Comment on Lone et al. Phylogenetic Relationships in Earthworm Megascolex Species (Oligochaeta: Megascolecidae) with Addition of Two New Species. Diversity 2022, 14, 1006

Abstract

Currently, on a global scale, integrated taxonomical works, by incorporating the molecular approach and traditional taxonomic methods have gained acceptance. Recently, Lone et al. (Diversity 2022, Phylogenetic Relationships in Earthworm Megascolex Species (Oligochaeta: Megascolecidae) with Addition of Two New Species) studied eleven Megascolex species (including two new species) from the Western Ghats biodiversity hotspot region of the Kerala state, India, by incorporating the integrated methods. The analysis of the results provided in Lone et al. indicated several discrepancies and shortcomings. They have overlooked or incorrectly described many key characters used in the Megascolex species identification and provided faulty figures. Apart from these, the paper had many factual as well as systematic errors. In this comment, based on the data provided by Lone et al., we critically reviewed their work, citing the errors and defects so as to help them to avoid similar issues in their future works and to obviate further confusions in the field of earthworm taxonomy.

1. Introduction

Currently, on a global scale, integrated taxonomical works have gained acceptance. Integrating traditional taxonomical methods with DNA data has greatly expanded taxonomic knowledge [1]. With the above approach, it is possible to resolve many of the phylogenetic relationships of the earthworm taxa [2,3]. According to Martinsson and Erséus [4], the molecular species delimitation of clitellates is on the move, especially in earthworms. Recently, Lone et al. [5] have made an attempt in this direction by incorporating the molecular approach (DNA barcode signatures using the mitochondrial gene cytochrome c oxidase 1–COI) and traditional taxonomic methods of eleven Megascolex species (including two new species) from the Western Ghats biodiversity hotspot region of the Kerala state. The genus Megascolex is chiefly confined to southern India (predominantly Western Ghats) and Sri Lanka [6,7,8]. Among the valid species of this genus, 36 species are endemic to Sri Lanka and 31 are found only in peninsular India, with 1 species common to both the countries [7,8,9,10], to which Lone et al. [5] added 2 more new species from the Western Ghats of the Kerala state. About 80% of the currently known earthworm species of the Kerala state were recorded in the early part of the last century, and several species are known only from the original description [11]. Hence, the work of Lone et al. [5] appears to be a step in the right direction. But the analysis of the data provided in Lone et al. [5] on the 11 Megascolex earthworm species from the Western Ghats of Kerala indicated discrepancies and shortcomings. They have overlooked or erroneously described certain key characters (e.g., intestine origin, shape of spermathecae, spermathecal diverticulum, etc.) used in the Megascolex species identification. There are factual as well as systematic errors throughout the work, and wrong or faulty figures have been provided. Recently, a work almost from the same group of authors (see Thakur et al. [12]) was published with similar errors in the taxonomically problematic moniligastrid earthworms. A few of those mistakes have been pointed out in a publication by Narayanan et al. [13], and the matter has been informed to the authors earlier. But similar kinds of taxonomical shortcomings again appeared in the present work of Lone et al. [5].

2. Materials and Methods

In this note, based on the data provided by Lone et al. [5], we critically reviewed their work, citing the errors and defects so as to help them avoid similar issues in their future works.

3. Results

A description of a species should include a definite morphological description, following the standard within the group [4]. Both the external morphological and the internal anatomical features are essential in earthworm species identification. Without descriptions of proper confirmatory characters, it is very difficult to distinguish between species. The description of a taxon should be supported with good illustrations of the diagnostic features of the taxon. Thus, some of the features, which cannot be sufficiently and appropriately described, can be illustrated in a drawing or photograph [14]. Hence, the diagram showing the ventral area of the anterior region and scientific illustrations of key anatomical features of species are of utmost importance in the identification of earthworms. Here Lone et al. [5] furnished a fairly good description of the morphological and anatomical characters and provided figures for each species they have documented. However, the bulk of Lone et al.’s [5] species descriptions are from the publications of Stephenson [6,15,16] and Aiyer [17], but at the same instance, they have wrongly described the key characters, such as the segmental origin of the intestine, shape of the spermathecae, spermathecal diverticulum, etc. used in the Megascolex identification.

Being an important taxonomical work, authors should have paid proper attention to writing the scientific names. On page number 2, the spelling of the species Megascolex lawsoni (Bourne, 1886) is given wrongly as M. lawsone, and M. cochinensis cochinensis is spelled as M. Cochinensis Cochinensis on page number 6. In the same paper, they have described two new species; for the first species, M. papparensis Lone, Thakur, Tiwari, James & Yadav, 2022, they have coined a corrupted toponym based on the Peppara Dam [5]; however, the authors have the right to coin the name. But this name is spelled as ‘Megascolex pepparensis sp. nov.’ twice on page number 15. In figure number 14, the scientific name of Drawida travancorensis Michaelsen, 1910, is given incorrectly as ‘D. travancorense’. While mentioning the zoological names, the scientific name is followed by the author’s name and year of publication, and this should be in plain letters and not in italics. However, in this work, ‘authors name and year’ are provided in italics. Details of the collection localities are very important and deserve proper care while including them in the text. Lone et al. [5], stated that the species M. auriculata Aiyer, 1929, and M. filiciseta Stephenson, 1915, were collected from the Periyar National Park, Kottayam, Kerala, and one sampling site of M. konkanensis konkanensis Fedarb, 1898, is in Mlappara, Periyar National Park, of Kollam district. It should be noted that the Periyar National Park is located in the Idukki district and not in Kottayam or Kollam districts, as stated by Lone et al. [5].

As per the International Code of Zoological Nomenclature recommendation [18], the type specimens should be deposited in permanently curated repositories, making them accessible for study (Art 16.4.2., Recommendation 16C and 72.10., Recommendation 72F). It means that type specimens are to be kept in a recognized, national or international research museum, facility, or institution that maintains a research collection. The National Biodiversity Authority [19] of India has selected 15 centers as designated repositories for the safeguard of new taxa discovered in India. As per the National Biodiversity Authority guidelines [19], “any person, who discovers a new taxon of biological resources occurring in India, is required to notify it to the relevant designated repository and deposit its holotype/isotype/paratype there”. Here, the type specimens of the new species described are kept in their own laboratory of the university, which, in fact, is not a recognized national repository for keeping the type collections. It should be noted that the same practice was followed earlier by the same group while describing a new species of Eutyphoeus from the Mizoram state of India (see Tiwari et al. [20]). Hence, we recommend that Lone et al. transfer the types to any one of the nationally designated repositories of India [20]. Another shortcoming in Lone et al.’s [5] work is that the majority of the figures provided for each species do not correspond with the original publication as well as the description they have provided; hence, it is difficult to visualize that the species are identified correctly.

3.1. Megascolex auriculata Aiyer, 1929

Stephenson [6] specified that in the case of Megascolex, “setae, at least in the middle and hinder parts of the body, are numerous (more than eight) in each segment”, which means a perichaetine setal arrangement. Similarly, he stated, “if a specimen shows an increase in the number of setae in any part of the body, it is a Megascolex”. In the original description of M. auriculata by Aiyer [17], it is clearly stated that the lumbricine arrangement occurs at the anterior portion, and from the middle, it changes to the perichaetine condition. In Lone et al.’s [5] work describing M. auriculata, it is stated that “setae lumbricine loses orientation posterior”, which means lumbricine occurs throughout with some kind of irregularity. Hence, following Stephenson [6], Lone et al.’s [5] specimen with lumbricine condition should be treated as a Notoscolex species and not Megascolex. In the original description and figure of M. auriculata by Aiyer [17], the spermathecal ampulla is long and thickly club-shaped, the basal portion being more than half as wide as the distal half; the spermathecal duct is very short with a unidiverticulate, ental diverticulum (Figure 1). Lone et al.’s [5] description and figure do not match with the above original description. Here, the ampulla is ovate and small with a very slender and sinuous spermathecal duct and a short, pointed, spear-like ectal diverticulum. Hence, the specimens of Lone et al. [5] under the name M. auriculata are not congeneric with the M. auriculata of Aiyer [17].

3.2. Megascolex cochinensis cochinensis Stephenson, 1915

In many earthworms, the segment in which the intestine begins is a chief feature of systematic importance [6]. In Megascolex, the origin of the intestine is one of the key features that distinguishes the species; hence, it is of species-specific importance. In the specimens provided by Lone et al. [5], the intestine begins at segment 14, while, actually in M. c. cochinensis, the intestine originates at segment 19. Hence, Lone et al.’s [5] specimens cannot be considered as M. c. cochinensis.

3.3. Megascolex filiciseta Stephenson, 1915

Stephenson’s [15] M. filiciseta description is based on three syntypes. In the original description, it is clearly stated that the origin of the intestine in M. filiciseta is in segment 15, whereas Lone et al. [5] stated that it is on segment 16; this would be a simple counting mistake.

3.4. Megascolex konkanensis konkanensis Fedarb, 1898

M. konkanensis konkanensis Fedarb, 1898, is a widespread native peregrine species in Kerala and the Western Ghats [7,11]. The specimens described by Lone et al. have a diameter of 4–5 mm, whereas this species only has a 2–3 mm diameter [6,21]. The anterior portion in this species is truncated, the prostomium is epilobus, and the tongue is narrow and small, but as per Lone et al. [5], the prostomium is epilobus with two short longitudinal grooves on the dorsal surface of the first segment. Such kinds of characters are not mentioned by the original authors, Fedarb [21] and Stephenson [6]. They also stated that the septa 5/6–11/12 are moderately thickened, whereas in Stephenson’s [6] words, “septa 6/7–12/13, thickened, the anterior ones as far as 9/10 fairly strongly, the rest gradually less so”. In this species, the intestine begins at segment 16 [6,21], whereas in Lone et al.’s [5] specimens, it starts from segment 18. Moreover, Lone et al.’s [5] figures depicting the genital region and spermathecae of M. konkanensis do not correspond with the actual description of M. konkanensis. The provided ventral view figure matches the description of M. cochinensis and not with M. konkanensis. The figures of M. konkanensis spermathecae from the original description (Figure 2a) by Fedarb [21] and Michaelsen [9] (Figure 2b) are given here for comparison. Hence, due to the contradicting anatomical features and figures provided by Lone et al. [5], the identity of the species is doubtful.

3.5. Megascolex polytheca polytheca Stephenson, 1915

In the description of M. polytheca polytheca Stephenson, 1915, by Lone et al. [5], the provided dimensions of the specimen are as follows: length 105–140 mm, diameter 3 mm, segments 159–194. Even though it is a variable feature, it falls well short of the dimensions provided by Stephenson [6]. This is an adiverticulate species [6,15,17], but the spermathecae’s figure by Lone et al. [5] shows a clear, small, club-shaped ectal diverticulum. The shape of the diverticulum is also different from the other two subspecies of this species group. Owing to the above-mentioned key differences, the species that Lone et al. [5] described here in the paper belongs to a different individual of this species complex and cannot be identified as the nominate form. However, the authors’ present initiation of the DNA barcode signatures (COI) of this group will be helpful in the future.

3.6. Megascolex polytheca zonatus Stephenson, 1915

The subspecies Megascolex polytheca zonatus Stephenson, 1915, on the whole, agrees closely with the nominate subspecies [15]. In this species, male pores are on whitish papillae in line with b setal lines, and the surface between the male pores is depressed [15]. But in the figure provided, they are shown to be between the bc setal lines and lacking concave depression. Indeed, they have repeated the same figure provided under M. polytheca polytheca on page number 10. In Lone et al.’s [5] description of M. polytheca zonatus Stephenson, 1915, it is stated that ‘a transverse groove at front end of the tongue is present’. But, as per the original description [15] of M. polytheca zonatus, the prostomium is epilobus and the ‘tongue’ is not cut off by a transverse groove. M. polytheca zonatus’s prostatic duct is somewhat wavy [6], although in the description of Lone et al. [5], it is described as short. Similarly, Lone et al.’s [5] description of the spermathecae is also contradictory. It is stated that the spermathecae are relatively smaller than M. polytheca polytheca. But a comparison of the provided figures gives the opposite view, where the spermathecae of M. polytheca zonatus are larger than that of the nominate form. In M. polytheca zonatus, spermathecal ampulla and duct are marked off; ampulla is ovoid, duct cylindrical, rather longer than and about half as wide as the ampulla; there is usually a slightly club-shaped diverticulum arising from the terminal portion of the duct, which is half as long to nearly as long as the duct (Figure 3) [6,15]. In the figure provided by Lone et al. [5], the ampulla is not ovoid; instead, it is elongate, and bent at its junction with the duct; the duct is slender and bent; and the diverticulum is smaller and 1/3 in length of the duct. As a result, the identity of this species is also in question, and it is not conspecific with M. polytheca zonatus.

3.7. Megascolex travancorensis travancorensis Michaelsen, 1910

In the case of M. travancorensis travancorensis Michaelsen, 1910, Lone et al. [5] stated that their specimens have one female pore; essentially, this species has paired female pores [6]. The spermathecal features and the figure provided by Lone et al. [5] contradict the description of the species provided by Michaelsen [9] and Stephenson [6]. According to Lone et al. [5], “spermathecae large, ampullae pear-shaped, dark in colour, distally narrowed, and severely bent at the opening. The duct is narrow than ampulla. A slender club-shaped distally somewhat bent diverticulum present”; they also provided a figure. This description and figure do not agree with the description available elsewhere and the original figure of the spermathecae (Figure 4) [6,9]. Here, the width of the duct is less than ½ the size of the ampulla, but in the original figure, it is roughly 1/5th the size of the ampulla. The diverticulum is slender and longer, with a bent at its ectal end [6,9], with almost the same length as that of the ampulla. But, in the figure provided by Lone et al. [5], it is too short with a bend at the ental portion of the diverticulum. Due to these drastic differences, the specimens provided by Lone et al. [5] definitely belong to a different species.

3.8. Megascolex triangularis Stephenson, 1925

The description of M. triangularis Stephenson, 1925, by Lone et al. [5] has serious disagreements with the original description. M. triangularis superficially resembles M. cochinensis. In M. triangularis, the first dorsal pore starts from the intersegmental furrow 4/5; here it is stated that it starts at 6/7. The description of male field provided by Lone et al. [5] differs drastically from the original description and figure (Figure 5) of Stephenson [16], where he stated that “in the midventral line of segment 18, and on the anterior half of the segment, extending from furrow 17/18 to the setal zone, is a small triangular depression, with its apex directed backwards; the depression is moderately deep, with clean-cut margins”. In Lone et al. [5], the male field takes the whole segment of 18, and it spans the intersegmental furrows 17/18 to 18/19. Lone et al. [5] stated that the septa 5/6–11/12 are thickened, while actually the septa 4/5–6/7 are thin, 7/8 is slightly thickened, 8/9–11/12 are somewhat strengthened, and 12/13/14 are slightly thickened [16]. In this species, the intestine begins in segment 16, whereas in the specimens described by Lone et al. [5], it begins on segment 14. In M. triangularis, the seminal vesicles are in segments 11 and 12; here it is stated that they are in segments 11 and 13. As per Stephenson’s [16] original description, “prostatic duct is relatively long, thin, shining, of the same diameter throughout”; in the specimens described by Lone et al. [5], the prostatic duct is not visible. The description of the spermathecal diverticula too differs significantly from the original description. In M. triangularis [16], the spermathecal diverticulum is “club-shaped, with an elongated stalk, its length equal to that of the duct or rather more” (Figure 5b); however, in Lone et al.’s [5] description and figure indicated a different nature, where it is with multiloculate diverticulum. Because of these discussed reasons, the species described under the name M. triangularis is certainly a different species.

3.9. Megascolex papparensis Lone, Thakur, Tiwari, James & Yadav, 2022

In their paper, Lone et al. [5] described two new species, M. papparensis and M. vazhichlensis Lone, Thakur, Tiwari, James & Yadav, 2022. As per the data provided in the paper, the description of M. papparensis is based on three specimens (one holotype and two paratypes). But in the dimension of the species, the range is not given; from this, one has to believe that all the three specimens have the exact same length, width, and number of segments, which is highly unlikely in earthworms. In the case of M. papparensis, it has been described that the spermathecal diverticulum is shorter than the ampulla, but in the figure provided (figure number 10C), it is slender, cylindrical, and longer than the ampulla (about 1.5 times the length of the ampulla). Due to this reason, the given figure of the spermathecae cannot be assigned to M. papparensis. When a new nominal taxon is established, authors should provide illustrations of the type specimens (whenever possible of the holotype or syntypes) showing key characteristics of the taxon (ICZN Art. 16.4.2, 16F) [18]. But here, one of the key distinguishing characters itself does not match with the description provided by Lone et al. [5].

3.10. Megascolex vazhichlensis Lone, Thakur, Tiwari, James & Yadav, 2022

As per the ICZN recommendation (ICZN Art. Recommendation 13A) [18], “when describing a new nominal taxon, an author should make clear his or her purpose to differentiate the taxon by including with it a diagnosis, that is to say, a summary of the characters that differentiate the new nominal taxon from related or similar taxa”. Such a diagnosis has not been provided by Lone et al. [5] for the two species in their work.

3.11. Other Concerns

Apart from the above-discussed taxonomical and systematical issues with regards to the identification of Megascolex species, there are other concerns regarding the work of Lone et al. [5]. Normally in taxonomic works related to earthworms, authors used to provide details such as the number of clitellates, aclitellates, and juvenile specimens examined, as well as their altitude and habitat. These details are helpful for other taxonomists, conservationists, and policymakers; however, such details are almost missing (except in a few cases) in the present work of Lone et al. [5]. In Figure 1 of the Lone et al. [5] paper, they have provided a map showing the collection localities of Megascolex from various geographical spots of Kerala, with inaccuracies and errors. As per the data, Lone et al. [5] had examined the materials of M. cochinensis cochinensis from the Idukki and Thrissur districts of Kerala state. But Figure 1 in their paper shows additional locations for M. cochinensis cochinensis in the Ernakulam district. Likewise, they have examined the materials of M. konkanensis konkanensis from Palakkad, Kollam, and Idukki (Mlappara, Periyar National Park is in Idukki district and not in Kollam district, as stated by Lone et al.) [5]. But the collection locality from the Palakkad district is not depicted on the map. One material each of the M. polytheca polytheca and M. polytheca zonatus species is from the two adjacent localities within the Eravikulam National Park of the Kannan Devan Hills, Idukki district. However, in the map, they portrayed them as widely separated from each other. From the data, M. ratus Cognetti, 1911, has been shown collected from both Thiruvananthapuram and Kollam districts; however, as per the map, all samples are from the former district, whereas, in the case of M. triangularis, the collection location is shown far away from the Kannan Devan Hills.

4. Conclusions

Improper descriptions of species will lead to unimaginable problems in earthworm taxonomy. Apart from this, the casual approach in making the illustrations of the species and its internal anatomical features also vitiated the quality of Lone et al.’s [5] paper. Proper taxonomic identification is a prerequisite for uploading the molecular data to the database. However, our present interpretation of this work is solely based on the data and figures provided by Lone et al. [5]. Hence, we suggest the authors address the mistakes and errors pointed out and publish a corrigendum by providing the precise description of the taxa and figures to avoid further confusions in the field of earthworm taxonomy.