Oerstedia fuscosparsa Abato & Yoshida & Kajihara 2023
Creators: name: Abato, Jamael
name: Yoshida, Ryuta
name: Kajihara, Hiroshi
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Nemertea
Hoplonemertea
Monostilifera
Oerstediidae
Oerstedia
Oerstedia fuscosparsa

description: Oerstedia fuscosparsa sp. nov.
(Figs 1, 2)
Material examined. ICHUM 8405, holotype; ICHU 8406, paratype.
Sequences. From holotype: see Table 1. From paratype: OP256563 (16S), OP256565 (28S), OP265742 (COI), OP253977 (H3).
Description. External features of holotype in living state (Fig. 1A, B, E, F). Body 7.9 mm long when stretched, width 0.6 mm, cylindrical, slender, firm, narrowing at anterior and posterior ends, with pale-yellow background postcerebrally (Fig. 1A, B). Head bluntly round anteriorly in dorsal view, not demarcated from body, whitish opaque in background colour, ornamented with a few, small, brownish dots on tip; single, wide, brownish, transverse cephalic colour band encircling all around head, with posterior edge mid-dorsally directing backward (Fig. 1E, F); another transverse colour band encircling posterior portion of head, deep brown in colour, mid-dorsally notched at anterior edge, situated post-cerebrally at short distance from cephalic colour band except on mid-ventral portion where these two bands are continuous (Fig. 1E, F); cephalic furrow not notable; with four squarely arranged orange ocelli contained within transverse cephalic colour band (Fig. 1E). Behind deep-coloured post-cerebral transverse colour band, additional 18 transverse bands present throughout body from posterior region of head to tail end, tightly arranged one after another, consisting of brown flecks; single, deep brown spot present on mid-dorsal portion of each of 18 bands (Fig. 1A).
External features of paratype in living state (Fig. 1C, D, G, H, I). Body 10 mm in length, 0.6 mm in width; tip of head less pigmented than holotype; posterior end of body narrowed (Fig. 1C, D); cephalic colour band light brown; post-cerebral colour band lighter than that of holotype, with anterior edge mid-dorsally projected forward but not continuous with cephalic colour band on any place (Fig. 1G, H); ocelli more clearly visible with anterior pair smaller than posterior (Fig. 1G, H, I). Body covered with brown patches (Fig. 1C, D), but transverse banding pattern not apparent in posterior body; without mid-dorsal deep brown spots (Fig. 1C).
Internal morphology in paratype. Proboscis nerves not distinct (Fig. 2A). Central stylet 42.0 µm in length; basis 36.7 µm in length, 11.2–15.2 µm in width, cylindrical in shape, bluntly round posteriorly; two accessory pouches, each containing 5–7 accessory stylets (Fig. 1J). Accessory lateral nerves present (Fig. 2B).
Etymology. The new specific name is a participle of the 1st/2nd declension (- us, - a, - um), a combination of the Latin words fuscus (meaning “dark”, “dim”, “black”, “brown”) and sparsus (“scattered”, “sprinkled”, “spotted”, “freckled”; from the verb spargo, meaning “[I] scatter”). In combination, fuscosparsa pertains to the the brownish spots/freckles scattered throughout the body of the species.
Diagnosis. An Oerstedia with a brownish cephalic colour band, a deep brown post-cerebral colour band in the posterior head region, and four orange ocelli. Post-cerebrally, the body is sprinkled with brownish aggregated spots or freckles in pale-yellow background forming transverse bands. Internally, the proboscis nerves are not distinct and accessory lateral nerves are present.
Type locality and distribution. At present, the species is only known from its type locality along the Pacific coast of Honshu, off Kouyatsu, Tateyema, Chiba, Japan, between 34°59.293′ N, 139°48.59′ E and 34°59.094′ N, 139°48.195′ E, 11–18 m deep, mudstone and sandy bottom; the in-situ water temperature was 18–20°C when the holotype and the paratype were collected by Ryuta Yoshida. From this place, Tetrastemma parallelos Abato, Yoshida & Kajihara, 2022 has also been collected (Abato et al. 2022).
Genetic distance and molecular phylogeny. The two specimens of O. fuscosparsa sp. nov. reported in this paper would belong to the same species with uncorrected COI p -distance value of 0.004 (0.4%) as to the 658-bp partial COI region, much lower than the 3%-rule COI genetic distance to infer that two ribbon worms are of different species (Sundberg et al. 2016). We therefore regard that the difference in pigmentation pattern observed between the two individuals in this paper is an intraspecific variation commonly observed among other Oerstedia species.
The phylogenetic analysis shows that our species forms a highly supported subclade with Oerstedia species collected from Simushir, O. dorsalis sensu Iwata, and O. phoresiae. Further, it indicates that O. fuscosparsa sp. nov. is sister to O. phoresiae, suggesting its placement within the Paroerstediella clade sensu Chernyshev & Polyakova (2022) of the genus Oerstedia (Fig. 3). This also means that our species is more closely related to O. phoresiae than to O. dorsalis s.str. and is grouped with other species from the Northwest Pacific. COI p -distances between our species and O. phoresiae and with O. dorsalis s.str. is 8.5% and 11.9%, respectively.
Taxonomic remarks. Of the 29 valid species of Oerstedia, two species have previously been known to possess transverse bands in the body; these are O. oculata and Oerstedia striata Sundberg, 1988, from both of which O. fuscosparsa sp. nov. can be distinguished in external features. Oerstedia polyorbis (Iwata 1954; Chernyshev 1993; Akhmatova et al. 2012) and O. striata are banded only dorsally, unlike O. fuscosparsa sp. nov. in which the bands are dorsoventrally continuous. In addition, one of the colour morphs of Oerstedia dorsalis s.l. (called “morph n”) was described to contain reddish-brown stripes/blotches transversally, although details on the continuity of these stripes were not given in Sundberg et al. (2009). However, these two “morph n” specimens are not closely related to the new species as supported by the phylogenetic analysis, with these “morph n” specimens being placed in a different clade (Fig. 3).
DNA-based taxonomy for the members of the genus Oerstedia seems to be indispensable for the reliable establishment of new species since polymorphism and intraspecific variation are predominant among the species in the genus (Bürger 1895; Brunberg 1964; Sundberg 1984, 1988; Envall & Sundberg 1993; Sundberg & Andersson 1995; Zaslavskaya & Chernyshev 2008; Sundberg et al. 2009; Akhmatova et al. 2012). Polymorphism and intraspecific variation in Oerstedia often result in problematic taxonomy; these can hide some cryptic species or mistakenly be used as evidence for species delineation (Sundberg 1998; Sundberg et al. 2009; Akhmatova et al. 2012). The two specimens of Oerstedia fuscosparsa sp. nov. reported in this paper show distinct pigmentation patterns in the head and body; the holotype has deep brownish cephalic pigmentation, apparent transverse bands in the body, and deep brownish spots mid dorsally while the paratype has light brown cephalic pigmentation, no obvious transverse bands in the posterior body, and no deep brownish spots mid-dorsally.
In traditional Oerstedia taxonomy, these obvious pigmentation differences could have been treated as evidence for different species (Iwata 1954; Kulikova 1987; Chernyshev 1993; Sundberg et al. 2009); however, the COI barcode sequences from the holotype and the paratype strongly suggested that both would belong to the same species despite the differences in external appearance. Here, we demonstrate, using our species, the necessity and importance of DNA-based taxonomy in the genus Oerstedia. The taxonomy of other selected polymorphic congeners of the genus has been verified using barcode sequences of these species (Sundberg & Andersson 1995; Strand & Sundberg 2005; Akhmatova et al. 2012). Utilizing barcode sequence data from these species has resolved inaccurate taxonomic reports established based only on internal and external morphology (Sundberg 1984, 1988; Sundberg & Janson 1988; Sundberg & Andersson 1995; Zaslavskaya & Chernyshev 2008; Akhmatova et al. 2012). With the recent developments in Oerstedia taxonomy, it is, therefore, appropriate to investigate polymorphism and intraspecific variation in those already named species using both morphological and barcode sequence data.
description: Published as part of Abato, Jamael, Yoshida, Ryuta & Kajihara, Hiroshi, 2023, Species description and phylogenetics of Oerstedia fuscosparsa sp. nov. (Nemertea: Monostilifera: Oerstediidae) from Japan, pp. 589-597 in Zootaxa 5249 (5) on pages 592-595, DOI: 10.11646/zootaxa.5249.5.6, http://zenodo.org/record/7701406