To date taxonomic relationship between the three genera: Samythella
Verrill, 1873; Eusamytha McIntosh, 1885, non Hartman, 1967;
and Eclysippe Eliason, 1955 has not been conclusively determined.
These three genera are either regarded as synonyms (Day, 1964)
or as independent genera (Fauchald, 1977). Hartman (1959) suggested
that the first two genera are synonyms and the third is an independent
genus. The latter point of view seems to us more accurate. Actually,
the species assigned to these three genera form two groups, distinguished
by the shape of the prostomium, the presence or absence of the
palea, the structure of the thoracic uncini and by the number
of abdominal uncinigers (AU = ÀÙÑ). We regard
these two groups as independent genera, which are not closely
related. The generic diagnoses which we have adopted are given
below.
Samythella Verrill, 1873, s.str. Type species
- S. elongata Verrill, 1873. Diagnosis - prostomium without
lobes, glandular shields and ridges; anterior margin straight,
buccal tentacles smooth, 3 pairs of smooth branchiae, paleae absent,
15 thoracic setigers (TS = ÒÙÑ), the last
12 are uncinigers, AU numerous (near 30), their number doesn't
constant within the species, uncini with tooth in a single row.
Nominal species: S. elongata Verrill, 1873, S. neglecta
Wollebaek, 1912, S. bathycola Uschakov, 1950, S. interrupta
Fauchald, 1972, S. pala Fauchald, 1972, S. pacifica
(McIntosh, 1885) - type species of the genus Eusamytha
McIntosh, 1885.
Eclysippe Eliason, 1955. Type species - E. vanelli
(Fauvel, 1936). Diagnosis - prostomium Ampharete-like:
3-lobed, without glandular shields and ridges; middle lobe rounded
anteriorly, 3 pairs of smooth branchiae, paleae present, 15 TS,
12 last are uncinigers, AU few (under 20), their numbers are constant
in the species, uncini with teeth in one or several rows. Nominal
species: E. vanelli (Fauvel, 1936) sensu Eliason, 1955
= E. eliasoni (Day, 1973), E.affinis (Day, 1963).
Systematic position of Eusamytha dubia Gallardo, 1968 is
quite obscure: in the description it is only indicated that the
species has pinnate buccal tentacles and uncini with teeth in
two rows. Since no other characteristic are specified, this species
should be regarded as insertae sedis until the type material has
been reconsider.
The diagnostic characteristics of all species of the genus Samythella
s.str., according to their original descriptions are given in
the table. The characteristics of S. bathycola are based
on reconsideration of the syntypes. From the table it is seen
that each species was described on the basis of one or a few specimens,
which prevent the authors individual variation. Only Verrill (1873)
had many specimens at his disposal, but his description was based
on single specimen as well. However, judging from the material
which we examined, all diagnostic characteristics vary, making
it impossible to diagnose the species without preliminary study
of their variations. We intended, after having determined the
nature of the variations, to isolate several taxa and identify
them with species described earlier and/or describe new ones.
We studied the variations in the characteristics which are used
in the taxonomy of Ampharetidae in all species of all specimens
of Samythella found in the collections of the USSR: collection
of the Department of General Ecology and Hydrobiology of Moscow
States University (342 specimens, 61 stations); of the Zoological
Museum of Moscow States University (4 specimens, 4 stations);
of the Zoological Institute of the USSR Academy of Sciences (18
specimens, 15 stations); and almost entire collection of the Institute
of Oceanology of the USSR Academy of Sciences (104 specimens,
12 stations) - in all, a total of 468 specimens from 92 stations
(fig. 1, black circles, white - literature data).
The number of AU is one of the basic specific characteristics
of Ampharetinae - is usually strictly constant in the adult specimens
of a single species. Genus Samythella is one of the few
exceptions. The ranges of fluctuation in the number of AS in the
specimens examined are as follows: in the Norwegian Sea - 11-37;
in the Sea of Okhotsk - 26-32; in the Gulf of Alaska - 22-36;
and in the north-western part of the Pacific ocean - 27-32. The
differences in numbers doesn't reflect presence of geographical
variation, but rather the size of sample and (lower limit) the
presence of juveniles in the sample. Encountered most often in
the Norwegian Sea are specimens with 31 AU; and in the Gulf of
Alaska - with 32 AU. Quite often the number of neuropodia differed
on the right and left sides of a specimen. In these cases the
greater number was taken as AS number.
In 1980, at station 3 (3 R/V "Alaid", 68 N, 10 E, 955-960
m) we took a sample in order to study the size-related variations
in the AU number. The catch of the Sigsbee trawl was completely
washed on O,5 mm sieve and sorted. As a result an unbiased sample
was obtained (the only one in the material examined) of 51 specimens,
including 47 whole specimens. Fig.2 shows the relationship between
the AU number and the body length. From the graph it is seen that
in worms with an overall body length (without branchiae) of under
approximately 15 mm, an increase in body length is accompanied
by an increase in the AS number. The Pearson's coefficient of
correlation between the AS number and the body length is 0.91,
and between the AS number and the length of abdomen - 0.90 (in
both cases the reliability is >99%). With further increase
in length the AS number remains approximately constant (averaging
30.5), although individual variations are observed (SD = 1.2).
Judging by the presence of oocytes in the body cavity, when the
worms are 17 mm, they begin to reproduce. Thus, the AS number
is not taxonomically significant in the genus.
In the vast majority of specimens the branchiae are located in
a single line without middle space (fig. 3 a), and are always
connected at the base by a membrane, which is less noticeable
in juveniles. All 6 syntypes S. bathycola have the same
kind branchiae (without middle gap) joined at the base by membrane.
Ontogetically the 2nd branchiae from the margin develop later
than the others. For example, at station R/V"Alaid"
3 specimens with a body length 5 mm and one - 6 mm had only two
pairs of branchiae (fig. 3 â); in one specimen 6 mm long
the second pair of branchiae barely developed (fig. 3 ã);
and in one specimen 8 mm long 2nd pair of branchiae were one-third
the length of the others (fig. 3 ä). It is extremely rare
for this pair of branchiae not to be developed in adults as well:
one specimen from the Arctic Basin 55 mm long (macerated in the
middle of the body) had only 2 branchiae on the left side (outer
thicker inner), but on right side there were 3 normally developed
branchiae. The transverse ridge which connects the branchiae is
virtually imperceptible in young specimens, nor are their branchiae
divided into distal and proximal parts, as is characteristic of
adult specimens.
Uncini. (fig. 3 e -í ). The teeth in all uncini are always
in a single row. The number of teeth in the thoracic uncini is
usually not constant even within a single neuropodium. A Newfoundland
specimen has uncini with 5 large tooth (fig. 3 ç), the
Norwegian Sea specimen - 5-6 (fig 3 ì, í); the Gulf
of Alaska specimen - 5; the Ochotsk Sea specimen (syntypes of
S. bathycola) - 5-6 (fig. 3 ë, æ); the N-W Pacific
specimen - 4-5 (fig. 3 e, æ). Usually the margin of the
uncini that is opposite the one bearing teeth is curved, but sometimes
uncini are encountered (in the same neuropodium) with a straight
row. Such specimens were found in the Norwegian and Kara seas.
The thoracic uncini of the syntypes of S. bathycola have
only straight edge.
The number of anal papillae is dependent on size of the pigidium.
Large ones bear 5-12 more or less pronounced papillae, which frequently
differ in size. The less pygidium the less papillae develop and
the smallest pygidia usually have a slightly wavy or even smooth
anal margin. Sometimes the papillae are imperceptible in large
pygidia as well. The size of the pigidia is probably depend on
contraction of the muscles during fixation since specimens that
differed in size could have pygidia of equal size and, on the
other hand, specimens of equal size often had pygidia that differs
greatly. The overall nature of the papillae on the pygidium is
very similar to that of the Terebellidae, in which this characteristic
is sometimes not regarded as taxonomic characteristic. Thus, the
number of anal papillae in the genus does not have taxonomic significance.
The number of TS is usually considers to be good generic characteristic
in Ampharetinae, although sometimes (in the genus Amage)
it is also used in specific diagnostics. In the vast majority
of the specimens there were 15 TS, 12 last - uncinigers. In the
Norwegian sea the following abbreviations were encountered: one
specimen with 16 TS (13 last uncinigers), one specimen with 14
TS (11 last uncinigers); one specimen with 15 TS and one extra
left neuropodium twice less than normal on 3rd TS. All of the
other characteristics of these specimens were identical with another
ones from the same samples. The variation in the TS number is
not unique for Samythella, I've seen it in Melinna elisabethae
McIntosh, 1922 and Lysippe labiata Malmgren, 1865.
The morphological identity of the topotypes of S. neglecta
and the syntypes of S. bathycola makes necessary conclusion
about their conspecify. The original description of S. elongata
as well as redescription of this species by Hartman & Fauchald
(1971) - unfortunately both lack figures - correspond entirely
with the descriptions of S. neglecta specimens that were
examined, including the specimens found near the type locality
of Newfoundland. Obviously, both species are also conspecific.
The taxonomic characteristics indicated by McIntosh (1885) in
a original description of Eusamytha pacifica do not this
species to be distinguished from S. elongata. The 14 specimens
that I examined, which were founded at 4 stations near the type
locality of E. pacifica at similar depth and bottoms doesn't
differ from others specimens of S. elongata that are found
in other regions. The statement made by McIntosh (1885) that "each
somit bears only process for hooks" is, according to Wollebaek
(1912) the single characteristic that distinguishes E. pacifica
from S. neglecta. Fauchald (1977) considers this characteristic
sufficient for separating the two genera - Samythella and
Eusamytha. However, this, in all likelihood, is simply
an indication that McIntosh' specimens were macerated. A similar
phenomenon is common in some of the material examined that was
fixed with ethyl alcohol, in which case non-macerated abdominal
sections with absolutely distinct rudimentary notopodia are sometimes
preserved. All of this compels us to regard Eusamytha pacifica
and Samythella elongata as synonyms and the genus Eusamytha
McIntosh - as a younger synonym of Samythella Verrill.
S. pala and S. interrupta have been described from
the Pacific slope near California, i.e. they are fairly isolated
from the specimens I examined of S. elongata from the Pacific,
but the depth are similar.
S. interrupta is distinguished by following characteristics:
1. The branchiae according to fig. are not connected by a membrane
at the base. However, in the description it is stated that branchiae
"are attached to a low distally smooth branchial membrane"
(Fauchald, 1972, pg. 313), i.e. figure is inaccurate, and the
structure of branchiae of S. interrupta is the same as
in S. elongata. 2. Branchial groups are well apart. As
it was mentioned above in specimens of S. elongata similar
size (4.5 mm) branchial structure varies so much, that it hasn't
taxonomical value. 3. There are a total of 13 AU - specimens of
S. elongata that are 4-5 mm long have 11-14 AU, i.e. there
are no differences. 4. The different number of anal papillae (6)
is a characteristic which has no taxonomic significance. Thus,
S. interrupta is obviously a younger synonym of S. elongata.
As far as S. pala is concerned,, the only characteristic
that distinguishes it from S. elongata is the AU number
(20) at an overall length of 25 mm. The examined specimens of
S. elongata of the same length have on 4 more AU. However
the variation in this character is considerable. Therefore, it
seems to us that prior to the study of the variation in AU number
in the type locality of S. pala this species should be
regarded as doubtfully different from S. elongata is AU
number, and consequently as its synonym.
Thus, the study of the variation in characteristics that have
been considered diagnostic for species of the genus Samythella
s.str. shows that all nominal species are synonyms of S. elongata
and hence the genus Samythella s.str. is monotypic. The
genus Eusamytha McIntosh, 1885 is a younger synonym of
the genus Samythella s.str., for its type species E.
pacifica is a younger synonym of S. elongata - the
type species of the genus Samythella.
A complete synonymy of S. elongata is given below [??omitted??]
as well as brief redescription based on all of the material examined
and on data on distribution, reproduction and zoogeography.
Description. Prostomium (fig. 3 á) without glandular ridges,
fields and eye-spots, anterior margin straight. Buccal tentacles
smooth, twice as long as branchiae, not retractable. Three pairs
of smooth branchiae, dorsally with a small longitudinal furrows.
Branchiae are arranged in one line, without middle gap, connected
at the base by a membrane (fig.3 a), Fifteen TS, the last12 are
uncinigers. Size of neuropodia and diameter of segments gradually
diminish caudally. No segments with modified notopodia. Abdomen
always with rudimentary notopodia. Abdominal neuropodia sit on
distinct longitudinal ridges, divided ventrally by a longitudinal
groove (ridges, groove and rudimentary notopodia are visible only
in well preserved material). Number of AU reaches 37 and is subject
to size-related and individual variation (fig.2 á). Number,
shape and distinctiveness of anal papillae vary greatly. Anal
cirri absent. Uncini with 4-6 large and 1 small (very rarely absent)
teeth in a single row. Most of the tube is rigid, cover with pebbles,
grit, Foraminifera etc. - all these materials can exist in different
proportions, to the point where all but one is absent - and rarely
covered with the detritus occurring in the chitinoid cells on
the outer tube surface. Posterior part of tube is soft, covered
with detritus, with transverse wrinkles (it usually missed).
Reproduction. In the Norwegian Sea specimens with oocytes in the
body cavity are found at depth of 400-1125 m at temperature range
of -0.94 to +1.40 C, from 15.VI to 14.XII. From December and June
only two juveniles were caught at 2 stations. Oocytes are in the
shape of irregular discs with a diameter ca. 0.3 mm and are yellowish-orange
in colour. In Newfoundland 18.VII.1959 one specimen from a depth
845 m had oocytes with diameters of up to 0.30 mm (shape and colour
as above). In the Gulf of Alaska on 07.V.69 at the depth of 1340-1540
m most of the specimens had oocytes in the body cavity. Maximum
diameter of them - 0.175 mm (shape and colour as above ). In
the N-W Pacific Ocean maximal diameter of oocytes - 0.350-0.500
mm (depth 5027-5460 m, 08.V; 24.IX; 03.X) and 0.350 mm (depth
3990 m, 23.V) (shape and colour as above).
The large sizes of the oocytes probably indicate the absence of
free-swimming larvae, which is typical of the family. Since all
samples with adults (longer 20 mm) contained specimens with oocytes
in the body cavity, spawning is probably year-round. Judging by
the fact that only half of the specimens among the large specimens
contained oocytes, the species is dioecious.
Distribution (fig.1). Northern Atlantic (128-2154 m), Davis Strait
(446-930 m); Arctic Ocean, including the Norwegian and Greenland
seas (125-1385 m), Northern Pacific (894-5460 m).
I would like to express my gratitude to P.V.Uschakov, V.G.Averintzev
and S.D.Chistikov for their valuable advises; L.A.Rittikh, R.Ya.Levenstejn,
V.V.Potin, L.I.Moskalev for making material available and S.D.Chistikov
for help in producing Fig.3.
species | nr of specms | nr of AU | nr of anal papillae & their shape |
S.bathycola | 6 | 26-32 | 0-14, different shape |
S.elongata | 1 | ca.35 | ca.8, two upper are longest |
S.interrupta | 1 | 13 | 6: 2 short dorsal, 2 longer lateral, 2 stout pad-like ventral |
S.neglecta | 3 | 29(30) | ca.8 |
S.pacifica | 1 | ca 31 | ? |
S.pala | 1 | 20 | 7:2 long v-lateral, 2 short lat, 2 big pad-like dorsal and 1 mid-v pad-like |
Fig.1.
Fig. 1. Distribution of S.elongata. 1 - investigated material; 2 - literature data
Fig.2.
Fig. 2. Connection amount of AU (n) with body's length (L) within Samythella spp. from st.3 R/V"Alaid"
Fig.3.
Fig. 3. Morphology of S.elongata a - frontal part of adult form st.2222 R/V"Sebastopol" (45 56' N; 47 42,2'W, 840 m); í - its prostomium; ó,ú,ñ - specimens from st.3 R/V"Alaid" (ó - specimens with length 5 mm, ú - 6 mm, ñ - 8 mm), a-ñ - dorsal view; e-¡ - thoracic uncini: Ñ,ª - specimen from st.3 R/V"Vitjaz", 44 42,9' N; 153 49"E, 5027 m, from the same neuropodia; º - specimen from st.2222 R/V"Sebastopol"; ¿ - specimen from st.5 R/V"Sadko"; 77 49,8 N; 104 07'E; 203 m; ^,½ -one of syntypes of S.bathycola, from the same neuropodia; ¼,¡ - specimen form st.2549 R/V"Sebastopol"; 63 N; 7 30'W; 710 m, from the same neuropodia. Scale (mm): á,í - 2,ó-ñ - 1,Ñ-¡ -0,05.
[Literature cited not included. Please see original text]