Dinophilus sp.

Jimi, Naoto, Minokawa, Takuya, Miura, Toru & Kajihara, Hiroshi, 2020, Meiobenthic Polychaete Dinophilus sp. cf. gyrociliatus (Annelida: Dinophilidae) from Japan with SEM Observation and DNA Barcodes, Species Diversity 25, pp. 213-218 : 214-217

publication ID	https://doi.org/ 10.12782/specdiv.25.213
persistent identifier	https://treatment.plazi.org/id/FB2087DE-9E78-1908-FC32-FE9FD5EEFB41
treatment provided by	Felipe
scientific name	Dinophilus sp.
status

Treatment

Dinophilus sp. cf. gyrociliatus Schmidt, 1857 ( Figs 1–4 View Fig View Fig View Fig View Fig )

? Dinophilus conklini: Uchida 1972: 29–34 View in CoL , fig. 1 [from an aquarium in Hokkaido University , which contained bryozoans collected from Akkeshi, Hokkaido, Japan, 2 m in depth] .

Material examined. ICHUM 6114 View Materials , 12 female specimens, mounted on a stub for SEM observation, 25 May 2017, collected by the second author, from an aquarium of the Research Center for Marine Biology, Tohoku University . ICHUM 6115 View Materials , 6 female specimens, mounted on a stub for SEM observation, 2 March 2019, collected by third author, from an aquarium of the Misaki Marine Biological Station, The University of Tokyo . Non-deposited specimens, 20 female specimens, whole specimens were used for molecular work, cultured from one parent specimen that was collected from the aquarium by the second author.

Brief description. Female. Body about 500–900 µm long, 100–250 µm wide in the cephalic part, cylindrical, segmentation obscure ( Figs 1A View Fig , 2A View Fig , 3A View Fig ), whitish or transparent in life ( Fig. 1A, B View Fig ), whitish in ethanol, no pigmentation. Prostomium rounded, palps and tentacles absent. Eyes present, one pair, reddish in life, oval ( Fig. 1A View Fig ). One pair of prosto- mial compound cilia present on apical head ( Figs 2B View Fig , 3B View Fig ). Eight transverse ciliary bands on dorsal side: first band Vshaped from dorsal view, with its backward-directing corner having only a few cilia on median line; second band having wide gap on its mid-dorsal portion, band present only outside of two eyes ( Figs 1A View Fig , 2B View Fig , 3B View Fig ); six posterior bands, with one band in each segment, having no mid-dorsal gap ( Figs 2A View Fig , 3A View Fig ). Ventral side of cephalic region ciliated ( Figs 2C View Fig , 3C View Fig ). Single, continuous, mid-ventral, longitudinal ciliary band running throughout body length ( Figs 2D View Fig , 3D View Fig ). A pair of nuchal organs present between second and third ciliary bands ( Fig. 2E View Fig ). Pygidium conical; anus situated dorsally; several cilia present around anus ( Fig. 2F View Fig ). Stomach yellowish. Eggs in posterior part of body ( Fig. 1A View Fig ).

Male. Body about 30–50µm long, 20–40 µm wide, transparent in life, oval, like a trochophore larva of annelids ( Fig. 4A View Fig ). Anterior end and all ventral side ciliated ( Fig. 4B View Fig ). Male inhabits in an egg capsule together with a female larva ( Fig. 4C View Fig ) and remains after the female gets out of the capsule ( Fig. 4D View Fig ).

Genetic sequence. Sequences of 16S ( RCMB, DDBJ LC545953 View Materials , 455 bp; MMBS, DDBJ LC545954 View Materials , 455 bp) and COI ( RCMB, DDBJ LC545951 View Materials , 658 bp; MMBS, DDBJ LC545952 View Materials , 658 bp) were determined from a female in the present material of Dinophilus sp. cf. gyrociliatus . Sequences of RMCB specimens differ by 0.009 (16S) and 0.118 ( COI) in terms of K2P distance from MMBS specimens. Our sequences differ by 0.019 (16S) and 0.148 –0.174 ( COI) in terms of K2P distance from China and USA specimens ( Table 1) ( Dahlgren et al. 2001; David and Halanych 2017).

Remarks. We could not find any morphological difference between the RMCB and MMBS specimens. Our morphological data suggest that our material is likely to be the same as Dinophilus conklini sensu Uchida (1972) , but may be different from D. conklini s. str. and D. gyrociliatus s. str. Assessing the precise taxonomic identity of our material requires detailed information about morphology and DNA barcode for D. conklini s. str. and D. gyrociliatus s. str. These ‘ s. str. ’ data should preferably be based on topotype specimens for each nominal species; namely, from Northeastern US ( D. conklini ) and the Faroe Islands ( D. gyrociliatus ), respectively. Unfortunately, such data are currently unavailable, making our taxonomic decision inconclusive. Meanwhile, we follow Shearer (1912) and Fauvel (1927) to regard D. conklini as synonymous with D. gyrociliatus .

The morphological similarity between our material and Dinophilus conklini sensu Uchida (1972) pertains the arrangement of ciliary bands in that i) the first band is Vshaped from dorsal view; ii) mid-dorsally, there is only a few cilia at the corner of the V-shaped first band; iii) there is a distinct gap on the mid-dorsal portion of the second band; and iv) the eyes are situated within the range of this gap, although slightly anterior to the level of the second band. The last character state is different from that of D. conklini s. str., in which the eyes may be situated outside the range of the gap ( Nelson 1907). Our present specimens from Asamushi showed sexual dimorphism, and thus are referable to D. gyrociliatus s. lat. Morphologically, our material possessed i) one ciliary band per a segment and ii) six posterior bands, which are also characteristic of D. gyrociliatus s. lat. ( Nelson 1907; Jones and Ferguson 1957). Dinophilus conklini was supposed to be different from D. gyrociliatus by having a mid-dorsal gap on the first and second ciliary bands, but some of the previous researchers (e. g., Shearer 1912; Fauvel 1927) regarded these gaps as representing intraspecific variation and synonymized D. conklini with D. gyrociliatus .

As of writing, there are two 16S entries ( AF380116 View Materials : Dahlgren et al. 2001; MG428625 View Materials , partial mitochondrial genome: David and Halanych 2017) available in public databases that are referable to the genus Dinophilus . Their source materials, both identified as D. gyrociliatus , were collected in Xiamen, China ( Dahlgren et al. 2001) and Beaufort, North Carolina, USA ( David and Halanych 2017), instead of the Faroe Islands, the type locality of the species ( Schmidt 1857); the sequences from China ( AF380116 View Materials ) and the USA ( MG428625 View Materials ) are exactly the same. The genetic distance between the 16S sequences from Asamushi and China / USA was 0.019 (K2P), approaching those values for interspecific variations recorded for nine other annelid families (0.012–0.26) ( Nygren 2014). These values imply that those dinophilids may represent biologically different ‘species,’ but more data should corroborate any conclusion. Measuring intra- and interspecific variations—in terms of both molecular sequence and morphology—is indispensable for future DNA taxonomy in Dinophilus . Besides, the species may be truly cosmopolitan, invasive species, or contamination (cf. Worsaae et al. 2019) occurring in China and USA. In this paper, we regarded the Japanese specimens as a single species. However, future studies are necessary for verifying the taxonomic identity of “ D. gyrociliatus ” worldwide.

Sudzuki and Sekiguchi (1972) reported dinophilids under the name of D. gyrociliatus from an aquarium of Tokyo University of Education (now University of Tsukuba), Tokyo, Japan. Sudzuki and Sekiguchi (1972) wrote that “All the ventral side of the body are densely ciliated”, which is also illustrated with line drawings ( Sudzuki and Sekiguchi 1972: textfig. 10F, H). They are thus different from our specimens, in which the mid-ventral ciliary band is more or less restricted to the median line ( Fig. 2C, D View Fig ).

Uchida (1972) argued that the ciliary-band morphology would be consistent within a species, and that it could be a useful character to discriminate different species in Dinophilus . To test Uchida’s (1972) hypothesis, DNA-taxonomic studies should be performed based on a number of specimens from as wide geographic area as possible, each of which must be examined in terms of the ciliary pattern with SEM. Such studies will confirm the taxonomic utility of the ciliary-band pattern, elucidating the extent of the intra- and interspecific variation. For proper application of the species names, topotype specimens for the existing nominal taxa should also be included in future studies.