Branchiomma sp.

Tovar-Hernández, María Ana, León-González, Jesús Angel De & Hendrickx, Michel E., 2025, Polychaeta collected during the research cruises TALUD aboard the R / V “ El Puma ” in the Mexican Pacific: Sabellidae and Serpulidae, Zootaxa 5663 (1), pp. 1-80 : 15-17

Branchiomma sp.

( Fig. 7 )

Material examined. ICML-EMU-14016: TALUD XV, St. 23, BC, 27º08'11"N 114º32'54"W, 01 August 2012, 581 m, 1 specimen ; ICML-EMU-14017: TALUD XVI, St. 4, BC, 28º47'54"N 115º43'47"W, 24 May 2013, 1,045 m, 1 specimen .

Description of material examined. Body pale, specimen ICML-EMU-14016 with typical, dark spots ( Fig. 7D– E ); specimen ICML-EMU-14017 unspotted, except for black interramal eyes. Branchial crown with some orange and brown bands in distal half of crown ( Fig. 7A–B ). Trunk 5.8 (ICML-EMU-14016)– 18.6 mm (ICML-EMU-14017) long; thorax 1.5 mm wide, in both specimens; branchial crown 4.2 (ICML-EMU-14016)– 6.1 mm (ICML-EMU-14017), 11 (ICML-EMU-14016)–12 (ICML-EMU-14017) pairs of radioles. Thorax with eight chaetigers, abdomen with 43 chaetigers (ICML-EMU-14016)–48 chaetigers (ICML-EMU-14017). Branchial crown with semicircular basal lobes, slightly involuted ventrally. Dorsal and ventral basal flanges both absent, reduced palmate membrane ( Fig. 7A ), radiolar flanges also absent; digitiform stylodes ( Fig. 7A, C, G ), except for strap-like macrostylodes at mid-length of radioles ( Fig. 7B, F ), up to twice length of neighboring pairs ( Fig. 7B, F ), unpaired basal stylodes present ( Fig. 7A ). Radioles with brown paired compound eyes along lateral margins, alternating with stylodes ( Fig. 7A, C, F–G ). Dorsal lips with long radiolar appendages; ventral lips and parallel lamellae present. Ventral sacs out of crown. Posterior peristomial ring collar with well separated dorsal margins; sub-triangular ventral lappets, with rounded tips, separated by mid-ventral incision. Interramal eyespots present throughout, large on first thoracic segments, progressively smaller posteriorly ( Fig. 7D–E ). Ventral shields in contact with thoracic neuropodial tori. Collar chaetae with superior narrowly-hooded chaetae and inferior spine-like chaetae, in oblique rows; following thoracic chaetigers with notopodia as conical lobes, with superior narrowly-hooded notochaetae ( Fig. 7H ) and inferior spine-like notochaetae ( Fig. 7H–I ). Thoracic uncini avicular, with two rows of teeth on top of main fang, occupying near half of main fang, breast well developed and distinctly short handle ( Fig. 7J ). Abdominal neuropodia as conical lobes with superior narrowly-hooded neurochaetae and inferior spine-like neurochaetae, in C-shaped arrangement. Uncini avicular, with two rows of teeth above main fang, breast well developed, and distinctly short handle ( Fig. 7K ). Bilobed pygidium. Pygidial eyes not seen. Tubes not preserved.

Remarks. Branchiomma is composed of 30 species ( Capa et al. 2019, 2021). For many years stylodes (shape, size and distribution), dentition of thoracic uncini, body size (discerning between small or large worms), branchial crown, dorsal lips and thorax length, degree of separation on dorsal margins of collar and gaps among ventral shields and tori were used to separate species of Branchiomma . These characters, however, are not informative as they are impacted by anesthetics and fixation methods or vary during ontogeny ( Keppel et al. 2015). In addition, the number of thoracic uncini is not reliable for the identification process, because it is highly variable in Branchiomma species, as they reproduce asexually by fission. Different numbers of uncini are the result of variation of regenerative processes, being typically eight in adults and lower numbers in regenerating individuals. All Branchiomma species have spotted bodies, but the size and distribution of spots are variable within a single species; in addition, these spots are lost gradually after preservation ( Keppel et al. 2015). Thus, proper identification for this group using morphological characters is problematic ( Capa et al. 2013b, 2021).Assessing the identity of species of Branchiomma requires a comprehensive generic revision, including DNA-based species delimitation analyses (del Pasqua et al. 2018; Capa et al. 2021).

Most species of Branchiomma have been described from shallow waters ( Tovar-Hernández & Knight-Jones, 2006) and there are only two species reported below 500 m deep ( Glover et al. 2025): B. bombyx ( Dalyell, 1853) and B. lucullanum (delle Chiaje, 1828). No species of Branchiomma has been reported deeper than 2,000 m ( Budaeva et al. 2014, Alalykina, 2020). In the present study, two specimens of Branchiomma were found off the west side of Baja California Peninsula, from 681–1,045 m deep, but additional samples are needed to properly identify the species.

Abiotic conditions. The specimens of Branchiomma sp. were collected from 681–1,045 m deep, under the following environmental conditions. Temperature: 3.60–6.44°C; salinity: 34.45–34.53; dissolved oxygen: 0.07– 0.78 ml O 2 /l; %MO: 5.15; sediments dominated by sand and silt (46.6% each) ( Table 1).

Distribution. West coast of Baja California and Baja California Sur, Mexico.

Genus Chone Krøyer, 1856

Figures

FIGURE 7. Branchiomma sp. A) Branchial crown, lateral view, B) lateral radiole from right branchial lobe, C) digitiform stylodes from basal part of radiole, D) thorax and interramal eyes, lateral view, E) abdomen, interramal eyes, lateral view, F) strap-like macrostylodes from medium part of radiole, G) digitiform stylodes from anterior part of radiole, H) thoracic chaetiger, I) spine-like thoracic chaetae, J) thoracic uncinus, K) abdominal uncinus. Scale bars: A, D–E) 1 mm, B) 3.5 mm, C, F–G) 0.1 mm, H) 75 µm, I–K) 20 µm. A–K: ICML-EMU-14017.