Bathychloeia cf. sibogae Horst, 1910

Neal, Lenka, Wiklund, Helena, Gunton, Laetitia M., Rabone, Muriel, Bribiesca-Contreras, Guadalupe, Dahlgren, Thomas G. & Glover, Adrian G., 2022, Abyssal fauna of polymetallic nodule exploration areas, eastern Clarion-Clipperton Zone, central Pacific Ocean: Amphinomidae and Euphrosinidae (Annelida, Amphinomida), ZooKeys 1137, pp. 33-74 : 33

Bathychloeia cf. sibogae Horst, 1910

Figs 6A-F , 7A-G , 8A-E , 9A-H , 10A, B

Material examined.

NHM_6880HW, NHMUK ANEA 2022.632, coll. 12/05/2021, box core, 10.3244, -117.1875, 4280 m, NORI-D, http://data.nhm.ac.uk/object/06f82805-e608-4715-af62-ab1d44df2a79; NHM_0821, NHMUK ANEA 2022.633, coll. 20/02/2015, EBS, 12.53717, -116.60417, 4425 m, UK-1, http://data.nhm.ac.uk/object/73a7200a-ae19-4c0c-8381-8d4509a318cf; NHM_2906, NHMUK ANEA 2022.634, coll. 20/02/2015, EBS, 12.53717, -116.60417, 4425 m, UK-1, http://data.nhm.ac.uk/object/d3848fcf-4cb2-49fd-b49c-e09422419a70; NHM_2115, NHMUK ANEA 2022.635, coll. 20/03/2015, EBS, 19.46457, -120.02542, 4026 m, UK-1, http://data.nhm.ac.uk/object/2cbc0d92-247c-4197-bd7a-4715adb5e8f4; NHM_3539, NHMUK ANEA 2022.636, coll. 02/03/2020, box core, 14.11729, -116.46109, 4148 m, OMS, http://data.nhm.ac.uk/object/083df63d-60e7-48ae-95c4-6a11a61b01e8; NHM_8922, NHMUK ANEA 2022.637, coll. 14/05/2018, box core, 10.39247, -117.46752, 4350 m, NORID-D, http://data.nhm.ac.uk/object/805f34aa-ec4f-4318-b18b-46447350aa1e.

Comparative material.

Bathychloeia cf. sibogae ; NHMUK ANEA.2022.455-456; 2 specimens; IN_251; IN2017_V03_110; 4010 m; South Pacific , Australia, off Fraser Island (-25.220, 154.160); col. 11/06/2017; EBS. Bathychloeia cf. sibogae ; AM W.52608 (1 specimen); IN2017_V03_103; South Pacific , Australia, off Moreton Bay (-27.008, 154.223); 4260 to 4280 m; coll. 10/06/2017; EBS. Bathychloeia cf. sibogae ; AM W.52609 (2 specimens); IN2017_V03_096; South Pacific , Australia, off Byron Bay (-28.678, 154.204); 2591 to 2566 m; coll. 07/06/2017; EBS. Bathychloeia cf. sibogae ; AM W.52610 (1 specimen); IN2017_V03_102; South Pacific, off Moreton Bay (-27.009, 154.223); 4274 to 4264 m; coll. 10/06/2017; beam trawl .

Diagnosis.

Body size variable, up to 18 mm long and 6 mm wide for larger specimens with 15 or 16 chaetigers (Figs 6A , 7A , 8A ); smaller specimens up to 2 mm long and 0.7 mm wide (Fig. 8C, D ). Body oval and compact; tapering anteriorly and posteriorly with mid-body chaetiger widest. Body pale yellow in alcohol, with rusty brown pigmentation in the mid furrow on anterior part of prostomium (Fig. 6C ). Live large specimens pink in colour (Fig. 8A ).

Prostomium indistinctly divided into an anterior and a posterior lobe; tightly surrounded by reduced first chaetigerous segment. Anterior lobe rounded, bearing a pair of lateral cirriform antennae plus a pair of slightly shorter ventrolateral palps. Posterior lobe bell-shaped, ca. as long as wide. One pair of tiny red eyes present (Fig. 7B ) Prostomium posteriorly extended into a conspicuous caruncle, reaching anterior margin of chaetiger 4, mostly free from the body wall, wedge-shaped with greatly undulated lateral margins with ca. 10 folds in larger specimens (Figs 6C , 7A, C ) and simple “tongue-like” structure in smaller specimens (Fig. 8C ). Slender cirriform style of median antenna ca. ½ the length of caruncle.

Parapodia biramous with distinctly separated rami, bearing cirri that are easily detached. Dorsal and lateral cirri slender, filiform, and long, present in notopodia; dorsal cirrus inserted dorsolaterally to notochaetae, lateral cirrus, inserted medially behind notopodial chaetae. Ventral cirri also filiform and elongated (particularly in chaetiger 1, Fig. 7E ), but on subsequent chaetigers shorter than dorsal or lateral cirri. First pair of branchiae always on chaetiger 5 where greatly enlarged (Figs 6B, E , 7F , 10A, B ). In large specimens branchiae with a large primary stalk with up to six smaller branches, each with many long slender lateral filaments (Figs 7F , 10A, B ); subsequent branchiae (if detected) much reduced in size (Fig. 6E ), bipinnate with up to seven branches (Fig. 8B ). In smaller specimens branchiae of chaetiger 5 also enlarged, but simpler, bipinnate, with a slender main stalk and up to seven pairs of lateral filaments (Fig. 8E ).

Notopodia with chaetae much larger and usually thicker than those of neuropodia, almost forming a “cage” over dorsum, obscuring the branchiae in some specimens, but very fragile and easily lost in most specimens, best preserved in juvenile specimens (Fig. 9A ). Both noto- and neurochaetae bifurcate of various lengths, and thickness of shafts and prongs (Fig. 9B-H ). Long prongs mainly with smooth margin (Fig. 9B, D, E, F, H ) or variably developed serrated margin on inner (Fig. 9C ) or outer margin (Fig. 9G ). Pygidium with dorsal anus and a pair of digitiform elongated cirri (Fig. 7G ).

Variation.

Molecular analysis suggests that smaller and larger specimens that differ predominantly in the form of caruncle and form of branchiae as described above, represent the same species. Therefore, the size difference likely represents different developmental changes.

Molecular information.

Only one CCZ specimen of B. cf. sibogae , specimen NHMUK ANEA.2022.633, was sequenced for all three genes, 16S, 18S and COI (Table 1 ). Three other specimens were successfully sequenced for COI and five for 16S only (Table 1 ). In addition, 16S (GenBank accession numbers ON900090 and ON900091) and COI (GenBank accession numbers ON903195 and ON903196) sequences were obtained from two specimens in the comparative material (NHMUK ANEA.2022. 455-456) that were collected from the abyssal South Pacific (off Australia). The COI sequences from this species matched four sequences on GenBank with accession numbers KJ736482-KJ736485, all four from other areas within CCZ ( Janssen et al. 2015). In the phylogenetic tree, the specimens from CCZ and Australia fall as a sister taxon to Bathychloeia cf. balloniformis (Fig. 5B ). The Bathychloeia clade is in an unresolved trichotomy with clades consisting of species from the genera Chloeia and Notopygos , although the trichotomy has low support (Fig. 5A ). Uncorrected ‘p’ from a COI alignment of 534 characters shows values among the nine B. cf. sibogae specimens ranging from 0.0 to 0.015, while the lowest value between B. cf. sibogae and its closest relative in our phylogenetic analysis, B. cf. balloniformis , is 0.18.

Remarks.

The enlarged branchiae of chaetiger 5 suggest close affiliation of CCZ specimens to Bathychloeia sibogae Horst, 1910 described from the Banda Sea, depth of 1100 m. Since its original description and subsequent re-description ( Horst 1912), specimens assigned to B. sibogae or B. cf. sibogae have been reported from vastly different geographic and more importantly bathymetric areas such as the Tasman Sea and off Kenya ( Kirkegaard 1995), Guinea Basin in SE Atlantic in depths of 5048-5144 m ( Böggemann 2009) and South Pacific in depths of 2566 m and 4260 m ( Gunton et al. 2021). Further, Böggemann (2009) suggested that syntypes (BMNH1885.12.1.11) of Chloenopsis atlantica (McIntosh) from the NE Atlantic (Canary Islands, ca. 2800 m depth) may in fact belong to B. sibogae due to presence of similar branchiae and two notopodial cirri.

Although the original definition of B. sibogae given by Horst (1910) was limited, a more detailed re-description was provided by Horst later ( Horst 1912). The type specimen ZMA.V.POL.124 was on loan and therefore not available for examination at the time of writing (J Bleeker, pers. comm.). Based of re-description of Horst (1912) CCZ specimens differ mainly in the presence of red eyes and form of branchiae that are bi-pinnate but with many slender filaments developed on lateral branches (Fig. 10A, B ), a character not reported by Horst (Fig. 10D ). CCZ specimens also correspond well with those reported by Böggemann (2009) from the abyssal SE Atlantic in having similar body shape and body size, presence of tiny eyes, form and distribution of parapodial cirri, well developed highly crenulated and folded caruncle (in larger specimens), enlarged branchiae on chaetiger 5 and form of pygidial cirri. However, Böggemann (2009) did not report the presence of long filaments of branchial lateral branches (Fig. 10E ). Additionally, specimens identified as B. cf. sibogae collected from the abyssal South Pacific were also available for morphological and molecular comparison (see also Gunton et al. 2021). Morphologically the South Pacific specimens agreed with those collected from CCZ, with long filaments on lateral branchial branches either present or absent (Fig. 10C ). Significantly, the molecular data (CO1, 16S and 18S markers) suggested that CCZ and South Pacific specimens belong to the same species, therefore the presence/absence of filaments on lateral branchial branches may be a matter of preservation or developmental character. Currently, no molecular data are available from the SE Atlantic specimens or from the type locality. Although it is unlikely that abyssal specimens belong to the same species as that described by Horst (1910) from 1100 m, due to lack of molecular data from type locality we cautiously ascribe CCZ-collected specimens to Bathychloeia cf. sibogae .

Distribution.

Central Pacific Ocean, Eastern CCZ, in the exploration areas UK-1, OMS, NORI-D (Fig. 1 ) and based on previous study in GBR (German) and IFREMER (French) exploration areas ( Janssen et al. 2015). Abyssal South Pacific, off Australia, ca. 4000 m.

Ecology.

It is of interest that a closely related form to the CCZ species known as Cholenopsis atlantica (McIntosh, 1885) has been described in association with a sponge growing on a dead coral coated with manganese of peroxide ( McIntosh 1885), while the CCZ species has been collected from the sediment associated with manganese nodules.

Figures

Figure 1. Map of CCZ of exploration areas and areas of particular interest, with targeted areas where samples of this study were collected highlighted in colours (see legend for explanation).

Figure 5. Majority-rule consensus trees from the Bayesian analyses with posterior probability values on nodes. Taxon names highlighted in blue are news species or new sequences for already known species. A Amphinomidae phylogenetic tree using a combined datasets for COI, 16 S, and 18 S with 26 terminal taxa of which Euphrosine foliosa (Euphrosinidae) was used as a root B Euphrosinidae phylogenetic tree using a combined datasets for 16 S and 18 S with nine terminal taxa of which Paramphinome jeffreysii (Amphinomidae) was used as a root.

Figure 6. Bathychloeia cf. sibogae (specimen NHMUK ANEA. 2022.633) A preserved specimen in ventral view B specimen in lateral view with large pair of branchiae on chaetiger 5 marked by arrows C anterior end in dorsal view with prostomium and caruncle (insert) D detail of mouth and anterior end in ventral view E branchiae on chaetiger 5 - 8 marked by arrows F detail of anterior end with anal cirri marked by arrow. Scale bars: 1 mm. Abbreviations: br - branchiae, ac - anal cirri.

Figure 7. Bathychloeia cf. sibogae (specimen NHMUK ANEA. 2022.634) A preserved specimen in dorsal view B anterior end in dorsal view C detail of the posterior end of caruncle D anterior end and mouth in ventral view E anterior end in lateral view with long ventral cirri on chaetiger 1 F large pair of branchiae on chaetiger 5 G posterior end in dorsal view with pair of anal cirri. Scale bars: 1 mm.

Figure 8. Bathychloeia cf. sibogae CCZ-collected specimens A large live specimen (NHMUK ANEA. 2022.633) in ventral view B live specimen (NHMUK ANEA. 2022.633) with midbody segments and associated branchiae in dorsal view, insert - the detail of branchiae from chaetiger 9 C small (juvenile) preserved specimen (NHMUK ANEA. 2022.635) in dorsolateral view D small (juvenile) preserved specimen (NHMUK ANEA. 2022.632) in dorsal view E detail of enlarged branchiae on chaetiger from specimen (NHMUK ANEA. 2022.632). Scale bar: 1 mm.

Figure 9. Bathychloeia cf. sibogae (specimen NHMUK ANEA. 2022.635) A overview of specimen in dorsal view B slender furcate notochaetae C prong with distinct serration on inner margin D slender short furcate chaeta E long stout furcate chaeta (marked by arrow) F smooth prongs G faintly serrated prong, outer margin H slender furcate chaeta. Scale bars: 250 µm (A); 100 µm (B), 50 µm (C, D, G, H); 100 µm (E).

Figure 10. Comparative figure of form of enlarged branchiae from chaetiger 5 showing variation in development of long branchial filaments, Ms - Main stalk, Lb - lateral branches, Lf - long filaments A Bathychloeia cf. sibogae CCZ specimen, NHMUK ANEA. 2022.633, in lateral view B Bathychloeia cf. sibogae CCZ specimen, NHMUK ANEA. 2022.634, specimen stained with Shirlastain, in dorsal view C Bathychloeia cf. sibogae South Pacific specimen NHM _ 215 in dorsal view D Bathychloeia sibogae after Horst (1912) E Bathychloeia sibogae after Boeggemann (2009). Scale bars: 1 mm.