A new species of Caligus (Copepoda, Siphonostomatoida) from the plankton of the Caribbean coast of Venezuela with a key to species

Resolving taxonomic and nomenclatural problems in the genus Caligus O.F. Mller, 1785 (Copepoda: Caligidae)

Supplementary descriptions are provided for six poorly known species of Caligus, based on a study of type and other material carried out by the late Roger F. Cressey but never published. As part of that study new illustrations were produced by Hillary Boyle Cressey who has kindly made these previously unpublished drawings available to this paper. The present account also contains critical re-assessments of the validity of several other species of Caligus Mller, 1785. It is proposed to recognise that: C. glacialis Gadd, 1910 and C. raniceps Heegaard, 1943 are junior subjective synonyms of the type species C. curtus Mller, 1785 and we consider the published geographical locality given for C. raniceps by Heegaard (1943) to be erroneous; C. guerini Guiart, 1913 is a junior subjective synonym of C. elongatus von Nordmann, 1832; C. mordax Leigh-Sharpe, 1934 is a junior subjective synonym of C. coryphaenae Steenstrup & Ltken, 1861; C. lessonius Risso, 1826 is not a caligid and is probably a junior synonym of the pandarid Demoleus heptapus (Otto, 1821); C. clavatus Kirtisinghe, 1964 is a junior subjective synonym of C. sphyraeni Pillai, 1963; C. rotundigenitalis Y, 1933 is a junior subjective synonym of C. torpedinis Heller, 1865; C. hyalinae Heegaard, 1966 is a junior subjective synonym of C. chelifer Wilson, 1905; C. biseriodentatus, Shen, 1957 is a junior subjective synonym of C. pauliani Nues-Ruivo & Fourmanoir, 1956; and C. cornutus Heegaard, 1962 can be formally treated as a junior subjective synonym of C. lobodes (Wilson, 1911) because the name C. cornutus belongs with the male holotype; the female allotype collected by Heegaard (1962) remains unidentified. We also conclude that C. mebachii Marukawa, 1927 was based on a young male of Euryphorus brachypterus (Gerstaecker, 1853) and a male of Caligus coryphaenae Steenstrup & Ltken, 1861 which was mistakenly identified as the female. A lectotype is designated for C. mebachii and this species is treated as a synonym of Euryphorus brachypterus. It is noted that C. hamatus Heegaard, 1955 is conspecific with, and has priority over, C. undulatus Shen & Li, 1959. However, given that C. undulatus is a high profile and well known species, frequently recorded from across the Pacific, Indian and Atlantic oceans, a case has been submitted to the ICZN to grant precedence of C. undulatus over C. hamatus. We reject the transfer of Chalimus tenuis Leidy, 1889 to Caligus by Fowler (1912) on the basis of lack of evidence supporting the transfer, and return it to Chalimus, where it can be treated as a species inquirendum within a genus that is no longer considered as valid. We consider that C. alalongae Kryer, 1863 and C. gracilis Dana, 1852 are species inquirenda. Caligus truttae is a nomen nudum because Giard (1890) provided no morphological information or illustration associated with the new name.

Morphological analysis of Caligus elongatus von Nordmann, 1832 (Copepoda: Caligidae) from the rosy goatfish Parupeneus rubescens (Mullidae)

Copepods are a common component of ectoparasite assemblages of all kinds of fish, from all environments and ecosystems. In the present investigation, a total of 80 specimens of the rosy goatfish Parupeneus rubescens were randomly collected from the Arabian Gulf, and then transported to the laboratory in order to be dissected and examined for the presence of copepodid infections. Copepod parasites were recovered from the gills of the infected fish. One copepod species within the Caligidae family was identified and labeled as Caligus elongates von Nordmann, 1832. This copepod species examined using light and scanning electron microscopy to observe the most characteristic generic features. Morphological and morphometric characterizations revealed differences between the identified species and other related copepodid species. Therefore, the present study showed that the rosy goatfish is a new host for this Caligus species and added a new locality record for this infection.

Discovery of the fish host of the 'planktonic' caligid Caligus undulatus Shen & Li, 1959 (Crustacea: Copepoda: Siphonostomatoida)

The siphonostomatoid copepod Caligusundulatus Shen & Li, 1959 has been widely reported from plankton samples obtained from neritic and oceanic waters off coasts of the Indo-West Pacific and Atlantic Oceans. Until now, its fish host has remained unknown. This copepod belongs to an intriguing group of congeners that, despite being part of a chiefly parasitic group, are consistently found as zooplankters. Quite unexpectedly, in October 2019, a fish host of C.undulatus was discovered in the Seto Inland Sea, Japan—namely, the Japanese sardinella Sardinellazunasi (Bleeker, 1854). Both juvenile (chalimus) and adult individuals of this caligid were observed as parasites of the fish host. The discovery suggests that the species has an alternative life cycle as previously proposed for other purportedly ‘planktonic’ congeners and might frequently switch hosts during the adult stage. Thus, the C.undulatus group is newly proposed as a species group in the genus, in which five species are known as planktonic. Some hypotheses on the modified life cycle of caligids also briefly discussed.

Two new species of the genus Caligus (Crustacea, Copepoda, Siphonostomatoida) from the Sea of Japan, with a note on the establishment of a new species group

Two new species of Caligus are described from the Japanese coast of the Sea of Japan. Caliguschinglonglinisp. nov. is based on a male specimen found in a plankton sample, whereas C.kajiisp. nov. was collected from the body surface of the host flathead Platycephalus sp. These two new species can be assigned to a distinct species group, the pseudorhombi group newly named and defined by the morphology of the genital complex in both sexes, and by the structure and armature of legs 2 and 4. The species group so far accommodates 19 species including these two new species. The morphology, host specificity and zoogeography of the species group are discussed herein and keys to species groups of Caligus and to species of the C.pseudorhombi species group are provided.