The parasitic polychaete known as Asetocalamyzas laonicola (Calamyzidae) is in fact the dwarf male of the spionid Scolelepis laonicola (comb. nov.)

Abstract

Abstract. The morphology of the obligately ectoparasitic polychaete Asetocalamyzas laonicola was studied by light and electron microscopy, and its taxonomic position was determined using molecular methods. The parasite has an extensive coelomic cavity, complete septae, and well‐developed segmental nephridia, circulatory, and digestive systems. The nervous system is rudimentary and without ganglia. The parasite's anterior region penetrates the tissues of the host, and opens into the host's body cavity. The epidermal tissues of the parasite and the host are highly integrated in the area of contact, and the parasite's cuticle is continuous with that of the host. Blood vessels of the parasite and the host may interlace in the fusion zone. The dorsal side of the parasite faces the dorsal side of the host. All parasites were males, but all hosts were females. In order to elucidate the uncertain systematic position of the parasite, molecular systematic studies were conducted. Parasite and host 18S rDNA sequences were virtually identical and revealed that both belong to the spionid cluster. These sequences differed from those of Scolelepis squamata and Scolelepis bonnieri by 2.7% and 0.9%, respectively. In addition, of seven partial sequences of the mitochondrial COI gene obtained from three parasites and four hosts, six were identical, and in one host–parasite pair, COI sequences differed by one substitution. Partial ITS2 sequences from one host–parasite pair were analyzed and also found to be similar but not identical, with two indels in a 645‐bp alignment. We conclude that the parasite is in fact a dwarf male of its conspecific spionid female host. Consequently, A. laonicola is transferred to Scolelepis (Spionidae), forming the new combination Scolelepis laonicola.

Two apparently unrelated groups of symbiotic annelids, Nautiliniellidae and Calamyzidae (Phyllodocida, Annelida), are a clade of derived chrysopetalid polychaetes

“…Aguado and San Mart ın (2009) did not consider C. amphictenicola for their phylogenetic analyses within Syllidae due to its uncertain position. Asetocalamyzas laonicola Tzetlin 1985 was initially placed within Calamyzidae but later was found to actually be dwarf males of the spionid Scolelepis laonicola (Tzetlin, 1985) by Vortsepneva et al (2008). Miura and Laubier (1989) were the first to discuss the similarities of C. amphictenicola and Nautiliniellidae, but explained their resemblance was convergence based on their similar ectoparasitic life.…”

Morphology of the nervous system of monogonont rotiferEpiphanes sentawith focus on sexual dimorphism between feeding females and dwarfed males

“…Among Spiralia (to which rotifers belong(40-42)) it has been reported in e.g. Cycliophora(43-47), Orthonectida(48), which are now considered parasitic annelids(49, 50), some octopi(51) and in several annelid clades including some dinophilids(52-54), Osedax (55-57), Spionidae(58, 59) and bonellid echiurans(60). There are two proposed mechanisms responsible for the origin of dwarfism: progenesis or reduction(61, 62), which are reflected in the morphology of the dwarfed forms, including their nervous system and musculature(52).…”

Species

“…It is not rare in initial observations of a group of organisms to be unable to know which are male and which are female, and due to their divergence in numerous characters, to actually assign them to different species. One recent example of this is the case study of Vortsepneva et al ( 2008 ), with the polychaete (an annelid worm) Asetocalamyzas laonicola , in the family Calamyzidae, initially described as a parasite of a polychaete in the Spionidae family. The authors offered new data on the organisms involved in this association.…”