Ohtakiana kakidaensis 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 : 22-25

Ohtakiana kakidaensis Fend & Torii sp. nov.

( Figs 2E , 6–7 )

ZooBank LSID: urn:lsid:zoobank.org:act:98055747-7DFF-4DFD-9961-B7EA8AEDE978

Holotype: NSMT An-1892: a mature worm, anterior end dissected, stained with borax carmine and slide-mounted, part of tail analysed for DNA (CE30883); COI DNA-barcode in GenBank (acc. no. PP988423 ); for other molecular data, see Table 1 .

Type locality: Japan, Shizuoka Prefecture, Kakida River , Doniwa, Shimizu-cho , Sunto-gun , 8 Jan 2010. Collected by T. Torii .

Paratypes: NSMT An-1893-1896 , from the type locality, 19 Aug 2008; one mature whole mount. 8 Jan 2010; one mature worm, anterior end and part of tail stained with hematoxylin, dissected, and slide mounted, part of tail analysed for DNA (CE30882) and for molecular data, see Table 1 ; one mature worm, dissected on slide; one immature worm with small gonads, whole mounted. All collected by T. Torii.

Etymology

From the Kakida River.

Description

Length of mature, preserved worms up to 40 mm; diameter 1.2– 1.5 mm in anterior segments, 1.1 mm in posterior segments; 94–105 segments ( Fig. 6A ). Prolobous, but prostomial groove may be faint; prostomium rounded-conical, length shorter than or about equal to width ( Fig. 7A, B ). Peristomium not elongate. Secondary annulation a very narrow anterior ring from IV or V ( Fig. 6A ), gradually increasing to more than 1/3 of segment length by mid-body, and up to 1/ 2 in posterior segments; furrows distinct anteriorly, less conspicuous from about XV. Epidermis to 40 μm thick and columnar in prostomium, vacuolated and 10–20 (median 12) μm thick in next few segments; cuticle about 1 μm. In middle and posterior segments, epidermis of posterior (setigerous) ring darkly staining (hematoxylin), 10–12 μm thick with large vacuoles; thinner in anterior ring (5–10 μm) and not darkly staining ( Fig. 7D, E, H ). Clitellum indistinct in external view, from about IX to XVI, but glandular epidermis may extend to XX; clitellar epidermis to 25–45 μm thick in two specimens. Secretory area of ventral glands on the ventral midline, one gland within the posterior annulus of each mid-body and posterior segment; secretory area may appear as a flat disk (to about 0.2 mm diameter) or may be produced as a low tubercle ( Figs 6A , 7D, E ). All chaetae paired, simple-pointed, without obvious keel or other ornamentation; chaetae sigmoid with a faint nodulus, thickness 6–10 μm anteriorly, to about 15 μm in posterior segments ( Figs 6C–F , 7F, G ). In anterior segments, ventral chaetae 180–260 μm long; in posterior half of body, ventrals 215–315 (mostly> 260) μm; dorsals slightly shorter and thinner. Chaetal formula (aa:bc:dd) in anterior and middle segments about 1:1:1.5 or 1:1:2; dorsal chaetae closer to lateral line than are ventral chaetae in anterior segments; on the lateral line in posterior segments. Chaetae in genital segments not modified.

Brain in peristomium ( Fig. 7B ). Septa indistinct anteriorly, thicker from 4/5. Pharynx II-III or IV, thickened and concave dorsally, forming a slight pouch, but otherwise not modified; pharyngeal glands (IV)V–VII(VIII) ( Figs 2E , 7C ). Chloragogen layer thin, beginning on gut by about VII; may be indistinct in posterior segments, and not apparent on blood vessels.

Blood-vascular system simple, without hearts, parietal vessels or subneural vessel. Long, convoluted commissural blood vessels in anterior segments. Dorsal blood vessel prominent, appressed to gut posterior to about VI; ventral blood vessel thin, between gut and ventral nerve cord. Other blood vessels difficult to see, but most posterior segments with one pair of lateral vessels, thin and convoluted dorsally, and straighter and thicker in ventral half. Nephridia difficult to see in available material; may be present in VIII and in many post-clitellar segments. Nephridial funnel small; postseptal part composed of long and convoluted tubules; for most of their length tubules paired or joined in ribbon-like clusters of four or more, forming loops extending to near dorsum ( Fig. 7K, L ), and terminating in a simple pore just anterior to ventral chaetae.

Midventral glands in XI–XII of mature worms, weak or absent for the next several segments, then well-developed in all segments posterior to about XXV; glands composed of a circular cluster of multicellular lobes, with individual cell extensions joining the external secretory surface; lobes of glands go to either side of the ventral nerve cord ( Figs 6C–F , 7I, J ). Each gland with 10 or more lobes 100–200 μm high, forming a mass to 250 μm wide in XI–XII and at mid-body, but smaller in other segments. No obvious glands in dorsal part of segment; no large glands associated with the chaetae. A single immature worm with small glands in XXII, larger glands, to about 200 μm wide, from about XXX.

Spermathecal pores inconspicuous, oval openings on lateral line, at 5/6, 6/7, and 7/8 ( Fig. 6B ). Spermathecae extend into VI, VII, and VIII, via short ducts (40–60 μm long by 30–40 μm diameter); ampullae of mated worms ovate, increasing in size from VI–VIII; the largest to 600 × 250 μm ( Fig. 6B ). Spermathecal ampullae with thick (20–50 μm), somewhat vacuolated epithelium; sperm in ampulla loosely clumped, but not associated with the epithelium, and not forming distinct arrangements.

Octogonadal, with two pairs of testes and two pairs of ovaries in consecutive segments. Testes small and narrow, extending to mid-segment in X and XI. Mature worms with sperm filling segment X, but no anterior sperm sacs; posterior sperm sacs extend as far back as XV or XVI. Male funnels on 10/11 and 11/12, slightly extending into anterior segment; male ducts plesiopore, about 500 μm long by 30 μm in diameter; winding, leading to simple and inconspicuous pores just anterior to ventral chaetae, in region of midventral glands ( Fig. 6B ).

Ovaries small, in XII and XIII; egg sacs with large, yolky eggs may extend 1 or 2 segments behind sperm sacs. Female funnels on 12/13 and 13/14; ducts plesiopore, simple and straight, about 150 μm long, leading to inconspicuous pores at the annular groove of the posterior segment, between ventral chaetae and anterior septum in XIII and XIV ( Fig. 6B ).

Guts were densely packed with dark organic matter, consisting of fine particles in one specimen; of coarser fragments/ pieces (30–150 μm diameter) in the other worms, and mixed with some small mineral particles and a few diatoms.

Site descriptions

The Kakida River is located on the southern slope of Mt Fuji in Shizuoka Prefecture. Although only 1.2 km long, it is regarded as one of the clearest major streams of Japan. The spring water is derived from the rainfall and snow on Mt. Fuji and flows at 7000 to 1 million tons of water per day.

Remarks

Morphology associates Ohtakiana kakidaensis with genera formerly assigned to the Haplotaxidae (s.l.) on the basis of their rather simple male ducts, but lacking the muscular pharynx, unpaired chaetae, and elongate body of Haplotaxis . Despite this general similarity to the genera newly assigned here to the Pelodrilidae, DNA results ( Fig. 1 ) suggest a separate family-level classification. Given the limited material available for morphological comparison, the only consistent diagnostic character separating Ohtakiana from Pelodrilidae specimens examined by us (as defined above) appears to be the prominent midventral glands in middle to posterior segments. By itself, this character is hardly convincing as a diagnostic character, given the general similarity of these glands to those in other clitellate taxa, e.g. the unknown Lumbriculidae sp. described below.

The species currently attributed to Pelodrilus ( Australia, New Zealand, South Africa, and central Asia) differ from Ohtakiana kakidaensis in having a single ovarian segment, intersegmental female pores, and usually a single spermathecal segment. Some Pelodrilus species have the anterior male pores shifted back behind the chaetae within XI, or even into XII in the type species, Pelodrilus violaceus . The five species of Delaya usually have three spermathecal segments, two ovarian segments, and two pairs of male pores located near the ventral chaetae in XI and XII, respectively. Large copulatory glands, paired and ventrolateral, are associated with ventral chaetae in or near the genital segments (VII, VIII, or IX to XII or XIII); these glands are compact ( Hrabě 1958: fig. 10) rather than multi-lobed. Species assigned to Hologynus , from Australia, New Zealand, and associated islands, differ from the new species in having male pores exiting close together in XI and XII, within large, ventral glands (Benham 1909: fig. 15, Michaelsen 1925: fig. 2). Most Hologynus species have only one spermathecal segment.

Other pelodrilid-like genera have been associated with the Haplotaxidae s.l. ( Omodeo 1987, Brinkhurst 1988), but specimens of these were unavailable for the present analysis; these include Alphadrilus smithii from New Zealand; Adenodrilus denticulatus from central Asia; and Omodeodrilus guanivorus from Guinea. Alphadrilus was described as having morphologically similar male and female ducts ( Brinkhurst 1966), in contrast to Ohtakiana (and the pelodrilid genera), where the male ducts are more elongate than the female ones. Adenodrilus denticulatus seems easily separated by a combination of bifid chaetae, long and slim tubular copulatory glands, a forward shift in gonad sequence to IX–XII (instead of X–XIII), and a single spermathecal segment with dorsal pores ( Čekanovskaja 1959) The gonad sequence is also shifted anteriad in O. guanivorus ; however, that species has only one testicular segment (in X) ( Omodeo 1987).

With regard to the known Japanese fauna, the reproductive organs of O. kakidaensis appear most similar to those of Heterochaetella glandularis , known from the Mino-o River, Osaka Prefecture (also in southern Japan). The two species also appear similar in general habitus, the simple pharynx, and the secondary annulation. Heterochaetella glandularis was assigned to a monotypic genus based on three unique characters: multicellular glands associated with dorsal chaetal bundles, clubshaped unicellular glands projecting into the coelom from the body wall, and each chaetal pair consisting of a large bifid and a smaller simple-pointed chaeta ( Yamaguchi 1953: figs 17–18). Thus, although it was described from the same region, both the genus and species names are derived from unusual somatic characters not shared with O. kakidaensis . Heterochaetella glandularis also differs from the new species in having four spermathecal segments (VI–IX), and it lacks the large ventral glands in reproductive and posterior segments. The distribution of chloragogen tissue is also unusual in Heterochaetella glandularis ; the cell layer is conspicuously thick, but limited to the surface of the dorsal blood vessel ( Yamaguchi 1953: fig. 11).

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 6. Ohtakiana kakidaensis from Kakida River, Japan.A, a whole worm, specimen CE30882 (Paratype, NSMT An-1895), showing robust habitus. B, reproductive organs in segments VI–XIV, CE30883 (Holotype, NSMT An-1892). C–F, midventral gland and ventral chaetae, from CE30883 (Holotype); (C) in XII, (D) in XXXVIII, (E) in mid-body (also showing dorsal chaetae), (F) in a tail segment.

Figure 7. Ohtakiana kakidaensis from Kakida River, Japan.A, D, E, stained with hematoxylin, others stained with carmine; (H) is from the holotype, CE30883 (NSMT An-1892), the other figures are from two of the non-sequenced paratypes. A, anterior end of unmounted worm. B, head of whole mounted worm, showing prostomium, mouth, brain, blood vessels.C, cleared whole mount, showing pharyngeal glands in IV–V (note the narrow anterior annuli in this region). D–E, middle segments of unmounted worm, facing right (D) ventrolateral view, (E) lateral view (ventral side up), showing secretory surfaces of midventral glands in the posterior annuli of middle segments (note the wide anterior and darkly stained posterior annuli). F–G, paired chaetae in anterior segments, (F) dorsal, (G) ventral. H, epidermis in post-clitellar segment, with anterior (right) and posterior annulus in one segment (dorsal edge above, surface view below). I–J, midventral glands in midbody, from dissected worm. K–L, Nephridia; (K) is lateral view of ducts and funnel; (L) an optical section of conjoined postseptal ducts.