01” W 7°0’01”

10-15

Baltic Sea

Boiensdorf,

Germany

N54°01’57”E 11°33’16”

10-15

Baltic Sea

Strande,

Germany

N54°26’10” E10°10’21”

10-15

East Atlantic

Roscoff,

France

N48°43’40” W3°59’07”

Room temp

(18-22°C)

Arctic Ocean

White Sea

N65°33’49” E36°36’33”

10-15

A. aurita

North Sea/

Skagerrak

Kristineberg,

Sweden

N58°14’59” Ell°26’57”

10-15

10 (KI)

Room temp

(18-22°C)

Mediterranean

Sea

Cattolica,

Italy

N43°58’14” E12°44’21”

15-23

15 (KI)

Room temp

(18-22°C)

Red Sea

Gulf of Aqaba

N29°31’58” E34°58’18”

West Atlantic

Woods Hole,

USA

N41°31’34” W70°40’41”

10-15

West Atlantic

Ilha Grande,

Brazil

S23°06’00” W44°10’22”

East Pacific

Monterey,

USA

N36°36’50” W121°53’40”

10-15

West Pacific

Kagoshima Bay,

Japan

N31°30’08” E130°38’ll”

Room temp

(18-22°C)

East Pacific

Friday Harbor,

USA

Coos Bay,

USA

N48°29’42” W123°00’03”

10-15

A. labiata

East Pacific

N43°23’00” W124°12’00”

10-15

Room temp

(18-22°C)

A. Jimbata

Sea of Okhotsk,

Pacific

Hokkaido, Japan

N44°10’10” E144°20’20”

10-15

culture 9 temperature was set from 23°C to 15°C and back to 23°C after 7 days. Three out of the seven

cultures in which strobilation actually occurred were additionally treated with potassium iodine (1.5 ml

KI in 100 ml seawater; Spangenberg 1967, 1968) because the short-term temperature decrease was not

sufficient to induce strobilation (Table 1). Scyphistomae and ephyrae were fed Artemia salina (Linne,

1758) nauplii once a week and every other day, respectively.

Morphological and statistical analyses

Scyphistomae

Scyphistomae were transferred to petri dishes and a 30-min period was allowed for them to relax and fully

re-expand. Afterwards, individuals were digitally photographed and morphometric measurements were

made using computer image analysis (ColorView, Soft Imaging System GmbH). Various morphological

features were documented (colour, shape, number of tentacles) as well as strobilation duration and

ephyrae production (Fig. 1). We took morphometric measurements as mentioned above following the

method developed by Straehler-Pohl (2009), Straehler-Pohl & Jarms (2010) and Straehler-Pohl et al.

(2011). The morphometric measurements of scyphistomae were compared by using the following ratios

(expressed in percent; abbreviations are explained in Table 2): CL/TBL; HL/TBL; StL/TBL; MDD/

TBL; CD0/CL; CD 1/CL; CD2/CL; CD3/CL; StID/CL (for original data please refer to Appendix A).

European Journal of Taxonomy 107: 1-23 (2014)

Ephyrae

Ephyrae were measured within 24 h after detachment. They were collected from petri dishes using a

pipette and transferred with a small amount of water to a glass slide with the manubrium facing up, where

they where allowed to relax for 5-10 minutes. They were photographed and measured as described above

for scyphistomae, including differences in rhopalial lappet- and gastric canal forms (Fig. ID). We took

morphometric measurements as mentioned above following the method developed by Straehler-Pohl

(2009), Straehler-Pohl & Jarms (2010)and Straehler-Pohl etal. (2011). The morphometric measurements

a b

Fig. 1 . Measurements of: A. Scyphistomae. B. Ephyrae. C. Lappets of an ephyra: the marginal lappet

can be divided into rhopalial lappet and lappet stem; also visible are the rhopalial and velar canals.

D. Rhopalial lappet and gastric canal forms of ephyrae in this study: 1. Rhopalial lappet forms (i.e. left

lappet): (a) pointed spoon-like, (b) round spatula-like, (c) lancet-like and (d) bread knife-like; 2. Rhopalial

canal forms: (a) forked, sharp points, (b) club-shaped, forked, sharp points and (c) spade-like; 3. Velar

canal forms: (a) spade-like and (b) rhombic. Abbreviations: RH = rhopalium; RhC = rhopalial canal;

RL = rhopalial lappet; Sta = statolith; UR = umbrella rim; VC = velar canal. Other abbreviations: see

Table 2. Modified after Straehler-Pohl & Jarms (2010).

GAMBILL M. & JARMS G., Comparison of different life stages of the genus Aurelia

Table 2. Measuring parameters for scyphistomae and ephyrae mainly according to Straehler-Pohl

(2009), Straehler-Pohl & Jarms (2010) and Straehler-Pohl et al. (2011).

Abbreviations for scyphistomae

Actual measurement for scyphistomae

TBL (Total Body Length)

length from hypostome tip to basal disc

CL (Calyx Length)

length from gastric cavity base to tentacle crown rim

HL (Hypostome Length)

length from tentacle crown base to hypostome tip

MDD (Mouth Disc Diameter)

widest diameter of mouth disc

StL (Stalk Length)

length from basal disc to gastric cavity base

CDO-3 (Calyx Diameter)

diameter of the calyx at four different areas

StlD (Stalk Initial Diameter)

diameter of the stalk at its beginning

Abbreviations for ephyrae

Actual measurements for ephyrae

TBD (Total Body Diameter)

2x total length of marginal lappet + diameter of central disc

CDD (Central Disc Diameter)

diameter of the central disc from the end of the gastric cavity

TMLL (Total Marginal/Rhopalial Lappet

Length)

length of the lappet stem + length of rhopalial lappet

LStL (Lappet Stem Length)

length from lappet base (line between the bases of two marginal lappet clefts)

to base of rhopalial niche (base of cleft between two rhopalial lappets)

RLL (Rhopalial Lappet Length)

length from rhopalial niche base to level of rhopalial lappet tips

ML (Manubrium Length)

length between base and rim of manubrium

AdD (Adradial Diameter)

adradial diameter of the central disc

RhTI (Rhopalar Tip Interspace)

space between the rhopalar tips

of ephyrae were compared by using the following ratios (expressed in percent; abbreviations are given

in Table 2): LStL/TMLL; RLL/TMLL; CDD/TBD; ML/TBD; RhTI/TBD; AdD/TBD; CDD/AdD; ML/

AdD; TMLL/TBD; LStL/TBD; RLL/TBD (for original data please see Appendix B).

We explored statistically significant differences between the 17 populations using a post-hoc, stepwise

Linear Discriminant Analysis (LDA) of the ratios based on the morphometric measurements (n = 6

individuals per population). Ephyra production and number of tentacles per scyphistoma (both n = 10)

were evaluated using a Kruskal-Wallis test, followed by a Tu key’s Honestly Significant Difference

(HSD) post-hoc test. The significance level was set at alpha <0.05. Statistical analyses were performed

using the software R 2.15.2 (R Core Team 2012).

Results

Morphological analyses

Scyphistomae

Scyphistomae of the 17 Aurelia populations were morphologically variable with respect to colour

and shape of the calyx, the shape of the hypostome, and the number of tentacles (Table 3). We were

able to distinguish four different calyx shapes (barrel, square, chalice, and cone) and four different

hypostome shapes (convex, cap, cylindrical, and cone). The number of tentacles varied significantly

among the populations (Kruskal-Wallis, H 16 = 67. 3, P > 0 .00001, n = 10). Pairwise comparison revealed

that population 12 (West Atlantic) was significantly different from all others (HSD, p < 0.05). In 10

of the 17 populations there was a consistent ranking of body proportion (CL > HL > StL) and stalks

in populations 4-6 (Baltic Sea and East Atlantic), 9 (Mediterranean Sea), 13 (East Pacific), 15 (East

Pacific) and 16 (East Pacific) were longer than the hypostome (CL > StL > HL; Fig. 2). There were

significant differences between ratios of hypostome length, calyx length and stem length in relation to

European Journal of Taxonomy 107: 1-23 (2014)

Table 3. Collected morphological features of the scyphistomae of Aurelia sp.; tentacles were counted

on 10 individuals

Polyp types

Culture Calyx shape

Calyx colour

Hypostome shape

Number of tentacles

(N=10)

barrel-like orange convex 15.8 ±0.79

square, jolted

orange

cap-like

15.9 ±0.32

barrel-like,

offset stalk

orange

cylindrical

16.2 ±0.42

barrel-like,

offset stalk

orange in the

middle, rest

milky white

cylindrical

15.9 ±0.57

2 mm

chalice-like,

long stem

little orange in

the middle, rest cylindrical

milky white

15.9 ±0.57

GAMBILL M. & JARMS G., Comparison of different life stages of the genus Aurelia

Polyp types

Culture Calyx shape

Calyx colour

Hypostome shape

Number of tentacles

(N=10)

square

orange cone-shaped

15.9 ±0.32

barrel-like

orange

convex

15.5 ±0.71

barrel-like

orange

cylindrical

15.8 ±0.42

cone-like milky white cone-shaped

16.2 ±0.42

square milky white barely convex

16.2 ±0.63

barrel-like

orange

convex, large

16.0 ±0

European Journal of Taxonomy 107: 1-23 (2014)

Polyp types Culture Calyx shape

cone-like,

slender

Calyx colour

Hypostome shape

Number of tentacles

(N=10)

milky white cap-like

28.8 ±2.6

orange in

calyx, milky

chalice-like white around cone-shaped

mouth disc and

tentacles

16.1 ±0.32

]

orange in

calyx, milky

chalice-like white around

mouth disc and

tentacles

cone-shaped 16.0 ± 0

orange in

calyx, milky

chalice-like white around cone-shaped

mouth disc and

tentacles

15.9 ±0.74

chalice-like light orange

cone-shaped

16.0 ±0

orange in

calyx, milky

chalice-like white around

mouth disc and

tentacles

cylindrical

16.2 ±0.63

GAMBILL M. & JARMS G., Comparison of different life stages of the genus Aurelia

601

a) 30

HL/TBL

1 1

-r -y-

—

— 1

1 1

llllMlI

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

StL/TBL

Fig. 2. Body proportions of polpys (shown as percentage). Error Bars show standard deviation.

Abbreviations: see Table 2.

European Journal of Taxonomy 107: 1-23 (2014)

Table 4. Analysis of Variances (ANOVA) for morphometric indices of scyphistomae and ephyrae.

Abbreviations: df = degrees of freedom; F = F-Ratio; p = p-Value. Other abbreviations: see Table 2

Comparison of scyphistomae

kkk

CL/TBL

16, 88

9.88

<0.001

* * *

HL/TBL

16, 88

9.87

<0.001

❖ * *

StL/TBL

16, 88

8.71

<0.001

❖ * *

Comparison of ephyrae

•k'k'k

RLL/TBD

6,35

16.17

<0.001

* * *

ML/TBD

6,35

6.98

<0.001

❖ * *

TMLL/TBD

6,35

24.73

<0.001

❖ * *

LStL/TBD

6,35

26.70

<0.001

❖ * *

CDD/TBD

6,35

39.63

<0.001

* * *

RLL/TMLL

6,35

16.87

<0.001

❖ * *

LStL/TMLL

6,35

16.87

<0.001

❖ * *

RhTI/TBD

6,35

8.69

<0.001

* * *

total body length of scyphistomae (ANOVA, p < 0.001, Fig. 2, Table 4). Most of the scyphistomae had

14 to 17 tentacles except cultures 15 and 16 (14 to 16) and culture 12 (27 to 33).

Strobilation

Strobilation occurred in 7 of the 17 populations (Tables 1, 5). In cultures 1 (North Sea) and 16 (East

Pacific), scyphistomae strobilated after a decrease in temperature. In cultures 2 (North Sea), 8 (North Sea

/ Skagerrak) and 9 (Mediterranean Sea), strobilation commenced after exposure to KI and a decrease in

temperature. Cultures 6 (East Atlantic) and 14 (Pacific) were maintained at 15°C and strobilated several

t im es The strobilation process from the development of the first constriction until detachment of the

last ephyra lasted 17 to 27 days. In six of seven cultures, at least ten scyphistomae strobilated. Only 1

scyphistoma strobilated in culture 1 (North Sea) and this culture was not included in further analyses

concerning the strobilation process. Cultures from the Pacific Ocean (cultures 14 and 16) had much

shorter strobilation times (17 to 18 days) compared to the four cultures from the East Atlantic Ocean /

North Sea (cultures 1, 2, 6 and 8) and the Mediterranean (culture 9). In these six cultures (i.e., excluding

culture 1), the mean (± standard deviation) number of ephyrae per strobila varied from 6.0 ± 0.9 to

21.1 ± 3.0 and was significantly different among cultures (Kruskal-Wallis H5 = 47.4, p < 0.001, n = 10).

The number of ephyrae per strobila in the Pacific cultures was significantly lower than that of the

remaining experimental cultures (HSD, p < 0.05).

Ephyrae

The colour of the ephyrae ranged from translucent white to translucent pink to reddish brown (Table 5).

The shape of the rhopalial lappets as well as the shapes of the rhopalial and velar canals differed between

cultures (Table 5). Lappet proportions of the ephyrae exhibited differences. Culture 6 (East Atlantic)

produced ephyrae showing ratios of rhopalial lappet (RLL) to lappet stem length (LStL) of almost 60%

whereas others were about 50% (Fig. 3). A factorial ANOVA revealed significant differences of body

proportions between all species (p < 0.001, Fig. 3, Table 4).

GAMBILL M. & JARMS G., Comparison of different life stages of the genus Aurelia

Table 5. Collected morphological features of the ephyrae of Aurelia sp.

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GAMBILL M. & JARMS G., Comparison of different life stages of the genus Aurelia

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Fig. 3. Body proportions of ephyrae (shown as percentages). Error bars show standard deviation.

Abbreviations: see Table 2.

European Journal of Taxonomy 107: 1-23 (2014)

Linear Discriminant Analysis (LDA)

Scyphistomae

The LDA based on ratios of morphometric measurements for scyphistomae did not identify any kind

of separation among the 17 populations. All populations overlapped to varying degrees except for

populations 2 (North Sea) and 16 (East Pacific; Fig. 4A).

Ephyrae

The LDA based on ratios of morphometric measurements for ephyrae suggested distinct classifications

(Fig. 4B) with overlaps between populations 9 (Mediterranean Sea) and 14 (Pacific), 1 and 2 (North

Sea), and a similar placement of populations 16 (East Pacific) and 9 (Mediterranean Sea). Ephyrae from

populations 6 (East Atlantic) and 8 (North Sea / Skagerrak) were completely isolated from each other

and from the other populations.

Discussion

Some morphological features of scyphistomae and ephyrae can be used to distinguish congeners while

others cannot. Straehler-Pohl & Jarms (2010) reported that the relation between rhoparlar lappet length

(RLL) and lappet stem length (LStL) and the development of the gastric system could be important

distinguishing features of genera but not species. Aurelia aurita from the North Sea has rhopalial (forked,

sharp points) and velar canals (rhombic) as well as lancet-like rhopalial lappets (Straehler-Pohl & Jarms

2010; Straehler-Pohl et al. 2011; Holst 2012b), which match ephyrae from population 2. In this study,

ephyrae have four different rhopalial lappet shapes, three different rhopalial canal shapes and two

different velar canal shapes, which supports the genetic evidence suggesting more than three species

within Aurelia (Dawson & Jacobs 2001; Dawson & Martin 2001; Schroth et al. 2002). Although colour

is another trait that depends on a variety of factors, when maintained on the same diet (Artemia nauplii),

5.0

-4

LD1

-15 -10 -5 0 5 10 15

LD1

o 1 A 2 -[-3 ; < 4 < >5 s /6 [X 7 M 8 <J>9

10 11 12 .13 : 14 ■ '5 # 16 A'7

Fig. 4. Linear Discriminant Analysis based on the morphology. A. Scyphistomae (17 cultures) of

Aurelia congeners. B. Ephyrae (7 of the 17 cultures) of Aurelia congeners. In each case, cultures can be

distinguished from one another by different symbols and corresponding numbers (see legend).

GAMBILL M. & JARMS G., Comparison of different life stages of the genus Aurelia

higher latitude scyphistomae produce white and translucent ephyrae and the degree of pigmentation

increased with decreasing latitude. Moreover, ephyrae produced by Pacific scyphistomae differed in

colour from those produced by scyphistomae collected from the Atlantic Ocean and Mediterranean

Sea. Therefore, colour can be a useful trait if compared among individuals maintained using the same

culture/feeding conditions.

The TDA we conducted using the morphometric data of ephyrae reveal a clear separation of the different

populations (Fig. 4b), which again supports the genetically indicated existence of more than three species.

The obvious partitioning clearly allows classifications to be made and these are discussed (below) in

light of known differences among the 17 populations.

In scyphistomae the colour of the calyx was not a reliable characteristic to differentiate among species,

since it was more or less the same in all scyphistomae. We expected differences similar to the ones found

in ephyrae, due to the same feeding conditions (Straehler-Pohl 2009; Straehler-Pohl & Jarms 2010; Holst

2012b). The shape of the calyx was a suitable character for separating species (e.g., a cup-like calyx is

characteristic of A. limbata [Straehler-Pohl 2009; this study]), although the morphology of the calyx and

hypostome can vary and can be misinterpreted (Berrill 1949; Straehler-Pohl 2009; Straehler-Pohl et al.

2011). Moreover, biotic and abiotic factors such as food intake, light intensity, salinity and temperature

may affect the shape and colour of these features (Spangenberg 1964; Willcox et al. 2007). The number

of tentacles is an obvious morphological feature of scyphistomae which also displays interspecific

variability, with A. aurita and A. labiata having 14 to 28 (Holst 2008; Straehler-Pohl 2009; this study)

and 14 to 21 (Gershwin 2001; Widmer 2006; this study), respectively. Scyphistomae of population 12

had between 27 and 33 tentacles and, based on this morphology, may not belong to Aurelia. Finally, the

length of the hypostome in relation to the stem has been reported to distinguish members of Scyphozoa

(Semaeostomeae: CT > HL > StT, Cepheida: StT > CL > HL, Rhizostomida: CL > StL > HL; Straehler-

Pohl 2009; Straehler-Pohl et al. 2011). In this study, StL was > HL in only 40% of the specimens;

this relationship is not suitable for distinguishing Aurelia congeners. Furthermore, we demonstrate that

morphometric measurements of scyphistomae cannot be used to distinguish among species within this

genus (Fig. 4A).

Lucas et al. (2012) provide a review of studies conducted on scyphistoma populations, including the

species-specific triggers for strobilation. We were able to induce strobilation in 7 of the 17 populations

using cues known to be effective for Aurelia species, including a decrease in temperature and, in some

cases, the addition of KI (Berrill 1949; Spangenberg 1967; see Lucas et al. 2012). Spangenberg (1964)

discovered that scyphistomae with large calices produce more ephyrae than small scyphistomae and

still have enough energy to regenerate the residuum (Straehler-Pohl & Jarms 2005). Scyphistomae are

often larger when grown at low salinities and low temperatures (Schroth et al. 2002; Willcox et al.

2007) and could therefore produce more ephyrae than smaller scyphistomae in warmer waters, possibly

due to higher availability of tissue. Our results suggested longer durations of strobilation and greater

numbers of ephyrae produced by scyphistomae collected from higher (colder) versus lower (warmer)

latitudes despite scyphistomae being maintained at the same temperature in the laboratory, even though

some populations needed the temperature drop and the consequent rise to start the strobilation process.

Naturally, the number of ephyrae produced by scyphistomae depends upon both endogenous and

exogenous factors (Lucas et al. 2012) and the effect of the latter make it difficult to use this trait to

differentiate species within one genus.

Classification

Historical reports and descriptions of species within Aurelia often used geographical distribution as a

distinguishing characteristic. However, geographical distributions of many planktonic organisms have

changed via transport in ballast waters and jellyfish introductions are commonly reported (Greenberg

European Journal of Taxonomy 107: 1-23 (2014)

et al. 1996; Purcell et al. 2007). The potential for mixing of different (potentially cryptic) species

within the same area demands that methods be found to reliably identify species. In the following, we

discuss the 17 populations in terms of the results of our morphological observations of scyphistomae

and ephyrae, morphometric measurements of ephyrae, recent genetic analyses as well as information on

geographical distribution.

Group 1

Populations 1-5, 7, 8: Agreement - A. aurita. All of these scyphistomae were collected from eastern

parts of the Atlantic Ocean and the Baltic Sea. Molecular (Dawson & Jacobs 2001; Schroth et al. 2002;

Dawson et al. 2005), distributional (Mayer 1910, 1917; Kramp 1961; Russell 1970) and our data as

described in Table 3 support this species identification for populations 1-5, 7 and 8. The effects of

changes in salinity on the morphological characteristics of scyphistomae and ephyrae are not known and

could influence classification based merely on morphology. However, morphometric measurements of

ephyrae (see Table 5) suggested that population 8 was morphologically distinct from populations 1 and

2. We speculate that populations 1 and 8 may be boreal species as suggested by Schroth et al. (2002).

The results of the LDA suggest that population 8 may be transitional between North Sea and Atlantic

populations, which is supported by the findings of Dawson et al. (2005). Group 1 is considered to be a

member to the initially described species, Aurelia aurita (Table 6).

Group 2

Population 6: Disagreement -Aurelia aurita which is likely another species. Scyphistomae in populations

6, 9 and 10 originated from geographically separate areas (North Sea, the Atlantic Ocean and Red

Sea, respectively); nevertheless their scyphistomae and ephyrae share some common morphological

characteristics (see Tables 3, 5). Unlike the genetic analyses reported by Schroth et al. (2002), our

morphometric measurements distinguish population 6 from all the other groups. Dawson & Jacobs (2001)

as well as Schroth et al. (2002) propose populations 6 and 14 to be the same species, and geographic

differences may not be valid given ballast water transport of conspecifics. Still, based on the literature

(Mayer 1910, 1917; Kramp 1961; Russell 1970) and our measurements, we suggest that population 6

represents the only member of group 2 and a new species, Aurelia sp. 1 (Table 6).

Group 3

Population 9: Disagreement - A. aurita which is likely another species. Animals from culture 9 were

collected in the Mediterranean Sea and the separation into a new species is supported by genetic

uniqueness (Dawson & Jacobs 2001; Dawson & Martin 2001; Schroth et al. 2002, Dawson et al. 2005).

Also, the morphology of the ephyrae shows unique features, e.g., the yellowish colour in combination

with the shape of the lappets and the shapes of rhopalial- and velar canals. Nonetheless, population 9

displays similar morphological features to A. aurita (Kramp 1961). Schroth et al. (2002) suggested a

transitional habitat called “Tethys,” which includes populations in the Mediterranean and Red Seas. We

therefore provisionally place culture 9 within the taxon Aurelia cruciata Haeckel, 1880 (Mayer 1910;

Kramp 1961) as it is located within the “Tethys” habitat.

Group 4

Population 10: Disagreement - A. aurita which is likely another species. Animals from population

10 were collected from the Gulf of Aqaba, also within this “Tethys” region defined by Schroth et al.

(2002) and Dawson et al. (2005). Individuals display a similar morphology to A. aurita (Kramp 1961).

We suggest placing population 10 within the taxon Aurelia maldivensis Bigelow, 1904 (Stiansy 1938;

Kramp 1961) considering its range of distribution within the “Tethys” habitat (see Table 6).

GAMBILL M. & JARMS G., Comparison of different life stages of the genus Aurelia

Table 6. Classification of the different populations (cultures 1-17) into eight different groups/species

based on our results (morphological and statistical: Linear Discriminant Analysis [LDA]) under

consideration of the literature (genetic and distributional data).

Culture

Origin

Proposed species

(a priori)

Was it the

proposed species?

Suggested species

Group

North Sea

yes

Aurelia aurita

North Sea

yes

Aurelia aurita

North Sea

yes

Aurelia aurita

Baltic Sea

yes

Aurelia aurita

Baltic Sea

yes

Aurelia aurita

East Atlantic

Aurelia sp. 1

Arctic Ocean

Aurelia aurita

yes

Aurelia aurita

East Atlantic

yes

Aurelia aurita

Mediterranean Sea

Aurelia cruciata

Red Sea

Aurelia maldivensis

West Atlantic

Aurelia flavidula

West Atlantic

Aurelia sp. 2

East Pacific

Aurelia labiata

Pacific

Aurelia labiata

East Pacific

Aurelia labiata

yes

Aurelia labiata

East Pacific

yes

Aurelia labiata

Pacific

Aurelia limbata

yes

Aurelia limbata

Group 5

Population 11: Disagreement - Aurelia aurita which is likely another, transitional species. Based on

known distributions of adult medusae (given the caveats of potential mixing) and morphological

features (Table 5), population 11 can be separated from the other Atlantic populations of A. aurita. This

population is possibly a member of the taxon Aurelia flavidula Peron & Tesueur, 1809 (Peron & Lesueur

1809; Mayer 1910; Kramp 1961) or Aurelia marginalis Agassiz, 1862 (Mayer 1910). Classification into

a different taxon seems reasonable at this point, even though these findings are not yet supported by

molecular data.

Group 6

Population 12: Disagreement-A aurita which is likely another species. Collected from Brazilian waters,

the morphology of scyphistomae (27-33 tentacles) of population 12 differs from all other populations.

The shape of the calyx in combination with the cap-like hypostome, as well as the very small size of the

scyphistomae, suggest differences from the other populations. Dawson & Jacobs (2001) found an Aurelia

species on the east coast of South America that also has a unique morphology. Mayer (1910) described

individuals off the Brazilian coast as A. aurita. Either there have been some misclassifications or both

European Journal of Taxonomy 107: 1-23 (2014)

species coexist in this area. Based on the results of this study and the currently available literature, we

suggest this population to be a separate species, which we call Aurelia sp. 2.

Group 7

Populations 13-16: Agreement - A. labiata. Both genetic analyses and morphological observations of

scyphistomae, strobilae and ephyrae and morphometric measurements in ephyrae correctly distinguished

populations 13-16 as A. labiata (Gershwin 2001; Dawson & Jacobs 2001; Dawson et al. 2005; Widmer

2005). The genetic relationship between populations 16 and 6 as reported by Schroth et al. (2002)

cannot be substantiated. Genetic analyses classify US west coast populations of Aurelia as A. labiata

(Dawson & Jacobs 2001; Dawson & Martin 2001; Schroth et al. 2002) and the morphology of both

ephyrae and adult medusae (Mayer 1910; Gershwin 2001; Dawson 2003; Widmer 2005) support this

classification. Nevertheless, differences in morphology and life cycle suggest that southern, central and

northern varieties exist (Gershwin 2001) or that these may represent different species (Dawson 2003).

Group 8

Population 17: Agreement - A. limbata. Our morphological observations of these scyphistomae match

those previously made by Uchida & Nagao (1963) and the species is confirmed by both morphological

(Kramp 1961) and genetic features (Dawson & Martin 2001; Schoth et al. 2002, Dawson et al. 2005)

of medusae. Aurelia limbata is found in the Northwest and Northeast Pacific, northern Japan, Western

Greenland, Alaska, Labrador and Siberia (Mayer 1910; Bigelow 1913; Uchida 1934; Kramp 1961).

Conclusion

We provide a detailed morphological dataset for the scyphistomae of 17 populations of Aurelia congeners.

Morphometric characteristics of ephyrae from 7 populations were good indicators of different species/

groups; still, morphometric data of scyphistomae collected and processed by the method of Straehler-

Pohl (2009), Straehler-Pohl & Jarms (2010) and Straehler-Pohl et al. (2011) where not separative in

order to distinguish among Aurelia species. Based on morphological differences (this study), genetic

differences (Dawson & Jacobs 2001; Dawson & Martin 2001; Schroth et al. 2002; Dawson 2003;

Dawson et al. 2005) and differences in geographical distribution (Mayer 1910; Kramp 1961; Russell

1970; Gershwin 2001; Widmer 2005), we suggest a separation of these 17 populations, which would

include 8 groups: A. aurita, A. labiata , A. limbata , two now Aurelia spp., and three formerly recognized

species. Our assessments agree with the a priori species assignments for 10 of the 17 populations. This

is another step towards understanding the complexity of the genus Aurelia and it reveals the importance

of considering the whole cnidarian life cycle, particularly differences in asexual propagation and

morphological characteristics of ephyrae, when attempting to distinguish species.

Acknowledgements

We would like to thank Prof. Myron A. Peck for helpful co mm ents on drafts of this manuscript. The

research leading to these results has received partial funding from the European Community’s Seventh

Framework Program (FP7/2007-2013) under Grant Agreement No. 266445 for the project Vectors of

Change in Oceans and Seas Marine Fife, Impact on Economic Sectors (VECTORS). The experiments

performed comply with the current laws of Germany.

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Manuscript received: 10 January 2014

Manuscript accepted: 16 September 2014

Published on: 26 December 2014

Topic editor: Rudy Jocque

Desk editor: Charlotte Thionois

Printed versions of all papers are also deposited in the libraries of the institutes that are members of the

EJT consortium: Museum national d’Histoire naturelle, Paris, France; Botanic Garden Meise, Belgium;

Royal Museum for Central Africa, Tervuren, Belgium; Natural History Museum, London, United

Kingdom; Royal Belgian Institute of Natural Sciences, Brussels, Belgium; Natural History Museum of

Denmark, Copenhagen, Denmark.

GAMBILL M. & JARMS G., Comparison of different life stages of the genus Aurelia

Appendix A. Morphological measurements of scyphistomae (mean ± sd) in mm.

Culture

TBL

MDD

StL

CD0

CD1

CD2

CD3

StID

4.11 ±0.30

2.67 ±0.33

0.77 ± 0.14

1.98 ±0.24

0.68 ±0.30

1.79 ±0.14

1.71 ±0.09

1.61 ±0.10

1.49 ±0.25

0.50 ±0.23

2.82 ±0.73

1.35 ±0.65

1.11 ±0.18

2.40 ±0.27

0.35 ± 0.13

2.35 ±0.26

2.15 ±0.29

1.93 ±0.36

1.60 ±0.40

0.51 ±0.25

3.85 ±0.67

2.11 ±0.31

0.93 ±0.25

2.15 ± 0.33

0.82 ±0.34

2.14 ± 0.39

2.03 ±0.34

1.85 ±0.39

1.58 ±0.34

0.54 ±0.06

5.23 ±0.45

3.52 ±0.56

0.69 ±0.22

1.73 ±0.17

1.02 ±0.55

1.79 ±0.22

1.78 ±0.23

1.80 ±0.44

1.74 ±0.46

0.50 ±0.11

4.30 ±0.52

2.18 ± 0.54

0.55 ±0.20

1.69 ± 0.18

1.57 ±0.53

1.64 ± 0.19

1.59 ±0.27

1.55 ± 0.31

1.30 ±0.26

0.24 ±0.05

2.89 ±0.34

1.64 ±0.35

0.62 ±0.20

1.85 ± 0.16

0.63 ±0.16

1.89 ±0.31

1.72 ±0.36

1.50 ± 0.35

1.28 ±0.34

0.40 ±0.13

2.87 ±0.35

1.47 ±0.23

1.03 ± 0.21

1.95 ±0.22

0.37 ±0.04

1.93 ± 0.16

1.77 ± 0.18

1.65 ± 0.17

1.40 ±0.20

0.50 ±0.18

3.46 ±0.32

2.00 ±0.25

0.80 ±0.22

1.61 ±0.20

0.66 ±0.19

1.78 ±0.24

1.79 ±0.29

1.66 ± 0.31

1.41 ±0.32

0.50 ±0.08

2.22 ±0.15

1.13 ± 0.14

0.41 ±0.14

1.52 ±0.05

0.69 ±0.14

1.43 ± 0.18

1.34 ± 0.18

1.11 ±0.27

0.87 ±0.28

0.32 ± 0.10

1.89 ± 0.19

1.08 ±0.20

0.41 ±0.16

1.48 ±0.07

0.40 ±0.07

1.52 ± 0.11

1.55 ± 0.14

1.43 ± 0.14

1.15 ± 0.19

0.29 ±0.06

3.25 ±0.31

2.11 ±0.19

0.71 ±0.11

1.57 ±0.07

0.43 ±0.16

1.54 ±0.08

1.35 ± 0.11

1.35 ± 0.10

1.32 ± 0.16

0.39 ±0.07

1.18 ± 0.26

0.66 ±0.23

0.31 ±0.08

1.01 ±0.11

0.20 ±0.04

1.05 ± 0.18

0.95 ±0.15

0.83 ±0.17

0.66 ±0.17

0.24 ±0.09

3.36 ±0.42

2.25 ±0.22

0.37 ±0.14

2.00 ±0.27

0.75 ±0.31

1.91 ±0.21

1.67 ± 0.21

1.53 ± 0.17

1.27 ± 0.15

0.38 ± 0.14

2.02 ±0.33

1.21 ±0.25

0.55 ± 0.16

1.38 ± 0.15

0.25 ±0.22

1.37 ± 0.15

1.22 ±0.14

1.16 ± 0.15

1.03 ±0.22

0.20 ±0.05

3.67 ±0.52

2.47 ±0.38

0.51 ±0.06

1.89 ±0.24

0.69 ±0.44

1.89 ± 0.38

1.81 ±0.32

1.65 ±0.25

1.32 ± 0.21

0.47 ±0.06

2.26 ±0.34

0.96 ±0.36

0.48 ±0.18

1.54 ±0.06

0.82 ±0.20

1.39 ±0.05

'vD

o’

-H

'vD

0.93 ±0.10

0.71 ±0.06

0.24 ±0.02

2.76 ±0.32

1.90 ±0.33

0.46 ±0.08

2.09 ± 0.15

0.41 ±0.12

2.13 ± 0.17

2.11 ±0.16

1.93 ±0.24

1.52 ± 0.35

0.45 ±0.15

Appendix B. Morphological measurements of ephyrae (mean ± sd) in in in

Culture

TBD

CDD

TMLL

LStL

RLL

AdD

RhTI

3.44 ±0.23

1.36 ± 0.13

1.03 ±0.06

0.52 ±0.02

0.51 ±0.05

0.38 ±0.05

1.45 ± 0.13

2.34 ±0.18

3.54 ±0.32

1.32 ± 0.10

1.15 ± 0.10

0.56 ±0.04

0.59 ±0.06

0.37 ±0.06

1.43 ±0.10

2.40 ±0.18

3.27 ±0.12

1.06 ±0.03

1.09 ±0.05

0.66 ± 0.03

0.43 ± 0.03

0.32 ±0.03

1.21 ±0.02

2.41 ±0.06

2.92 ±0.09

1.29 ±0.04

0.77 ±0.04

0.39 ± 0.03

0.38 ± 0.04

0.29 ±0.05

1.38 ±0.03

2.05 ±0.02

2.76 ±0.21

0.95 ±0.07

0.92 ±0.08

0.46 ± 0.06

0.46 ± 0.03

0.26 ± 0.02

1.05 ±0.07

1.98 ± 0.19

3.37 ±0.11

1.21 ±0,08

1.10 ± 0.03

0.56 ± 0.02

0.55 ± 0.02

0.29 ± 0.03

1.31 ±0.07

2.41 ±0.12

3.97 ± 0.16

1.39 ± 0.10

1.33 ±0.06

0.68 ± 0.04

0.65 ±0.05

0.50 ±0.03

1.48 ±0.09

2.89 ±0.08