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Research Article
On the identity of Chamaedrilus glandulosus (Michaelsen, 1888) (Clitellata, Enchytraeidae), with the description of a new species
expand article infoSvante Martinsson, Emilia Rota§, Christer Erseus
‡ University of Gothenburg, Göteborg, Sweden
§ University of Siena, Siena, Italy
Open Access

Abstract

The taxonomy of Chamaedrilus glandulosus (Michaelsen, 1888) s. l., most commonly known previously as Cognettia glandulosa, is revised. A recent molecular systematic study has shown that this taxon harbours two cryptic, but genetically well separated lineages, each warranting species status. In this study these two lineages are scrutinized morphologically, on the basis of Michaelsen’s type material as well as newly collected specimens from Central and Northern Europe. Chamaedrilus glandulosus s. s. is redescribed and Ch. varisetosus sp. n. is recognized as new to science. The two species are morphologically very similar, differing mainly in size, but seem to prefer different habitats, with Ch. glandulosus being a larger aquatic species, and Ch. varisetosus being smaller and mainly found in moist to wet soil.

Keywords

Cognettia, Chamaedrilus, cryptic species, Oligochaeta, taxonomy

Introduction

In 1888 Michaelsen described an enchytraeid worm, Pachydrilus sphagnetorum var. glandulosus Michaelsen, 1888, as a variant of P. sphagnetorum Vejdovský, 1878. The description was based on material from the banks of the Bille and Elbe rivers in Hamburg, northern Germany. These two taxa were then transferred to Marionina Michaelsen, 1890 (in Pfeffer 1890), and P. sphagnetorum var. glandulosus was considered a good species, Marionina glandulosa, separate from M. sphagnetorum (Michaelsen 1900). Later Friend (1919) assigned both species to Chamaedrilus Friend, 1913, an action seldom noticed by subsequent authors. For instance, when Nielsen and Christensen (1959) established Cognettia, they transferred Marionina glandulosa to their new genus without considering its previous placement in Chamaedrilus. Nielsen and Christensen’s (1959) concept of Cognettia came to embrace a number of terrestrial and freshwater enchytraeids and until recently it has been widely accepted. However, as noted by Schmelz and Collado (2010) and now more closely investigated by ourselves (Martinsson et al. 2014), Cognettia is indeed a junior synonym to Chamaedrilus. For details about the complex taxonomical history and a formal revision of Chamaedrilus, see Martinsson et al. (2014).

Several cryptic forms have been found within well-known morphology-based taxa of former Cognettia (Martinsson and Erséus 2014). The morphospecies Chamaedrilus sphagnetorum s. l. was found to be a non-monophyletic assemblage of at least four species; these have been revised and described by Martinsson et al. (2014). The taxon Ch. glandulosus, on the other hand, traditionally distinguished from sphagnetorum by the possession of secondary septal glands and longer spermathecal ectal ducts (Nielsen and Christensen 1959), was shown by both nuclear and mitochondrial DNA evidence to consist of two separately evolving lineages in Northern Europe. These two lineages appeared as sister species, i.e., representing a monophyletic group (Martinsson and Erséus 2014). According to Christensen (1959) Ch. glandulosus s. l. reproduces both by fragmentation and parthenogenetically, but the eggs must be activated by spermatozoa for normal development (Christensen 1961). However it is still possible that at least one of the two cryptic species occasionally reproduces biparentally. Uniparental reproduction makes species delimitation problematic, in particular when referring to the biological species concept (Mayr 1942). However, as discussed by Martinsson and Erséus (2014), asexual organisms form distinct clusters and can be delimited using the unified species concept by de Queiroz (2007). According to this concept, the sole requirement of a species is that it is a separately evolving metapopulation lineage, and criteria (e.g. morphological differences, reproductive isolation, or gene tree monophyly) from any of the more traditional species concepts can be used to delimit the lineages. The greater the number of criteria supporting a divergence, the stronger the case is for speciation, but, even a single piece of evidence, if properly substantiated, may be enough to establish lineage separation.

The aim of this study is to revise the taxonomy of Chamaedrilus glandulosus s. l. by delimiting Ch. glandulosus s. s., with the designation of a lectotype, and describing Ch. varisetosus sp. n.

Material and methods

This study is based on two syntypes of Pachydrilus sphagnetorum var. glandulosus Michaelsen, 1888, from the original syntype series of ten, borrowed from the Zoological Museum of Hamburg University (ZMUH), Germany, of which one is here designated as lectotype, plus material analysed by Martinsson and Erséus (2014), and new specimens collected in northern and central Europe. A list of all examined specimens, with locality data and GenBank accession numbers for DNA-barcodes is given in Table 1.

List of material included in this study, with specimen identification numbers, voucher numbers, collection data, GPS coordinates, and GenBank accession numbers for COI barcodes. Voucher numbers in bold indicate type specimens, barcode numbers in bold are newly generated sequences. Locality data are given in the form: country, province, municipality and locality; GPS coordinates are given as decimal degrees. CZ = Czech Republic, FIN = Finland, GER = Germany, NOR = Norway, SWE = Sweden.

Species Spm. nos. Museum voucher nos. Sexual maturity Collection locality Coordinates Leg. Coll. date Barcode Acc. nos.
N E
Ch. glandulosus ZMUH V 429a mature GER. Hamburg, Hamburg, Bille River bank 53.54 10.09 W. Michaelsen Pre 1888 -
Ch. glandulosus ZMUH V 429b immature GER. Hamburg, Hamburg, Bille River bank 53.54 10.09 W. Michaelsen Pre 1888 -
Ch. glandulosus CE2011 SMNH133613 immature SWE. Västergötland, Vårgårda, Lången Lake littoral 57.9973 12.5868 C. Erséus Jun 30 2006 KF672372
Ch. glandulosus CE2841 SMNH133614 immature SWE. Öland, Borgholm, Räpplinge, stream 56.8195 16.9444 A. Ansebo, L. Matamoros & C. Erséus Jun 13 2007 KF672374
Ch. glandulosus CE2887 SMNH133615 submature SWE. Södermanland, Vingåker, Låttern Lake littoral 59.0854 16.0426 C. Erséus Jul 30 2007 KF672375
Ch. glandulosus CE2888 SMNH133616 submature SWE. Södermanland, Vingåker, Låttern Lake littoral 59.0854 16.0426 C. Erséus Jul 30 2007 KF672376
Ch. glandulosus CE2889 SMNH133617 immature SWE. Södermanland, Vingåker, Låttern Lake littoral 59.0854 16.0426 C. Erséus Jul 30 2007 KF672377
Ch. glandulosus CE2890 SMNH133618 immature SWE. Södermanland, Vingåker, Låttern Lake littoral 59.0854 16.0426 C. Erséus Jul 30 2007 KF672378
Ch. glandulosus CE2891 SMNH133619 immature SWE. Södermanland, Vingåker, Låttern Lake littoral 59.0854 16.0426 C. Erséus Jul 30 2007 KF672379
Ch. glandulosus CE8510 SMNH133620 immature SWE. Lappland, Kiruna, Abisko, marsh pond 68.3485 18.9719 D. Fontaneto Jul 6 2007 JN260143
Ch. glandulosus CE10655 SMNH133612 immature FIN. Keski-Suomi, Jyväskylä, Alvajärvi Lake littoral 62.315 25.730 H. Saarikoski Fall 2009 JN260270
Ch. glandulosus CE17761 SMNH142041 immature SWE. Södermanland, Vingåker, Hjälmaren Lake littoral 59.133 15.814 C. Erséus Jul 27 2012 KP878475
Ch. glandulosus CE17806 SMNH142042 immature SWE. Södermanland, Vingåker, Hjälmaren Lake littoral 59.133 15.814 C. Erséus Jul 27 2012 KP878476
Ch. glandulosus CE18516 SMNH142043 submature SWE. Västergötland, Lerum, Aspen Lake littoral 57.7656 12.2525 C. Erséus & B. Williams Jun 1 2013 -
Ch. glandulosus CE18517 SMNH142044 mature SWE. Västergötland, Lerum, Aspen Lake littoral 57.7656 12.2525 C. Erséus & B. Williams Jun 1 2013 KP878477
Ch. glandulosus CE18518 SMNH142045 immature SWE. Västergötland, Lerum, Aspen Lake littoral 57.7656 12.2525 C. Erséus & B. Williams Jun 1 2013 KP878478
Ch. glandulosus CE20212 SMNH142046 immature NOR. Östfold, Halden, Enningdalselva River 58.9099 11.5210 C. Erséus Oct 12 2013 KP878474
Ch. varisetosus CE2634 SMNH133600 immature SWE. Öland, Borgholm, S Greda, sandy soil 56.9929 16.8765 A. Ansebo, L. Matamoros & C. Erséus Jun 12 2007 KF672367
Ch. varisetosus CE2931 SMNH133601 immature SWE. Öland, Borgholm, Egby, peaty soil 56.8621 16.8539 A. Ansebo, L. Matamoros & C. Erséus Jun 12 2007 KF672368
Ch. varisetosus CE4027 SMNH133602 immature SWE. Skåne, Ystad, Nyvangsskogen, wet soil 55.5606 13.8239 C. Erséus May 31 2008 KF672369
Ch. varisetosus CE4028 SMNH133603 immature SWE. Skåne, Ystad, Nyvangsskogen, wet soil 55.5606 13.8239 C. Erséus May 31 2008 KF672370
Ch. varisetosus CE6626 SMNH133604 immature SWE. Uppland, Vallentuna, Brottby,peaty soil 59.5477 18.2467 C. Erséus Jun 4 2009 KF672371
Ch. varisetosus CE9376 SMNH133605 immature SWE. Medelpad, Timra, Söråker, forest soil 62.5235 17.4782 C. Erséus Jun 8 2010 KF672424
Ch. varisetosus CE9517 SMNH133606 immature SWE. Lappland, Kiruna, Björkliden, peat 68.4262 18.3509 C. Erséus Jun 12 2010 JN260194
Ch. varisetosus CE9524 SMNH133607 immature SWE. Lappland, Kiruna, Björkliden, river 68.4277 18.4448 C. Erséus Jun 12 2010 KF672425
Ch. varisetosus CE9525 SMNH133608 immature SWE. Lappland, Kiruna, Björkliden, river 68.4277 18.4448 C. Erséus Jun 12 2010 JN260195
Ch. varisetosus CE9526 SMNH133609 immature SWE. Lappland, Kiruna, Björkliden, river 68.4277 18.4448 C. Erséus Jun 12 2010 JN260282
Ch. varisetosus CE9536 SMNH133610 immature SWE. Lappland, Kiruna, Kiruna, forest soil 67.8546 20.2173 C. Erséus Jun 13 2010 JN260198
Ch. varisetosus CE9581 SMNH133611 immature SWE. Lappland, Vilhelmina, Klimpfjäll, grassland soil 65.0621 14.8066 C. Erséus Jun 15 2010 JN260206
Ch. varisetosus CE11485 SMNH142026 immature SWE. Västergötland, Lerum, Almekärr, wet soil 57.7614 12.2706 C. Erséus & A. Achurra Apr 23 2011 KP878462
Ch. varisetosus CE18904 SMNH142027 immature NOR. Telemark, Hjartdal, Kovstulheia, stream 59.8182 8.7222 C. Erséus & B. Williams Jun 13 2013 KP878463
Ch. varisetosus CE19031 SMNH142028 immature NOR. Telemark, Kviteseid, Kviteseid, wet forest litter 59.3532 8.5196 C. Erséus & B. Williams Jun 13 2013 KP878460
Ch. varisetosus CE19052 ZMBN99905 mature NOR. Buskerud, Hol, Örtedalsåna River, wet moss 60.4866 7.8562 C. Erséus Aug 10 2013 KP878464
Ch. varisetosus CE19113 SMNH142029 immature NOR. Buskerud, Hol, Geilo, forest soil 60.5329 8.2113 C. Erséus Aug 11 2013 KP878465
Ch. varisetosus CE19117 SMNH142030 immature NOR. Buskerud, Hol, Geilo, forest soil 60.5329 8.2113 C. Erséus Aug 11 2013 KP878466
Ch. varisetosus CE19677 SMNH142031 immature NOR. Sör-Tröndelag, Tydal, Langsvola, litter 62.8388 11.805 C. Erséus Aug 14 2013 KP878467
Ch. varisetosus CE19716 SMNH142032 immature NOR. Sör-Tröndelag, Röros, Hitterdalen, stream bank 62.6060 11.6599 C. Erséus Aug 15 2013 KP878461
Ch. varisetosus CE19749 SMNH142033 immature NOR. Sör-Tröndelag, Röros, Doktortjönna Lake shore 62.5763 11.3745 C. Erséus Aug 15 2013 KP878468
Ch. varisetosus CE19818 ZMBN99906 submature NOR. Hedmark, Engerdal, Nymoen, wet moss 61.6569 11.8164 C. Erséus Aug 15 2013 KP878469
Ch. varisetosus CE19819 SMNH Type-8732 submature NOR. Hedmark, Engerdal, Nymoen, wet moss 61.6569 11.8164 C. Erséus Aug 15 2013 KP878470
Ch. varisetosus CE19823 SMNH142034 immature NOR. Hedmark, Engerdal, Nymoen, wet moss 61.6569 11.8164 C. Erséus Aug 15 2013 KP878471
Ch. varisetosus CE19831 SMNH142035 immature NOR. Hedmark, Engerdal, Nymoen, wet moss 61.6569 11.8164 C. Erséus Aug 15 2013 KP878472
Ch. varisetosus CE19832 SMNH142036 immature NOR. Hedmark, Engerdal, Nymoen, wet moss 61.6569 11.8164 C. Erséus Aug 15 2013 KP878459
Ch. varisetosus CE20021 SMNH142037 immature NOR, Östfold, Hvaler, Asmalöy, dry soil 59.0630 10.9396 C. Erséus Sep 22 2013 KP878473
Ch. varisetosus CE20046 SMNH142038 immature NOR. Östfold, Fredikstad, Trosvik, litter on clay 59.2364 10.9012 C. Erséus Sep 23 2013 KP878479
Ch. varisetosus SM171 SMNH142039 immature CZ. NW Moravia, Okres Šumperk, Králický Sněžník, moss in stream 50.1499 16.8624 K. Elliott & S. Martinsson Jun 15 2013 KP878457
Ch. varisetosus SM172 SMNH142040 immature CZ. NW Moravia, Okres Šumperk, Králický Sněžník, moss in stream 50.1499 16.8624 K. Elliott & S. Martinsson Jun 15 2013 KP878458

Newly collected specimens were DNA-barcoded using the cytochrome c oxidase subunit I (COI) marker, as described by Martinsson and Erséus (2014); DNA was extracted from a few posterior-most segments of each worm, using Epicentre QuickExtract DNA Extraction Solution 1.0, following the manufacturer’s instructions, while the rest of the specimen was used for morphological studies, i.e., as a voucher. All new barcodes were matched with COI sequences of Cognettia glandulosa ‘A’ and ‘B’ from Martinsson and Erséus (2014). For tissue samples of the over 100 years old syntypes, newly designed primers were tested to amplify a short part of COI, as well as a fragment of the ribosomal 16S mtRNA gene, respectively, but these attempts were unsuccessful.

Unless otherwise mentioned in the descriptions, all information refers to the studied material only, in that the two taxa treated in this paper have previously been classified as one and the same species. Michaelsen’s syntypes were first studied as temporary mounts in glycerol. The newly designated lectotype was then stained with paracarmine and permanently mounted in Canada balsam on a slide as outlined by Erséus (1994), and so were all other voucher specimens (including the types of Ch. varisetosus sp. n.). All measurements and observations were made on preserved and somewhat compressed animals under a compound microscope (Leitz Laborlux K). As the posterior parts of the specimens were used for DNA extraction, the body size is arbitrarily given as the length of the 20 anteriormost segments and the width in segment XII (latter representing not clitellum but general body width). This size estimate was used also in Martinsson et al. (2014). In the descriptions, body measurements are given as the range followed by the mean ± 1 standard deviation. Differences in size between the two species were visualised with boxplots (Fig. 1, where asterisks denote the outliers), and tested by using two-sided t-tests performed in SPSS v. 22 (SPSS Inc., Chicago). Sketches were drawn using a camera lucida and used as templates for producing digital illustrations with Adobe PhotoShop.

Figure 1.

Boxplots showing differences in body size between Chamaedrilus glandulosus (Michaelsen, 1888) sensu stricto and Ch. varisetosus sp. n. A Length of 20 anteriormost segments B Width in segment XII. Both differences are significant (two-sided t-tests; P = 1.5E-5 and P = 5.5E-5, respectively).

The geographical distributions consider the origin of our material as well as that of COI barcode matches in BOLD (Barcoding of Life Data Systems, Ratnasingham and Hebert 2007). The Barcode Index Numbers (BIN) (Ratnasingham and Hebert 2013) are given under Remarks, for respective species. The BIN system clusters the sequences to produce operational taxonomic units that are assumed to closely correspond to species (http://www.boldsystems.org).

All specimens studied, including new types, are deposited in the Swedish Museum of Natural History (SMNH), Stockholm, the University Museum Bergen (UMB), Norway, and the Zoological Museum Hamburg (ZMUH), Germany; all COI barcodes are deposited in GenBank (see Table 1).

Taxonomy

Chamaedrilus glandulosus (Michaelsen, 1888), sensu stricto

Fig. 2

Pachydrilus sphagnetorum var. glandulosus Michaelsen, 1888: 490, plate 23, fig. 2a–c.

Marionia sphagnetorum var. glandulosa; Michaelsen 1889: 29.

Marionina glandulosa; Michaelsen 1900: 74.

Chamaedrilus glandulosus; Friend 1919: 174, partim.

Enchytraeoides glandulosa; von Bülow 1955: 257.

Cognettia glandulosa; Nielsen and Christensen 1959: 43, fig. 30, partim; Schmelz and Collado 2010: 79, partim.

Cognettia glandulosa B; Martinsson and Erséus 2014.

Lectotype

ZMUH V 429a, mature anterior part, in alcohol, leg. W. Michaelsen, date not given (before 1888).

Type locality

GERMANY: Hamburg, banks of Bille River, in detritus (“Billeufer, im Detritus”) (N 53.54°, E 10.09°).

Paralectotype

ZMUH V 429b, immature specimen, in alcohol; same collection data as for lectotype.

Additional type material

(not studied). Paralectotypes ZMUH V 429b, 8 specimens in alcohol, same collection data as for lectotype.

Other material

See Table 1. In total 15 specimens, of which 1 from Finland, one from Norway and 13 from Sweden (whereof one mature and three submature). All specimens except one are DNA barcoded (Table 1).

Diagnosis

Can be separated from all other European species of Chamaedrilus except Ch. varisetosus by its unique combination of 2–4 pairs of well-developed secondary pharyngeal glands, two chaetae per lateral bundle in preclitellar segments, and three chaetae in all other bundles, spermathecae with comparatively long ectal ducts, and genitalia shifted forward 3–4 segments (in relation to normal placement in Enchytraeidae). No characters completely separate this species from Ch. varisetosus sp. n., but specimens of Ch. glandulosus are usually larger and have only two chaetae in the lateral bundles of preclitellar segments, whereas Ch. varisetosus usually has three chaetae in lateral bundles of III-V. Furthermore, Ch. glandulosus is found in aquatic habitats only (i.e. submerged under water for most of the time), whereas Ch. varisetosus is found in both aquatic and terrestrial habitats; so far we have not found them occurring together.

Description

EXTERNAL CHARACTERS: Size: length of 20 anteriormost segments 3.49-6.68 mm, mean 4.55±0.87 (n=11); body width in XII 0.24–0.56 mm, mean 0.42±0.10 (n = 14). Chaetae sigmoid without nodulus, 60–100 µm long, chaetal formula 2,(3)-3:3-3, with 3 lateral chaetae per bundle from VII-IX; in sexually mature specimens, ventral chaetae, or both ventral and lateral chaetae, missing in the segment bearing male pores (VIII or IX). In the sexually mature and submature specimens examined, clitellum poorly developed.

INTERNAL CHARACTERS: Brain concave posteriorly, 160–210 µm long. Pharyngeal glands 3–4 primary pairs; 2–4 pairs of well-developed secondary glands (Fig. 2A), secondary glands behind the first pair of primary glands sometimes missing. Dorsal blood vessel arising in XVI–XX. First pair of nephridia present at 7/8–8/9; nephridia with efferent duct originating antero-ventrally, close to septum; anteseptale consisting of funnel only; postseptale elongate (Fig. 2C–D). Chloragogen cells granulated; 35–55 µm long. Coelomocytes granulated, round to oval, 25–30 µm long.

Figure 2.

Chamaedrilus glandulosus (Michaelsen, 1888) sensu stricto. A Anterior part of body (immature specimen) in lateral view, indicating chaetal distribution and the size, shape and number of pharyngeal glands B Sperm funnel, ental tract of vas deferens and penial bulb, to show their relative size proportions C Nephridium at septum 8/9, lateral view D Nephridium at septum 10/11, lateral view E Spermatheca F Spermatheca redrawn from Michaelsen (1888). Abbreviations: eg = ectal gland; pb = penial bulb; sa = spermathecal ampulla; sd = spermathecal duct; sf = sperm funnel. Scale bars: 200 µm (A); 50 µm (B–E).

Seminal vesicle distinct and unpaired in one specimen (CE18516), poorly developed in all other mature or submature specimens. Other genitalia paired. Sperm funnel about 200 µm long, tapering, 25 µm wide basally, 50 µm wide proximally; collar 55–60 µm wide. Spermatozoa on collar in a few mature/submature worms. Vas deferens long, simple, with several loops, about 12 µm wide. Penial bulb poorly developed, about 25 µm wide, 60–65 µm long (Fig. 2B). Male pores in VIII or IX. Spermathecae paired; pores located slightly below lateral chaetae; ectal duct smooth, 240 µm long, about 17 µm wide; ectal gland 35–40 µm in diameter; ampulla oval, about 150 µm long, not attached to oesophagus (Fig. 2E); sperm in ampulla of lectotype only. Spermathecae confined to V or entering into VI.

Habitat and distribution

Occurs in freshwater habitats, in sand and gravel bottoms in lakes and small streams, and climbing on vegetation and dead wood in water. Barcoded specimens document occurrence in Finland, Germany, Norway and Sweden, but the species is probably more widely distributed, not only in Europe. For instance, Ch. glandulosus s. l. has also been reported from North America: the records by Nurminen (1973) and Healy (1996) are insufficiently described and cannot even tentatively be assigned to any of the two species, and the records by Schlaghamerský (2013) and Schlaghamerský et al. (2014) are likely to be Ch. varisetosus, see under Habitat and distribution for that species.

Biology

Seems to reproduce mainly parthenogenetically; specimens with developing genitalia are found from June to July (Sweden).

Remarks

Michaelsen (1888; 1900) described this species as sturdier than Ch. sphagnetorum, with 2 chaetae per preclitellar lateral bundle and three chaetae in all other bundles. This together with the fact that Michaelsen’s type material was collected at an aquatic site makes us confident that our new material is conspecific with Michaelsen’s species. Michaelsen (1888) described the spermathecae in vivo as very long (“they often project, in spite of much meandering, up to the segment VII”) and the ampullae to consist each of an ectal enlargement followed by a long connecting tube and an expanded ental chamber (Fig. 2F). In our new material the spermathecae seem to be either not fully developed or much contracted after fixation: they show simple oval ampullae, not differentiated into ectal and ental compartments. In the mature lectotype we can only follow the spermathecae to what we interpret as the ampullar ectal enlargement. Chamaedrilus glandulosus is larger than Ch. varisetosus described below. Both the length of the 20 anteriormost segments (P = 1.5E-5) and the width in segment XII (P = 5.5E-5) differ significantly between the two species (Fig. 1).

This species is represented in BOLD by BIN: AAT8923.

Chamaedrilus varisetosus sp. n.

Fig. 3

Chamaedrilus glandulosus; Friend 1919: 174, partim.

Cognettia glandulosa; Nielsen and Christensen 1959: 43, fig. 30, partim; Schmelz and Collado 2010: 79, partim.

Cognettia glandulosa A; Martinsson and Erséus 2014.

Holotype

ZMBN99905, CE19052, mature, anterior part, COI barcode acc. no. KP878464, leg. Christer Erséus, Aug 10, 2013.

Type locality

NORWAY: Buskerud, Hol, at Örtedalsåna River (S of Haugastöl), elevation 1,075 m above sea level (N60.4866°, E7.8562°).

Paratypes

ZMBN99906, CE19818, submature, anterior part, COI barcode acc. no. KP878469; NORWAY: Hedmark, Engerdal, Nymoen at Femundelva (Trysilelva) River, at Nordre Husfloen Farm (N61.6569°, E11.8164°), leg. Christer Erséus, Aug 15, 2013. SMNH type-8723, CE19819, submature, anterior part, COI barcode acc. no. KP878470. Same collection data as for the other paratype.

Other material

See Table 1. Twenty-seven immature specimens, of which 2 from the Czech Republic, 12 from Norway, and 13 from Sweden, all DNA-barcoded.

Etymology

The species is named after the variation in numbers of chaetae in the lateral preclitellar bundles.

Diagnosis

The new species can be separated from all other European species of Chamaedrilus except Ch. glandulosus s. s. by its unique combination of 3–4 pairs of well-developed secondary pharyngeal glands, two chaetae in most lateral bundles in preclitellar segments, and three chaetae in all other bundles, spermathecae with comparatively long ectal ducts, and genitalia shifted forward 3–4 segments (in relation to normal placement in Enchytraeidae). No characters completely separate this species from Ch. glandulosus, but specimens of Ch. varisetosus are generally smaller, have shorter chaetae and smaller internal organs, and usually have a few preclitellar lateral bundles with three chaetae (Ch. glandulosus constantly has two chaetae per lateral bundle in preclitellar segments). Furthermore, Ch. varisetosus is mainly found in moist to wet soils, whereas Ch. glandulosus is only found in aquatic habitats.

Description

EXTERNAL CHARACTERS: Size: length of 20 anteriormost segments 2.33–4.38 mm, mean 2.89±0.59 (n = 13); body width in XII 0.20–0.42 mm, mean 0.28±0.07 (n = 20). Chaetae sigmoid without nodulus, 50–60 µm long, chaetal formula 2,3-(2),3:3–3; most specimens with 3 chaetae in lateral bundles of III(or IV)-V and 2 chaetae in the other lateral preclitellar bundles, but some specimens have 2 chaetae in all preclitellar lateral bundles; in sexually mature specimens, chaetae missing in the segment bearing male pores (VIII or IX). In the mature and submature specimens examined, clitellum only developed (but poorly) in the segment bearing the male pores and ½ a segment posterior and anterior to that segment.

INTERNAL CHARACTERS: Brain slightly concave posteriorly, concave anteriorly, 125–140 µm long, about twice as long as broad (Fig. 3D). Pharyngeal glands, 3–4 primary pairs; 3–4 pairs of well-developed secondary glands (Fig. 3A), secondary glands behind the last pair of primary glands sometimes missing. Dorsal blood vessel arising in XIII–XVII, rarely in XI or XVIII. First pair of nephridia present at 8/9–11/12; nephridia with efferent duct originating antero-ventrally, close to septum; anteseptale consisting of funnel only; postseptale oval, elongate (Fig. 3E). Chloragogen cells granulated, 20–30 µm long. Coelomocytes finely granulated, round to oval, approximately 20 µm long.

Figure 3.

Chamaedrilus varisetosus sp. n. A Anterior part of body (immature specimen) in lateral view, indicating chaetal distribution and the size, shape and number of pharyngeal glands B Male genitalia of a mature worm with male pores in segment VIII C Spermatheca D Brain, dorsal view E Nephridium at septum 10/11, lateral view. Abbreviations: eg = ectal gland; pb = penial bulb; sa = spermathecal ampulla; sd = spermathecal duct; sf = sperm funnel; vd = vas deferens. Scale bars: 200 µm (A); 50 µm (B-E).

Seminal vesicle unpaired, distinct in all three mature/submature specimens. Other genitalia paired. Sperm funnel about 100 µm long, 40–50 µm wide; collar indistinct, 25–30 µm wide. Spermatozoa not observed on collar. Vas deferens long, with several loops, about 5–7 µm wide. Penial bulb poorly developed, about 25 µm wide, 35–40 µm long (Fig. 3B). Male pores in VIII or IX. Spermathecae paired; pores located slightly below lateral chaetae; ectal duct smooth, 225 µm long, approximately 15 µm wide; ectal gland 25–30 µm in diameter; ampulla about 150 µm long, with ectal enlargement, followed by a contraction and a tubular to oval ental chamber; no sperm observed in ampulla; ampulla not attached to oesophagus (Fig. 3C). Spermathecae entering into VI.

Habitat and distribution

Found both in aquatic and terrestrial habitats. In freshwater found on stony bottoms in rivers, on land found in both deciduous and coniferous forest as well as in grassland soils. Known from Canada (BOLD record), the Czech Republic, Finland (BOLD record), Norway and Sweden, but may be more widely distributed in Europe and North America. Schlaghamerský’s (2013) description of C. glandulosa from Michigan fits our description of Ch. varisetosus. This and Schlaghamerský’s et al. (2014) records from Minnesota and Wisconsin are likely to refer to the same species.

Biology

Parthenogenetic reproduction more limited in time (maturing specimens found in August in Norway) than fragmentation (observed in May-September in Sweden and Norway). Worms with regenerating tails and/or heads rather frequent. This species may correspond to the population studied by Christensen (1959), in which the number of mature worms was high for a short period during the autumn. The variation in number of the lateral chaetae corresponds to that given in the diagnosis by Nielsen and Christensen (1959).

Remarks

This species is represented in BOLD by BIN: AAT9501.

Discussion

The two species treated in this paper, Chamaedrilus glandulosus sensu stricto and Ch. varisetosus sp. n., are easily separated morphologically from other species of Chamaedrilus by a unique combination of characters: the secondary pharyngeal glands are well developed in several segments, there are two chaetae in most preclitellar lateral bundles, but no enlarged chaetae, the genital organs are shifted forwards, and the spermathecae have comparatively long ectal ducts. The two species are morphologically similar and they have therefore been regarded as a single taxon by previous authors (e.g., Nielsen and Christensen 1959; Schmelz and Collado 2010). As demonstrated in the present paper, they can only be separated by their body size, chaetal size (and prevailing number) and, when fully grown, by the proportions of most internal organs. Genetically, however, they are well separated from each other (Martinsson and Erséus 2014), and they are also ecologically separated, with Ch. glandulosus found in aquatic habitats, whereas Ch. varisetosus is predominantly found in moist to wet soil. Ecological and physiological differences have been found between cryptic lineages in morphospecies of various organisms (e.g. Beauchamp et al. 2002; Feckler et al. 2014; Sattler et al. 2007), and if such lineages are not formally recognized and named, the differences may continue to be overlooked or neglected.

Martinsson and Erséus (2014) found Chamaedrilus glandulosus and Ch. varisetosus sp. n. to be sister species, nested within a part of the sphagnetorum-complex, making the latter non-monophyletic. The sphagnetorum-complex also turned out to be morphologically more heterogeneous than Ch. glandulosus s. l. (Martinsson et al. 2014), which could probably be, at least partly, explained by its non-monophyly. However, not even the two morphologically indistinguishable species, Ch. sphagnetorum s. s. and Ch. pseudosphagnetorum Martinsson et al., 2014 came out as sister species in the phylogenetic study (Martinsson and Erséus 2014).

Without the genetic data, the delimitation of Ch. glandulosus and Ch. varisetosus would have been much more challenging, all the more so because these worms, like those in the sphagnetorum complex, are mostly found sexually immature. It should also be considered that these species, even when mature, actually reproduce uniparentally, as mentioned in the introduction and discussed earlier by Martinsson and Erséus (2014). Uniparental reproduction makes species delimitation harder; however, we still believe this is possible using the unifying species concept (see Introduction). In the present case, we have a combination of genetic, ecological and morphological differences, supporting the split of Ch. glandulosus s. l. into two species. It should further be noted that it is not known with certainty if Christensen (1959; 1961) studied both species, or only one of them. As mentioned in the description, Ch. varisetosus seems to correspond well with the taxon studied in his 1959 paper and also fits the description given by Nielsen and Christensen (1959). Until the mode(s) of reproduction is (are) studied again for the two species, we cannot exclude the possibility that one or both species may reproduce biparentally, at least occasionally.

Genetic studies discovering cryptic and unnoticed diversity need to be followed by formal taxonomic revision, including careful morphological scrutiny, updated descriptions and species names, if possible based on barcoded types. We believe that an integrative approach, combining genetic and morphological data with as much as possible of ecological and physiological information, will strengthen studies of enchytraeid systematics.

Acknowledgements

We are indebted to Ainara Achurra, Anna Ansebo, Kerryn Elliott, Diego Fontaneto, Lisa Matamoros, Hanna Saarikoski and Bronwyn Williams for assistance with field work or for providing specimens in other ways; and to Marcus Svensson and Per Hjelmstedt for lab assistance. Helma Roggenbuck (ZMUH) is thanked for loaning us material. Kerryn Elliott kindly checked the language of the manuscript. Financial support to the first author was given by Wilhelm och Martina Lundgrens Vetenskapsfond; and to the last author by the Swedish Research Council (VR) and the Swedish Research Council for Environment, Agricultural Science and Spatial Planning (FORMAS), the Swedish Taxonomy Initiative (ArtDatabanken), the Norwegian Taxonomy Initiative (Artsdatabanken) and the Adlerbert Research Foundation.

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