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A forgotten cirripedological gem: a new species of whale barnacle of the genus Cetopirus from the Pleistocene of the United States West Coast

Published online by Cambridge University Press:  07 November 2022

Alberto COLLARETA*
Affiliation:
Dipartimento di Scienze della Terra, Università di Pisa, via S. Maria 53, 56126 Pisa, Italy. Museo di Storia Naturale, Università di Pisa, via Roma 79, 56011 Calci, Italy.
Mark BOSSELAERS
Affiliation:
Koninklijk Belgisch Instituut voor Natuurwetenschappen, Operationele Directie Aarde en Geschiedenis van het Leven, Vautierstraat 29, 1000 Brussel, Belgium. Koninklijk Zeeuwsch Genootschap der Wetenschappen, Kousteensedijk 7, 4331 JE, PO Box 378, 4330 AJ Middelburg, the Netherlands.
Patricia A. HOLROYD
Affiliation:
University of California Museum of Paleontology, 1101 Valley Life Sciences Building, Berkeley, CA 94720-4780, USA.
Ashley DINEEN
Affiliation:
University of California Museum of Paleontology, 1101 Valley Life Sciences Building, Berkeley, CA 94720-4780, USA.
*
*Corresponding author. Email: alberto.collareta@unipi.it
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Abstract

A small lot of fossil whale barnacles from the Upper Pleistocene of California and the Middle Pleistocene (Chibanian) of Oregon (United States West Coast), described in a 1972 unpublished MA thesis, are formally described and illustrated herein. In that thesis, a new genus and species name were proposed; however, according to the International Code of Zoological Nomenclature, they have no taxonomic standing and are thus unavailable. Based on our reappraisal, two specimens in this lot belong to a new, extinct species that can be assigned to the purportedly extant genus Cetopirus. Cetopirus polysyrinx sp. nov. differs from congeners in that its secondary T-shaped flanges are multitubiferous internally, that is, they are perforated by a high number of irregularly-sized and irregularly-spaced tubules that result in a spongy aspect in transverse section. Whether or not this peculiar condition had any adaptive significance is difficult to determine. Considering that Cetopirus is currently known as an obligate epibiont of right whales (including the North Pacific form Eubalaena japonica (Lacépède 1818)), the host of C. polysyrinx sp. nov. was E. japonica or some other species of Eubalaena. The Plio-Pleistocene deposits of the Pacific coast of North America have yielded a rather idiosyncratic fossil whale barnacle fauna, inclusive of the genera Cetolepas, Cryptolepas and now Cetopirus, which seemingly contrasts with all other coeval assemblages worldwide, the latter being in turn dominated by Coronula spp.

Type
Spontaneous Article
Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
Copyright © The Author(s), 2022. Published by Cambridge University Press

1. Introduction

Fifty years ago, Clark William Davis, a graduate student at San Francisco State University, USA, authored one of the most relevant contributions to the modern understanding of the skeletal anatomy and functional morphology of the extant and extinct whale barnacles (Cirripedia: Coronulidae) in the form of a MA thesis (Davis Reference Davis1972) that is currently available online (Collareta et al. Reference Collareta, Harzhauser and Rasser2022a). In that thesis, entitled ‘Studies on the barnacles epizoic on marine vertebrates’, Davis (Reference Davis1972) informally described a new genus and species of whale barnacle, ‘Polysyrinx zulloi’, on the basis of a handful of fossils from the United States West Coast. However, both the names ‘Polysyrinx’ and ‘P. zulloi’ have not been formally published and are thus unavailable in light of the International Code of Zoological Nomenclature (1999: articles 8 and 9; see also Dubois et al. Reference Dubois, Crochet, Dickinson, Nemésio, Aescht, Bauer, Blagoderov, Bour, de Carvalho, Desutter-Grandcolas, Frétey, Jäger, Lavilla, Löbl, Louchart, Malécot, Schatz and Ohler2013), whereas they are published herein as nomina nuda (International Code of Zoological Nomenclature 1999: articles 11 and 13, and glossary). While we were unable to track down the author of this particular MA thesis, we did succeed in tracing three out of four specimens referred by Davis (Reference Davis1972) to ‘Polysyrinx zulloi’. Below we describe Davis' new coronulid taxon on solid nomenclatural grounds and discuss its palaeontological significance.

2. Material and methods

2.1. Institutional abbreviations

CAS: California Academy of Sciences (San Francisco, California, USA); LACM: Natural History Museum of Los Angeles (Los Angeles, California, USA), in the Invertebrate Paleontology (=LACMIP) department; UCMP: University of California Museum of Paleontology (Berkeley, California, USA).

2.2. Digital imaging

Two of the specimens studied herein were scanned by one of us (PAH) on a Phoenix Nanotom-M nanofocus X-ray computed tomography (CT) system in the Functional Anatomy and Vertebrate Evolution Laboratory at the University of California-Berkeley at a resolution of 10 microns per pixel. Reconstructed slices were cropped in Fiji 1.53q (Schindelin et al. Reference Schindelin, Arganda-Carreras, Frise, Kaynig, Longair, Pietzsch, Preibisch, Rueden, Saalfeld, Schmid, Tinevez, White, Hartenstein, Eliceiri, Tomancak and Cardona2012), rendered in three dimensions using Slicer 4.11 (Fedorov et al. Reference Fedorov, Beichel, Kalpathy-Cramer, Finet, Fillion-Robin, Pujol, Bauer, Jennings, Fennessy, Sonka, Buatti, Aylward, Miller, Pieper and Kikinis2012) using the SlicerMorph extension (Rolfe et al. Reference Rolfe, Pieper, Porto, Diamond, Winchester, Shan, Kirveslahti, Boyer, Summers and Maga2021), segmented and the segmentation exported as an STL file. The resultant STL file was imported into Meshlab (Cignoni et al. Reference Cignoni, Callieri, Corsini, Dellepiane, Ganovelli, Ranzuglia, Scarano, De Chiara and Erra2008) and decimated to approximately one-third the number of original faces to produce a smaller, web-viewable PLY file using their variant of quadric edge-collapse decimation (Garland & Heckbert Reference Garland and Heckbert1997). Both the cropped CT-stack and decimated PLY files were uploaded to MorphoSource.org.

3. Geological framework

The whale barnacle fossils dealt with in the present paper are represented by three specimens, including the holotype and a single paratype of a new species of Cetopirus, plus a third specimen that is left herein in open nomenclature.

As reported by Davis (Reference Davis1972), one of these originated from LACM locality 1210, San Pedro, Los Angeles County, California, USA (Fig. 1). Also referred to as LACMIP 1210, this locality is described in the museum records as a ‘bed of fossil shells in unconsolidated sand thickening from 2 feet at west end to 6 feet at east end; where it is underlain by single layer of cobble conglomerate and has some cross bedding in layers with fossils above.’ This bed no longer appears to be accessible, but did occur on the small bluff formed by the Gaffey Syncline, between modern-day N. Gaffey Street and the West Basin in the northwestern part of the town of San Pedro, approximately where Westmont Drive and industrial buildings sit today. The locality was mapped in Wehmiller et al. (Reference Wehmiller, Lajoie, Kvenvolden, Peterson, Belknap, Kennedy, Addicott, Vedder and Wright1977; fig. 2h) and Muhs et al. (Reference Muhs, Miller, Whelan, Kennedy, Fletcher and Wehmiller1992; fig. 3). Woodring et al. (Reference Woodring, Bramblette and Kew1946) recognised the deposits cropping out in this area as being entirely part of their ‘first terrace’ of the Palos Verdes Sand Formation. Wehmiller et al. (Reference Wehmiller, Lajoie, Kvenvolden, Peterson, Belknap, Kennedy, Addicott, Vedder and Wright1977) recorded amino acid stereochemistry values from the bivalve genus Saxidoma from LACM 1210 and assigned the locality to the early part of the Marine Isotope Stage (MIS) 5. Muhs et al. (Reference Muhs, Miller, Whelan, Kennedy, Fletcher and Wehmiller1992) showed that faunas from Woodring et al.'s (Reference Woodring, Bramblette and Kew1946) ‘first terrace’ represented two temporally different highstands, with LACM 1210 being assigned to the 125 ka highstand (i.e., MIS 5e). Based on the most recent synthesis of data bearing on the age of MIS 5e sites along the west coast of North America (Muhs et al. Reference Muhs, Wehmiller, Ryan and Rovere2021; Muhs Reference Muhs2022), the age of locality LACM 1210 is estimated to be 130 to 115 ka.

Figure 1. Location of the finds of Cetopirus polysyrinx sp. nov. along the Pacific coast of the USA. Geographical base map after wikimedia.org.

According to Davis (Reference Davis1972), two additional specimens were recovered from UCMP localities B7376 and B7380, near Cape Blanco, Curry County, Oregon, USA (Fig. 1). With regard to the former locality, it was described as in the ‘same horizon as B7375 and about 100 feet south’. Both UCMP B7375 and B7376 were collected by Jack A. Wolfe and Victor A. Zullo during the same field trip, but data on geology and location were recorded only on the locality card for B7375. UCMP B7375 occurs in a well-sampled stretch of uplifted terraces exposed on cliffs north of the mouth of the Elk River, Curry County, Oregon, USA, that have produced diverse invertebrate assemblages and rarer marine mammals. The invertebrate assemblages were the topic of an unpublished PhD thesis by Roth (Reference Roth1979) and the vertebrate faunas were most recently reviewed by both Boessenecker (Reference Boessenecker2013a) and Welton (Reference Welton2015). Locality UCMP B7375 was collected by Wolfe and Zullo in March 1960 from a unit described in the UCMP records as ‘25 feet below the conglomerate in the lower buff sandstone’ approximately 100 feet along the cliff. Topographically, the site corresponds to the area where Welton (Reference Welton2015) measured his Section 1 at Goldwasher's Gully, the northernmost of four sections, and containing the vertebrate localities UCMP V74042 and NMMNH 9241. The locality description suggests that the site is in the Lower Brown Sandstone Member, an interpretation also indicated in Roth (Reference Roth1979). This unit falls within all modern interpretations of the Port Orford Formation (e.g., Boessenecker Reference Boessenecker2013a; Wiley et al. Reference Wiley, McClaughry, Ma, Mickelson, Niewendorp, Stimely, Herinckx and Rivas2014; Welton Reference Welton2015), although older literature and records (e.g., museum locality registers; Leffler Reference Leffler1964; Davis Reference Davis1972; Roth Reference Roth1979) refer to this unit as part of the Elk River Formation.

UCMP B7380 occurs in the same stretch of uplifted terraces as UCMP B7375 and B7376, between Welton's (Reference Welton2015) sections 3 and 4, where the lower part of the Port Orford Formation is covered (see also Boessenecker, Reference Boessenecker2013a; fig. 1.4 for an outcrop photograph). Fossils were collected in situ from the Upper Brown Sandstone Member by Wolfe and Zullo in March 1960 and again in 1961 by a class field trip from the University of California, Department of Paleontology. UCMP B7380 is stratigraphically higher than B7375 and B7376, being separated from the Lower Brown Sandstone Member by approximately 14 m of the Blue Argillaceous Sandstone Member. Welton (Reference Welton2015) followed Baldwin (Reference Baldwin1945, Reference Baldwin1959) in including the Upper Brown Sandstone Member in the Elk River Beds, whereas Boessenecker (Reference Boessenecker2013a) and Wiley et al. (Reference Wiley, McClaughry, Ma, Mickelson, Niewendorp, Stimely, Herinckx and Rivas2014) considered it to be part of the Port Orford Formation. Whichever stratigraphic nomenclature is used, molluscs from the Upper Brown Sandstone Member (from LACM locality 3960) were dated to 500,000 ± 100,000 years via amino acid racemisation, and the rocks are reported to have normal palaeomagnetic polarity (Wehmiller et al. Reference Wehmiller, Lajoie, Sarna-Wojcicki, Yerkes, Kennedy, Stephens and Kohl1978). Kennedy et al. (Reference Kennedy, Lajoie and Wehmiller1982) also reported a potentially younger age interpretation (early MIS 3) of a terrace at Cape Blanco on the basis of amino acid racemisation, but also noted that the fauna was otherwise indistinguishable from the cool-water fauna associated with late stage 5 localities. Both studies indicate that these rocks and their associated faunas are Chibanian (Middle Pleistocene) in age, although currently available data do not permit greater refinement.

In addition to the specimens described here, Roth (Reference Roth1979) noted the presence of a single plate from this same area at UCMP locality B7371, in the Upper Brown Sandstone Member. He referred it to Cetopirus complanatus (Mörch Reference Mörch1853), but the specimen was not formally catalogued and could not be located at the UCMP. Roth (Reference Roth1979) also noted that the record of Coronula (Cetopirus) in the Pleistocene of Oregon listed by Newman et al. (Reference Newman, Zullo, Withers and Moore1969) was likely based on his specimen, although we cannot exclude the possibility that they were referring to the specimens described here, especially as Zullo, being co-author of the paper by Newman et al. (Reference Newman, Zullo, Withers and Moore1969), was also one of the collectors. Interestingly, the occurrence of Coronula complanata (=Cetopirus complanatus) in Late Pliocene [sic] deposits at Cape Blanco, Oregon was also reported by Zullo (Reference Zullo1969).

4. Systematics

Family Coronulidae Leach, Reference Leach1817

Genus Cetopirus Ranzani, Reference Ranzani1817

Type species: Lepas complanata Mörch, Reference Mörch1853, Late Pleistocene to Recent (possibly extinct; see Bosselaers et al. Reference Bosselaers, Van Nieulande and Collareta2017).

Distribution: Early Pleistocene to Recent. Currently known as an obligate epibiont of Eubalaena spp., living in temperate seas.

Diagnosis (emended after Collareta et al. Reference Collareta, Margiotta, Varola, Catanzariti, Bosselaers and Bianucci2016): Body within a depressed, often dome-shaped shell, consisting of six subequal compartments; circumference subcircular in apical view; orifice of the body chamber rounded–hexagonal, not larger than the basal opening; opercular valves present, much smaller than the orifice; sheath short, smooth to somewhat grooved, whose basal edge does not project freely; ala square and thin; compound radius moderately to very thick, whose closely spaced, copiously branching sutural septa originate from a main septum running along the outer edge of the radius; external radius rather narrow and transversely striated; paries thin, provided with broad longitudinal ribs having T-shaped terminations (primary T-shaped flanges) that form a secondary outer lamina; primary T-shaped flanges perforated by longitudinally elongated tubes or tubules; secondary T-shaped flanges present in the form of minute projections that abut from the primary T-shaped flanges; core of the ribs solidly calcified; ribs externally flattened, ornamented by weak transverse growth folds and fine longitudinal striae, lacking transverse interlocking crenulations; apex of the shell presenting four ribs forming three cavities in-between; secondary branching very symmetrical and frequent, occurring near the apex of the shell and resulting in the basal edge of each compartment presenting a tree-like aspect.

Cetopirus polysyrinx sp. nov.

(Figs 2–4)

Figure 2. Cetopirus polysyrinx sp. nov. (holotype), LACMIP 1210.158, isolated right compartment (carinolatus) collected at San Pedro (Los Angeles County, California, USA) from Upper Pleistocene deposits. (a) external view; (b) basal view; (c) alar view; and (d) central view. Photographs by Lindsay Walker.

Figure 3. Cetopirus polysyrinx sp. nov. (paratype), UCMP 131833, isolated right compartment (carinolatus) collected near Cape Blanco (Los Angeles County, California, USA) in Middle Pleistocene (Chibanian) deposits. (a) external view; (b) internal view; (c) radial view; and (d) alar view. Photographs by Bob Day.

Figure 4. Cetopirus polysyrinx sp. nov., close-up of the inner structure of the primary T-shaped flanges, indicated by arrowheads, as observable in transverse cross-section of the shell (broken surfaces). (a) LACMIP 1210.158 (holotype), photograph by Lindsay Walker; and (b) UCMP 131833 (paratype), photograph by Bob Day. Divisions of the scale bars equal 0.1 mm in panel (a) and 1 mm in panel (b).

?1961 Coronula complanata – Zullo, p. 14

?1969 Coronula (Cetopirus) – Newman et al., p. R289

1972 ‘Polysyrinx zulloi’ [unavailable name, published herein as a nomen nudum] – Davis, p. 36 (partim); figs 35–37, 39, 40

Diagnosis: A Cetopirus species in which the secondary T-shaped flanges that comprise the primary outer lamina are internally multitubiferous, being perforated by a high number of irregularly-sized and irregularly-spaced tubules that provide them with a spongy aspect in transverse section.

Holotype: LACMIP 1210.158 (=LACMIP Type 14915), isolated right carinolatus.

Etymology: The new species name derives from the Greek and means ‘many tubes’, which appears very appropriate in light of the multitubiferous condition of its primary T-shaped flanges. The same combination of Greek words was selected by Davis (Reference Davis1972) as the (unavailable) genus name of his (unpublished) new taxon. Thus, our choice also pays a due tribute to Davis' remarkable contribution to cirripedology.

Type locality: LACM locality 1210, San Pedro, Los Angeles County, California, USA (Fig. 1). Davis (Reference Davis1972; 37) further detailed the site as follows: ‘North end of Los Angeles Harbor District Yard, Torrance, Calif. Bed begins 2/5 miles due east of intersection of Westmont Drive and Gaffey Street and runs east for 3/5 mile.’

Type horizon: Palos Verdes Sand Formation, Upper Pleistocene.

Paratype: UCMP 131833, isolated right carinolatus.

Locality and horizon of the paratype: UCMP locality B7380, near Cape Blanco, Curry County, USA (Fig. 1). Port Orford Formation, Chibanian. Davis (Reference Davis1972) further detailed the site of the find as follows: ‘Fossils from bluff sandstone about 75 ft. above beach in the northwest quarter of Sec. 18 (Cape Blanco quad., USGS 1954 ed. map).’

Description, comparisons and remarks: Both LACMIP 1210.158 and UCMP 131833 conform to the typical outline of Cetopirus compartments as detailed in the diagnosis above (Figs 2, 3).

The holotype (note that the same specimen was proposed as the holotype of ‘Polysyrinx zulloi’ by Davis Reference Davis1972) consists of a partly damaged right carinolatus lacking part of the radius as well as the lowermost portion of the paries (although the periphery is locally preserved) (Fig. 2). The sheath is distinctly grooved in its radial portion (corresponding to the alar depression sensu Collareta et al. Reference Collareta, Reitano, Rosso, Sanfilippo, Bosselaers, Bianucci and Insacco2019), less prominently so in its alar portion (Fig. 2d). The thin, small ala displays a serrated distal margin (Fig. 2c). Both the sutural edges of the compartment are as thick as the compartment itself (Figs 2c, d). Judging from its overall morphology, LACMIP 1210.158 was part of a dome-shaped shell.

The paratype (note that the same specimen was proposed as one of the paratypes of ‘Polysyrinx zulloi’ by Davis Reference Davis1972) consists of a right carinolatus that is broken transversely to the ribs some 6–7 mm below the basis of the sheath. The sheath is smooth throughout (Fig. 3b) (Fig. 3). The distal margin of the ala is regularly serrated (Fig. 3D). The sutural edges of the wall plate are almost as thick as the wall plate itself (Figs 3c, d). In profile view (Figs 3c, d), UCMP 131833 features a slightly sigmoidal outer wall that hints at a truncated-conical, irregularly depressed shell shape. This feature may be interpreted as an unusual growth form due to substrate anomalies or clustering with other nearby whale barnacle individuals. A cropped CT-stack and a three-dimensional (3D)-model of UCMP 131833 are available via MorphoSource at https://doi.org/10.17602/M2/M432082 and https://doi.org/10.17602/M2/M432154, respectively.

In both the holotype and the paratype, the primary T-shaped flanges (sensu Collareta et al. Reference Collareta, Newman, Bosio and Coletti2022b) are internally perforated by a high number of irregularly-sized and irregularly-spaced tubules that lend them a spongy aspect in transverse section (Fig. 4). In the Recent species Cetopirus complanatus, each of these flanges is mostly hollow and its ‘opposite [i.e., inner and outer] sides are seen to be connected by shelly longitudinal plates’ (Darwin Reference Darwin1854), the resulting tubules being large and arranged in a single row (Collareta et al. Reference Collareta, Margiotta, Varola, Catanzariti, Bosselaers and Bianucci2016; fig. 4a). In turn, in the extinct species Cetopirus fragilis Collareta et al. Reference Collareta, Margiotta, Varola, Catanzariti, Bosselaers and Bianucci2016, the core of each flange is calcified, and a few tubules occur apart from the main axis of the flange, being aligned parallel to the outer wall and separated from each other by relatively thick septa (Collareta et al. Reference Collareta, Margiotta, Varola, Catanzariti, Bosselaers and Bianucci2016; fig. 4b). The peculiar condition observed in C. polysyrinx sp. nov. was described by Davis (Reference Davis1972; 40) as follows: ‘[t]he outermost laminar complex of the flange possesses one to three longitudinal tubes per septal pair, the majority being two. […] In paratype UCMP XXXXXb [ = 131833], a […] carinolateral plate, […] the number of tubes varies from one to three, the majority being two.’

Davis (Reference Davis1972) regarded LACMIP 1210.158 and UCMP 131833 as representative of a new coronuloid genus and species, which he informally named as ‘Polysyrinx zulloi’. However, both these specimens display characters that are regarded as diagnostic of Cetopirus, namely: flat and broad parietal ribs, which tend to bifurcate symmetrically and lack transverse interlocking crenulations (Darwin Reference Darwin1854); thin and square alae (Darwin Reference Darwin1854); a basal edge of the sheath that does not project freely (Darwin Reference Darwin1854); a rather depressed outline (Pastorino & Griffin Reference Pastorino and Griffin1996); a narrow radius (Pastorino & Griffin Reference Pastorino and Griffin1996) that is strongly striated transversely (Collareta et al. Reference Collareta, Margiotta, Varola, Catanzariti, Bosselaers and Bianucci2016); and primary T-shaped flanges that are internally perforated by longitudinal tubules (Darwin Reference Darwin1854). At the same time, these specimens differ from the other congeners known to date by displaying secondary T-shaped flanges that are internally multitubiferous, and as such, somewhat spongy; furthermore, they differ from C. fragilis by virtue of their thicker sutural edges. All things considered, LACMIP 1210.158 and UCMP 131833 are best interpreted as representing a new, extinct species – Cetopirus polysyrinx sp. nov. – within the Recent genus Cetopirus.

Davis (Reference Davis1972) included two additional specimens in the hypodigm of ‘Polysyrinx zulloi’, namely, an uncatalogued compartment kept in the palaeontological collections of the CAS and UCMP 131832. Whereas the former specimen – originating from UCMP locality B7375 – seems to be lost (Christine Garcia, pers. comm., December 2021), the latter is an isolated carina that seemingly differs from Cetopirus based on at least one character, and as such, is provisionally identified herein as belonging to cf. Cetopirus polysyrinx (see below).

cf. Cetopirus polysyrinx

(Fig. 5)

Figure 5. cf. Cetopirus polysyrinx, UCMP 131832, isolated carina collected near Cape Blanco (Los Angeles County, California, USA) in Middle Pleistocene (Chibanian) deposits. (a) external view; (b) internal view; and (c) right alar view. Photographs by Bob Day.

Referred material: UCMP 131832, isolated carina.

Occurrence: UCMP locality B7376, near Cape Blanco, Curry County, USA. Port Orford Formation, Middle Pleistocene (Chibanian). Davis (Reference Davis1972; 37) described the site of the find as ‘100 ft. south of UCMP locality B7375. UCMP Loc. B7375: 100–200 ft. south of large gully in Sec. 12 (Cape Blanco quad., USGS 1954 ed. map).’

Remarks: While resembling Cetopirus polysyrinx sp. nov., and especially the holotype, in overall outline and outer wall microstructure (Davis Reference Davis1972; fig. 38), UCMP 131832 also displays a strongly grooved sheath and remarkably thin sutural edges (Fig. 5). Whereas the occurrence of strong grooves on the sheath may be considered to be interspecific variability, the thin sutural edges of UCMP 131832 are more difficult to assess taxonomically. Indeed, in Recent Cetopirus shells, the compartmental sutures are not that thin, not even in carinal plates (see e.g., the carina of Cetopirus complanatus illustrated by Pastorino & Griffin Reference Pastorino and Griffin1996; figs 4–6). As both LACMIP 1210.158 and UCMP 131833 resemble C. complanatus in terms of thickness of the compartmental sutures, for the moment we do not include UCMP 131832 within the hypodigm of C. polysyrinx sp. nov. It is hoped that additional finds of this species will shed light on this issue. The quest for new specimens of C. polysyrinx sp. nov. may also include the Middle Pleistocene remains from the Atsumi Group of Japan that were reported by Kobayashi et al. (Reference Kobayashi, Goda, Ohira and Karasawa2008; pl. 1, fig. 22) and Karasawa & Kobayashi (Reference Karasawa and Kobayashi2022; pl. 2, figs. 1–2) as belonging to Coronula sp., as they strongly recall Cetopirus by displaying a short sheath, thick and narrow radii that are externally striated, and low ribs that tend to branch frequently.

A cropped CT-stack and a 3D-model of UCMP 131832 are available via MorphoSource at https://doi.org/10.17602/M2/M432057 and https://doi.org/10.17602/M2/M432151, respectively.

5. Discussion and conclusions

As already observed by Davis (Reference Davis1972), Cetopirus polysyrinx sp. nov. is seemingly unique among extant and extinct coronulid species in that its secondary outer lamina (sensu Collareta et al. Reference Collareta, Newman, Bosio and Coletti2022b) comprises primary T-shaped flanges that are internally multitubiferous and somewhat spongy (Fig. 4). By contrast, the early Pleistocene species Cetopirus fragilis displays fewer tubules within a more calcified secondary outer lamina, whereas in the Recent form Cetopirus complanatus the primary T-shaped flanges are more hollowed out and plate-like septa alternate with large tubules that run parallel to the outer wall. Whether the development of tubules that alternate with longitudinal septa within the primary T-shaped flanges has an adaptive significance is not easily determined. It may have provided the basal edge of the shell with additional grasping structures to supplement the similarly shaped secondary T-shaped flanges in penetrating into a moulting substrate by cutting out thin strings of the host's skin (Collareta et al. Reference Collareta, Newman, Bosio and Coletti2022b); alternatively, it could have represented a solution for enhancing shell growth rates while saving calcium carbonate and preserving structural strength, which in turn may prove useful if space competition and/or hydrodynamic energy are high (Chan & Høeg Reference Chan, Høeg, Thiel and Watling2015; Coletti et al. Reference Coletti, Collareta, Bosio, Urbina-Schmitt and Buckeridge2019). In addition, whether or not C. fragilis, C. polysyrinx sp. nov. and C. complanatus comprise a lineage characterised by a progressive hollowing of the secondary outer lamina is also unclear to date.

The Recent species C. complanatus is currently known as an obligate epibiont of right whales (Mysticeti: Balaenidae: Eubalaena spp.), as no confirmed records exist to date involving other hosts (Chemnitz Reference Chemnitz1785; Darwin Reference Darwin1854; Watson Reference Watson1981; Scarff Reference Scarff1986; Holthuis et al. Reference Holthuis, Smeenk and Laarman1998; Fertl & Newman Reference Fertl, Newman, Würsig, Thewissen and Kovacs2018). A North Pacific record of C. complanatus was provided by Scarff (Reference Scarff1986), who reported on shells of Coronula diadema (Linnaeus Reference Linnaeus1767), Coronula reginae Darwin, Reference Darwin1854 and C. complanatus occurring on a right whale off Half Moon Bay, California, USA. Although Scarff (Reference Scarff1986) identified this cetacean individual as belonging to Eubalaena glacialis (Müller Reference Müller1776), the North Pacific right whales are currently known to comprise a separate species, Eubalaena japonica (Lacépède Reference Lacépède1818) (Rosenbaum et al. Reference Rosenbaum, Brownell, Brown, Schaeff, Portway, White, Malik, Pastene, Pateneude, Baker, Goto, Best, Clapham, Hamilton, Moore, Payne, Rowntree, Tynan, Bannister and DeSalle2000); the latter is currently regarded as endangered (Cooke & Clapham Reference Cooke and Clapham2018), as its western and eastern populations could count no more than 300 and 30 individuals, respectively (Brownell et al. Reference Brownell, Clapham, Miyashita and Kasuya2001; Wade et al. Reference Wade, Kennedy, LeDuc, Barlow, Carretta, Shelden, Perryman, Pitman, Robertson, Rone, Salinas, Zerbini, Brownell and Clapham2010). Another record that seemingly hints at C. complanatus on modern North Pacific right whales is in Oyamada Tomokiyo's book ‘Isanatori Ekotoba’, published in Japanese in 1829 and translated into English (albeit, allegedly, not without errors) by Yamada (Reference Yamada1983) (Omura Reference Omura1986; Scarff Reference Scarff1986). Therein, drawings of stalked and acorn barnacles occur beside illustrations of the baleen and blubber of a right whale; the illustrated cirripedes include a depressed form that the accompanying description mentions as approximating a ‘sake cup’ (which is much reminiscent of the dome-like shell of C. complanatus, although it may also apply to C. reginae) (Yamada Reference Yamada1983; fide Scarff Reference Scarff1986). (It may also be noted that one of the coronulid specimens figured in the ‘Isanatori Ekotoba’ has the shell divided into five compartments; curiously, the associated text also describes whale barnacles as ‘pentagonal or hexagonal’ in shape.)

In light of the host specificity of extant whale barnacles, other (sub)fossil finds of Cetopirus have been regarded as marking the passage of ancient populations of Eubalaena (Álvarez-Fernández et al. Reference Álvarez-Fernández, Carriol, Jordá, Aura, Avezuela, Badal, Carrión, García-Guinea, Maestro, Morales, Perez, Perez-Ripoll, Rodrigo, Scarff, Villalba and Wood2014; Collareta Reference Collareta2016; Collareta et al. Reference Collareta, Margiotta, Varola, Catanzariti, Bosselaers and Bianucci2016, Reference Collareta, Marean, Jerardino and Bosselaers2017; Bosselaers et al. Reference Bosselaers, Van Nieulande and Collareta2017). Cetopirus polysyrinx sp. nov. also was, in all likelihood, an obligate commensal of right whales, either E. japonica or some other species of Eubalaena. Strengthening this interpretation, the occurrence of Eubalaena in the Middle or Upper Pleistocene of the broad North Pacific realm is documented by a single specimen dredged from the sea floor off Taiwan (Tsai & Chang Reference Tsai and Chang2019); furthermore, stratigraphically older finds referred to Eubalaena shinshuensis Kimura et al. Reference Kimura, Narita, Fujita and Hasegawa2007 and Balaenidae indet. are known from the Upper Miocene to Lower Pliocene of Japan (Kimura Reference Kimura2009), whereas specimens of cf. Eubalaena spp. are known from the Pliocene of central California, USA (Boessenecker Reference Boessenecker2013b).

The coasts of North America represent a privileged location for investigating the evolutionary history of the coronuloid barnacles, not least because they are home to the earliest members of this superfamily (Ross & Newman Reference Ross and Newman1967; Zullo Reference Zullo1982; Collareta & Newman Reference Collareta and Newman2020; Perreault et al. Reference Perreault, Collareta and Buckeridge2022). Furthermore, the Pliocene and Pleistocene deposits of the Pacific coast of North America have yielded a rather idiosyncratic fossil coronulid fauna. Indeed, two extinct whale barnacle species have been described on the basis of – and are currently limited to – a few fossil finds from the United States and Mexican West Coast, namely, Cetolepas hertleini Zullo, Reference Zullo1969 and Cryptolepas murata Zullo, Reference Zullo1961. The former is a greatly enigmatic coronuline species of subcylindrical shell shape that is known from the Upper Pliocene (Vendrasco et al. Reference Vendrasco, Eernisse, Powell and Fernandez2012) San Diego Formation of San Diego County, California, USA (Zullo Reference Zullo1969). There is no hint, for this extinct genus and species, of what sort of host it might have been on. Cryptolepas murata was described from Upper Pleistocene deposits exposed at San Quintín, Baja California, Mexico, and is currently regarded as belonging to the same genus as Cryptolepas rhachianecti Dall, Reference Dall1872, an obligate epibiont of grey whales (Eschrichtius robustus (Liljeborg, Reference Liljeborg1861)) (Newman & Abbott Reference Newman, Abbott, Morris, Abbot and Haderlie1980; Bradford et al. Reference Bradford, Weller, Burdin and Brownell2011; Hayashi Reference Hayashi2012; Bosselaers & Collareta Reference Bosselaers and Collareta2016; Taylor et al. Reference Taylor, Abella and Morales-Saldaña2022). (Although Bosselaers & Collareta (Reference Bosselaers and Collareta2016) were hesitant about the genus-level assignment of C. murata, the high-quality photographs provided by Taylor et al. (Reference Taylor, Abella and Morales-Saldaña2022) clearly confirm that this extinct species belongs to Cryptolepas.) Remains of C. murata co-occur with the holotype of C. polysyrinx sp. nov. in the Palos Verdes Sand strata exposed at San Pedro, Los Angeles County, California, USA (pers. obs. by AC, December 2021), thus evoking the co-occurrence of grey and right whales off the Pacific North American coast during the Late Pleistocene. Zullo (Reference Zullo1961, Reference Zullo1969) envisaged C. murata as ancestral to C. rhachianecti, and the former as originating through C. hertleini from a Cetopirus-like ancestor (but see e.g., Davis Reference Davis1972 for an alternative hypothesis). If this inference is correct, the discovery of Pliocene representatives of Cetopirus could be anticipated. Whatever the likelihood of Zullo's phyletic reconstruction, the composition of the North-West Pacific coronulid fossil fauna – including Cetolepas, Cryptolepas and now Cetopirus – seemingly contrasts with all other coeval assemblages worldwide, which are dominated by Coronula spp. (e.g., Beu Reference Beu1971; Bianucci et al. Reference Bianucci, Di Celma, Landini and Buckeridge2006a, Reference Bianucci, Landini and Buckeridge2006b; Buckeridge et al. Reference Buckeridge, Chan and Lee2018, Reference Buckeridge, Chan and Lin2019; Collareta et al. Reference Collareta, Insacco, Reitano, Catanzariti, Bosselaers, Montes and Bianucci2018a, Reference Collareta, Regattieri, Zanchetta, Lambert, Catanzariti, Bosselaers, Covelo, Varola and Bianucci2018b).

6. Acknowledgements

The present work is meant as a homage to the seminal cirripedological work by Clark William Davis (San Francisco State University).

We warmly thank Lindsay Walker (formerly at LACM), Juliet Hook (LACM), Austin Hendy (LACM), Bob Day (UCMP volunteer), Christine Garcia (CAS) and Peter D. Roopnarine (CAS) for their invaluable support throughout the present study. Not only did they search for the specimens that have been studied herein; they also provided precious curatorial information as well as high-quality photographs.

John S. Buckeridge (Earth & Oceanic Systems Group, Royal Melbourne Institute of Technology), Ray T. Perreault (Jarreau Scientific), Giovanni Bianucci (Università di Pisa), Giovanni Coletti (Università di Milano Bicocca) and the late William A. Newman (Scripps Institution of Oceanography) deserve our most sincere gratitude for many fruitful and illuminating discussions in the fields of coronulid palaeontology and neontology. We are sincerely indebted to John W.M. Jagt (Natuurhistorisch Museum Maastricht), John S. Buckeridge and Andrew J. Ross (National Museums Scotland), whose thorough and constructive reviews greatly contributed to improve an early draft of this paper. Not least, thorough support by Susie Cox (Earth and Environmental Science Transactions of the Royal Society of Edinburgh Editorial Office) is also kindly acknowledged.

7. Financial support

Funding and training for computed tomography scanning was provided by the Doris O. and Samuel P. Welles Fund of the UCMP, Department of Integrative Biology, and the FAVE/Tseng Laboratory. The research of the first author is supported by a LinnéSys: Systematics Research Fund grant (funded by the Linnean Society of London and the Systematics Association).

8. Conflicts of interest

None.

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Figure 1. Location of the finds of Cetopirus polysyrinx sp. nov. along the Pacific coast of the USA. Geographical base map after wikimedia.org.

Figure 1

Figure 2. Cetopirus polysyrinx sp. nov. (holotype), LACMIP 1210.158, isolated right compartment (carinolatus) collected at San Pedro (Los Angeles County, California, USA) from Upper Pleistocene deposits. (a) external view; (b) basal view; (c) alar view; and (d) central view. Photographs by Lindsay Walker.

Figure 2

Figure 3. Cetopirus polysyrinx sp. nov. (paratype), UCMP 131833, isolated right compartment (carinolatus) collected near Cape Blanco (Los Angeles County, California, USA) in Middle Pleistocene (Chibanian) deposits. (a) external view; (b) internal view; (c) radial view; and (d) alar view. Photographs by Bob Day.

Figure 3

Figure 4. Cetopirus polysyrinx sp. nov., close-up of the inner structure of the primary T-shaped flanges, indicated by arrowheads, as observable in transverse cross-section of the shell (broken surfaces). (a) LACMIP 1210.158 (holotype), photograph by Lindsay Walker; and (b) UCMP 131833 (paratype), photograph by Bob Day. Divisions of the scale bars equal 0.1 mm in panel (a) and 1 mm in panel (b).

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Figure 5. cf. Cetopirus polysyrinx, UCMP 131832, isolated carina collected near Cape Blanco (Los Angeles County, California, USA) in Middle Pleistocene (Chibanian) deposits. (a) external view; (b) internal view; and (c) right alar view. Photographs by Bob Day.