Leiochrides guangxiensis Lin, Garcia-Garza , Lin, & Wang, 2020,
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https://dx.doi.org/10.3897/BDJ.8.e59726 |
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lsid:zoobank.org:pub:16AE6297-A5BB-42E5-BACB-A2848756067C |
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https://treatment.plazi.org/id/76C6AAAD-B4C1-5EC6-990D-B68E727B1158 |
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Leiochrides guangxiensis Lin, Garcia-Garza , Lin, & Wang, 2020 |
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sp. n. |
Leiochrides guangxiensis Lin, Garcia-Garza, Lin, & Wang, 2020 sp. n.
Materials
Type status: Holotype. Occurrence: individualCount: 1; lifeStage: adult; Taxon: kingdom: Animalia; phylum: Annelida; class: Polychaeta; family: Capitellidae; genus: Leiochrides; specificEpithet: guangxiensis; Location: higherGeography: South China Sea; continent: Asia; waterBody: South China Sea; country: China; stateProvince: Guangxi Province; locality: the Beibu Gulf, off Guangxi Province ; verbatimDepth: 12 m; verbatimLatitude: 21.626°N; verbatimLongitude: 108.6376°E; Event: samplingProtocol: Grab sampler; eventDate: 27-10-2017; habitat: muddy sediment; Record Level: institutionID: Third Institute of Oceanography, Ministry of Natural Resources; institutionCode: TIO-MNR; basisOfRecord: PreservedSpecimen GoogleMaps
Description
Holotype (TIO-BTS-Poly-111) complete, but broken into four fragments. Anterior fragment (Fig. 2 View Figure 2 A) measuring 21.2 mm long by 1.7 mm wide for 40 chaetigers; two middle fragments with 25 chaetigers and 27 chaetigers, respectively; posterior fragment heavily coiled, measuring 63.1 mm long for more than 150 chaetigers. Color in alcohol tan on thorax (Fig. 3 View Figure 3 B) and whitish tan on abdomen. Prostomium short and conical, with blunt anterior end (Fig. 2 View Figure 2 A and 3B). Everted proboscis globular, with numerous minute papillae (Fig. 2 View Figure 2 B and 3B). Peristomium achaetous, wider than long, same length as chaetiger 1, but narrower (Fig. 2 View Figure 2 A and B). Eyespots not observed. Nuchal organs indistinct. Thorax areolated from peristomium to chaetiger 6 (Fig. 3 View Figure 3 B and C), weakly areolated on chaetigers 7-8, remaining segments smooth. Lateral groove distinct from chaetiger 2 to end of anterior fragment (Fig. 2 View Figure 2 A and 3A).
Thorax with an achaetous peristomium and 12 chaetigers (Fig. 2 View Figure 2 A, B and 3A). Chaetiger 1 uniramous, with only capillaries in notopodia (Fig. 2 View Figure 2 C). Chaetigers 2-10 with only capillaries in both rami (Fig. 3 View Figure 3 A). Chaetigers 11-12 transitional with notopodial capillaries and neuropodial hooks (Fig. 2 View Figure 2 D and 3E). Intersegmental grooves distinct in thorax, except between peristomium and chaetiger 1. Chaetigers 6-10 biannulate (more evident in lateral view), wider than long (Fig. 2 View Figure 2 A and B). Notopodia dorso-lateral in first chaetiger, gradually moving dorsally to end of thorax, and neuropodia ventro-lateral (Fig. 2 View Figure 2 A and B). Chaetal fascicles inserted just posterior to mid-line of thoracic segments (Fig. 2 View Figure 2 A and B). Notopodia of chaetigers 1-12 and neuropodia of chaetigers 2-10 each with 20-30 capillaries per fascicle; neuropodia of chaetigers 11-12 with approximately 50 hooks per fascicle. Thoracic hooks of similar shape to abdominal hooks, but shaft markedly longer. Lateral organs located between noto- and neuropodia, closer to notopodia in thorax and anterior abdomen, as small rounded pores (Fig. 3 View Figure 3 E); those in posterior abdomen indistinct. Genital pores not seen.
Transition between thorax and abdomen indistinct, marked by change in chaetal arrangement (Fig. 3 View Figure 3 A and E) and MGSP (Fig. 2 View Figure 2 A and B). Abdominal segments shorter than posterior thoracic chaetigers in anterior abdomen, tapering gradually to pygidium. Parapodial lobes slightly swollen in anterior abdomen (Fig. 3 View Figure 3 D and F), yet reduced in posterior abdomen (Fig. 3 View Figure 3 G and I). Notopodial hooks present from chaetiger 13 (first abdominal chaetiger). Notopodial lobes well separated throughout abdomen (Fig. 2 View Figure 2 A, B, E and F). From abdominal chaetiger 11, gap between notopodial lobes of same chaetiger becoming larger to end of anterior fragment (Fig. 2 View Figure 2 A). Chaetal fascicles positioned posterior to mid-segment in anterior abdomen (Fig. 3 View Figure 3 D and E), and near posterior edge of segment in posterior abdomen (Fig. 3 View Figure 3 G-I). Abdomen with hooks only, approximately 30 hooks per fascicle in notopodia and more than 100 hooks per fascicle in neuropodia.
Notopodial and neuropodial abdominal hooks similar along body, with long anterior shaft, developed shoulder, angled node, distinct constriction, and short hood (Fig. 2 View Figure 2 H); posterior shaft longer than anterior one, attenuated to terminal end (Fig. 3 View Figure 3 L). Hooks (Fig. 3 View Figure 3 M) with three rows of teeth above main fang: two large teeth in basal row, a larger median tooth, and four smaller teeth above basal teeth. Main fang subtriangular, longer than wide (Fig. 2 View Figure 2 I).
Notopodial branchiae present in posterior abdomen, located on posterior edge of segment, may be retractile (Fig. 3 View Figure 3 H-K). At first, notopodia with 3-6 papillary branchiae (Fig. 3 View Figure 3 H); towards the pygidium, the branchial lobes gradually increasing in number and length, and the largest branchial fascicle with up to 17 finger-shaped filaments (Fig. 2 View Figure 2 F); then decreasing in number to end of the body (Fig. 3 View Figure 3 J and K). More than 10 achaetous segments without branchiae before pygidium (Fig. 2 View Figure 2 G). Pygidium with four digitate anal cirri (Fig. 3 View Figure 3 J and K)
Methyl green staining: Dark blue stain from post-chaetal part of chaetiger 7 to chaetiger 10 (Fig. 2 View Figure 2 A); medium blue stain from peristomium to pre-chaetal part of chaetiger 7, as well as on chaetigers 11-12. Abdominal region without any distinct staining pattern (Fig. 3 View Figure 3 A).
Etymology
The specific name is derived from the type locality, Guangxi Province.
Distribution
Currently known from the Beibu Gulf, northern South China Sea.
Ecology
The new species inhabits shallow subtidal waters where sediment is characterized by high percentage of mud.
Taxon discussion
The taxonomic and ecological knowledge of this genus is very rare in China, although Leiochrides species have been previously recorded ( Liu 2008). This genus is characterized by having 12 thoracic chaetigers, of which the last one or two thoracic chaetigers may only have capillaries or be transitional with notopodial capillaries and neuropodial hooks ( Magalhães and Blake 2017). Our specimen in the present study agrees well with the generic diagnosis. Morphological characters used for the separation of species within this genus include the following: the number of transitional thoracic chaetigers, the shape of first chaetiger, the dentition of abdominal hooks, the number of anal cirri, and the presence/absence of branchiae on posterior abdomen. Amongst all described Leiochrides species worldwide, L. guangxiensis sp. nov. is closely similar to L. branchiatus Hartman, 1976 from the Bay of Bengal and L. deltaicus (Capaccinoi-Azzati & Martin, 1992) from north-western Mediterranean Sea in having the last two thoracic chaetigers transitional with notopodial capillaries and neuropodial hooks, uniramous chaetiger 1, and the presence of notopodial branchiae on posterior abdomen. However, L. guangxiensis sp. nov. differs from L. branchiatus in that abdominal hooks of the new species have seven teeth in three rows above main fang instead of three teeth in triangular arrangement as in L. branchiatus . L. guangxiensis sp. nov. can also be distinguished from L. deltaicus in the maximum number of branchial filaments per fascicle and the number of anal cirri. L. guangxiensis sp. nov. bears branchiae with up to 17 branchial filaments per fascicle and pygidum with four anal cirri, whereas in L. deltaicus , posterior abdomen has 2-4 branchial lobes per fascicle and pygidium with three anal cirri. As for MGSP, the new species stains dark blue from the postchaetal area of chaetiger 7 to chaetiger 10, medium blue on the remaining thoracic chaetigers, and light green staining on the abdomen, these characters being distinct from those of other Leiochrides species.
The dentition of abdominal hooks is widely used in capitellid taxonomy, as their ultrastructure is highly specific ( Hartman 1947). The characteristic feature of the genus Leiochrides is that abdominal hooks bear two larger teeth in the basal row above the main fang, although the number of small teeth may vary amongst Leiochrides species. Green (2002) pointed out that this mentioned character is conservative in Leiochrides species, as also present in species of Capitellethus and Leiocapitella . These three genera show similarities in general appearance and the difference amongst these genera is in relation to the number of thoracic chaetigers ( Magalhães and Blake 2017). In addition to one or two transitional chaetigers, the structural similarity of basal teeth in abdominal hooks amongst these three genera ( Capitellethus - Leiochrides - Leiocapitella complex) indicates that they might have a close taxonomic relationship, which should be reviewed as suggested by Green (2002) and Magalhães and Blake (2017). Molecular data should be incorporated to help verify their phylogenetic relationship in the future.
In this study, the taxonomic status of the genus Pseudoleiocapitella Harmelin, 1964 and Leiochrides norvegicus Fauchald, 1972 was found to be doubtful when reviewing the literature on capitellid species related to Leiochrides . The monospecific genus Pseudoleiocapitella was established by Harmelin (1964) for P. fauveli (see pp 90-92, Pl.Ⅺ, figs. 1-7 in Harmelin 1964), characterized by the uniramous chaetiger 1, chaetigers 1-10 with only capillaries, chaetigers 11-12 with notopodial capillaries and neuropodial hooks, and the absence of branchiae. The chaetal arrangement of Pseudoleiocapitella fauveli matches the expanded generic definition of Leiochrides proposed by Magalhães and Blake (2017), indicating it might be a Leiochrides species. Leiochrides norvegicus was described by Fauchald (1972), based on specimens from the deep Sognefjorden off western Norway. Fauchald (1972) assigned this species to the genus Leiochrides , due to the thorax with 12 chaetigers. However, L. norvegicus has the first two abdominal chaetigers with notopodial capillaries and neuropodial hooks, which did not match the generic diagnosis of Leiochrides . Observed from its chaetal arrangement in the anterior part, L. norvegicus actually bears 14 instead of 12 thoracic chaetigers, of which the last two thoracic chaetigers are transitional. If so, L. norvegicus should be a Leiocapitella species rather than a Leiochrides species. In addition to the number and location of transitional chaetigers, other morphological characters of L. norvegicus have also been found in the members of Leiocapitella , such as uniramous chaetiger 1 and the presence of branchiae on posterior abdomen ( Green 2002, Magalhães and Blake 2017). According to the above analysis, the genus Pseudoleiocapitella Harmelin, 1964 and Leiochrides norvegicus Fauchald, 1972 need a revision, and it would be necessary to examine the type materials of Pseudoleiocapitella fauveli and Leiochrides norvegicus .
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