Bathyvermilia rolandobastidai, Kupriyanova & Flaxman, 2024

Bathyvermilia rolandobastidai View in CoL n. sp.

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Fig. 4A–H View Figure 4

Material examined. Holotype:W.53399 (LK250), Christmas Island SE (10°34'13"S, 105 41'23"E), depth 643–997 m, GoogleMaps

06/07/2021.

Paratypes: W.53398 (LK247), same as above (1 spec, photo and SEM); W.54907 (1 spec) .

Description. Tubes: white or slightly brownish, opaque, circular in internal in cross-section, more or less semicircular in external cross-section with attachment area narrowly wider than tube width ( Fig 4A, B View Figure 4 ), attached to substrate throughout their length. Tube surface with numerous (6–7) low keels and some occasional, slightly elevated peristomes ( Fig. 4A, B View Figure 4 ).

Radioles: 10–11 pairs arranged in two semicircles. Inter-radiolar membrane and stylodes absent. Each radiole ending in a thick filamentous tip as long as pinnules.

Peduncle: smooth circular in cross-section, slightly thicker than normal radioles and inserted as a 2 nd radiole.

Operculum: semi-globular, with flat or slightly depressed chitinous endplate ( Fig. 4A, B View Figure 4 ). Constriction at junction of basal part of operculum and peduncle present. Pseudoperculum absent.

Collar and thoracic membranes: collar trilobed, with ventral and two latero-dorsal lobes. Thoracic membranes continuing to thoracic chaetiger 5.

Thorax: Seven thoracic segments, 6 with uncini ( Fig. 4C View Figure 4 ). Collar chaetae limbate of two sizes ( Fig. 4D View Figure 4 ). Rest of chaetae limbate plus Apomatus chaetae ( Fig. 4F View Figure 4 ). Thoracic tori positioned along mid-lateral line of thorax, triangular depression absent. Thoracic uncini saw-shaped with 8–9 teeth and pointed anterior fang ( Fig. 4E View Figure 4 ).

Abdomen: with up to 60 chaetigers. Anterior abdominal chaetae flat narrow geniculate with blunt teeth ( Fig. 4G View Figure 4 ), replaced by capillary chaetae on posterior segments.Anterior abdominal uncini saw-shaped with 12 teeth and simple pointed fang ( Fig. 4H View Figure 4 ). Uncini of middle and posterior abdominal segments rasp-shaped, with up to 13 teeth in profile and 2–3 teeth per row. Short achaetous anterior abdominal zone present. Posterior glandular pad present.

Size: total body length up to 15 mm, width of thorax up to 0.8 mm. Radioles and operculum accounting for one third of entire length. Tube up to 1.2 mm wide with lumen of up to 1.0 mm in diameter.

Diagnostic remarks. The species in the genus are distinguished by tube structure, and to a lesser degree, by the length of the thoracic membranes and details of opercular structure. The new species is easily recognisable from all congeners by its characteristic tube with numerous low keels and occasional transverse ridges/peristomes. Tubes are also very distinct in B. challengeri (with numerous transverse ridges close to each other), B. eliasoni (with three longitudinal ridges raised into curved spines), B. gregrousei (tetragonal in cross-section, slightly spirally twisted) and B. langerhansi (with smooth shiny surface, sub-triangular in cross-section with a median keel, but lacking lateral keels, peristomes, and transverse ridges).

Bathyvermilia islandica , B. kupriyanovae and B. zibrowiusi are similar in having tubes circular in cross-section, with smooth shiny surface and distal peristomes. The tube of B. islandica is attached to the substrate for all its length, forming a distinct peripheral basal flange and undulated peristomes are sometimes present along the tube but are rare. Bathyvermilia islandica is also distinct in having long thoracic membranes ending at the 7 th thoracic chaetiger, they are wide up to the 2 nd segment, and then narrow sharply. Bathyvermilia zibrowiusi is most similar to B. kupriyanovae as both species have tubes with wide peristomes and thoracic membranes extending to the 4 th chaetiger. The main difference between them is the opercular endplate with developed concentric ridges in B. zibrowiusi , as opposed to simple chitinous endplate with some calcareous inclusions in B. kupriyanovae .

The molecular results of this study did not support monophyly of the genus Bathyvermilia ; alternatively, the data suggest that the new species does not belong to the genus Bathyvermilia . However, because morphology of Bathyvermilia rolandobastidai n. sp. fits the generic diagnosis of the genus Bathyvermilia well, we decided against the change in nomenclature until further molecular data become available.

Distribution. Only known off Christmas Island, South Indian Ocean, 643– 997 m.

Etymology. The species is named after Professor Rolando Bastida-Zavala (Universidad de Mar, Oaxaca, Mexico) to honour his important contributions to taxonomic studies of Serpulidae .