Reinstatement of Euarche rudipalpa ( Polychaeta : Acoetidae ) , with remarks on morphology and body pigmentation

Eupanthalis rudipalpa Amaral & Nonato, 1984 was described based on three incomplete, colorless specimens and has not been reported since its original description; the epithet rudipalpa means “hirsute palps”, a characteristic that separates it from other congeneric species. Eupanthalis McIntosh, 1876 and Euarche Ehlers, 1887, and their respective type species, E. kinbergi McIntosh, 1876 and E. tubifex Ehlers, 1887, were considered synonyms (E. rudipalpa as a junior synonym of E. tubifex, a cosmopolitan species) by some authors, because both have sessile eyes and two or three antennae. Nonetheless, these two genera are, in fact, distinct. Their type species can clearly be separated using some prostomial features. We provide an emended diagnosis of Euarche, and re-instate E. rudipalpa, redescribing it based on a Brazilian specimen (original type specimens lost). Illustrations showing body pigmentation pattern and a key to all species of Eupanthalis are also provided.

Acoetid polychaetes are large, tubicolous worms that usually appear in very low densities in oceans; in most cases, species have been described based on single specimens and have seldom been recorded again (BUCHANAN 1894, DARBOUX 1899, FAUVEL 1914a, PETTIBONE 1989).AMARAL & NONATO (1984) described Eupanthalis rudipalpa based on three incomplete, colorless specimens, and named it because it has hirsute palps, which separate it from other species.Probably following FAUCHALD (1977), they assigned their new species to Eupanthalis McIntosh, 1876. FAUCHALD (1977) was following the revision of the family by BUCHANAN (1894), who regarded Euarche Ehlers, 1887 as a junior synonym of Eupanthalis.
Eupanthalis was proposed by MCINTOSH (1876), with E. kinbergi as its type species.It is characterized by sessile eyes, whereas the other known genera have pedunculate eyes (BAIRD 1868, GRUBE 1876), and by having a pair of lateral antennae, but no median one: "There is no tentacle (= median antenna) in the specimen; but on each side of the median groove there is a filiform or slightly subulate antenna."(MCINTOSH 1876).Euarche was proposed by EHLERS (1887), with Euarche tubifex as the type species, for species that have sessile eyes (oculis non pedunculatis) and three antennae (tentaculis 3).BUCHANAN (1894) reviewed Acoetidae and diagnosed Eupanthalis as having: "three prostomial tentacles, except (?) in E. tubifex" and explained this in a footnote: "McIntosh's remark that there is 'no' median 'tentacle in the specimen' (actually E. kinbergi but the quote was given for E. tubifex) seems rather to imply that there may once have been one, which has been lost by accident."Consequently, BUCHANAN mistook the type species of Eupanthalis and Euarche, and assumed that McIntosh had seen a species that came to be described 11 years later.Since these two genera were regarded as synonymous, thinking that their type species were also synonyms was probably an unavoidable consequence, and E. tubifex was regarded as a junior synonym of E. kinbergi by several taxonomists (FAUVEL 1914a, b, AUGENER 1918, MONRO 1928, HARTMAN 1938).
PRUVOT & RACOVITZA (1895) objected the generic arrangement proposed by BUCHANAN, but their observations were overlooked by later authors.Despite the fact that the characters of the anterior end proposed by them have been later extensively used for separating similar genera, and their relevance was highlighted by FAUVEL (1897): "Les meilleures caractères pour la classification des Acoetidés restent donc ceux tirés du nombre, de la forme et de l'implantation des appendices céphaliques et ceux tirés des soies et des parapodes", the best characters for acoetid classification are in the number, shape and insertion of cephalic appendages, and those of chaetae and parapodia.PETTIBONE (1989) regarded Eupanthalis and Euarche as distinct and re-established Euarche, indicating that Eupanthalis has two antennae, whereas Euarche has three.She also proposed a further difference between the two, which is the presence and extension of papillae along the palp's surface, being smooth in Eupanthalis or with papillae restricted to half their length, whereas in Euarche palps have papillae over at least two-thirds of their length.BARNICH & FIEGE (2003) clarified the differences by indicating that Euarche has median antenna, and anterior chaetigers biramous, whereas in Eupanthalis there is no median antenna, and anterior chaetigers are subbiramous, usually without notochaetae.

Reinstatement of
PETTIBONE (1989) regarded some previously described species as junior synonyms of E. tubifex, including E. rudipalpa.Due to this expanded definition, E. tubifex ended up having a cosmopolitan distribution.The name encompassed specimens from the Gulf of Mexico (type locality), Gulf of Panama, Western Africa, South America, the Indian Ocean, and also specimens from Japan (IMAJIMA 1997) and the Mediterranean Sea (BEN-ELIAHU & FIEGE 1994, BARNICH & FIEGE 2003).However, we believe that E. tubifex is composed of different species that can be separated by using features of the anterior end, as demonstrated in the present work.In this contribution we propose an emended diagnosis of Euarche, a redescription of E. rudipalpa re-establishing the taxon as a valid species; and provide illustrations based on recently collected material, showing the pigmentation pattern of the body.A key to all species of Euarche is also provided.

MATERIAL AND METHODS
One specimen was collected in the Santos Basin, in the Brazilian continental shelf.Some parapodia were removed and mounted in ethanol-glycerol for semi-permanent preparations.In one parapodium, chaetae were trimmed to observe their arrangement in frontal view, as suggested by IMAJIMA (1997).Some other parapodia were cross-sectioned to observe enteric diverticula.A series of digital photographs were stacked by using the Helicon Focus software.It is a program for focus stacking or, in other words, a post-processing technique that extends the depth of field in photographs.The material is deposited at the Polychaeta Collection, from Universidade do Estado do Rio de Janeiro (UERJ).
Remarks.Most diagnostic features are rather easy to discern; however, some notopodial features might be difficult to evaluate, because they are often reduced to a small notoacicular lobe, being better developed on anterior chaetigers, with notochaetae delicate and scarce, usually emerging below the lobe.On the middle and more posterior parapodia, notopodia are barely developed and notochaetae are often lost.Even in parapodial mounts, notopodia can be difficult to discern because notoacicula migrate ventrally, being placed slightly above neurochaetal bundle bases.However, notochaetae have a slightly different orientation, being directed obliquely from the bundle, whereas neurochaetae tend to have a more or less parallel orientation.
Distribution.Brazil, off state of Rio Grande do Sul and Santos Basin, at 195 m depth in medium sand (in original description), now extended to deep water (2013 m).
Remarks.This specimen mostly fits the original description of Eupanthalis rudipalpa Amaral & Nonato, 1984 but di-rect comparison with type material was not possible because the type specimens seem to be lost (Mônica Petti, pers.com.).Due to the presence of three antennae, and palps with papillae throughout their length, the species must be transferred to Euarche Ehlers, 1887, as already indicated by PETTIBONE (1989: 14).Eupanthalis rudipalpa must be reinstated because it clearly differs from other species in the genus, as shown in the key below.Euarche rudipalpa resembles E. tubifex in the size of the anterior eyes, which are about twice as large as the posterior ones.This similarity might explain why the two species were regarded as synonyms.However, E. rudipalpa and E. tubifex differ in the relative size of antennae and palps, and in the relative extent of papillae series along palps.In E. rudipalpa, papillae extend throughout the palps, and palps are about three times Recent compilations (HUTCHINGS 2000) have mentioned the presence of enteric diverticula in the parapodia of Acoetidae; however, only one plate containing some illustrations is available for this feature.It was provided by DELLE CHIAJE (1841b: pl.99) for Polyodontes maxillosa (Ranzani, 1817), without any explanation for the figures.The author only provided a Latin diagnosis for the species.These illustrations were not reproduced from earlier works, including the original description (RANZANI 1817), and show complex enteric diverticula penetrating the parapodia, separated by constricted tunnels.Each diverticulum has lateral and distal sacs per segment; two other globose structures were regarded as testis, perhaps, because they were indicated with a letter "t".The second illustration was provided by STORCH (1968: 268, fig. 4) for a cross section of an anterior segment of Panthalis oerstedi Kinberg, 1856, but he provided little information about lateral caeca.In E. rudipalpa, lateral connections were not observed probably because the gut was too contracted, but their extensions inside parapodia are confirmed.MCINTOSH (1900: 402) indicated that in P. oerstedi enteric caeca were "large and elliptical, with a narrow neck", and this was illustrated by STORCH (1968).

Euarche rudipalpa (Polychaeta: Acoetidae), with remarks on morphology and body pigmentation Sergio I. Salazar-Vallejo 1,2,4 , Alexandra E. Rizzo 2 & Marcelo V. Fukuda 3
Eupanthalis McIntosh, 1876 and Euarche Ehlers, 1887, and their respective type species, E. kinbergi McIntosh, 1876 and E. tubifex Ehlers, 1887, were considered synonyms (E.rudipalpaas a junior synonym of E. tubifex, a cosmopolitan species) by some authors, because both have sessile eyes and two or three antennae.Nonetheless, these two genera are, in fact, distinct.Their type species can clearly be separated using some prostomial features.We provide an emended diagnosis of Euarche, and re-instate E. rudipalpa, redescribing it based on a Brazilian specimen (original type specimens lost).Illustrations showing body pigmentation pattern and a key to all species of Eupanthalis are also provided.
ABSTRACT.Eupanthalis rudipalpaAmaral & Nonato, 1984was described based on three incomplete, colorless specimens and has not been reported since its original description; the epithet rudipalpa means "hirsute palps", a characteristic that separates it from other congeneric species.KEY WORDS.Acoetids; color pattern; Eupanthalis; key to species; Polychaetes.