Taxonomic observations on the larval forms of Cyclops leuckarti are being discussed and compared with Cyclops oithonoides var. hyalina. Observations include Nauplius and Metanauplius stages. The author concludes that specific differences are recognisable even in the nauplius stages

Gelmini, G.

English

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FBA Translation (New Series) No. 125 
GELMINI G. 
Contributions to the knowledge of larval development in Cyclops leuckarti Claus. 
Natura, Milano, 19, 89-96 (1928) 
Translated by W.J.P. Smyly. 
In examining the plankton of the lake of Ghirla (Varesotto), I 
have sometimes observed numerous individuals of a species of Cyclops 
which in all characters resembles Cyclops leuckarti (Claus) except 
that the hyaline membrane of the last segment of the first antenna 
appears all finely serrated with two strong notches instead of one, 
as is figured in Schmeil (1892). Given the perfect identity of all 
other characters, this little difference does not seem to me sufficient 
reason for creating a new variety: it would be possible to treat this 
perhaps as a local variety but I reserve this for discussion in the work 
which I am in the course of doing on the plankton of the lake of Ghirla. 
The purpose of this short note is to study the larval forms of 
C. leuckarti which have many characters in common with C. oithonoides 
var. hyalina, the larval development of which is described recently 
by Manfredi, (1925). Drawings of the two forms are so much alike 
that it seems to me interesting to find out what differences there 
may be, however small, which may permit the identification of the 
nauplius and metanauplius of these two Cyclops. 
Taking account of the researches of Ziegelmayer (1925, Zeit.f.Wiss, 
B.126) I have tried to recognise the first stages of development 
but, though having followed some cultures, I have never had the fortune 
to examine newly hatched nauplii, nor to find the cast-skins in my 
culture vessels. 
However, the morphological difference between naup I & II is small 
which I could not make out from material preserved in formalin. 
Fig. 2 (title: I nauplius) refers then probably to that which according 
to Ziegelmayer is the 2nd stage naup and which is indicated in the 
drawing of Manfredi as nauplius I. For clarity in naming, I will 
indicate with the name of orthonauplius (following the nomenclature 
of Dietrich) the stage I nauplius and successively the other stages 
by name as I, II, III, IV, V nauplius: I, II, III, IV, V metanauplius. 
[metanauplius = copepodid]. 
Nauplius series 
Nauplius I in C.leuckarti has an almost perfect oval-shape and, 
as observed in C. oithonoides the posterior extremity does not show 
any sign of bifurcation. On this extremity is inserted a single pair 
of feathered setae which differ from those of C. oithonoides var. hyalina 
in being much shorter and not curved at the tip. Near the insertion 
of this fine hair one sees a transverse series and two oblique series 
of very fine spines. Some setules (which increase in number in each 
successive stage) one observes on the ventral side of the nauplius. 
Their position is a little diverse as in C. oithonoides var. hyalina, 
as one can easily see in comparison between the figure given here 
and the corresponding figure in the work of Manfredi. Observing the 
drawings of the II, III, & IV nauplius of Cyclops oithonoides var. hyalina 
(which are not given in the work of Manfredi but which I was able to 
see as well) I have established that the II & III nauplius are not 
characterized by any particular difference. In the IV nauplius there 
is a difference in C.oithonoides of the body which is considerably 
elongated: there are well shown traces of a division into three 
segments. (fig. 3). This segmentation becomes much more evident 
in the successive stages. It is important to note that while in 
C.oithonoides, the longest seta of the maxilla 
is that in the middle of the expedite, in C, leuckarti the longest and 
least robust is that to the outside of the same expodite. The caudal 
setae are three on the side and of them only the outside is hairy. 
In the IV nauplius, Cyclops leuckarti (fig. 4) has a form less 
tapering than that of C.oithonoides var. hyalina . The distal segment 
of the expodite of the II antenna carries three plumose setae; the 
endopodite carries three lateral setae of which only the median is 
plumose. (In Cyclops oithonoides the terminal setae of the expodites 
are two and the lateral setae of the endopodite also two). In the IV 
stage the jaws are worth considering, indeed the spines have maintained 
the same relations in this respect to the length as to their positions. 
At the base of the maxilla on the inside is a plate less pointed than 
a spine and on the outside is scarcely pointed. The I & II pairs 
of swimming feet instead are well visible: so much so that one can 
clearly distinguish endopodite and exopodite one from the other. 
In the 1st pair, the endopodite is provided with three well-developed 
spines of which the median is the largest and the expodite is provided 
with 4 spines of which the two inner ones are plumose. This pair of 
limbs is here much more developed than the corresponding one in 
Cyclops oithonoides var. hyalina. The outline of the furca is well 
marked and carries 3 pairs of rather long spines. One other character 
in which the two species differ one can observe in the cast skin of 
the nauplius. In that of Cyclops oithonoides, there is an oval hole 
situated dorsally through which the new nauplius escaped from its old 
shell. In Cyclops leuckarti however the empty shell appears torn at 
the anterior end. 
Metanauplius (= copepodid) stages: 
The first metanauplius of C.leuckarti (Fig. 5) has small dimensions 
with the first antenna of 6 segments provided with long plumose setae. 
The mouth parts are very similar to those of the adult, however 
the external margin of the maxilla (Fig. 5b), characteristic of the 
species, show small notches scarcely visible except under the highest 
power of the microscope. The furca is well developed: of the 4 terminal 
stetae that inside (innermost) is the longest. In the succeeding stages 
one observes nothing in particular however the notched margin of the 
maxilla becomes more evident still in the third metanauplius (Fig. 6). 
In this stage appears also well evident the hyaline membrane of the two 
last segments of the 1st antenna. In the following table is indicated 
the series of divisions of the segments of the 1st antenna during 
its development. 
Summarizing, the fundamental differences between the larval forms 
of these two species are very small, but still sufficient to distinguish 
even the 1st nauplius stage. They consist principally: 
1) in a shorter length and curvature of the terminal setae 
and a different arrangement of the fine setae of the ventral 
surface (1st 2nd and 3rd nauplius). 
2) in the more slender form of the body which shows also a 
sketchy segmentation and in the distribution of the 
spines of the maxilla (4th or 5th nauplius). 
3) in the inferior margin notched of the maxillary limb 
which one finds in all the copepodids. Also noteworthy 
is the developmental series of the segments of the 1st 
antenna, indeed in the fourth copepodid the antenna is 
composed of 11 segments, a condition noted also in 
C. bicuspidatus, C.serrulatus, C. prasinus, C. oithonoides 
var. hyalina, C.albidus, C.vernalis and C.strenuus. 
The results of this short investigation confirm the hypothesis 
of Grandori that specific differences are recognisable even in the 
nauplius stages: and the fact is all the more noteworthy in the case 
which I have considered, in as much as one is dealing with nauplii 
belonging to species which are very much alike, namely C. leuckarti 
& C.oithonoides var. hyalina. 
It is worth noting the fact that, in the the fourth copepodid has 
11 segments in the antenna and this antenna passes unchanged to the 
5th copepodid In the instead the antenna of 9 segments in the 3rd 
copepodid remains the same in the 4th copepodid and only in the 5th 
copepodid divides into 11 segments. 


 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Notice 
 
 
Please note that these translations were produced to assist the scientific staff of the 
FBA (Freshwater Biological Association) in their research. These translations were 
done by scientific staff with relevant language skills and not by professional 
translators. 
 
 
 


Contributions to the knowledge of larval development in Cyclops leuckarti Claus [Translation from: Natura, Milano 19, 89-96, 1928]

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Contributions to the knowledge of larval development in Cyclops leuckarti Claus [Translation from: Natura, Milano 19, 89-96, 1928]

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