Myxicola boki, Putignano & Langeneck & Giangrande, 2024

Putignano, Matteo, Langeneck, Joachim & Giangrande, Adriana, 2024, The forgotten diversity of the genus Myxicola (Polychaeta: Sabellidae) in North America: redescription of historical taxa and description of two new species, Journal of Natural History 58 (37 - 40), pp. 1393-1427 : 1400-1404

Myxicola boki sp. n. Putignano, Langeneck & Giangrande, 2024

( Figures 3 , 4 )

Holotype

MCZ-47069A; USA, Maine, Cumberland, Casco Bay, station 6; georeferenced by Penny Benson on 12 June 2018 as 43.6334180°N, 70.049491°W (error radius: 20,641 m); collected by Joseph A. Cushman on 28 August 2002; fixed and preserved in 70% ethanol; identified by Harlan K. Dean as M. infundibulum .

Paratype

One specimen from the same locality as holotype; MCZ-47069B .

Description

Holotype complete, body yellowish, with anterior peristomial ring sightly darker than rest of body ( Figure 3A–C ). Body cylindrical with slightly dorso-ventrally flattened abdomen. Crown of same colour as most of body ( Figure 3A ). No information concerning live colouration. Body 7.3 cm long, 8 thoracic and 84 abdominal chaetigers; maximum width 4 mm; thorax longer than wide. Crown 1.4 cm long, with 23 pairs of radioles; ratio body/crown length of 5.21. Peristomium 2 mm long (distinctly longer than thoracic segments); anterior and posterior peristomial rings divided dorso-laterally by a narrow rut, with anterior ring darker than posterior; mid-ventral lobe of anterior peristomial ring triangular, prominent, distally rounded with a clearer colouration; peristomium low, leaving the junction between crown and body visible laterally; remarkably narrow and deep mid-lateral incision splitting branchial lobes in ventral and dorsal halves ( Figure 3B, C ). Dorsal lips with short, yellowish, filiform dorsal radiolar appendages, with rounded point ( Figure 3D ); pinnular appendages and ventral radiolar appendages both absent; ventral lips yellowish, low and wide, extending dorsoventrally along inner surface of base of radiolar lobes, connecting ventrally to these; parallel lamellae and ventral sacs both absent ( Figure 3D ). Outer surface of radioles translucent, connected by a high semi-transparent palmate membrane. Radiolar tips>1/7 of total radiole length, of same colour as radioles, lanceolate with elongate tapering bare tip (thinner than pinnulae) ( Figure 3E ); pinnules thin and blunt, up to>1/5 of total radiole length, of same colour as radioles, with a strictly alternating arrangement; distal pinnules the longest, but abruptly shortening to beginning of radiolar tip. Radiolar skeleton as 6–7 rows of cells, in circular arrangement around axis of radiole, in cross section, two dorsal-most rows with cells distinctly larger than other rows, surrounded by hyaline matrix; graft cells for pinnular skeleton squared and small, undivided, ventrally contiguous to the latter ( Figure 3G ); radiolar and peristomial eyes not visible. Glandular girdle near the posterior margin of chaetiger 2. Lateral eyes not visible, possibly due to fixation artefact; pygidium posteriorly truncate, pygidial eyes not visible ( Figure 3F ). Numerous narrowly hooded thoracic notochaetae, distinctly thin, with elongated tapering tip, arranged in tufts; peristomial notochaetae with slightly narrower hood ( Figure 4A, B ); chaetigers 2–8 with curved acicular uncini, with 3–4 small teeth not reaching half of the relatively long main fang ( Figures 4D, E , 15C ); thoracic tori inconspicuous. Few abdominal neurochaetae, almost identical to thoracic notochaetae, but forming less conspicuous tufts than those on thorax, number of chaetae per fascicle decreasing through abdomen ( Figure 4C ). Abdominal uncini with single, short tooth above the main fang, usually not exceeding ¼ of main fang length ( Figure 4F, G ), longer than that in a few uncini ( Figure 4H–J ); breast squared, main fang high, as long as or slightly longer than breast; handle vestigial, uncini as high as long ( Figures 4F, G , 15D ).

Remarks

These specimens were examined to verify the presence of M. steenstrupi KrØyer, 1856 in the Bay of Fundy. As stated for the new species described above, size, body/crown ratio and total number of segments suggest that M. steenstrupi is a small species belonging to the ‘ infundibulum group’, characterised by a proportionally longer crown. Although the members of these species seem to have a similar number of radioles (17–21 pairs for M. steenstrupi and 23 for M. boki sp. n.), the length and morphology of the radiolar tips and pinnules differ between the groups, specimens of M. bokii sp. n. having shorter tips (1/3 against>1/7) and pinnules (1/3 against>1/5). Finally, dorsal radiolar appendages show morphological differences between these two species, being sublaminar, elongated-triangular in M. steenstrupi . KrØyer (1856) explicitly stated that he did not find uncini, but this might be due to the poor quality of the equipment available to the author at the time, in comparison to our modern techniques, rather than to an actual absence. Darbyshire (2023) briefly described syntypes of M. steenstrupi from Faroe Islands and Greenland, stating that they were badly preserved, and that the majority of the diagnostic characters could not be properly examined. Nonetheless, this description suggests similarity in morphology of ventral lips and dorsal radiolar appendages, reported as enlarged and lobate and small and digitiform ( Faroe Islands specimens) or slender and digitiform ( Greenland specimens). However, as Darbyshire (2023) stressed, this material is not in good condition, and more detailed analyses, possibly on new material, are needed to ascertain the identity of M. steenstrupi .

Some differences can be found also in comparison to line drawings by Bush (1905): thoracic uncini appear markedly curved, with a short main fang ( Figure 14L 1–L 4 ), and abdominal uncini show a smaller and shorter main fang with a single, long apical tooth ( Figure 14M 1 , M 2 ). Also, the vestigial handle is absent. All this allows us to differentiate members of M. steenstrupi from the examined specimens of M. bushae sp. n.

Comparison with the neotype of M. infundibulum by Darbyshire (2023) shows clear differences in the morphology of lips and associated structures, radiolar skeleton arrangement, shape of peristomium, morphology of abdominal uncini and pigmentation, leaving only the morphology of thoracic uncini similar. The comparison with M. polychroma Darbyshire, 2023 unveils remarkable similarity to M. boki sp. n. in the shape of the mid-ventral lobe, while morphology of lips and associated structures, shape of radiolar tips, radiolar skeleton arrangement, morphology of thoracic and abdominal uncini all differentiate these species.

Myxicola boki sp. n. is a species of the ‘ infundibulum group’ (8 thoracic chaetigers), whose members present an intermediate number of abdominal chaetigers between larger and smaller forms ( Putignano et al. 2023). The currently accepted Myxicola species which share a similar general morphology with respect to the specimens attributed here to M. boki sp. n. are M. cosentini Putignano, Gravili and Giangrande, 2023 and M. pacifica Johnson, 1901 . However, important differences separate this new taxon: members of M. cosentini show distinct club-like radiolar appendages, extremely long and tapering radiolar tips and a radiolar skeleton composed of two cell rows, while individuals of M. pacifica have different abdominal uncini (concerning both general appearance and number of apical teeth), as well as differences on the crown (radiolar skeleton, radiolar tips and mid-ventral lobes; see Putignano et al. 2023).

Etymology

The species is named after the Maine-born folklorist and singer-songwriter Gordon Bok, who seems to describe something similar to a sabellid in a passage of his song “Sailor’s Carol” ( Bok, 1992): ‘[…] Only the deep garden/ Where green lilies grow/ And the sailors rolling/ On the sea’s blue snow […]’.

Distribution and ecology

Casco Bay; potentially present along the North American Atlantic Coast, from Bay of Fundy to New York State, as several records of M. infundibulum for the north-western Atlantic Ocean might refer to this species. No information concerning the ecology of members of this species is reported.

Figures

Figure 1. Myxicola bushae sp. n. A. entire worm; B, C. peristomial ring, ventral and lateral view; D. complex of ventral and dorsal lips; E. radiolar tip; F. pygidium; G. scheme of radiolar cross section. (g: glandular girdle, barely visible; p.e: pygidial eyes)

Figure 2. Myxicola bushae sp. n. A. peristomium notochaeta; B. 4th chaetiger thoracic notochaeta; C. 24th chaetiger abdominal neurochaeta; D–F. 4th chaetiger thoracic uncinus, lateral and frontal view; G–J. 24th chaetiger abdominal uncini, lateral and frontal views. Scale bars: 0.02 mm.

Figure 3. Myxicola boki sp. n. A. entire worm; B, C. peristomial ring, ventral and lateral view; D. complex of ventral and dorsal lips; E. radiolar tip; F. pygidium; G. scheme of radiolar section. (r.a: radiolar appendages)

Figure 4. Myxicola boki sp. n. A. peristomial notochaeta; B. 4th chaetiger thoracic notochaeta; C. 24th chaetiger abdominal neurochaeta; D, E. 4th chaetiger thoracic uncinus; F–J. 24th chaetiger abdominal uncini, lateral and frontal views. Scale bars: 0.02 mm

Figure 14. Drawings of uncini and chaetae of the different Myxicola taxa originally described by Bush (1905). A–E, Myxicola conjuncta: A1–A3, thoracic notochaetae; B1, B2, spear-shaped thoracic notochaetae; C, spear-shaped abdominal neurochaeta; D1–D3, thoracic uncini; E1, E2, abdominal uncini). F–J, Myxicola glacialis: F1–F3, thoracic notochaetae, of which F2 from the peristomium; G1, G2, Abdominal neurochaetae; H1, H2, spear-shaped thoracic notochaetae; I, thoracic uncini; J1, J2, abdominal uncini). K–M, Myxicola steenstrupi sensu Bush (1905): K, thoracic notochaeta, ‘[…] similar to the ones from the abdomen […]’; L1–L4, thoracic uncini; M1, M2, abdominal uncini).N, O, Myxicola affinis: N1, N2, thoracic uncini; O1, O2, abdominal uncini. Drawings from Bush (1905).

Figure 15. Photographs of thoracic and abdominal uncini, respectively, of American Myxicola species: A, B. M. bushae sp. n.; C, D. M. boki sp. n.; E, F. M. conjuncta.