A new species and a new species record of Orbiniidae Hartman, 1942 (Annelida, Polychaeta) from China

Abstract A new species of the orbiniid genus Phylo Kinberg, 1866, P.heterochaetussp. nov., is described based on material collected from the northern Yellow Sea, China. This is the thirteenth species in Phylo. The new species can be easily identified by the combination of the following characters: anterior thorax with 13 chaetigers, interramal cirri absent, anterior thoracic neuropodia with 4 or 5 rows of uncini, intermixed with a few subuluncini in the first 1 or 2 rows, and a ventral fringe of numerous stomach papillae present on chaetigers 12–24. Phylofimbriata is recorded for the first time from China seas.


Introduction
Phylo Kinberg, 1866belongs to Orbiniidae Hartman, 1942 and differs from the other genera of that family in having species with modified spines on posterior thoracic chaetigers. Although species of Phylo are closely related to Orbinia species based on molecular analyses (Bleidorn 2005;Bleidorn et al. 2009), Phylo is retained as a genus because the presence of posterior thoracic modified spines is a distinctive and easily recognized characteristic for species of Phylo (Blake 2017). Hartman (1957) reviewed this genus and described four species in detail, including the type species, P. felix Kinberg, 1866. Subsequently, Day (1961, 1977, Mohammad (1980), Hartmann-Schröder and Rosenfeld (1990), and Blake (2017Blake ( , 2020Blake ( , 2021 described additional Phylo species. According to this literature, 14 species of Phylo are currently recognized and considered valid (Blake 2021;Read and Fauchald 2021).
The genus Phylo is characterized as follows: branchiae first present from chaetiger 5-7; thoracic neuropodia fringed, with several postchaetal lobes; posterior thorax and anterior abdominal chaetigers with subpodial lobes, usually forming a ventral fringe; thoracic neurochaetae including blunt uncini or subuluncini and crenulated capillaries; posterior thoracic chaetigers with modified spines.
According to Liu (2008), four species have been documented from Chinese waters: Phylo felix, Phylo ornatus (Verrill, 1873), Phylo kupfferi (Ehlers, 1874), and Phylo nudus (Moore, 1911). We checked specimens previously identified as P. felix deposited in the Marine Biological Museum of the Chinese Academy of Science and found the report of the species from Chinese waters to be a misidentification. These specimens were identified as a new species, which is described and illustrated in this study. Additionally, we describe and illustrate Phylo fimbriata based on specimens collected from the East China Sea. This is the first record of P. fimbriata from Chinese waters.

Material and methods
Material checked in this study was collected from the northern Yellow Sea and East China Sea and deposited in the Marine Biological Museum of Chinese Academy of Science, with a few specimens retained by the present college of the first author (Yancheng Teachers University, YCTU). All the specimens were preserved in 75% ethanol solution. Detailed morphological structures were examined under a Zeiss Stemi 2000-C stereomicroscope. Photography and line drawings were made using an AxioCam MRc 5 digital camera attached to a stereomicroscope and a compound microscope. Specimens were stained with rose bengal to observe details of parapodial lobes and subpodial lobes. For SEM observations, selected parapodia were detached from the specimens, rinsed in absolute ethanol, dehydrated, coated in gold, observed, and photographed using a scanning electron microscope.
The following abbreviations are used: Description. All specimens incomplete, posterior end missing, holotype with 60 chaetigers, 34 mm long and 5 mm wide. Body elongate, about same width throughout; thorax depressed, abdomen cylindrical.
Etymology. The species is named for the thoracic neuropodia with two kinds of uncini. Type locality. Northern Yellow Sea, China.
Remarks. This species is unusual in the genus in having anterior thoracic neuropodia with 5 or 6 rows of uncini intermixed with a few subuluncini in the first 1 or 2 rows. Phylo heterochaetus sp. nov. is similar with P. ornatus (Verrill, 1873) for: 1) anterior thoracic neuropodia with rows of uncini, 2) lacking interramal cirri, 3) anterior thorax with 13 or 14 chaetigers. They can be easily distinguished by 1) species of P. heterochaetus sp. nov. with 4-8 posterior thoracic chaetigers, while the latter species with 13 or more chaetigers; 2) species of P. heterochaetus sp. nov. with 10 or 11 subuluncini intermixed with first 2 rows uncini, while the latter species lacks subuluncini; 3) modified spines hastate in P. heterochaetus sp. nov. and acicular in P. ornatus.
Prostomium short, conical, tapering to rounded tip; eyepots absent; nuchal organs narrow groove at junction with peristomium. Peristomium an asetigerous segment, distinctly separated from prostomium and chaetiger 1; mouth with anterior oral lip arising from posterior margin of peristomium, posterior oral lip from anterior margin of chaetiger 2. Proboscis everted, consisting of 2 large, inflated lobes.
Both thoracic notopodia and neuropodia with fringed postchaetal lobes; notopodium half as broad as the neuropodium, broadly palmate (Figs 4A, 5A). Notopodia with single conical postchaetal lobe from chaetiger 1, increasing gradually to about 6 lobes on posterior thoracic chaetigers; postchaetal lobes equivalent in size and shape on anterior chaetigers, with inner lobe separate and becoming longer than the outer ones on the posterior chaetigers (Fig. 4A, C). Abdominal notopodial postchaetal lobe arising from narrow base, broadly triangular (Fig. 4B).
Pygidium not observed. Distribution. East China Sea (China); Suruga Bay, Miyagi Prefecture (Japan). Remarks. Phylo fimbriata (Moore, 1903), which was first reported by Moore (1903) from Suruga Bay and North Japan, has fringed postchaetal lobes on the thoracic notopodia unlike most species of Phylo. Okuda (1937) redescribed this species based on specimens from Miyagi Prefecture. The morphology of present specimens agrees well with the original description of specimens from Japan.