Bopyrus crangorum (Fabricius, 1798)

(Fig 2)

= Bopyrus squillarum Latreille, 1804 n. syn.

Material examined: Ovigerous female neotype, 9.5 mm (RMNH. CRUS. I.1667) and mature male (2.15 mm) from non-ovigerous female Palaemon adspersus (22.1 mm CL, including rostrum) collected by P. Buitendijk from Genoa, Italy, July 1927.

Distribution: Eastern part of the temperate Northern Atlantic, western part of the temperate Northern Pacific (Bourdon 1968).

Hosts: Temperate Northern Atlantic: Palaemon adspersus Rathke, 1836 (= P. squilla (Linnaeus, 1758); type host), P. elegans Rathke, 1836, P. serratus (Pennant, 1777), P. xiphias Risso, 1816, Processa edulis (Risso, 1816); temperate Northern Pacific: P. pacificus (Stimpson, 1860), P. serrifer (Stimpson, 1860) (Bourdon 1968).

Remarks: The type species of the genus Bopyrus has almost universally been cited as Bopyrus squillarum Latreille, usually with a publication date of 1802; however, the author and date of the genus name, the correct name for the type species, and the date of the species name are all incorrect. The genus name Bopyrus first appeared on page 83 of Bosc (1801a) (“An X” of the French Republican calendar; published before 22 October 1801 fide Low 2012) with a description of the characters of the genus and a reference to the paper of Fougeroux de Bondaroy (1772) that described, but did not name, a bopyrid found on a shrimp. As no mention of any included species was given, this is not an available name according to the ICZN. The genus name Bopryus next appeared on page 213 of Bosc (1801b) (“An X”; published before 26 December 1801 fide Low 2012) with another description, attribution of the name to Latreille, another reference to the paper of Fougeroux de Bondaroy (1772) and inclusion of Monoculus crangorum Fabricius, 1798 as the sole species in the genus as Bopyrus crangorum (i.e., the type species by monotypy). Note that the genus Monoculus Linnaeus, 1758 was suppressed by the International Commission of Zoological Nomenclature (1954; Opinion 288) but this Opinion did not mention Monoculus crangorum; ostensibly because it is not one of the names originally included in the genus. The genus and species are therefore correctly cited as Bopyrus Bosc, 1801 and Bopyrus crangorum (Fabricius, 1798), however, the use of this name for the type species was questioned by subsequent authors.

The genus name Bopyrus next appeared on page 43 of Latreille (1802) (“An X”; published 6 Nov 1802 fide Dupuis 1986) but with no mention of Bopyrus squillarum. The only species included in Bopyrus by Latreille (1802) was Monoculus crangorum Fabricius, 1798 as was also true for Bosc (1801b). Latreille (1804) (“An XII”; published Feb–Mar 1804 fide Dupuis, 1986) more fully diagnosed Bopyrus and introduced the name Bopyrus squillarum (as “ bopyrus squillarum ”) as a replacement name for Bopyrus crangorum. Latreille’s (1804: 55) rationale as to the need for a replacement name was faulty in that he stated “This species of bopyre will be for me the prawn bopyre, bopyrus (sic) squillarum. As it is not found on the crustaceans that make up the crangon (sic) genus of Fabricius, I do not think I should retain the specific name given to it by this author, monoculus (sic) crangorum ” (translated from the French). Latreille (1804), therefore, replaced the name of the type species for a reason that is not permissible under the ICZN, i.e., simply because he believed that the parasite did not occur on a species of Crangon Fabricius, 1798. The parasite does not, in fact, occur on crangonids but this is irrelevant as to the correct name of the species.

Giard & Bonnier (1890) recognized the priority of Monoculus crangorum as the type species of Bopyrus but further confused matters by abandoning both Fabricius’ and Latreille’s species names and replacing them with their own set of names, each linked to a single species of host (reflecting Giard’s belief that each parasite species had only a single host; see Kuris 1974). They wrote: “The name B. squillarum given by Latreille in 1804 does not have priority: Fabricius had previously (1798) called the same crustacean Monoculus crangorum. As this designation may have suggested that it was a Crangon parasite, it was rejected by all subsequent zoologists, with the exception of Bosc, which was renamed Bopyrus crangorum. But the name Bopyrus squillarum is subject to similar criticism. It may be assumed that the epicarid in question is only a parasite of Palaemon squilla Linné. Even by restricting the use of this appellation and applying it only to the P. squilla parasite, the inextricable complication of synonymy would not be avoided. Therefore, we believe it is better to completely abandon the name given by Latreille, as Latreille abandoned the name given by Fabricius, and we will designate the various species of European bopyrids as follows...” (translated from the French). Giard & Bonnier (1890) provided five new names for what they considered distinct species of Bopyrus, one for each host, and all of which were synonymized with B. squillarum by Sars (1898). However, while Sars (1898) likewise recognized M. crangorum as the senior synonym of B. squillarum (or, as spelled by Sars, “ sqvillarum ”), he nevertheless attempted to justify the continued use of the junior name for the species: “This form was first recorded by O. Fabricius as Monoculus crangorum; but as the specific name proposed by that author involves a confusion of shrimps with prawns, it is impossible to retain it and therefore, though the older one, it ought to give place to that proposed by Latreille.” We are unclear as to what Sars’ precise issue with shrimps versus prawns was, as these are common names and have been subject to different interpretations over time. Currently, “shrimps” are generally considered to be carideans while “prawns” are dendrobranchiates but also Palaemon spp. and Macrobrachium spp.; however, it may have been different in 1898 (both Crangon and Palaemon are caridean genera). It should also be pointed out that the author of M. crangorum was J. C. Fabricius, not O. Fabricius.

The reasons given for replacing the name Monoculus crangorum by Latreille (1804) and Giard & Bonnier (1890) are not allowed under ICZN Article 18 (“The availability of a name is not affected by inappropriateness…”). If these names were competing names independently given to the same taxon by different authors (i.e., synonyms), then the argument could be made to have the senior synonym suppressed in favor of the commonly used B. squillarum but these are not competing names sensu ICZN Article 23 as B. squillarum is an invalid replacement name for M. crangorum and reversal of precedence is therefore not possible. The valid name for the type species of Bopyrus Bosc, 1801 (not Latreille 1802) is Monoculus crangorum Fabricius, 1798 in the combination Bopyrus crangorum (Fabricius, 1798).

The type host of B. crangorum is Palaemon squilla (Linnaeus, 1758) fide Fabricius (1798); the current name for this species is Palaemon adspersus Rathke, 1836 (see De Grave & Fransen 2011). It is not clear how many female specimens Fabricius examined and he did not describe the male of the species. In any case, the type specimen(s) of Monoculus crangorum is/are not extant (Zimsen 1964). Given the multiple names used by Giard & Bonnier (1890) for specimens occurring on different hosts and the possibility of cryptic species, especially given the geographic and host range of this species, we, in the interest of fixing the name of the type species, hereby select a dextral ovigerous female, 9.5 mm (RMNH.CRUS. I.1667) as the neotype of Monoculus crangorum Fabricius, 1798 (Fig. 2C, D); the neotype is accompanied by a mature male (2.2 mm) (Fig. 2E, F) and parasitized a non-ovigerous female Palaemon adspersus (Fig. 2A, B; 22.1 mm CL including rostrum; originally identified as P. squilla by A.M. Buitendijk; ID verified by C.H.J.M. Fransen, Aug 2022), collected by Buitendijk from Genoa, Italy in July 1927. The species was redescribed in detail by Bourdon (1968) based on a female and male pair obtained from a specimen of P. serratus (18.9 mm CL excluding the rostrum); he examined numerous specimens obtained from four different species of Palaemon from France and Italy, including the specimen selected here as the neotype.

Note that records of B. squillarum (e.g., Chopra 1923; Savant & Kewalramani 1964; Deshmukh 1987) from the Western Indo-Pacific on Palaemon styliferus (H. Milne Edwards, 1840) and Nematopalaemon tenuipes (Henderson, 1893) should all probably be referred to Bopyrus bimaculatus Chopra, 1923.

Note on monogenean flatworms putatively associated with bopyrid isopods: The monogenean Allodiclidophora squillarum (Parona & Perugia, 1889) Yamaguti, 1963 was originally reported from Bopyrus squillarum collected in the Adriatic Sea. Although there are verified reports of monogeneans attached to cymothoid isopods that feed on primary fish hosts (see Bouguerche et al. 2022), Parona & Perugia (1889) is the only report of a monogenean/bopyrid association. Parona & Perugia (1889) did not mention the identity of the host of B. squillarum and many authors have repeated this record without comments (Price 1943; Dawes 1956; Bychowsky 1961). At least some authors erroneously assumed that the host of B. squillarum was a fish (Bychowsky 1961; Radujković & Šundić 2014). In fact, Yamaguti (1963) erected Allodiclidophora with Mesocotyle squillarum as the type species and indicated as part of the generic diagnosis that species in this genus were “parasitic on Cymothoba (sic) in mouth cavity of Maenidae.” This is clearly in error and other authors may have similarly assumed that B. squillarum is a cymothoid. As indicated by Overstreet (1983) and Bouguerche et al. (2021), the host of B. squillarum is a shrimp. Considering that subsequent to the report of Parona & Perugia (1889) no monogeneans have been recorded from any bopyrid, it is possible that the report is a case of a sampling error (i.e., the monogenean fell off a fish host and was incidentally collected with B. squillarum). A study of the morphology of A. squillarum and the fact that other monogeneans associated with parasitic crustaceans (cymothoids and caligid copepods) are epibionts of the crustaceans that feed on the fish hosts (Ohtsuka et al. 2018; Bouguerche et al. 2022), we feel it is highly unlikely that A. squillarum feeds on a bopyrid or shrimp host. Bouguerche et al. (2021) listed B. squillarum as a host of the monogenean Cyclocotyla bellones Otto, 1823 but presumably this is an error due to others (e.g., Radujković & Šundić 2014) who previously considered A. squillarum a synonym of C. bellones.