Redescription of Nothobomolochus triceros (Bassett-Smith, 1898) (Copepoda, Cyclopoida, Bomolochidae), with descriptions of the male and copepodids V-II of the species

Nothobomolochus triceros (Bassett-Smith, 1898), based on specimens recovered from the original host Pampus argenteus (Euphrasen, 1788) in Japan, are redescribed, and the male, both sexes of copepodids V and IV, and sex undetermined copepodids III and II of the species are described for the first time. The maxilliped is sexually dimorphic only in the adult in Bomolochidae, on the other hand, the rostral plate, antennule, and legs 1, 4, and 5 are sexually dimorphic in Nothobomolochus throughout the adult and copepodids V-IV. Sex is as yet undetermined in copepodids III and II in the genus.

Influence of Microalgae Diets on the Biological and Growth Parameters of Oithona nana (Copepoda: Cyclopoida)

Several species of the planktonic free-living genus Oithona have been successfully used in the larviculture of marine fish and shrimp. However, few studies have been published that allow us to estimate the potential of Oithona nana culture under controlled conditions. This work evaluated the effect of the microalgae Isochrysis galbana and Chaetoceros calcitrans as single (200,000 cells/mL) and mixed diets (100,000 + 100,000 cells/mL) on population and individual growth, ingestion rate, number of spawnings, fertility, development time by stage, and sex ratio of O. nana. We cultured this copepod at 28 ± 0.5 °C, 35 PSU salinity, 125 lux, and 12:12 photoperiod. Results showed that diet had no effect on the final population level (6273–7966 ind/L) or on individual growth, nor on sex ratio, with less males than females. With C. calcitrans, O. nana had a higher filtration rate (57 ng C/ind/day). On the other hand, a mixed diet induced a higher number of spawns (0.4 events/day) and nauplii per spawn (23 ind). Similarly, a single or mixed diet, containing I. galbana, accelerated the development rate by 6.33–7.00 days. We concluded that O. nana can be cultured with both microalgae, indicating its potential use in an intensive system for production. However, more research is required to improve the productivity of O. nana rearing.

Redescription of Triceracolax pagri Izawa, 2021 (Copepoda, Cyclopoida, Bomolochidae), with descriptions of copepodids IV and III of the species

Triceracolax pagri Izawa, 2021 is redescribed on the basis of specimens of both sexes recovered from the bucco-branchial cavity of the original host, Pagrus major (Temminck & Schlegel, 1843). Both sexes of copepodid IV and the male copepodid III, collected together with the adults, are described for the first time, and sexually dimorphic features in late copepodid stages are discussed.

Two new marine cyclopinids (Crustacea: Copepoda: Cyclopoida) from interstitial habitats in Korea

Marine cyclopoids, and especially cyclopinids, are poorly studied because their diversity is highest in marginal habitats, such as intertidal interstitial and anchialine caves, or in highly inaccessible abyssal and hadal depths. Two new cyclopinids are described here, both from two different sandy beaches in Korea. Among four species currently recognized in the genus, Heterocyclopina koreaensis sp. nov. is most closely related to H. vietnamensis Pleşa, 1969 from similar habitats in Vietnam. Koreacyclopina wellsi gen. et sp. nov. shares its sexually dimorphic third exopodal segment of the second leg with the Antarctic genus Pseudocyclopina Lang, 1946, but differs from all six known species by numerous features, some of which are observed for the first time within cyclopinids. Both Korean species belong to the family Hemicyclopinidae, but the monophyly of this group has not yet been demonstrated.

Naricolax holinorum sp. nov. (Copepoda, Cyclopoida, Bomolochidae) parasitic in the nasal cavity of the blackhead seabream Acanthopagrus schlegelii (Bleeker, 1854) (Pisces, Sparidae) in Japan

Naricolax holinorum sp. nov. is described based on specimens of both sexes recovered from the nasal cavity of Acanthopagrus schlegelii (Bleeker, 1854) (Pisces, Sparidae) in Japan. This species was erroneously redescribed first as N. atypicus Ho, Do & Kasahara, 1983 by Ho & Lin (2005) based on specimens of the female collected from the nasal cavity of A. schlegelii in Taiwan.

Xarifiid Copepods (Copepoda: Cyclopoida: Xarifiidae) Parasitic in the Coral Psammocora columna Dana, 1846 from Taiwan

A comprehensive knowledge of relationships between coral and coral-associated organisms is essential for the conservation studies of the coral reef community, yet the biodiversity database of coral-inhabiting copepods remains incomplete. Here we surveyed in a widely distributed scleractinian coral, Psammocora columna Dana, 1846, and newly discovered two endoparasitic copepod species, Xarifia yanliaoensis sp. nov. and Xarifia magnifica sp. nov. These two new species are described based on specimens collected in Taiwan, and they share several common morphological characters of Xarifia copepods, i.e., region dorsal to fifth legs having three posteriorly directed processes unequally. However, X. yanliaoensis sp. nov. is distinguishable from other species by the morphology of the endopods of legs, antenna, maxilla, and maxilliped (in both genders). The morphological characters of X. magnifica sp. nov. are the endopods of legs, leg 5, and maxilliped in the male. Including the two new species described in the present work, the genus Xarifia Humes, 1960 belongs to the cyclopoid family Xarifiidae Humes, 1960 currently consists of 94 species, and eight of them live in association with the Psammocora coral. A comparison table and a key to the species of Xarifia from Psammocora corals are given herein.

Study of chromatin diminution in Cyclops kolensis (Copepoda, Crustacea) by radiobiological methods

The experimental results show that at doses of 20 Gy and 100 Gy, the development of Cyclops kolensis Lilljeborg, 1901 (Copepoda, Cyclopoida) embryos ceases at the 16-cell stage, without affecting the course of chromatin diminution. A dose of 200 Gy terminated the process of chromatin diminution in some of the embryos. These results support the hypothesis that cytoplasmic factors in the egg play an important role in the process of chromatin diminution.

Redescription of Naricolax sphyraenae Izawa, 2020 (Copepoda, Cyclopoida, Bomolochidae), with a correctional description of copepodid IV of the species

As in the original description of Naricolax sphyraenae Izawa, 2020, copepodid IV female of the species was described based on a wrong judgement of the sex, the species is redescribed and both sexes of copepodid IV of the species are correctively described, while additionally copepodid V male of the species is described for the first time, based on specimens newly collected from the original host, Sphyraena pinguis Günther, 1874 (Pisces, Sphyraenidae) from Japan.

Genome size in cyclopoid copepods (Copepoda: Cyclopoida): chromatin diminution as a hypothesized mechanism of evolutionary constraint

Genome size is a fundamental property of organisms that impacts their molecular evolution and life histories. The hypothesis that somatic genome sizes in copepods in the order Cyclopoida are small and evolutionary constrained relative to those in the order Calanoida was proposed 15 years ago. Since then, the number of estimates has almost doubled and the taxon sampling has broadened. Here we add 14 new estimates from eight genera of freshwater cyclopoids that vary from 0.2 to 6.6 pg of DNA per nucleus in the soma; all except one are 2.0 pg DNA per nucleus or smaller. This new sample adds to the pattern of genome size in copepods and is remarkably similar to the distribution on which the original hypothesis was based, as well as those of subsequently published estimates. Embryonic chromatin diminution, during which large portions of DNA are excised from the presomatic cell lineage, is reported in Paracyclops affinis (G.O. Sars, 1863). This diminution results in a somatic genome that is one half the size of the germline genome. When the sizes of the germline genomes carried in presomatic cells of cyclopoid species that possess chromatin diminution are considered, the prediminuted germline genome sizes of cyclopoid embryos overlap with the distribution of calanoid somatic genome sizes, supporting the hypothesis that chromatin diminution has functioned as a mechanism to constrain somatic nuclear DNA content in cyclopoid copepods. Geographically based variation in genome size among populations is also reviewed.