Whole-body regeneration, the ability to reconstruct complete individuals from small fragments, is rare among ribbon worms (phylum Nemertea) but present in the pilidiophoran species Lineus sanguineus. This species can regenerate complete individuals from a tiny midbody section, and even from a quarter of a piece, provided it retains a fragment of a lateral nerve cord. While a few other unrelated species of ribbon worms are also excellent regenerators, L. sanguineus is unique in having evolved its regenerative abilities quite recently and thus offers an exceptional opportunity to gain insight into the evolutionary mechanisms of regeneration enhancement. Interestingly, both its sister species Lineus lacteus and Lineus pseudolacteus, a third species derived from the recent hybridization of the other two, differ in their regeneration abilities: while L. lacteus is uncapable of regenerating a lost head, L. pseudolacteus is capable of anterior regeneration, albeit at a slower rate than L. sanguineus. L. sanguineus has a worldwide distribution in temperate shores of both hemispheres, is readily found at intertidal habitats, and can survive, feed and be bred through asexual replication with minimal effort in laboratory settings. All the above make this species a superb candidate for studies of regenerative biology. In this chapter, we present protocols to collect, identify and breed L. sanguineus to study the extraordinary whole-body regeneration abilities found in this species.

We performed molecular phylogenetic analyses using nucleotide sequence data from five genes (16S rRNA, cytochrome c oxidase subunit I, 18S rRNA, 28S rRNA, histone H3) determined from 36 specimens representing 25 (10 named, 15 unnamed) species of lineid heteronemerteans collected in Sagami Bay, Japan, along with other sequences obtained from public databases. External features of the 25 species are briefly described and illustrated. Lineus fuscoviridis Takakura, 1898 is transferred to Notospermus Huschke, 1830. Our molecular analysis indicated that one of our Notospermus specimens from Sagami Bay and material previously collected from the Seto Inland Sea are conspecific with Notospermus geniculatus (Delle Chiaje, 1822) s. str. [the year of publication is not 1828 as previously regarded], originally described from Naples, Italy. The new species Siphonenteron nakanoi is established; our tree shows it as the sister taxon to Siphonenteron bilineatum Renier in Meneghini, 1847; it differs from the latter in having more diffuse, scattered yellow pigmentation at the anterolateral margin of the head on each side. Pros and cons of lumping and splitting Lineidae in future studies are discussed.

Having been reported in 1898 for the first time from Japanese waters, the lineid heteronemertean Lineus longifissus auct. is known to inhabit tidal flats under the influence of the warm Kuroshio Current along the coasts of Honshu and southwestward, characteristically with a uniformly raisin-colored to black body lacking a caudal cirrus. The taxonomic identity of the Japanese L. longifissus auct. has been questioned by specialists because of some obvious morphological differences between Lineus longifissus (Hubrecht, 1887) s.str. (now in Heteronemertes Chernyshev, 1995), originally described from the subantarctic region. In the present study, we describe the Japanese L. longifissus auct. as Corsoua takakurai sp. nov. Before the present study, the genus Corsoua Corrêa, 1963 had been monotypic with the type species Corsoua kristenseni Corrêa, 1963 from the Caribbean. We infer the phylogenetic position of Corsoua takakurai within Lineidae based on the mitochondrial 16S rRNA and cytochrome c oxidase subunit I, and the nuclear 18S rRNA, 28S rRNA, and histone H3 genes.

Micrura alaskensis Coe, 1901 is a common intertidal heteronemertean known from eastern and northwest Pacific (Alaska to Ensenada, Mexico and Akkeshi, Japan, respectively). It is an emerging model system in developmental biology research. We present evidence from morphology of the adults, gametes, and sequences of cytochrome c oxidase subunit I and 16S rRNA genes that it is not one, but a complex of five, cryptic species. All five of these species co-occur at least in part of their geographic range (e.g. southern Oregon). Preliminary cross-hybridization experiments suggest that at least some of these species are reproductively isolated. The five species share characteristics of adult morphology (e.g. accessory buccal glands) and at least four are known to possess a unique larval morphotype--pilidium maculosum. We propose that these characters define a new genus, Maculaura gen. nov., which contains the following five species: Maculaura alaskensis comb. nov., Maculaura aquilonia sp. nov., Maculaura cerebrosa sp. nov., Maculaura oregonensis sp. nov., and Maculaura magna sp. nov. It is unclear which of the five species Coe originally encountered and described. We chose to retain the name \"alaskensis\" for the species that current researchers know as \"Micrura alaskensis\", although, presently, it is only known from Washington and Oregon, and has not been collected from Alaska. Maculaura aquilonia sp. nov. is the only member of the genus we have encountered in Alaska, and we show that it also occurs in the Sea of Okhotsk, Russia.