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Analysis of taxonomical features of the genus Samythella (Polychaeta, Ampharetidae).

I. A. Jirkov

Department of Hydrobiology, Biological Faculty

Moscow State University

[Translated by I. Jirkov from the original published 1986 in: Zool. Zh., 65, 3 :325-332 (in Russian, with English summary).]

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.

Samythella elongata Verrill, 1873.

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.

Diagnostic characters of Samythella spp.


nr of specms

nr of AU

nr of anal papillae & their shape


0-14, different shape


ca.8, two upper are longest


6: 2 short dorsal, 2 longer lateral, 2 stout pad-like ventral



ca 31

7:2 long v-lateral, 2 short lat, 2 big pad-like dorsal and 1 mid-v pad-like

Fig.1.Distribution map of Samythella

Fig. 1. Distribution of S.elongata. 1 - investigated material; 2 - literature data

Fig.2. Distribution plot of Samythella

Fig. 2. Connection amount of AU (n) with body's length (L) within Samythella spp. from st.3 R/V"Alaid"

Fig.3. Morphology of Samythella

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]

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Last edit 18 May 1997.