Three species of the genus Nothria Malmgren, 1867 were described from the Arctic Ocean: N. conchylega (Sars, 1835), N. hyperborea (Hansen, 1878), and N. britannica (McIntosh, 1903). Soon the last two (Fauvel, 1923) were considered as synonyms of N. conchylega. N. conchylega pointed out as one of the most common Polychaeta of the Barents Sea (Zenkevitch, Brotskaja, 1937) as characteristic and even main species of its bottom community (Filatova, 1938; Leibson, 1939; Zatsepin, Rittikh, 1968). In 1982 the situation have changed: Fauchald (1982) revised the type materials of these three species and revive them. So we faced with the necessity to revised and re-identify tens thousand of specimens. However, when we tried to do it we unexpectedly faced with situation when no one of our specimen, even worms collected within distance 50-100 km from the type localities of all three species didn't agree with Fauchald's descriptions. So while our preparing monograph on Arctic Polychaeta we had to research taxonomy of the species inhabited this ocean (full review of the genus was made by Kucheruk, 1985). A priori we proposed that impossibility to use Fauchald's revision reflect under-estimate by him variations. So based on studying morphological characters we tried to determine taxonomical value of the characters into our material and separate species, than to try to identify them with nominal ones. Variations of several characters: segment of starting of branchiae, structure and composition of setae within the tree anterior parapodia were investigated by Kucheruk (1980). We in our research limited only with investigation of characters visible under stereomicroscope, i.e. characters which can be really used by scientists while determination of large material: serial number of the segment of starting of branchiae with cirriform ventral cirri, postsetal lobes, foliose presetal lobes, subacicular hooks; the number of rings on ceratophores, comparative length of median, inner lateral and outer lateral occipital antennae, presence or absence of simple and pectinate setae on 2nd setiger (S = ÙC), the form of subacicular setae on 1st S. The connection of all these characters with worm's size was investigated as well. As measure of size we used d10 - the distance between external margins of ventral cirri of 10th S. The same was used by Kucheruk (1980).
All mentioned above characters were investigated through in 252 specimens from Arctic ocean, especially from the Norwegian Sea, the type locality of all three species. Variation serial number of the segment of starting of branchiae was investigated above this in 478 specimens (at all 730) from Arctic ocean, N-W parts of Pacific Ocean and Atlantic Ocean (Tab. 1). Elicited taxonomical characters were used while identification of ca. 10,000 specimens from ca. 500 samples from the Arctic Ocean.
By presence or absence of simple and pectinate setae into 2nd S all investigated specimens can be parted in two morphotypes: morphotype A, possessing these setae, and morphotype B lacking them. These two morphotypes can't be parted further on the base of investigated by us features. The variation of characters in two morphotypes is following.
All investigated characters can be divided in two groups: depended and independent on worm's size.
Presence or absence of subacicular hooks on 3rd S; number of S with cirriform ventral cirri; the form of subacicular setae on 1st S; presence or absence of simple and pectinate setae on 2nd S; number of S with foliose presetal lobes; S of starting of branchiae; and number of rings on ceratophores do not depend on worm's size.
All others characters: S of starting intrafascicular setae; last S with postsetal lobes; comparative length of antennae more or less depend on worm's size.
Two characters independent on size - number of S with cirriform ventral cirri and presence or absence of subacicular hooks on 3rd S - do not vary and are the same in both morphotypes. Both have two S with cirriform ventral cirri (on the 3rd they are transitional to pads) and always subacicular hooks on 3rd S (sometimes they are broken and are discovered hardly).
There are simple and pectinate setae on 2nd S always in morphotype A and never in morphotype B. There are foliose presetal lobes on two anterior S in both morphotypes. These lobes are transitional shape to digitiform on 2-4 S, from 5th-7th S they are digitiform. There are no significant difference in number of S with transitional shape of presetal lobes between morphotypes. As to number of rings of ceratophores, morphotype A have 0-4, while morphotype B - 2-4, it looks like development of this character depends on contraction ceratophores due fixation.
Subacicular hooks are unidentate within morphotype A (small extra teeth develops very seldom), and distinctly bidentate within morphotype B. Last character independent on size setiger of starting of branchiae (table 2) vary according Kucheruk(1980) within morphotype A (called there N. conchylega) from 8-15 S. So Kucheruk didn't reckoned this character valuable taxonomically. However variation within researched material far less. Geographical variation of this character is small: compare for example st. 13 (the Barents Sea) and 34/24 (Kuril Is.). The full variation limits within both morphotypes don't almost overlap. It's necessary to mention that the smallest specimens (all - morphotype A) are abranchiate: on the st. 115 abranchiate specimens have d10 = 0.75-1.2 mm, on the st. 1467 - 1.1 mm.
Thus, from the investigated by us characters as key's ones can be used following: presence or absence of simple and pectinate setae on 2nd S, the shape of subacicular hooks on 1st S, number of S with subacicular hooks, presence or absence of branchiae.
Morphotypes A and B differ with the first and the last characters. Because these characters don't connect functionally and morphotypes while co-existing don't hybridise, they have to be considered as distinct species.
Such characters, as number of anterior S with foliose presetal lobes and number of S with cirriform ventral cirri due presence gradual transitions are somewhat subjective and so have low taxonomical value.
To use the rest investigated characters for taxonomy of Nothria is besides the purpose due their huge variation.
The variation limits of the investigated characters of both morphotypes and the same characters of all nominal species of the genus are given in table 3, mostly after redescription of Fauchald (1982). It follows from the table, that none from our morphotypes doesn't agree with re-descriptions of Fauchald (1982). May be both are new species? But in this case, however, it isn't clear why there are no any of re-described by Fauchald (1982) species in checked by us material (above 10,000 specimens). It seems more correct to permit that there are some mistakes in Fauchald's re-descriptions. Namely, because broken subacicular setae of 3rd S are visible hardly it may be Fauchald overlooked them and N. hyperborea have them. It's necessary to mention that author of this species (Hansen, 1882) wrote straight that "The bristles ... are of three kinds, viz.: - 1) acicular bristles, similar to those on the two anterior segments..." If our proposition is correct, morphotype A is N. hyperborea, and morphotype B is N. atlantica (Hartman, 1965) the species didn't included by Fauchald in genus Nothria.
What is N. conchylega depends on the serial number of S where simple and pectinate setae start (Fauchald didn't mention it). If they start from 2nd S, N. conchylega is the oldest synonym of N. hyperborea, because all others theirs characters are the same. If they are absent on 2nd S, N. conchylega is distinct species, absent in our material. The last proposition seems to us less probable, but taking into account different senses been given by different authors to "N. conchylega" we think the usage of name N. hyperborea before re-examination of the types N. conchylega will help the brightness of sense of the taxon.
As to N. britannica, it's similar to morphotype B and can't be morphotype A because of segment of starting of branchiae and the shape of subacicular setae. But, according to Fauchald there are simple and pectinate setae on 2nd S in it. It is characteristic for morphotype A, not B. So the characters of this species induce us to take it as distinct. But at the same time, there are both morphotypes in the samples collected near Shetlands Is. (many of the within 50-100 km from the type locality of N. britannica), in three cases even in the same samples, while N. britannica isn't found. So, it's possible that types of N. britannica are the mixture from morphotypes A and B.
Done above conclusions about synonymy of N. atlantica, N. britannica, N. conchylega and N. hyperborea probably are partly erroneous. It's obviously, however, that Fauchald's (1982) revision didn't only make clear, but vice versa, mixed taxonomy of genus. So, we think it's necessary to revise all types ones more, taking into account lumped by us taxonomical value of characters.
Comparison of characters 12 nominal species of the genus (table 3) shows that only six from them are probably distinct: N. hyperborea, N. atlantica, N. hawaiensis Pettibone, 1970, N.occidentalis Fauchald, 1968, N. solenotecton (Chamberlin, 1919), N. abyssia Kucheruk, 1978. According to the characters, which on the base of our research have to consider as taxonomical (1-4 into table) N. mannarensis Rangarajon et Mahadevan, 1961 can't be differ from N. hawaiensis, N. textor Hartman et Fauchald, 1971 - from N. atlantica, N. anoculata Orenzanz, 1974 are very similar with N. hyperborea (it's necessary to mention that author of taxa reckoned it only as subspecies of N. conchylega). Taxonomical position of N. conchylega and N. britannica were discussed above.
Redescription of N. hyperborea (morphotype
A) and N. atlantica (morphotype B) are given below.
Prostomium is rounded with 2 almost globular frontal palps. 5 occipital antennae: median, inner lateral and outer lateral. Ceratophores are distinctly shorter than ceratostyles, don't achieve the anterior margin of the prostomium., with 0-4 rings. Outer lateral antenna turned behind achieves 1-3 S, inner lateral and median - 5-12 S. First segment without parapodia, bears 2 dorsal cirri; 2nd segment = 1st S, bears enlarged and rotated forwards parapodia which bear unidentate subacicular hooks (very seldom small extra teeth develops). Parapodia of 2nd and 3rd S bear except subacicular hooks simple and pectinate setae. Intrafascicular setae present from 8-16 S depending on worm's size to almost end. Ventral cirrus is digitiform on two anterior S, on 3rd it has transitional shape, further back is pad-like. Presetal lobes is foliose on two anterior S, on next 2-4 it has transitional shape, further back is digitiform. Postsetal lobes are present on 5-20 S anterior S, depending on worm's size, they are cirriform, but on the last S become digitiform. Branchiae present from 11-15 S to almost end. Segment of starting branchiae doesn't depend on worm's size, small specimens are abranchiate.
Up to 3.5 mm width and 120 mm length. Number of segments 34-58 depending on size. Tube are flattened, with thin translucent inner lining and is covered by small stones, bivalve fragments etc.
The species easily differ by presence of simple and
pectinate setae on 2nd S and presence of branchiae. The only species
N. occidentalis is characterised with these characters,
but it differ by starting of branchiae from 8th S but 11th-15th,
however Kucheruk(1980) pointed out that in Alaska bay branchiae
in N. hyperborea can start from 8th S, so validity of N.
occidentalis needs in corroboration.
Prostomium is rounded with 2 almost globular frontal palps. 5 occipital antennae: median, inner lateral and outer lateral. Ceratophores are distinctly shorter than ceratostyles, don't achieve the anterior margin of the prostomium., with 2-4 rings. Outer lateral antenna turned behind achieves 1-4 S, inner lateral -5-12 S and median - 5-14 S. First segment without parapodia, bears 2 dorsal cirri; 2nd segment = 1st S, bears enlarged and rotated forwards parapodia which bear only bidentate subacicular hooks, second teeth develops well. Parapodia of 2nd S bear only subacicular hooks as well. Parapodia of 3rd S bear except subacicular hooks simple and pectinate setae. Further back subacicular hooks are absent. Intrafascicular setae present from 9-14 S depending on worm's size to almost end. Ventral cirrus is digitiform on two anterior S, on 3rd it has transitional shape, further back is pad-like. Presetal lobes is foliose on two anterior S, on next 1-4 it has transitional shape, further back is digitiform. Postsetal lobes are present on 11-26 S anterior S, depending on worm's size, they are cirriform, but on the last S become digitiform. Branchiae present from 9-11 S independent on worm's size to almost end.
Up to 5 mm width and 150 mm length. Number of segments 35-60 depending on size. Tube are flattened, with thin translucent inner lining and is covered by small stones, bivalve fragments etc.
The species easily differ by absence of simple and
pectinate setae on 2nd S and presence of branchiae. The only species
N. hawaiensis (= N. mannarensis) is characterised with
these characters, but it differ by absence of subacicular setae
on 3rd S., however this setae can be missed (as it is shown above
for N. hyperborea) in this case the validity of N. hawaiensis
needs in corroboration.
Authors thank N.V.Kucheruk and G.M.Beljaev for valuable
advises on preparing the article.
The headers for tables 1 and 2.
Ship, expedition station N E or W depth
Table 2. Variation of serial number of segment of starting branchiae.
station segment of starting branchiae number of number
8 9 10 11 12 13 14 15 16 mean specimens abranch.
The footers for table 3.
* - after Fauchald (1982) - 2
**- Fauchald (1982) didn't investigate the material
***- after Pettibone (1970), Fauchald (1982) didn't mention
****- after Hartman (1965), Fauchald (1982) didn't mention
+- after Detinova (1985), Fauchald (1982) didn't mention
1-presence or absence of simple and pectinate setae on 2nd S
2,3 - segment of starting of branchiae (2-limits;3-mean);
4 - number of S with subacicular hooks;
5 - number of S with foliose presetal lobes;
6 - number of S with digitiform ventral cirrus;
7 - number of S with postsetal lobes;
8 - segment of starting of intrafascicular setae;
9 - number of rings on ceratophores;
10 - 12 which S achieves turned behind 10 - median antenna, 11 - inner lateral; 12 - outer lateral antenna.
+ - present; 0 - absent;- - absence of data.
[Literature cited not included. Please see original text]