A revision of the cladoceran genus Simocephalus (Crustacea, Daphniidae)

62 Pages·1998·31.6 MB·

by  Marina J Orlova-Bienkowskaja

Bull. nat. Hist. Mus. Lond. (Zool.) 64(1): 1-62 Issued 25 June 1998
THE NATURAL
A revision of the cladoceran genus HISTORY MUSEUM
29 JUN 1998
Simocephalus (Crustacea, Daphniidae)
PRESENTED
MARINA J. ORLOVA-BIENKOWSKAJA fe
A.N. Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Leninsky prosp. 33, Moscow
117071 Russia
CONTENTS
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S. exspinosus (De Geer, 1778) .......-..:006
S. congener (Koch, 1841) ..........eseeeeeeee
S. (acutirostratus) species ZTOUP ..........0..
S. acutirostratus (King, 1853) ...........0
S. victoriensis Dumont, 1983 .............0-
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SYNOPSIS. Simocephalus, a world-wide genus of littoral freshwater Daphniidae is reviewed in full for the first time. Four
subgenera are recognized, one subgenus and two species are newly described. Eight species and subspecies are synonymized, a
number of previously synonymized species are reinstated and two species are transferred to the genus Daphnia. Thus, twenty
species are considered as valid members of the genus Simocephalus: subgenus Simocephalus s. str.: S. vetulus, S. elizabethae, S.
gibbosus, S. vetuloides, S. mixtus and S. punctatus sp. noy.; subgenus S. (Coronocephalus): S. serrulatus, S. semiserratus and S.
mirabilis sp. nov.; subgenus S. (Aquipiculus): S. latirostris, S. lusaticus andS. heilongjiangensis; new subgenusS . (Echinocaudus):
S. exspinosus, S. congener, S. acutirostratus, S. obtusatus, S. daphnoides, S. rostratus, S. brehmi, S. victoriensis. For each species,
accounts are given of nomenclature, distribution and morphology (with original figures ).A key for identification of subgenera and
species is provided.
© The Natural History Museum, 1998
M.J. ORLOVA-BIENKOWSKAJA
to be cosmopolitan, pantropical efc. are in fact groups of closely
INTRODUCTION
related species, with restricted distributions. Obviously, a world-
Freshwater Daphniidae of the genus Simocephalus Schédler, 1858 wide revision of Simocephalus is necessary. Such an attempt is
are common in littoral aquatic vegetation all over the world. These made here.
8tailless water fleas9 have been known since the middle of the 18th The genus Simocephalus has been divided into four species
century (Schaeffer, 1755), but their taxonomy remains unsettled, groups: S. (vetulus), S. (exspinosus), S. (serrulatus) andS . (latirostris)
with 61 specific and subspecific names proposed. Morphological (Orlova-Bienkowskaja, 1993a). The diagnostic characters of the
variability is poorly known. This makes the taxonomic status of groups are stable and well-expressed in all representatives. Interme-
certain forms doubtful, since they may not represent taxa, but diate forms are absent. Furthermore, different characters are
merely morphological varieties. The descriptions of numerous spe- congruent, that is, they combine species into the same groups. Thus
cies are inadequate. Furthermore, some species which are supposed the species groups are given the rank of subgenera.
Fig. 1 Morphology of Simocephalus. a4abdomen, ab 4 anal bay, ae 4aesthetes, at 4 anal teeth, al 4 antennule, a2 4 base of antenna (antenna is not
shown), d4denticles of inner surface of ventro-posterior valve angle, dap 4 distal abdominal process, dd 4denticles of 8orsal valve margin, dh 4
depression of head shield between head and valves, dpva 4 dorso-posterior valve angle, dv 4 point of divergence of valves, dvm 4 dorsal valve margin, e 4
eye, f 4fornices, fr 4frons, g 4 gut, h4heart, hp 4 the place of head pores, 0 4ocellus, p4postabdomen, pap 4 proximal abdominal process, pe 4
postabdominal claw, pe 4 parthenogenetic eggs, ps 4 plumose setae of inner surface of ventral valve margin, pym 4 posterior valve margin, r4rostrum, s 4
setules of inner surface of posterior valve margin, sa 4 supra-anal angle, sp 4 sensory papilla of antennule, ss 4 sensory setae, vhm 4 ventral head margin,
vvm 4 ventral valve margin, 1st 4 1st trunk limb, 2nd 4 2nd trunk limb, 3rd 4 3rd trunk limb, 4th 4 4th trunk limb, Sth 4 5th trunk limb.
REVISION OF SIMOCEPHALUS DAPHNIIDAE 3
morphological hiatus between them. I also use four-dimensional
MATERIALS AND METHODS
cluster analysis (average method) to determine which series are
close to each other. Diagrams of characters and cluster analysis are
About ten thousand specimens from more than three hundred locali-
independent of each other, because the former operates only with
ties all over the world have been studied. Females of all species
extreme values, the latter only with average values of characters.
except S§. /usaticus, males of nine species, and museum types of
Therefore, if both methods give the same result, it is reliable.
fifteen taxa have been examined. Material examined is in the follow-
ing collections and institutions: AC 4 author9s collection deposited
in Zoological Museum of Moscow State University, AM 4 Austral-
ian Museum, Sydney, Australia, BMNH 4 The Natural History MORPHOLOGY
Museum, London, Great Britain, MCA 4 Museum of Central Africa,
Tervuren, Belgium, MNO 4 Museum of Nature, Olten, Switzerland, Female
MV 4 Museum of Victoria, Australia, SAM 4 South Australian
Museum, Adelaide, Australia, ZI 4 Zoological Institute of the Rus- Valves
sian Academy ofS ciences, St.-Petersburg, Russia, ZICC 4 Cladocera
Maximum height of valves posterior to the middle. (Figs 1; 3B,C).
collection of ZI, ZICW 4 G.Ju. Werestchagin9s collection in ZI,
Posterior margin (Fig. l:pvym) oblique, almost straight. Point of
ZIPD 4 plankton depository of ZI, ZMC 4 Zoological Museum of
divergence of valves (Fig. I:dv) dorsal to dorso-posterior angle
Copenhagen, Denmark, ZMO 4 Zoological Museum of Oslo Uni-
(Fig. |:dpva). Dorsal, posterior and ventral margins with denticles
versity, Norway, ZMU 4 Zoological Museum of Uppsala University,
or smooth. Denticles arranged in 2 rows on dorsal margin (Fig.
Sweden.
I:dd). Inner valve surface with a row of plumose setae on ventral
Original figures are made with the aid of a camera lucida. Keys
margin (Fig. 1:ps), a row of setules groups on posterior margin (Fig.
and diagnoses are based on adult specimens. The following addi-
l:s) and 2-5 plumose denticles near ventro-posterior angle (Fig.
tional abbreviations are used: CBS 4 canadian balsam slide, MPA 4
I:d). Parthenogenetic female with 1-30 eggs in brood pouch.
material preserved in alcohol, PSEM 4 preparation for scanning
Ephippium containing | egg (Fig. 3C).
electron microscopy, PVAS 4 polyvinyl alcohol slide, 9 ad. 4 adult
parthenogenetic female, 9 juv.4juvenile parthenogenetic female, ° e.
Reticulation
4 ephippial female. Morphological terms used below are shown on
Valves and head reticulated. Reticulation consists of oblique stripes
Fig. 1.
somewhat intersecting in mostof carapace and head and of polygons
In some cases I use a cluster analysis and diagrams of characters
along valve margin and in front of eye.
for differentiation between closely related species. Four metric
characters are used (Fig. 2): W/L 4 ratio between width of dorso-
Head
posterior valve prominence and body length, M/L 4 ratio between
Comparatively small, noticeably delimited by depression on dorsal
length of dorso-posterior valve prominence and body length, G/L 4
side (Fig. 1:dh). Rostrum always pointed, long or moderate. Frons
ratio between height of dorsal valve margin and body length, D/L 4
(Fig. 1:fr) rounded, pointed or right-angled, with denticles or devoid
ratio between diameter of dorso-posterior valve prominence and
of them. Ventral head margin (Fig. 1:vhm) with depression, deep or
body length. Body length (L) was measured with an ocular microm-
shallow, near rostrum. Fornices very broad (Figs 4; 5; 1:f). Posterior
eter. Other measurements were made by drawing the body outline of
part of head with 3 main connected head pores, transversally orien-
each specimen with the aid of the camera lucida and measuring the
tated (Fig. 5, HP) and 2 minute lateral head pores seen only with
details with an ordinary rule.
scanning electron microscope, or without head pores. Eye and
Statistical analysis employed the computer system 8Statgraphics9.
ocellus always present.
Two-dimensional diagrams of characters are used for the detection
of morphological hiatus between closely related species. Each
Appendages
specimen of each series is represented as a point on a coordinate
Antennule tubular (Figs 6C), having 9 aesthetes at end and | sensory
plane. Coordinates of the point are equal to measurements of the
papilla proximally. Mandibles, maxillule and labrum as shown in
specimen. Each series or group of series is represented with the
Figs 4, 6. Antenna (Fig. 7) comparatively short, ends of distal
polygon including the points corresponding to all specimens. If the
segments reach only middle of valves. Proximal part of basipod with
polygons of two series/ groups of series do not overlap, there is a
2 setae (Fig. 7E), outer side of distal part with a seta (Fig. 7D), inner
side of distal part with a spine (Fig. 7C). Contrary to the opinion of
Manujlova (1964), the length of the distal seta does not differ in
different species. Exopod of antenna of 4; endopod of 3 cylindrical
segments. Second segment of exopod with a short spine, third with
a seta, fourth with 3 setae, of which one shorter than others and
curved (Fig. 7B). First and second endopod segment each with 1
seta, third segment with 3 setae. Contrary to the opinion of Behning
(1912) and Manujlova (1964) number of setae on each trunk limb
does not differ in different species. Interspecific differences concern
only the length of certain setae. The structure of trunk limbs (Figs 6;
8-11) has been described in detail (Orlova-Bienkowskaja, 1993b).
Postabdomen (Figs |:p; 12A,B)
Fig. 2 Measurements of valves. G 4 height of dorsal valve margin, W 4 High, with anal bay (Fig. 1:ab), supra-anal angle (Fig. 1:sa) and 2
width of dorso-posterior valve angle, D 4 diameter of dorso-posterior rows of anal teeth (Fig. |:at). Distal anal teeth large, covered with
valve angle, M 4 length of dorso-posterior valve angle. setules. Proximal teeth small, smooth. Dorsal part with groups of
M.J. ORLOVA-BIENKOWSKAJA
Fig. 3 S. vetulus. A, male, B, parthenogenetic female attached to a surface, C, ephippial female.
setules. Postabdominal claws long (Fig. 1:pc), slightly curved, with more distended than in female (Fig. 6B), with 2 sensory papillae
2 rows of setules and/or spines on concave side. Anus (Fig. |:ab) in proximally. First and second trunk limbs (Figs 8B,C; 13) differ
anal bay. from corresponding limbs of female in several details (Orlova-
Abdomen with 2 processes (Fig. 1:pap,dap). Bienkowskaja, 1993b) (Figs 8A and C). Postabdomen narrower
than in female (Fig. 14A). Vas deferens opening on supra-
Male
anal angle (Fig. 14B,C) or distally. Fewer anal teeth than in fe-
Dorsal valve margin straight (Fig. 3A), ventral margin with an male.
embayment anteriorly. Head pores larger, antennules shorter and Abdominal processes absent.
REVISION OF SIMOCEPHALUS DAPHNIIDAE
Fig. 4 S$. vetulus head and mouth parts.
VARIABILITY small eye and ocellus (Fig. 16A) and all those from the second
(parthenogenetic and ephippial females and males) a large one (Fig.
16B). Individuals from the sample of 5. 11. 1990 were kept at room
Age variability is similar in all species (Fig. 15). New-born fe-
males do not differ much from males: The brood pouch is small temperature. By the 17th day the size of the eye and ocellus in all
and the dorsal valve margin almost straight. The prominence on cases had become small (Fig. 16C).A similar result was obtained for
the dorso-posterior valve angle, if it present, is not distinct. Cara- S. serrulatus.
pace denticles are small and cover less of the valves than in Ocellus size is also affected by illumination intensity. It decreases
adults. Older females have a more distinct and sharp dorso-poste- in darkness (Jermakov, 1924) and if the ventral part of the head is
rior valve prominence. The shape of the brood pouch in the adult covered by epibionts (personal observation) (Fig. 16D). Ocellus
depends on the number of eggs. The head grows slower than the shape varies within populations. In females of Simocephalus s. str. it
carapace. Valve shape in new-born males differs from that of is straight or curved, widened in the middle or bifurcated at the end.
adults only in the absence of an embayment in the proximal part In males of these species and in both sexes in species of other
of the ventral margin. The number of anal teeth correlates with subgenera it is round or rhomb-like. The frons in S. (Coronocephalus)
size in females. The ocellus in juveniles is shorter than in adults. bears a variable number of denticles. Individuals with and without a
The postabdomen of neonates of both sexes lacks an anal bay, prominence at the ventral head margin occur in all species except S.
supra-anal angle (Figs 12C; 15C), abdominal processes. The gibbosus, S. elizabethae and S. obtusatus. A dorsal embayment
fourth endite prominence of the first limb has a large hook bear- between carapace and head is more or less developed in all species.
ing a denticle at its end in the adult male (Fig. 8B) and small hook Sometimes, there is a small prominence on the head near this
lacking a denticle in the juvenile (Fig. 8D). The curved setae of embayment (Fig. 16F).
the second, third and fourth endite prominences of the second There are pigmented spots in the valve tissue. Their shape and
limb are short in juvenile males and longer than the base of the colour differ within populations. The colour is green, brown or
plumose seta of the first prominence in adults (Fig. 13B4D). The orange and as a rule correlates with the colour of the gut contents.
morphology of third, fourth and fifth trunk limbs in males and all According to Green (1966) carotenoid pigmentation depends on the
trunk limbs in females does not depend on age. food composition.
Eye and ocellus size are subject to seasonal variation. This was The number of denticles at the ventro-posterior angle of the
discovered in the following way: two series of S. vetulus were valves varies from two to six. No correlation between number of
collected in the same water-body in the Moscow region on 12. 5. denticles and size was observed. There is some variability in shape
1990 and 5. 11. 1990. All specimens from the first sample had a of the postabdomen and abdominal processes (Fig. 17).
6 M.J. ORLOVA-BIENKOWSKAJA
Female. Dorso-posterior valve angle rounded or with rounded
SYSTEMATIC ACCOUNTS
prominence. Valves without dorsal keel. Posterior corner of
ephippium without protuberance (Fig. 3C). Ocellus elongate (ex-
ception: S. punctatus). Setae of 2nd and 3rd endite prominence of
Subgenus Simocephalus s. str.
2nd trunk limb as long as 0.3 and 0.2 of basal segment of plumose
seta of lst prominence respectively (Fig. 9B). Postabdomen with
TYPE SPECIES. Simocephalus vetulus (O.F. Miller, 1776) 10-15 anal teeth on each side. Supra-anal angle rounded (Fig. 12A).
Male. Supra-anal angle pointed (Fig. 14). Vas deferens opening
DIAGNOSIS. Both sexes. Frons rounded, without denticles (Fig. 18).
there. Postabdomen with 5-8 anal teeth on each side. Dorso-poste-
Head shield without depression. Head pores present (Fig. 5). Inser-
rior valve angle rounded or with small rounded prominence (Fig.
tion of antennules at base of rostrum. Antennule short in
3A). Males of the following species have been examined: S. vetulus,
correspondence with short rostrum, with neitherridges nor denticles
S. mixtus, S. vetuloides, S. punctatus, S. elizabethae. They do not
on inner side (Fig. 6B,C). Aesthetes longer than base of antennule.
differ from each other, so only females are described.
Postabdominal claws without spines (Fig. 12D,E). Inner and outer
side of claw with fine setules. Anal bay of postabdomen narrow, REMARKS. Fig. 19A gives the cluster analysis of sixteen series
rounded, with anal teeth (Fig. 12A). (each consisting of twenty specimens) from sixteen European
Fig.5 S$. vetulus. Head shield. HP 4 head pores.
REVISION OF SIMOCEPHALUS DAPHNIIDAE
Fig. 6 S. vetulus. A, maxillule, B, antennule of male, C, antennule of female, D, mandibles, E, molar region of mandibles.
populations of Simocephalus s. str. The dendrogram consists of 2 have also one series of S. vetulus from Morocco, but these specimens
large clusters. The first of them combines the populations 1413 (thin are in poor condition and it is impossible to measure them.
line), and the second combines 14416 (thick line). This means that
S. vetulus (O.F. Miiller, 1776)
the similarity within both clusters is stronger than between them. In
other words, we can presume that populations 1-13 and 14-16 Figs 3-18
belong to two separate species. The diagrams of characters provide
Daphne vetula O.F. Miiller, 1776: 199; Daphnia sima O.F. Miiller,
support for this presumption (Fig. 19B,C). The areas occupied by
1785: 91: Monoculus nasutus Jurine, 1820: 133; Monoculus sima:
populations |413 (thin line) and by populations 14416 (thick line)
Jurine, 1820: 129; Simocephalus vetulus: Schédler, 1858: 18; S.
on the diagram only overlap to a minor extent at one point. There-
vetulus var. angustifrons Lilljeborg, 1900: 171;S. vetulus var. brandti
fore, there is a morphological hiatus between these groups.
Cosmovici, 1900: 156 syn. nov. (nec Daphnia brandtii Fischer,
Examination ofthe types shows that one of these species is S. vetulus
1848); S. vetulus angustifrons: Behning, 1941: 181; S. vetulus
(1-13); the other is S. mixtus (14-16).
gebhardti Ponyi, 1955: 313; S. mixtus hungaricus Ponyi, 1956: 57.
Similar reasoning shows that 2 species of Simocephalus s. str.: S.
mixtus and S. vetuloides occur in Eastern Siberia (Fig. 20). There TYPE MATERIAL. The types appear to be lost. S. vetulus is often
appear to be 3 species in Eurasia: S. vetulus in Europe, S. vetuloides confused with closely related species, so the designation of a
in Eastern Siberia and S. mixtus in all regions of Asia and in Eastern neotype is necessary. Neotype (designated here): Denmark, Zea-
Europe. The latter species is rather variable. land, vicinity of Copenhagen. Dyrehaven, 55°46'N, 12°34'E, 11. 5.
All measured African specimens (9 series) belong to S. mixtus. I 1901: MPA: 9 ad. (ZMC, CRU-319).
M.J. ORLOVA-BIENKOWSKAJA
Fig. 7 S. vetulus, antenna. A, general view, B, curved seta of exopod distal segment, C, inner side of basipod, distal part, D, outer side of basipod, distal
part, E, basipod proximal part.
MATERIAL EXAMINED. Neotype. Type material of junior synonyms: DIAGNOSIS. Measurements. 2 9 ad.: 1.342.9mm.,@ Qe.: 1,2-
S. vetulus angustifrons Lilljeborg, 1900: Lectotype (designated 1,9mm,c'oO 9: 1,14-1,3mm.
here): Sweden, Uppsala, 9. 10. 1882, leg. Lilljeborg: MPA: 92 ad. Female. Dorso-posterior valve prominence short, with narrow base
(ZMU, 399). Paralectotypes collected with lectotype: MPA: and large diameter (Fig. 18). Its diameter greatly exceeds its length
13 9 Qad., 339 Qjuv., 72 Qe., SSA (ZMU, 399). Other speci- (Fig. 2). Dorsal valve margin low, not protruding backward. Depres-
mens: More than 2000 specimens (? Qad.,2 9 juv., 2 Qe.,c0°o9) sions above and below dorso-posterior prominence small and shallow.
from 30 localities (Fig. 21) in Denmark, Greenland, Poland, Bul- Ventral head margin straight or slightly concave, sometimes with
garia, European Russia, Ukraine, Georgia, Morocco, deposited in small prominence. Deep depression on ventral head margin near
AC, ZMC, ZICW. Some specimens are selected from the samples rostrum. Ocellus elongate.
from ZIPD.
REVISION OF SIMOCEPHALUS DAPHNIIDAE
Fig.8 S. verulus. A, 1st limb of female, B, hook of endopod of Ist limb of adult male, C, Ist limb of male, D, hook of endopod of Ist limb of juvenile male.
DISTRIBUTION. (Fig. 21) Europe, North Africa. This species was renamed this species Daphnia sima. The name 8vetulus9 is not
previously assumed to be cosmopolitan (Manujlova, 1964). But the grammatically correct (Dumont, 1977). 8Vetula9 means 8an old
investigation of specimens from different regions shows, that S. women. This is not an adjective, but a substantive. Its gender cannot
vetulus occurs in Europe and North Africa only. In other regions it is alter. However, it is not necessary to change the name 8S. vetulus9,
replaced by closely related species: S. mixtus, S. vetuloides, S. because it has come into common use.
gibbosus, S. elizabethae and S. punctatus. Some authors in the 19th century (Lievin, 1848; Baird, 1850;
Leydig, 1860) supposed S. exspinosus and S. congener to be syno-
REMARKS. The original description of S. vetulus is very short: nyms of S. vetulus. According to recent data, S. vetulus differs very
<Daphne Vetula cauda inflexa, testa mutica9 (Miiller, 1776). This is much from these species and even belongs to another subgenus.
appropriate for any species of Simocephalus. Later, Miiller (1785) According to Jurine (1820), S. nasutus (Monoculus nasutus
10 M.J. ORLOVA-BIENKOWSKAJA
4=S SS Se=t FF
= SET
aCn oe, s
KSyEeNL EE
Yi, KKKK e
KK
SMMMAAQ0y5s SS
xe
Fig. 9 S. vetulus, female 2nd trunk limb. A, general view, B, endopod.
differs from S$. vetulus (Monoculus sima) in rostrum shape. How- S. vetulus var. angustifrons Lilljeborg differs from the typical
ever, judging from the illustrations in the original description, these form in the presence of a prominence on the ventral head margin.
species are identical. Information about the types of S. nasutus is Some authors (Behning, 1941; Manujlova, 1964) consider this
lacking. I agree with Lilljeborg (1900), that S. nasutus is a junior variety to be a subspecies, but I believe it to be a synonym, because
synonym of S. vetulus. I have found specimens both with and without the prominence in the
S. vetulus var. brandti Cosmovici was described from Romania. type material of S. vetulus var. angustifrons (Fig. 22). Moreover the
There is no information about the type material. Cosmovici (1900) animals with such a prominence sometimes occur in the most of
writes that he named this variety thus because it is intermediate Simocephalus species.
between S. vetulus and S. brandtii Fischer (= S. serrulatus). Refer- S. vetulus gebhardti and S. mixtus hungaricus were described
ring to the illustrations by Cosmovici, it is the junior synonym of S. from Hungary. The author (Ponyi, 1955, 1956) writes that these
vetulus. subspecies differ from S. vetulus vetulus in head shape and denticles