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By Leonarp Doncaster, B.A., Scholar of King’s College, Cambridge. 


(With Plate XIII, and Text-figures 39 and 40.) 

Amone the pelagic organisms, collected by Mr Stanley Gardiners Expedition in the 
Maldive Archipelago in the years 1899 and 1900, were considerable numbers of Chaetognatha. 
They were fished chiefly at night, in moderate depths, and were preserved directly in 
4 per cent. formalin. They are divided into two parts, viz. some were collected between 
Dec. 10 and Jan. 10, and the rest in April. Those obtained in the winter were much 
more abundant both in individuals and species, the number of specimens submitted to me 
being about 900 in the winter months compared with rather over 250 in April. 

In classifying the group I have followed Langerhans (“ Wurmfauna von Madeira,” Zeitschr. 
wiss. Zool. Bd. XXXIV. p. 132, 1880) and Strodtmann (“Systematik der Chaetognathen,” 
Archiv Naturgeschichte, Jahrgang 58, Bd. 1. p. 333, 1892), and have used the names Sagitta, 
Spadella and Krohnia in the sense which they have defined, viz. 

Sagitta forms with two pairs of lateral fins, and two rows of teeth; 
Spadella with one pair of lateral fins on the tail segment only, and two rows of teeth; 

Krohnia with one pai of lateral fins extending on the trunk and tail, and one row 
of teeth. 

The Chaetognatha from the Maldives include several species well known from European 
waters, and others which have been procured only from the American coast or from Japan, 
but a considerable proportion (6 species out of 15) appear to be undescribed. Sagitta is 
much the most abundant genus, but Spadella is represented by one moderately common 
species, while only two specimens of Krohnia were found. 

In a Note at the end of the “List of the Species” I have added the description 

of a new species, found by the late Mr F. P, Bedford at Singapore. 



I, Genus Sagitta Slabber. 
1. Sagitta enflata Grassi. 
Strodtmann, Archiv Naturgeschichte, Jahrg. 58, Bd. 1. p. 348, 1892. 

This species is very abundant both in winter and in April, making up perhaps fifty 
per cent. of each collection, It agrees with Grassi’s description in most points; the tail 
segment is however rather shorter in proportion to the trunk, and the teeth are sometimes 
more numerous. Exactly the same differences are described by Aida (Annot. Zool. Jap. 
Vol. 1. p. 18, 1897) between the S, enflata found in Japan and those of European waters. 

This species has been hitherto recorded from the Mediterranean, Madeira and Japan. 

2. Sagitta magna Langerhans. 
Strodtmann, Archiv Naturgeschichte, Jahrg. 58, Bd. 1. p. 348, 1892. 

Fairly abundant in the winter, but not found in April. Only a few specimens reached 
a length of 3 em. Did not differ in any points from Grassi’s and Strodtmann’s descriptions. 

Recorded hitherto from Madeira and the Mediterranean. 

3. Sagitta tricuspidata Kent. 
Strodtmann, Archiv Naturgeschichte, Jahrg. 58, Bd. 1. p. 342, 1892. 

A rather scarce species in the winter, and not found in April. It is the largest species 
found, some specimens attaining a length of nearly 4cm. In shape it is like S. magna, 
but slightly narrower, and while the posterior fins of magna are nearly semicircular, those 
of tricuspidata are broader near thew posterior ends, The ovaries are long and slender, 
and may extend to the front end of the anterior fins; the longest observed were 1'5 em. 
in length, Hooks 4—8, anterior teeth 3, posterior 1; but in several specimens, making up 
a large proportion of the whole number, there were 2 anterior and either 2 or 4 posterior 
teeth. The posterior teeth are attached to a cuticular bar which bears a number of 
rounded projections. Such projections are commonly found in other Sagittas, corresponding 
in number and position with the teeth, and are in some cases sharply pointed, and in this 
species, although the teeth are reduced to very few, the projections remain, but are rounded 
off. A similar condition exists in S. magna. The corona ciliata is short, on the head 
and neck. 

This species has very few distinguishing characters; it is separated from magna chiefly 
by the absence of the very long moveable teeth in the anterior row, and from hexuptera 
by the small number of posterior teeth, but when the latter are as numerous as four, it 
becomes difficult to separate them with certainty. ‘The teeth seem to have been reduced, 
and are at present very variable, but the typical number for the species is three anterior 
and one posterior. 

Recorded from the Pacific, the Atlantic, the Mediterranean and the Indian Ocean. 


4. Sagitta serratodentata Krohn. 
Strodtmann, Archiv Naturgeschichte, Jahrg. 58, Bd. 1. p. 347, 1892. 

A moderately common species both in winter and spring. Some specimens had as many 
as 18—20 posterior teeth and 10 anterior, instead of 12 and 8 respectively as are normal 
in European waters. 

Hitherto recorded from the Mediterranean, the Atlantic, and Japan. 

5. Sagitta hispida Conant. 
F. S. Conant, Johns Hopkins Univ. Cire. Vol. xiv. p. 77, 1896, and xv. p. 82, 1896. 

This species was rather scarce in the material collected in the winter, but in that 
obtained in April it was very abundant. It is characterized by the thickness and solidity 
of the body-wall, the thickened ectoderm behind the head, the intestinal diverticula in the 
neck, and the great number of tactile prominences. The teeth in the specimens from the 
Maldives were sometimes more numerous. than in Conant’s description; Aida mentions the 
same fact in specimens from Japan. Corona ciliata long and waved; in one specimen I 
found it divided into two parts, an anterior and a posterior. 

Described previously from the Atlantic coast of America, the West Indies, and Japan. 

6. Sagitta regularis Aida, (Plate XIII, fig. 7.) 
T. Aida, Annot. Zool. Jap. Vol. 1. p. 17, 1897. 

Occurred in small numbers in the winter. This species is very small, rarely more than 
5mm. The tail is one-third of the length of the whole. The fins are narrow, semi- 
elliptical, and have rays extending to the base. The tail fin and the posterior lateral 
fin both touch the vesiculae seminales, which are small. The ovaries extend to the 
anterior paired fins. The epidermis is thickened through the whole length of the animal, 
but very much so behind the head, so that there is no neck. ‘The number of tactile 
prominences is very large, and they are arranged: with great regularity. The intestine has 
diverticula at its beginning. Hooks 7, anterior teeth about 4, posterior about 6. Corona 
ciliata rather long, waved, with a constriction in the middle. It is shorter than that of 
S. hispida, and lies entirely on the trunk. 

Hitherto recorded only from Japan. 

7. Sagitta flaccida Conant. 
F. S. Conant, Johns Hopkins Univ. Cire. Vol. xv. p. 82, 1896. 

Only one specimen of this species was found, and it occurred in the collection made 
in April, The species resembles S. enflata very closely, but differs in the form of the 
teeth. There are seven or eight anterior and 10—12 posterior teeth, and they are longer 
and more slender than in enflata, and the inner ones, especially of the anterior row, are 
much longer than the outer. 

Described only from the Bahamas. 


8. Sagitta robusta nov. sp. (Plate XIII, figs. 1.4, 1B.) 

This species is abundant in the material collected in winter, but scarce in that obtained 
in April. It is characterized by the great thickness of the body-wall, especially of the 
longitudinal muscles. 

The length of mature specimens is 16 em. of which the tail segment makes up one- 
fourth. The head is broad; the anterior fin is as long as the posterior, but narrower, its 
front end is opposite the posterior end of the abdominal ganglion. Both posterior 
lateral fins and tail fin reach the vesiculae seminales. The fin-rays do not extend quite 
to the base of the fins. The epidermis is thickened behind the head. The corona 
ciliata is long and narrow, beginning in front of the eyes just behind the brain, and is in 
shape an elongated ellipse, without the cross-shape found in S. bipunctata. There is a pair 
of diverticula at the beginning of the intestine, like those in S. minima. The ovaries are 
extremely long, and extend in fully mature specimens to the anterior transverse septum, so 
that the coelom of the trunk becomes almost obliterated. The vesiculae seminales project 
somewhat. Hooks usually 8, with very small points; anterior teeth 9, posterior 10—14. 

I have found this species also among Chaetognatha collected at Singapore. 

9, Sagitta ferox nov. sp. (Plate XIII, fig. 2.) 

A species closely resembling S. robusta, but distinguished by several constant differences. 
Tt is less abundant than the latter, and did not oceur in the April collection. 

The body-wall is very thick, with powerful muscles. The tail segment is rather more than 
one-fourth of the whole length, which is about 12cm, The fins are almost as in S. robusta, 
but the posterior does not quite reach the vesiculae seminales, which project only slightly. 
The epidermis is slightly thickened behind the head. There are intestinal diverticula as in 
S. robusta, and the ovaries are extremely long, as in the latter, but they do not quite reach 
the front end of the trunk-cavity. Hooks 5, or sometimes 6, very thick and powerful, with 
rather blunt points; anterior teeth about 6, posterior 10, with blunt points and rather broad. 

As will be seen from the above description, this species differs very slightly from the 
last, and should possibly be classed with ‘it. In some points, however, there is a constant 
difference. There are never more than 6 hooks in ©. ferow, and there are usually only 5, 
while in S. robusta there are 7 or 8, and the hooks of ferox are thicker and have larger 
point-pieces than in the other species. The teeth of feros are also thicker and rather fewer 
in number. In no specimen was the corona ciliata found complete in feros, but from the 
traces that remain it seems to resemble that of robusta. When preserved in formalin feros 
always has a faint pink colour, while robusta is white or yellow, and is rather less opaque. 

10. Sagitta gardineri nov. sp. (Plate XIII, figs. 5A, 5 B.) 
A moderately abundant species in the winter collection. 

Length 25 cm. Body thick and transparent, resembling that of S. magna. Head broad 
and short. Tail segment one-fifth of length of whole. Fins like those of S. magna; the 
rays do not quite reach the base. Ovaries when mature rather long, extending to the 
posterior end of the anterior fin; they are thicker and shorter than in S. magna, but 
proportionately longer than in S. enflata. Vesiculae seminales spherical, placed at the front 


end of the tail fin. Corona ciliata entirely on the head; pear-shaped, with the narrow end 
lying just behind the brain, in front of the eyes. Hooks 8—10; anterior teeth small, 
about 10; posterior larger, pointed, varying from 12 to 16. 

This species is intermediate between S. hexaptera and enflata in size and in the form 
of the ovaries, and it differs from both in the larger number` of teeth. Although it is 
closely connected with these two species, yet the differences are so constant that there can 
be no doubt of its distinctness. i 

ll. Sagitta pulchra nov. sp. (Plate XIII, figs. 4A, +B.) 
A moderate number of this species occurred both in the winter and spring collections. 

Its length is 2 cm., of which the tail segment makes up one-sixth. The body is slender, 
with a thin body-wall, so that this species is intermediate between the large, inflated, and the 
smaller muscular types of Sagitta. The head is small, and the epidermis somewhat thickened 
behind the head, The anterior fin begins at the abdominal ganglion, and is rather long, 
so as to be separated by a short distance only from the posterior, The front half of the 
anterior fin is very narrow and has no rays; the posterior part is rather wide. The posterior 
fin is like the anterior in shape, but the part without rays is shorter and that with rays 
wider. The rays do not extend quite to the base. 

The ovaries are rather long and slender, the vesiculae seminales small. The whole of 
the tail coelom is filled with developing spermatozoa. ‘The corona ciliata is moderately long; 
it begins in front of the eyes and rather more than two-thirds of its length is on the 
trunk; it is narrow and its sides parallel. Hooks 6, rather curved and slender; anterior 
teeth about 6, posterior about 10. 

This species is of interest in combining the characters of two groups of Sagitta, viz. 
the larger species, which have a thin body-wall, short corona and in which only part of 
the tail coelom is filled with developing sperm; and secondly the smaller species with thick 
body-wall, long corona and tail full of sperm-morulae. 

12. Sagitta polyodon nov. sp. (Plate XIII, figs. 3 A, 3 B.) 
Found in fair abundance in both winter and spring. 

This species is superficially very like S. serratodentata. Its length is about 1:2 cm., the 
tail one-fourth of the whole. The shape is that of serratodentata. The fin-rays spring from 
the base of the fins. The ovaries are long, extending to the anterior fins. The vesiculae 
seminales are rather large and projecting. The hooks are 6—7, with no serrations; anterior 
teeth 9—10, posterior 26; they are slender, truncated at the end, with small processes. The 
corona ciliata is long and rather wider just behind the neck than elsewhere. 

This species is distinguished at once by the great number of its teeth, which are 
more numerous than in any other known species. -It resembles Béraneck’s description of 
S. bedoti' in many ways, but differs in having a corona, in the length of the ovaries, 
and the greater number of teeth. Since Béraneck described S. bedoti from preserved 
specimens, in which the corona is often destroyed in one species while well-preserved in 

1 E. Béraneck, ‘‘ Chétognathes de la baie d'Amboine,” Rev. Zool. Suisse, Vol. 11. p. 147, 1895. 


others, it is possible that in this point he was mistaken; but, since the absence of the 
corona is a definite part of the diagnosis of S. bedoti, the present species cannot be 
identified with it. 

13. Sagitta septata nov. sp. (Plate XIII, fig. 6.) 
Moderately common both in winter and in spring. 

It is a small species, generally less than 1 cm, The tail segment is a third of the whole. 
The fins are narrow, especially the anterior. There is no epidermal thickening behind the 
head, but the body-wall as a whole is thicker in the posterior part of the trunk than 
anteriorly, There are intestinal diverticula like those of S. minima. The vesiculae seminales 
are very small. The ovaries are long, extending to the ventral ganglion, and the ova have 
a very curious appearance in fully adult specimens. They become pressed together so that 
they are flattened anteriorly and posteriorly, and the flattened faces have the appearance of 
septa dividing the trunk into a series of compartments on each side, 

In no specimen was the corona well preserved, but it could be seen from the fragments 
remaining that it lies both on the head and on, at least, the beginning of the trunk, 
Hooks 6—8, anterior teeth 6—8, posterior 13—16, rather narrow and pointed. 

The most prominent characteristic of this species is the peculiar structure of the ovaries 
(Plate XIII, fig. 6 and Text-fig. 39). The eggs appear to have 
their shells well developed, and the “septa” are due to the shells 
of two eggs being pressed together. In section it appears that 
when the eggs assume this condition they are already in the 
oviduct, which is greatly dilated, for when followed back the cavity 
containing the eggs is found to open at the usual pore of the 
oviduct; this view is supported by the fact that the large eggs 
lie at the outer sides of the ovaries, next to the body-wall, and Fre. 39. Transverse section of 

that no other oviduct is visible, and further that the usual germinal Sagitta septata in the region 
epithelium appears between the large eggs and the alimentary canal. of the ovaries. The ripe 
The animals appear to be undergoing histological degeneration, for teres) en 
the alimentary canal has lost its lining cells for the most part, which are probably the en- 
and through the greater part of the body is much reduced in size. larged oviducts. The ger- 
A condition comparable with this is frequently found in S. minima. minal epithelium is seen lying 
A very similar arrangement of the eggs occurs in a fully adult at the inner ridelon each pi 

i 7 : à M h i; E É these spaces, connected with 
Krohnia pacifica in Mr Gardiner’s collection, so that it is not quite the alimentary canal by a 
peculiar to Sagitta septata. mesentery. 

Il. Genus Spadella Langerhans. 

14. Spadella draco Krohn. 
Strodtmann, Archiv für Naturgeschichte, Jahrg. 58, Bd. 1. 1892, p. 356. 

This species was plentiful in the winter but did not occur in the summer, It agrees 
in every way with the published descriptions. I found a number of specimens in which 
the remarkable parenchymatous tissue was entirely absent,. and was at first inclined to 
regard them as a new species, but afterwards found some in which part of the parenchyma 



remained, showing that it had become detached during preservation or in transit. Some of 
the best-preserved specimens have a bright yellow colour in formalin, while others are 


This species has been previously recorded from the Mediterranean, 
both sides of the Atlantic, Java and Japan. 

II. Genus Krohnia Langerhans. 
15. Krohnia pacifica Aida. 
T. Aida, Annot. Zool. Jap. Vol. 1. p. 19, 1897. 

Only two specimens of this species were obtained; one in the 
winter and one in the April collection. It is only 7 mm. in length, 
but the ovaries show it to be mature. In the specimen taken in 
April the latter had large eggs (text-fig. 40), pressed together as 
described above in Sagitta septata. The tail is a third of the whole 
length. Both tail-fin and lateral fin meet the vesiculae seminales, 
which are ovoid. The tactile prominences have very long bristles. 
Hooks 9, pointed, with very small end-pieces. Teeth 13, very long; 
the row of one side meets that of the other side. The eyes are very 
near together. 

There can be no doubt that this is the Krohnia pacifice described 
by Aida; the teeth are slightly more numerous, and the green colour 
which he mentions is not visible in preserved specimens. He de- 
scribes the mouth as a transverse slit, but this appears to me to 
be due to a sort of lip overhanging the mouth anteriorly; the true 
mouth is as usual longitudinal. 

Previously described only from Japan. 


I include here the description of a new species of Sagitta 
obtained by the late F. P. Bedford at Singapore. It was accom- 
panied by a few specimens of S. enjflata and S. robusta. There was 
only one specimen, which is not fully mature; the condition of the 
ovaries however shows that it is not very young. 

Sagitta bedfordii nov. sp. 

Very small; an individual apparently nearing maturity, measures 
only 35 mm, ‘Tail one-third of whole. Fins narrow, with rays 
springing from the base and placed unusually far apart. Corona 
ciliata imperfectly preserved, but lying both on head and trunk, and 
apparently short and pear-shaped. Body-wall thick, with epidermal 
thickening behind the head. Hooks 10, anterior teeth 2, posterior 2, 
all, especially the anterior ones, long, narrow and pointed, like those 
of S. magna. 

The number and shape of the teeth is sufficient to distinguish 
this species at once from all the other small species.] 


Fie. 40. Krohnia pacifica. A 
specimen taken in April, 
which has a number of ripe 
eggs on each side arranged 
with their shells in contact, 
giving the appearance of 
transverse septa. These 
eggs, as in Sagitta septata, 
are probably in the oviduct. 




The examination of the specific characters and the geographical distribution of the 
Chaetognatha leads to several points of interest. In the first place, it is found that most 
species are world-wide in their distribution, and are obtained in almost all the warmer seas; 
only a few species have been observed in very limited areas, and since Sagitta flaccida and 
S. regularis, which had hitherto been recorded only from the West Indies and Japan 
respectively, have now been found also in the Indian Ocean, it seems probable that some, 
if not all, the remaining local species will be known eventually to have a wider range. 

Individuals of the same species have as a rule the same characters in whatever part of 
the world they occur, but there are a number of exceptions to this rule; for example, 
the S. serratodentata from the Maldive Group had usually a greater number of teeth than 
those of the Mediterrancan, and Aida records the same fact in respect of several species 
from Japan. But the characters, which are used to distinguish the species of the Chaeto- 
gnatha, are very variable in themselves, so that examples from the same locality differ 
considerably from one another, and it is sometimes a matter of difficulty to determine 
these species with certainty; for example, the individuals described above as S. tricuspidata, 
which have an arrangement of teeth different from that of the type, might be referred to 
S. hexaptera, in which the teeth were fewer than the normal, and so in other cases. 

In fact, it almost seems that the species in the Chaetognatha are not very definitely fixed, 
but graduate into one another to some extent, although they can be separated into several 
groups, which are very distinct; for example, Sagitta hexaptera, S. tricuspidata, S. magna 
and S. lyra form a well-marked group of large species, which can be separated at a glance 
from the type represented by S. hispida and S. regularis. 

The question of species in the Chaetognatha is an interesting one from the point of 
view of evolution, for in most seas a great number of individuals of various species are 
found together but all having, as far as we know, similar habits and living mingled 
together. Geographical isolation or differences of habitat apparently do not exist, and 
probably most species breed through the greater part of the year, so that there can be 
no separation by differences of breeding season. 

In many instances two species, living together, are so closely allied that it is very 
difficult to distinguish them, in which case it seems hardly possible that the separation 
can have been due to natural selection. Possibly the great variety of Chaetognatha found 
together, all living under the same conditions and with similar habits, may be best explained 
by supposing the species to be very ancient, and that the different species haye arisen in 
different parts of the world and have become spread by currents or other means of dispersal, 
until they are found in all the seas where the temperature is sufficiently high. The 
characters by which the species are distinguished, such as hooks, teeth, proportions of the 
body and fins, etc., are very variable within certain limits, as has been shown above. If, 
then, a part of the ocean became partly or wholly separated from the rest by geological 
changes, in the course of time this variability would undoubtedly cause the fauna, so cut 
off, to become different from the remainder, and, when they again became intermingled, 
they would be classed as different species. The Chaetognatha offer this problem in a 


peculiarly prominent manner, for there are few other groups of animals of which as many 
as ten or even more species of one genus are found together in exactly the same environment. 

The question of the nature and extent of the variation in each species is also of 
interest, for there are indications that the characters commonly relied upon as distinctive 
may sometimes be very untrustworthy. It has been pointed out how in some species local 
races exist with slightly different characters, as in the case of Sagitta serratodentata and 
S. hispida, but some species are markedly variable in the same locality. For example, 
besides the variation in number of the teeth in S. tricuspidata mentioned above, it was 
found that while the typical number of hooks is 8, one specimen had only 4, another 
5, and others 7 on each side. 

I observed a more remarkable case of this at Naples, which possibly indicates that 
the hooks are lost to some extent at maturity. The species in question was Sagitta lyra, 
which Grassi in his monograph (Fauna et Flora des Golfes von Neapel; I Chetognati) 
describes as being very rarely found sexually mature, while immature specimens are 
comparatively common. At Naples during the early spring of 1901 immature specimens 
were frequent in the “Auftrieb” from no great depth, and many were of considerable size, 
eg. as much as 28mm. with only most minute rudiments of ovaries and testes, and no 
trace of genital ducts. In April, however, a number of specimens were caught in the 
neighbourhood of Capri at depths of 400 and 1000 metres, and these were mostly sexually 
mature. Those from the greater depth were remarkable in that a large proportion had 
only three hooks on each side instead of seven, although others were nearly or quite mature 
with the normal seven hooks. These examples had otherwise all the characters of S. lyra, 
except that the head was perhaps shorter and broader than usual. 

These facts seem to indicate that either there are two closely allied species or varieties 
included under the name S. lyra, or that when maturity is reached, four out of the seven 
hooks on each side are, in some cases at least, lost. It also seems to suggest that when 
mature this species migrates to a much greater depth, for no fully adult specimens were 
taken at the surface. Grassi did most of his work at Messina, where the currents bring 
up to the surface animals which normally live in deep water, and this probably accounts for 
his finding occasional adult specimens. 

With regard to variation in different localities, it appears that most of the widely 
distributed species differ to some extent in widely separated areas, as is mentioned above 
in respect to the teeth. It is interesting to note that in all cases in the present collection, 
where the teeth differed in number from those of the European variety, they were more 
numerous, so that the average number of teeth in specimens from the Indian Ocean is 
considerably greater than from Europe. Another character which distinguishes the Eastern 
Sagittas from the European as a whole is the frequency of intestinal diverticula in the neck; 
these are found only in one European species, but five, or more than one-third of the whole, 
of those from the Maldives possess them. ‘The same fact has been noticed by Conant with 
regard to the American Sagittas, a large proportion of which have the diverticula. 

The fact that so many species should be common to the Eastern coast of America and 
to the Indian Ocean, although not found between, is remarkable, but is probably explained 
by the absence of complete lists from the Southern Atlantic. When the latter area has 
been more carefully examined, it will probably be seen that this apparent discontinuous 





is not real. It is rather surprising, however, that a species like S. hispida, 

recorded from the Bahamas and the coast of the United States, and therefore in the path 
of the Gulf Stream, should not yet have been found in the North-eastern Atlantic, 

In conclusion I wish to thank Mr ©. Forster Cooper, B.A., for drawing the figures in 
the accompanying plate. 


The corona ciliata has been represented as a dotted line, except in Fig. 7. 

Fie, 1 A. 


Sagitta robusta nov. sp., outline. 1 B. The same, head and neck, 
Sagitta ferox nov. sp., head and neck. 

Sagitta polyodon nov. sp., outline. 3 B. The same, head and neck. 
Sagitta pulchra nov, sp., outline. 4 8. The same, head and neck. 
Sagitta gardineri nov. sp., outline. 5B. The same, head and neck. 
Sagitta septata nov. sp., showing peculiar structure of the ovaries. 

Sagitta regularis Aida, showing thickened epidermis, corona, and ovaries.