A new species of Peniculus (Copepoda: Siphonostomatoida) parasitizing mesopelagic myctophid fish: first discovery of colonization of the genus in deep water

Susumu Ohtsuka,Jun Nishikawa,Geoffrey A Boxshall

doi:10.1051/parasite/2018057

Abstract

Peniculus hokutoae n. sp. is described on the basis of an ovigerous adult female parasitizing the caudal fin of the myctophid fish Symbolophorus evermanni (Gilbert, 1905), collected from Suruga Bay, Japan. This is the first record of parasitism by this genus on mesopelagic myctophid fish. The new species is easily distinguished from other congeners in: (1) the presence of a conical process anterior to the rostrum; (2) the secondary elongation of the first pedigerous somite; (3) the incorporation of the third and fourth pedigerous somites into the trunk; (4) the unilobate maxillule bearing two unequal apical setae; (5) the lack of any processes on the first segment of the maxilla. Four morphological patterns of the cephalothorax, neck and anterior parts of the trunk can be found in the genus. We infer that initial colonization of a mesopelagic myctophid fish as host is likely to have occurred when the diurnally-migrating myctophid host was feeding in near-surface waters at night and was exposed to infective stages of Peniculus.

Highlights

The siphonostomatoid family Pennellidae is a group of highly transformed copepods typically infesting fish as their final hosts, as meso- or ectoparasites [4]
Castro-Romero [7] established the two new genera Propeniculus and Pseudopeniculus to accommodate two species formerly placed in Peniculus
Moon and Choi [17] independently described a new species of Peniculus, P. quadratus Moon & Choi, 2014 from Korea, and mentioned that 15 species were accommodated in the genus, including species belonging to Propeniculus and Pseudopeniculus

Summary

Introduction

The siphonostomatoid family Pennellidae is a group of highly transformed copepods typically infesting fish as their final hosts, as meso- or ectoparasites [4]. Myctophid fish are one of main host groups for these deep-sea pennellids [3, 20]. During deep-sea zooplankton surveys in Suruga Bay, middle Japan by Tokai University, an undescribed species of the pennellid genus Peniculus infesting the caudal fin of a myctophid fish (Fig. 1A) was found, in addition to the recent discovery of a new pennellid genus and species Protosarcotretes nishikawai Ohtsuka, Lindsay & Izawa, 2018 [Japanese name: houraieso-no-namida (new), Japanese, meaning a tear drop of Pacific viper fish] parasitic on Pacific viper fish [20]. The present paper provides a taxonomic description of the. Undescribed new pennellid on the myctophid fish, together with notes on host-specificity, distribution and colonization of Peniculus

Materials and methods

Discussion