Achaeta gemmata, Schmelz & Chen & Józefowska, 2024

Schmelz, Rüdiger M., Chen, Juanjuan & Józefowska, Agnieszka, 2024, Two new species of Achaeta (Enchytraeidae, Oligochaeta) from afforested post-mining and post-fire sites in Poland, Zootaxa 5437 (1), pp. 1-14 : 6-11

Achaeta gemmata sp. nov.

( Figures 3 , 4 )

Holotype. CEP-DZ-149414-N, adult specimen, anterior 23 segments, unstained whole-mount, with DNA sequences COI PP079496 , ITS PP084618 .

Type locality. Poland, Rudziniec Forest District , forest regenerated after fire, pine stand ( Pinus sylvestris L.), 50°18’09.5”N 18°24’47.7”E, soil type podsol, pH 3.8 (H 2 O) .

Paratypes. CEP-DZ-149415-N, adult specimen, anterior 15 segments, unstained whole-mount, with DNA sequence ITS PP084619 . CEP-DZ-149416-N to CEP-DZ-149430-N, 15 specimens (8 adult, 3 subadult, 4 juvenile), mostly complete (3 amputees), stained whole mounts. 33 specimens (5 adult, 17 subadult, 11 juvenile), stained whole mounts, in the 1st author’s collection. From type locality or adjacent sites overgrown by Larix decidua , Betula pendula , and Quercus robur L.; soil type podsols, sandy and loamy-sandy texture, pH (H 2 O) 3.7–4.8 .

Further material. A total of c. 1700 specimens, investigated and identified in vivo, from type locality or adjacent sites. Of these: 33 specimens (5 adult, 17 subadult, 11 juvenile), stained whole mounts; 9 specimens, fixed in Bouin’s fluid, preserved in 70% ethanol; c. 130 specimens, preserved in 100% ethanol; from type locality or adjacent sites. Material in the 1st author’s collection.

Diagnosis. Body length 4.5–5 mm; up to 38 segments; pyriform glands and oesophageal appendage absent; pharyngeal glands with secondary lobes in V and VI; two pairs preclitellar nephridia, at 6/7, 7/8; clitellum interrupted ventrally, complete dorsally, cells in conspicuous longitudinal rows; dorsal rows consisting of hyalocytes and interspersed granulocytes; lateral and ventrolateral rows with granulocytes only; last ventral row in longitudinal line with male pores; seminal vesicle absent; male glands small and widely separate; spermatheca length c. 1.5 segments, ectal pores laterally.

Description. Body length (fix) 4.4–4.9 mm. Body diameter (fix) 0.11–0.25 mm; 0.11–0.15 mm at V, 0.15–0.25 at XII, 0.14–0.17 mm at XX. Segment number 31–38 (N=11; 32–34, eight specimens, 31, 35, 38, one specimen each).

Pyriform glands absent, lentiform glands enlarged to ellipsoid cushion-like intracoelomic papillae in anterior segments: dorsally one pair in I anteriorly of brain ( Fig. 3A , 4A ), laterally one pair per segment in II to X ( Fig. 3A , 4G ); ventrally one pair per segment ( Fig. 3A,B ), first pair in III, IV or V, last preclitellar pair in XI, only slightly enlarged; behind clitellum from XIII on, reducing in size in following segments, absent in posterior body half. In living specimens, dorsal papillae in I and lateral papillae conspicuous, ventral papillae inconspicuous. Papillae longer than wider than high. Size of lateral papillae varying among specimens, and often also within a specimen; maximum length 32–50 μm, minimum length 18–32 μm, mean length 27–34 μm. Length within an individual varying, e.g., between 50 μm and 32 μm or 32 μm and 20 μm. Ventral papillae 21–25 μm long and 14–20 μm wide. Papillae not developed in all positions. Additionally, 2 pairs of segmental lentiform cells dorsally, inconspicuous, only seen in whole mounted specimens: one pair closely behind septum, the other pair at level of lateral papillae.

Brain ( Fig. 3A , 4A ) about 1.7x as long as wide, posteriorly slightly convex, sometimes straight, length 80– 90 μm (viv), 70–73 μm, fix. Ventral nerve cord ganglionic from V. Pharyngeal glands ( Fig. 3A , 4C ) all widely connected dorsally, in V and VI no subdivision into dorsal and ventral lobes; secondary ventral glands in V, VI. Oesophageal appendage absent or not distinguishable light-microscopically. Dorsal blood vessel from VII. Intestine widening gradually, no intestinal diverticula. Pars tumida of midgut in region XXIX–XXXIV, in 3.5–4 consecutive segments. Two pairs of preclitellar nephridia ( Fig. 3A , 4B ), at 6/7, 7/8; anteseptale with coils of canal, bulky, postseptale 1.5x as long as anteseptale, septal constriction slight or absent, postseptale gradually merging into short and thick efferent duct, terminal vesicle absent. Postclitellar nephridia from 15/16 or further back, of similar shape but postseptale more slender and stretched than in preclitellar nephridia. Coelomocytes ( Fig. 4D ) pale, flat, disc-shaped, with varying amounts of refractile granules in the centre, periphery often as a flat hyaline frame; cells almost as wide as long, length 30–35 μm.

Clitellum from XII–1/2XIII, saddle-shaped, no dorsal interruption; cells in conspicuous longitudinal rows; dorsal rows consisting of hyalocytes and interspersed granulocytes ( Fig. 4I ); lateral and ventrolateral rows with granulocytes only ( Fig. 3B , 4H ); last ventral row in longitudinal line with male pores ( Fig. 3B ).

Testis in XI, ovary in XII ( Fig.3B ). Seminal vesicle absent, spermatogonial cysts free in XI dorsally.Spermatozoa 36 μm, heads 14 μm. Sperm funnels ( Fig. 4F ) small, about 2–2.5x as long as wide, 60–100 μm by 26–40 μm, collar almost as wide as funnel body. Vas deferens often coiled in dense regular spirals, diameter 6–7 μm. Male pores ( Fig. 3B ) on body surface, widely distant, surrounded by area glareosa. Male glandular bulb spherical, diameter 25–35 μm (fix), pierced centrally by vas deferens; distance of bulbs 1.5–2x bulb diameter.

Spermathecae ( Fig. 3A , 4C ) short, extending into VI, rarely VII; often confined to V. Ectal pores lateral. Ectal duct slightly longer than wide, 20–24 μm by 14–20 μm (fix, N=6); ampulla 24–34 μm wide (fix, N=6), separated by a constriction from ectal duct in fixed specimens; spermatozoa placed obliquely in ampullar lumen; connecting tube thin, ental reservoir spherical, 30–36μm wide (fix, N=4).

Etymology. Named after the conspicuous lateral papillae. Due to their serial arrangement and easy recognition they appear as true gems when large numbers of specimens have to be identified to species level.

Remarks, morphology. This new species is most similar to Achaeta camerani , a common species in Northern and Central Europe ( Schmelz & Collado 2010) and with additional records from NW Spain ( Collado & Martínez-Ansemil 1996) and Japan ( Nakamura & Christensen 1978). Both species often occurred together at the same plot or even in the same soil sample. They agree in (1) body size, (2) absence of pyriform glands, (2) presence of secondary pharyngeal gland lobes in V and VI, (3) preclitellar nephridia at 6/7, 7/8, (4) absence of a seminal vesicle, (5) short spermathecae with lateral ectal pores, and, most conspicuously, in (6) the saddle-shaped clitellum, without dorsal interruption and with cells arranged in distinct longitudinal rows.

Differences of A. camerani are based on own observations but confirm the details given in Graefe (1980), Chalupský (1992), and Dózsa-Farkas and Felföldi (2017): (1) Oesophageal appendage in V; (2) no conspicuously enlarged papillae; (3) coelomocytes larger, with a thinner margin, and with more granules in the centre; (4) dorsal blood vessel from VIII (in adult specimens); (5) spermathecae smaller, confined to V; (6) no clitellar gland cells in front of and behind the male pores; (7) longitudinal gland cell rows of clitellum with either hyalocytes or granulocytes, not both types in one row: dorsally two longitudinal rows of hyalocytes on each side, each separated by a longitudinal double row of granulocytes.

The first three of these differences are recognizable already in juvenile specimens. Of these the oesophageal appendage, present in A. camerani and absent in A. gemmata sp. nov., is most useful for the separation of these two species, whereas differences in papillae and coelomocytes are not always clearcut: lateral papillae can be small and inconspicuous in juveniles of A. gemmata sp. nov., whereas the lateral lense-shaped epidermal gland cells of A. camerani , found in exactly the same location as the papillae in A. gemmata sp. nov., may be inflated to resemble rudimentary or incipient papillae. Considering the coelomocytes, there is overlap in the thinness of the outer margin and the degree of inner granulation.

This new species belongs to the group of Achaeta species without pyriform glands. All species of this group have spermathecal pores in lateral position (vs. ventral in most of the species with pyriform glands) and most of them have lentiform epidermal gland cells in segmentally fixed and repetitive positions. These cells vary among species in number, colouration, and size. Segmental series of enlarged lentiform gland cells with conspicuous inner bulges of the body wall or protrusions beneath it, called papillae in this paper, are described from three further species, A. antefolliculata Dózsa-Farkas & Boros, 2005 , A. hanagarthi Schmelz, 2008 , and A. paranensis Schmelz, 2008 . In all of them, they are developed in different positions:

A. antefolliculata , described and known so far only from Hungary, has one pair each of enlarged lentiform gland cells laterally in III, IV, V, VI, and one dorsal pair in I: this dorsal shift in I is also seen in A. gemmata sp. nov. ( Fig. 3A ). These glands appear to be as large as the lateral papillae in A. gemmata sp. nov. Further differences to the new species are segment number (20–21), only one pair of secondary pharyngeal gland lobes, in V, a smaller spermatheca, which is always confined to V, and clitellar glands cells in transverse rows with a narrow dorsal interruption. Achaeta hanagarthi Schmelz, 2008 and A. paranensis Schmelz, 2008 , both originally described and so far known only from Brazil, have enlarged lentiform gland cells only in ventral, but not in lateral, position; these glands are similar in shape and size to the ventral glands in A. gemmata sp. nov., which are notably smaller than the lateral ones. Further differences to the new species are as follows: A. hanagarthi : no secondary pharyngeal gland lobes, 1st nephridium at 7/8, clitellum widely open dorsally; A. paranensis : oesophageal appendage present, large in V, with canal in IV, intestinal diverticulum in VII, only one pair of preclitellar nephridia, at 5/6.

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The lentiform glands in Achaeta etrusca Rota, 1995 may also belong here (see Rota 2015) even though a figure ( Rota 2015, Fig. 4A ) suggests that they are less enlarged and more similar to the ordinary lentiform gland cells such as found in A. pannonica Graefe, 1989 , A. iberica Graefe, 1989 , A. diddeni Graefe, 2007 , and A. brevivasa Graefe, 1980 . All lentiform gland cells that we consider as enlarged have two different compartments: a non-staining central region which connects with the body surface, and a strongly staining peripheral region which extends into the body cavity. It is mainly this staining region which is responsible for the increase in size of the lentiform gland cells. These two regions are also distinguishable in living organisms, as an inner and outer circle (comp. Fig. 4G ). Schmelz et al. (2008) refer to enlarged and non-enlarged cells as “ type I” cells and “ type II” cells, respectively, but the difference between them is probably only one of degree.

Apart from the gem-like lateral papillae, the dorsal pattern of the clitellar gland cells is a most conspicuous feature of this new species. The complete coverage with longitudinal rows—i.e., the absence of a mid-dorsal gap— is already distinguishable in subadult specimens ( Fig. 4E ), but the full pattern with alternating hyalocytes and granulocytes within a row is only seen in fully adult specimens (comp. Fig. 4I and 4E ). As a further peculiarity, the most ventral row of granulocytes encloses the male pores, and one or two rows of granulocytes may be widened to form incomplete double rows ( Fig. 4H , black asterisk).

Remarks, molecular comparison. Fourty-two COI sequences of 16 species of Achaeta , some of them without valid names, are publicly available. According to uncorrected p-distances calculated based on COI sequences ( Table 2 ), high interspecific distances to A gemmata sp. nov. were observed (15.7%–21.8%), except for one specimen, identified as Achaeta cf. brevivasa Graefe, 1980 (0%, GenBank accession number: GU902034) by Erséus et al. (2010), and collected from Sweden. This specimen should be considered as a misidentified Achaeta gemmata sp. nov. Unfortunately, there is no voucher of this specimen for a morphological comparison. Chen et al. (2022) redescribed Achaeta brevivasa collected from China; the specimens correspond well with the original description. The three respective COI sequences (GenBank accession numbers: ON419115–ON419117) differ in 16.4% from that of Achaeta cf. brevivasa sensu Erséus et al. (2010) . There are no DNA sequences from the type series of A. brevivasa and currently no other specimens identified as A. brevivasa with available DNA sequences.

Figures

FIGURE 3. Achaeta gemmata sp. nov., drawings from whole mounts. A. Anterior end, segments 0–VIII, latero-dorsal view. In this specimen, ventral papillae begin at IV. Pharyngeal glands shaded dark-grey. B. Clitellar region, ventral view.

FIGURE 4. Achaeta gemmata sp. nov., photographs from living specimens. A. Head region, dorsal view, showing prostomial papillae (arrows) antero-laterally of brain (asterisk). B. Nephridium at 7/8; the funnel is covered by the ental reservoir (er) of the spermatheca. C. Spermathecae between pharyngeal glands of IV and V, dorsal view, both ectal pores focused. D. Coelomocytes. E. Clitellum, dorso-lateral view, as seen in a subadult specimen. F. Sperm funnels on both sides of the intestine. G. Lateral papillae (arrows) of segments III–V. H. Clitellum, lateral view. White asterisk: First lateral row with alternating hyalocytes and granulocytes. Dark asterisk: incipient double row of granulocytes. I. Clitellum, dorso-lateral view. Note the absence of a mid-dorsal interruption.

Tables

TABLE 2. Species records of Achaeta spp. with publicly available COI-DNA barcodes, and their genetic differences to the holotypes of the two new species, calculated as uncorrected p-distances based on COI-DNA sequence differences. Only one sequence per species record is presented here. Distance between the two new species is 2.0. *: Specimen misidentified, see text

	Specimen ID	Genbank Accession N.º	Country	Reference	Achaeta florens sp. nov.	Achaeta gemmata sp. nov.
Achaeta aberrans Nielsen & Christensen, 1961	CE875	GU902030.1	Sweden	Erséus et al. 2010	0,19	0,18
Achaeta affinis Nielsen & Christensen, 1959	919	KY583145.1	Hungary	Dózsa-Farkas & Felföldi 2017	0,19	0,20
Achaeta affinis Nielsen & Christensen, 1959	none	GU453383.1	Denmark	Christensen & Glenner 2010	0,20	0,19
Achaeta bibulba Graefe, 1989	CE1206	GU902031.1	Sweden	Erséus et al. 2010	0,20	0,21
Achaeta bibulba Graefe, 1989	e115	MT159573.1	Russia	Lebedev et al. (unpublished)	0,19	0,21
Achaeta bifollicula Chalupský, 1992	CE1035	GU902032.1	Sweden	Erséus et al. 2010	0,19	0,16
Achaeta bohemica ( Vejdovský, 1879)	885	KY583141.1	Hungary	Dózsa-Farkas & Felföldi 2017	0,19	0,18
Achaeta cf. bohemica ( Vejdovský, 1879)	CE1766	GU902033.1	Italy	Erséus et al. 2010	0,16	0,18
Achaeta brevivasa Graefe, 1980	CJJ92	ON419115.1	China	Chen et al. 2022	0,18	0,16
Achaeta cf. brevivasa Graefe, 1980	CE1234	GU902034.1	Sweden	Erséus et al. 2010	0,20	0,00*
Achaeta camerani ( Cognetti, 1899)	903	KY583144.1	Hungary	Dózsa-Farkas & Felföldi 2017	0,22	0,21
Achaeta camerani ( Cognetti, 1899)	CE790	GU902035.1	Sweden	Erséus et al. 2010	0,22	0,21
Achaeta danica Nielsen & Christensen, 1959	901	KY583142.1	Hungary	Dózsa-Farkas & Felföldi 2017	0,19	0,16
Achaeta cf. danica Nielsen & Christensen, 1959	860	KY583134.1	Hungary	Dózsa-Farkas & Felföldi 2017	0,19	0,20
Achaeta iberica Graefe, 1989	CE1051	GU902036.1	Sweden	Erséus et al. 2010	0,20	0,17
Achaeta macroampullacea Dózsa-Farkas et al., 2018	1091	MG252131.1	Korea	Dózsa-Farkas et al. 2018	0,21	0,17
Achaeta tothi Dózsa-Farkas & Felföldi, 2017	882	KY583140.1	Hungary	Dózsa-Farkas & Felföldi 2017	0,21	0,19
Achaeta unibulba Graefe, Christensen & Dózsa-Farkas, 2005	851	KY583130.1	Hungary	Dózsa-Farkas & Felföldi 2017	0,20	0,19
Achaeta unibulba Graefe, Christensen & Dózsa-Farkas, 2005	CE812	GU902037.1	Sweden	Erséus et al. 2010	0,20	0,19
Achaeta sp.	1143	MH124585.1	Korea	Nagy et al. (unpublished)	0,18	0,17
Achaeta sp.	BIOUG08058-B10	MF544984.1	Canada	deWaard et al. 2019	0,26	0,22
Achaeta sp.	812_E7	LT905364.1	Switzerland	Vivien et al. 2017	0,18	0,17
Achaeta sp.	1021_E7	LT903839.1	Switzerland	Vivien et al. 2017	0,20	0,19