New annelid species from the deepest known whale-fall environment: Bathykermadeca thanatos sp. nov. (Annelida: Polynoidae)

A new species of polynoid annelids, Bathykermadeca thanatos sp. nov., is described based on specimens collected from sunken whale bones in the Nansei-Shoto Trench in the Philippine Sea at a depth of 4974 m. The cetacean-carcass community at the site exceeds the deepest record reported to date. This new species can be distinguished from other members of the genus by the following features: i) there is only one type of neurochaetae, ii) the teeth lack serration and grow inwardly, iii) median antenna extends beyond the tip of frontal filament, iv) nephridial papillae are present in segments 12–15, and v) there are about 50 notochaetae in each parapodium.

Free-living stages of the parasitic copepod Lernanthropinus labracoglossae Izawa, 2014 (Siphonostomatoida, Lernanthropidae), reared from eggs

Free-living stages, comprising two naupliar stages and the infective copepodid I, of the parasitic copepod Lernanthropinus labracoglossae Izawa, 2014 are described. The larvae were reared from eggs detached from an ovigerous female, recovered from the branchial lamellae of the Japanese actinopterygian fish Labracoglossa argentiventris Peter, 1866 (Kyphosidae). The number of naupliar stages prior to copepodopid I in the Lernanthropidae is the same as in the Caligidae, Pseudohatschekidae and Trebiidae. The copepodid I of the species has a frontal filament, as do representatives of the Caligidae, Pandaridae and Trebiidae. However, this is regarded as a vestigial feature in the last two families. Copepodid I of L. labracoglossae has a 6-segmented antennule, including the naked first segment, as do the first copepodids of eudactylinid copepods.

Artificial Settlement of Sea Lice, Caligus Rogercresseyi Boxshall & Bravo, 2000 (copepoda, Caligidae), on Tissues of Fish Used As Substrate

Caligus rogercresseyi is the main ectoparasitic copepod affecting salmon and trout farming in Chile. The aim of this study was to evaluate under laboratory conditions the ability of copepodids of C. rogercresseyi to settle on fin, scale, and skin tissues taken from a wild host, the rock cod (Eleginops maclovinus) and an exotic host (Oncorhynchus mykiss), and evaluate the effects of inductors, such as conditioned water and fish mucus, on the process. The assessment was carried out simultaneously for each host and inductor, using a single pool of larvae (N = 1800). Three replicates per treatment were done and the settlement as well as the development stage of the frontal filament were recorded after 24 h. A total of 341 copepodids were able to settle on the different tissues and hosts. The host showing the higher settlement was E. maclovinus (N = 215; 23.9%) compared to O. mykiss (N = 126; 14%); the tissue showing the higher number of settled copepodids was the skin (N = 126; 48.4%), followed by fin (N = 140; 41.1%) and scales (N = 36; 10.5%). Regarding inductors, neither conditioned water (N = 112; 32.8%) nor mucus (N = 113; 33.1%) showed significant differences with the control without inductor (N = 116; 34%). Inductors did not have a significant effect on the development of the frontal filament, neither for E. maclovinus, nor for O. mykiss tissues, thus suggesting the tissues used were able to induce a positive response on these processes. This is the first work reporting a successful settlement of a species of sea louse in tissue extracted from fish.

Changes in structure of the frontal filament in sequential developmental stages of Caligus elongatus von Nordmann, 1832 (Crustacea, Copepoda, Siphonostomatoida)

The frontal filament of larval and adult Caligus elongatus was examined using light and electron microscopy. No trace of a frontal filament was evident in eggs, nauplii, or young copepodids. The structure develops in older copepodids in a cuticular pocket in the cephalothorax. Upon infecting a fish, the filament extrudes and attaches permanently to the host. The subsequent chalimus stages inherit the filament. Before moulting, the "frontal organ" produces an extension lobe, which is attached to the old filament by each subsequent chalimus stage during the moult. The structure of the frontal filament is described and illustrated, as well as some details of the frontal organ. Some new terms are proposed for the elements of the filament and the organ. The suggestion is made that the life cycle of C. elongatus includes five, not four, chalimus stages.

Moulting and mating in Lepeophtheirus pectoralis (Copepoda: Caligidae)

Prior to moulting, the preadult Lepeophtheirus pectoralis produces a temporary frontal filament which attaches the animal to the surface of the host during ecdysis. This filament is extruded from a frontal organ previously thought to have a chemoreceptory function. During ecdysis the exuvium splits at the anterior margin and is shed posteriorly by contractions of the body. After hardening of the exoskeleton the copepod detaches itself from the frontal filament and is free-living on the host during intermoult. Males in precopula position hold on to the dorsal side of the female, with the second antennae grasping the anterior end of the female's genital complex. During the ecdysis of the female, most males release their hold on the female, and are usually found close to her on the host. Copulation occurs between an adult male and an adult female with a hardened exoskeleton. In the copula position the male holds on to the female's genital complex with the second antennae, but now on the ventral side of the female. Two spermatophores are extruded and then transferred simultaneously to the female with the aid of the second pair of swimming legs. Tubes originating from the spermatophores connect them to the orifices of the receptaculum seminis. These tubes seem to grow out of the spermatophores after expulsion. After copulation, the male retains a precopula position before releasing the female. No agonistic behaviour has been observed between a precopulating/copulating male and additional males. However, during the ecdysis of the female, a new male may take over the female, but mating does not seem to be assortative for size in Lepeophtheirus pectoralis.

Developmental stages of Alebion lobatus Cressey, 1970 (Copepoda: Euryphoridae) found parasitic on the sandbar shark (Carcharhinus plumbeus (Nardo, 1827)) in the western North Atlantic, and a phylogenetic analysis of the genus Alebion Krøyer, 1863

Three stages of copepodids, two preadults, and male and female adult Alebion lobatus collected from sandbar sharks (Carcharhinus plumbeus) in the western North Atlantic are described. Copepodids were found on the external body surface of hosts in hollows which were apparently formed by the absence of one to several placoid scales. A frontal filament was not observed in any developmental stage and the second antennae appeared to be the primary prehensile appendages. Two equally most parsimonious cladograms are presented as hypotheses of phylogenetic relationship for the eight known species of Alebion.

Experimental Studies of the Reproductive Behaviour of the Parasitic Copepod Lernaeocera Branchialis (Pennellidae)

Egg-producing Lernaeocera branchialis (L.) are usually found in the gill cavity of cod (Gadus morhua (L.)) and whiting (Merlangius merlangus (L.)) (Kabata, 1979). The early larval development of the copepod includes two free-swimming nauplius stages followed by the first infective stage, the copepodite (Sproston, 1942). On an intermediate host, usually flounder (Platichthys flesus (L.)), the copepodite moults into a chalimus larva which is attached by its frontal filament to the gill tips of its host. After four successive chalimus stages, the parasite reaches maturity and copulation occurs on the flatfish host.