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Data on the external morphology are reviewed and new information is provided about the structure of the first naupliar instar of Parthenopea subterranea Kossmann, a rare and poorly known species of rhizocephalan barnacles. The taxonomic position of P. subterranea, which has so far been uncertain, is discussed. A new family, Parthenopeidae fam. nov., is erected to include a single genus, Parthenopea, with a single species, P. subterranea. The distinctive characters of the new family are described.

Data are presented about the invasion level of commercially important crabs in the Sea of Okhotsk by rhizocephalan barnacles. Some general information concerning the structure, life cycle, and reproductive strategy of the parasitizing rhizocephalans and the effect on the Decapoda host. Practical recommendations have been proposed to decrease the infestation level in populations of commercially important crabs and to prevent parasitization of healthy populations.

We studied the infestation level of the coastal crab Hemigrapsus sanguineus by a cirripede barnacle Polyascus polygenea in Peter the Great Bay (Vostok Bay, Sea of Japan) in 1998–1999. It is shown that the externae of the parasite usually appear on the surface of the host’s body at the time when the crab attains sexual maturity (at a carapace width of 14–15 mm). More often we encountered infested crabs of a medium size, with a carapace width of 25–29 mm. The level of crab invasion did not depend on the sex of the host. In the summer period the proportion of infested crabs in different habitats ranged from 7 to 84%. The greatest number of crabs bearing the externae of the parasite was registered in an area with a boulder-pebble surface and small surf waves.

The effects of seawater temperature (12, 16, 20, 22, and 25°C) and salinity (of 8 to 34‰) in different combinations on the larvae of the rhizocephalan Peltogaster reticulatus (Crustacea: Cirripedia), a parasite of the hermit crab Pagurus proximus, were examined. The development of P. reticulatus is comprised of five naupliar stages and one cypris stage. Nauplii have a specific structure, the flotation collar encircling the dorsal side of the larval body. Larvae lack the pigmented nauplius eye, and they show no positive phototaxis. Successful naupliar development occurred in temperature and salinity ranges of 16–25°C and 20 to 34‰, respectively; but all nauplii died at 12°C and 16‰. The duration of each naupliar stage increased under lowering of the seawater temperature. At 22–25°C and 26–28‰, the entire development cycle was completed in 72–80 h; and at 16°C and 20‰ it lasted 153 h. The cypris larvae showed a greater resistance to decreased salinity in comparison with the nauplii. At temperatures of 16–25°C and salinities of 14 to 34‰, the lifespan of cyprids was 6 to 12 days, and it decreased at increasing temperature.

We performed histological studies on trophic and reproductive systems of colonial interna in Sacculina polygenea, a parasite of the coastal crab Hemigrapsus sanguineus. The trophic system that performs functions of absorption, accumulation, and transportation of nutrients from the hemolymph of the host comprises the trophic epithelium of distal canals and transporting trunks. The reproductive system of interna consist of nuclei (early stages of development of the primordia of externae) and the primordia of externae in later stages of development. It has been shown that during morphogenesis of the nucleus two primordia arise, a primordium of the externa itself and a primordium of its trophic system. In the primordium of the ovary, we found oogonia; early oocytes and vitellogenic oocytes were found in the ovaries of the late primordia of the externae. The damaging effects of the interna on the ovaries and testes of the crab host are discussed. Thus, we have found numerous elements of reproductive and trophic systems in the colonial interna of S. polygenea. The term individual is proposed to be used for the externa in rhizocephalan barnacles with its trophic system.

The responses of the larvae of the cirripede barnacle Peltogasterella gracilis (Crustacea: Cirripedia: Rhizocephala) that parasitizes the hermit crab Pagurus pectinatus to different combinations of seawater temperature (25, 22, 20, 16, and 12°C) and salinity (from 34 to 8‰) were studied in a laboratory. The nauplii of P. gracilis completed the entire cycle of development at 22 to 12°C in a narrow range of salinity (from 34 to 28‰), which agrees well with the environmental conditions of the crab hosts' habitat. At favorable temperatures (22–20°C) and salinity (34–28‰), the nauplii reached the cypris stage in 88 ± 2 h, while at 12°C and 34–30‰, the naupliar development took 156 ± 5 h. The cypris larvae appeared more resistant compared with the nauplii, in terms of changes in both the temperature and salinity of seawater. They actively swam at all experimental temperatures and in the salinity range of 34–18‰. At temperatures (22–16°C) and salinities (34–24‰) favorable for the cyprids, their longevity in plankton equaled 6–10 days. Thus, the nauplii of P. gracilis is the more vulnerable stage of development in the life cycle of this parasitic barnacle. The tolerance against changes in environmental factors is due to the adaptive capabilities of parasitic larvae and the environmental conditions in the habitats of its host, a typical marine crustacean. The insignificant parasitization rate of the hermit crab by its rhizocephalan parasite may be explained by the death of the nauplii of P. gracilis, which occurs when they enter to the surface water layer.

Larval development of the rhizocephalanSacculina polygenea (Crustacea: Cirripedia: Rhizocephala) parasitizing the coastal crabHemigrapsus sanguineus was studied in Vostok Bay, the Sea of Japan. At 22–23°C, the entire cycle of larval development takes 2.5 days and includes five naupliar stages and one cypris stage. Like other rhizocephalans, the larvae ofS. polygenea are lecithotrophic and only grow slightly in size in the course of development, and like all sacculinids, they have no flotation collar. The naupliar stages IV and V have a tubercle between the furcal rami; this tubercle is absent in the larvae of the genusPeltogasterella, but it has been described inS. carcini. The first seta of the antennule only disappears completely at the fourth stage, although it is markedly reduced at the third stage. No morphological differences, except differences in size, are found between male and female nauplii.

We carried out an in vitro histological and TEM investigation of the organization of the interna of Peltogasterella gracilis(Crustacea: Rhizocephala), a parasite of the hermit crab. The colonial interna of P. gracilisincludes a reproductive system with multiple nuclei (externa rudiments) and a trophic system of absorbing lampbrush and transportation canals. The nucleus forms a cluster of embryonic stem cells. In the distal parts of the trophic system, there are cells that function in the absorption, processing, and storage of trophic substances. Cells filled with trophic resources disintegrate (evidently by apoptosis), releasing trophic substances and cell remnants into the canal cavity formed through this process. The parasitic phase of the P. gracilislife cycle is characterized by the loss of the basic morphological features and complete pattern of organization of the arthropods and by chaos and fractalization in the interna.

We studied, under laboratory conditions, the larval development of a rhizocephalan barnacle Sacculina pilosellaVan Kampen et Boschma, 1925, which parasitizes the kelp crab Pugettia quadridens(de Haan) in Vostok Bay, Sea of Japan. It is shown that at 22–23°C, the whole cycle of larval development takes about 3 days. The larvae of S. pilosellaare lecithotrophic; their development, like in other rhizocephalans, comprises five naupliar instars. Like the larvae of all sacculinids, the nauplii of S. pilosellahave no flotation collar. In their structure, the larvae of S. pilosellaare similar to the nauplii of the “typical” sacculina, S. carcini(elongated body outline, long furcal branches, and weakly pronounced segmentation of the abdomen). On the other hand, the characteristic outgrowth inbetween the furcal branches that is characteristic of stages IV and V in S. carciniand S. polygeneais absent in the larvae of S. pilosella.The first seta on the antennula of S. pilosellacompletely disappears only at stage IV; however, at stage III, it is already significantly reduced. No morphological differences have been revealed between male and female larvae of S. pilosellaexcept certain size differences.