Limpluvia setoensis Fend & Torii, 2024

Martin, Patrick, Fend, Steven, Martinsson, Svante, Klinth, Mårten, Torii, Takaaki & Erséus, Christer, 2024, Towards an integrative revision of Haplotaxidae (Annelida: Clitellata), Zoological Journal of the Linnean Society (zlae 141) 202 (4), pp. 1-38 : 26-29

Limpluvia setoensis Fend & Torii sp. nov. (clade 5 in Fig. 1 ) ( Figs 2G , 8–9 )

ZooBank LSID: urn:lsid:zoobank.org:act:34CDDCF2-7E25-4EB1-A088-E70B6BC75B77

Holotype: NSMT An-1897 : a mature worm, anterior end dissected and slide mounted, part of tail analysed for DNA (CE30790); COI DNA-barcode in GenBank (acc. no. PP988456 ); this individual was not used in our phylogenetic analyses.

Type locality: Japan: Shizuoka Prefecture: Seto River , Terashima, Fujieda-shi , 34.8830 °N, 138.2156 °E, elevation 54 m, 8 Jan 2010; collected by T. Torii.

Paratypes: NSMT An-1898 , from the type locality (8 Jan 2010): anterior end on slide, tail analysed for DNA (CE30789) COI DNA-barcode in GenBank (acc. no. PP988419 ); for other molecular data, see Table 1 . NSMT An-1899–1900: two whole mounts. NSMT An-1901 , from Asahina River , 34.9431 °N, 138.2583 °E, 9 Dec 2007: one dissected, slide mounted specimen. NSMT An-1902–1903 , from Asahina River, Hazama , Okabe-cho, 34.9432 °N, 138.2584 °E, 6 Jan 2008: two whole mounts. All collected by T. Torii.

Other material: NSMT An-1904–1914. From the type locality, 8 Jan 2010; two whole mounts and two dissected. Asahina River , Fujieda-shi, Gyokuro-no-Sato, 34.9509 °N, 138.2509 °E, 2 May 2008 ; three partially mature whole mounts. Asahina River , 34.9431 °N, 138.2583 °E, 9 Dec 2007; four dissected .

Etymology

From the Seto River.

Description

Length of preserved specimens 17–25 mm, 60–70 segments. Diameter 0.4–0.6 mm in X, maximum diameter to 0.7 mm. Prostomium rounded, length less than width, separated from peristomium by dorsal groove; peristomium not elongate ( Figs 8B , 9A ). Epidermis in anterior segments 12–16 μm thick, in clitellum 20–35 μm, and 4–10 μm posteriorly. Circular muscle of body wall 10–12 μm, longitudinal muscle layer 30–40 μm thick in anterior segments. Clitellum with unordered glandular cells XI–XIII or XIV. Secondary annulation a narrow anterior ring from III, usually distinct in pre-clitellar segments; may be obscure or lacking in posterior segments.

Chaetae simple-pointed, moderately sigmoid, dorsal and ventral pairs similar or dorsals slightly shorter; length 140–228 μm in anterior region (shorter in II–III), 146–214 μm posteriorly; thickness 5–7 μm; nodulus 0.41–0.52 the chaetal length from the tip ( Figs 8C, D , 9F ). Dorsal chaetae absent in II.

Brain in peristomium ( Figs 8B , 9A ). Septa not thickened. Pharynx wall moderately thickened in II–III (IV), thicker dorsally (to 50 μm), covered with a dorsal pad of apparently glandular cell bodies ( Figs 8B , 9B ). Pharynx with paired, apparently tubular organs (pharyngeal diverticula) to about 200 μm long by 30–40 μm wide, joining the pharynx dorsolaterally at about intersegment 2/3, extending to about 3/4 ( Figs 8A–B , 9C ); tubules transparent and difficult to observe. Chloragogen layer thin and indistinct on gut.

First nephridia usually paired in VIII; nephridia in a few posterior segments, starting in XIV, typically about XIV–XVII and XX–XXV. Nephridial ducts are simple tubules, without postseptal expansion; tubules folded, with multiple loops conjoined in part ( Figs 8E , 9D ); anteseptal funnels small; ducts terminate in simple tubes leading to inconspicuous nephridiopores just anterior to chaetae. Blood vessels are simple commissures in preclitellar segments, long and sinuous in II–III, shorter in IV– VIII; not observed in posterior segments. Ventral blood vessel originates at about 2/3.

Multilobed, weakly-staining, glands usually occurring singly in one or more segments from VI to XIII in mature worms ( Figs 2G , 8F–G , 9G–H ), each gland formed of 8–14 multicellular lobes (height 100–250 μm), entire gland mass to 150–300 μm wide; glands converge to an indistinct, ectal secretory surface about 100 μm wide. Gland position variable; may be midventral or ventrolateral, in anterior or posterior part of segment. Mature worms also have more darkly staining glands paired in XI, behind ventral chaetae, surrounding male pores, and extending to the posterior septum; appearing as two longitudinal rows of 5–10 multicellular lobes in ventral view ( Fig. 8H ); gland mass 150 μm x 350 μm; secretory area indistinct, 120–190 μm diameter ( Figs 8F–I , 9I–J ).

Spermathecal pores inconspicuous, on lateral lines at septum 8/9, or near 8/ 9 in IX; male pores inconspicuous, within secretory area of ventral glands behind chaetae in XI, the anterior just behind ventral chaetae, the posterior just anterior to septum 11/12; female pores on chaetal line at intersegment 12/13. Testes extend to about mid-segment in X and XI; ovaries in XII, may be elongate, extending to the posterior septum, rarely into XIII; sperm sacs X–XIII or XIV. Egg sacs extending back to XV or XVI; eggs large and yolky; female funnels simple, to 150 μm high.

Tubular spermathecal duct short, total length 40–60 μm ( Figs 8F–G , 9E ). Spermathecal ampulla of mated worms elongate-sacciform, length 400–800 μm, width 70–120 μm, extending through IX ( Fig. 8F–G ). Ampulla with thin, non-glandular epithelium (12–24 μm); sperm loosely arranged or lined up along epithelium.

Male funnels 80–160 μm high and convoluted, on 10/11 and 11/12; usually anterior and posterior pairs similar ( Figs 8F , 9I ), but posterior funnels smaller and without sperm in two unmated specimens. Male ducts (vasa deferentia) thin (12–25 μm) and convoluted, length 260–360 μm; posterior pair penetrates the posterior septum, forming a small loop in XII before entering XI ( Fig. 8F, I ); both pairs appear free in the coelom, without entering body wall musculature; ducts travel through the ventral gland mass and end separately in anterior and posterior pores within the secretory area of each gland, on line of ventral chaetae ( Figs 8G, H , 9J ). Male ducts are simple tubes throughout their length, not expanded as atria or otherwise modified.

Live specimens swim actively, resembling lumbriculids in the field. Guts were densely packed with dark-coloured, fine particulate organic matter, with small amounts of very fine mineral particles and diatoms, suggesting that these worms are ordinary detritivores.

Site descriptions

The Seto River and its tributary, the Asahina River are located in central Shizuoka Prefecture. A large quantity of subsurface water emerges as springs around the type locality. Although the amount of flow from springs is unknown, many subterranean crustaceans [e.g. Mackinia japonica Matsumoto, 1956 , Nipponasellus hubrichti ( Matsumoto, 1956) , Eoniphargus kojimai ( Uéno, 1955) , Lucioblivio kozaensis Tomikawa, 2007 ] are found there (Torii, unpubl. data).

Remarks

Morphologically, L. setoensis could be attributed to the Lumbriculidae based on the semiprosoporous male ducts with a post-septal loop of the posterior pair, considered byBrinkhurst (1989) to be ancestral for the family. However, among species associated with the Lumbriculidae , simple male ducts, lacking an atrium, are a character shared only with the monotypic Kurenkoviamagna Sokolskaya,1969,fromKamchatka.Moreover, our phylogenetic analysis supports that L. setoensis is outside (a monophyletic) Lumbriculidae s.s. and instead, it is the sister to the clade comprising the latter plus all Hirudinea. Kurenkovia magna is sufficiently different from typical lumbriculids that it was later assigned to a monotypic family, the Kurenkovidae Sokolskaya, 1983 , although it is still assumed to be a lumbriculid by some authors ( Brinkhurst 1989, Timm 1999), based on the (morphological) cladistic analysis of Brinkhurst (1989). Unlike typical lumbriculids, anterior and posterior ducts of L. setoensis and K. magna species open in separate male pores beneath a glandular mass (compare Fig. 8G with Sokolskaja 1983: fig. 23). In addition to a similar arrangement of male ducts, both species have unpaired ‘copulatory glands’ in some non-genital segments, and paired glands surrounding the male pores. Both species have spermathecae laterally placed, two segments anterior to the male pores (i.e. in IX or VII).

Inclusion of the new species within Kurenkovia would be problematic, as this would require a broadened definition of the genus to also accommodate a shift of reproductive organs by two segments, i.e. male and spermathecal pores in XI and IX, respectively, vs. IX and VII in K. magna . Kurenkovia magna also differs from the new species in that the vasa deferentia are partially embedded in the body wall (a character associated with Crassiclitellata or ‘megadriles’); moreover, it has unique structures (termed ‘rudimentary atria’) in VIII (Sokolskaya 1983: fig. 23-2). As the latter are not connected to the male ducts, they may resemble glandular structures in some species of Rhynchelmis Hoffmeister, 1843 ( Lumbriculidae ), or perhaps the prostate glands of some megadrile families.

Other characters of L. setoensis are atypical for the Lumbriculidae , but occur in some genera. Male and female pores are one segment posterior to the usual lumbriculid position in X– XI, with gonads beginning in X instead of IX ( Brinkhurst 1989). The spermathecal pores are anterior to the usual positions in the Lumbriculidae , and their lateral position is also uncommon, but not unknown in lumbriculids (e.g. Martinidrilus carolinensis Fend & Lenat, 2007 ). The lack of obvious pharyngeal glands, other than the two tubular organs described above, is certainly unusual, and the nephridia are composed of multiple conjoined tubules, apparently without the glandular, post-septal expansion typical of lumbriculids (cf. Fend and Brinkhurst 2010: fig. 4A). Unfortunately, it is difficult to assess details of these and other organs (e.g. the blood vessels) in the available material.

Despite erecting a new family for K. magna, Sokolskaja (1983) suggested the species could instead be attributed to the Haplotaxidae s.l. (as traditionally defined) on the basis of morphology. The simple male ducts are somewhat similar to those of Hologynus species (now in the Pelodrilidae ) where the posterior male duct has shifted forward; for example, Benham (1909) considered the posterior male pore of Hologynus aucklandicus (Benham, 1909) to be in XI, although it appears to be at the anterior margin of XII in figure 15 of that paper. The anterolateral placement of the spermathecal pores is also consistent with typical haplotaxids and pelodrilids.

As already mentioned, in the present phylogenetic analysis, L. setoensis is sister to the clade containing lumbriculids and hirudinean taxa, but as K. magna was not available for study, the relationship to that genus is unknown. Rather than compromise the status of Kurenkovia (or Kurenkovidae ), based only on limited morphological data, it seems best at this point to propose a new family, which is well supported by the molecular analysis.

Figures

Figure 1. Phylogenetic tree of Clitellata estimated with Bayesian inference in MrBayes, using a concatenated set of markers, i.e. 12S, 16S, COI, 18S, and 28S. The tree is rooted such that Parvidrilidae and Randiellidae (also Clitellata) appear as lineages outside the rest of the ‘Clitellata’ tree, a position strongly supported by the metagenomic analyses of Erséus et al. (2020). Haplotaxid like taxa are shaded.Support values at branches are posterior probabilities, scale represents expected number of changes/site. Capital letters at the end of the species codes in Haplotaxis indicate countries of origin.BEN: Benin, FR: France, GR: Greece, IT: Italy, JP: Japan, SE: Sweden, US: USA. Inset, photo of live specimen of Haplotaxis spSE in its natural habitat, soil soaked in groundwater, photo: Johan Wingborg, and photo of live specimen of Haplotaxis spBEN6, photo: Patrick Martin.

Figure 2. Comparison of anterior ends of haplotaxid-like worms analysed here, schematic figures with emphasis on somatic characters. C, F, and H are from the genetically analysed specimens, the other figures are based on individuals from the same site (and usually same date) as the analysed worms, but better fixed for morphology. A, Haplotaxis spUS2 from Corral Creek, Idaho, USA.Oral cavity of gut is contracted, muscular pharynx extends through two segments.B, Haplotaxis spJP2 from Gudari-numa, Aomori, Japan.Oral cavity of gut is expanded, muscular pharynx is shorter than in the Idaho specimen. C, Haplotaxis spJP1 from Kakida River, Shizuoka, Japan.Timm’s glands are larger than in (A) or (C), muscular pharynx is short.D, Haplotaxoides decipiens from Guadalupe Creek, California, USA.E, Ohtakiana kakidaensis from Kakida River, Shizuoka, Japan. F, Pelodrilus cf. darlingensis from Western Australia. G, Limpluvia setoensis from Asahina River, Shizuoka, Japan. H, undetermined Lumbriculidae, specimen CE32192, from Euchre Creek, Oregon, USA.

Figure 8. Limpluvia setoensis, drawings of worms from Seto River (A, D, E, F, G, I) and Asahina River (B, C, H). F, H, and I are from paratypes; others are from non-types. Alcohol was a poor tissue fixative for this delicate species, and morphological observations were largely based on non-sequenced specimens. A, anterior end, ventral view, showing pharynx and pharyngeal diverticula.B, anterior end, lateral view.C, ventral chaeta pairs, from left to right, segments IX, XIII, XIV.D, ventral chaeta pair in VI. E, nephridium. F, reproductive organs in a mated worm, lateral view.G, reproductive organs in a mated worm, ventrolateral view. H, male pores with associated gland, and anterior male duct, ventral view. I, reproductive organs in a partially mature worm, lateral view. All figures oriented with worm facing right.

Figure 9. Limpluvia setoensis, photos of worms from Asahina River (A–H) and Seto River (I, J). C, E, F, H, I, and J are paratypes, others are non-types.A–B, anterior end, lateral view, showing pharynx.B, detail of glandular mass on dorsal pharyngeal pad. C, ventral view of pharynx, arrows showing diverticula.D, nephridial ducts. E, spermathecal duct, ventral view. F, chaeta pairs, ventral (left) and dorsal. G–H, ventrolateral glands in VII; (G) ventrolateral view, (H) lateral view.I, male funnels and ventral gland surrounding male pores in XI.J, posterior vas deferens entering ventral gland in XI.