A new name, Kirkegaardia, is proposed to replace Monticellina Laubier, 1961, a bitentaculate cirratulid polychaete genus, that is a junior homonym of the turbellarian Monticellina Westblad, 1953 (Platyhelminthes, Rhabdocoela). In addition, the opportunity is taken to complete a major revision of the genus including the redescription, revalidation, and separation of three species previously referred to synonymy with K. dorsobranchialis (Kirkegaard, 1959) and five other previously described species. In addition, 16 new species are described from the western North Atlantic, eastern and central Pacific, off western South America, and seas around Antarctica, bringing the total number of species in the genus to 38. Included are two new species of the unusual mud ball worms, first reported as Tharyx luticastellus Jumars, 1975, from southern California deep basins. A review of all 38 species reveals that three distinct species groups may be identified within the genus in addition to 5-6 spe...

Pelvicachromis sacrimontis Paulo, 1977 was originally described on the basis of an iconotype in an aquarium journal. Herein, the validity of the name as well as the species status is discussed, an updated diagnosis and description of the species is given, and a neotype and a series of paraneotypes is designated. The species differs from congeners in a combination of coloration features including a broad dark midlateral band, the absence of blue and reddish dots in the caudal fin of males, and the specific coloration of the dorsal fin in females.

Notomastus bermejoi sp. nov. from the Gulf of California shelf is described, illustrated, and compared with its congeners bearing hooded hooks in thoracic chaetigers. This new species is characterized by the presence of a prostomial palpode, only notopodia in the first chaetiger, hooded hooks in neuropodia of chaetiger 11, and its distinct methyl green staining pattern consisting of: chaetigers 1-4 slightly stained, chaetigers 5-10 with green bands encircling the segments, and a darker, solid, green band encircling the body in chaetigers 11-12. It is mainly distributed in the central Gulf of California in fine sand bottoms (62-96%) at 32-106.4 m depth, tolerating a wide range of temperature (13.2-17.59 °C), dissolved oxygen (0.8-4.93 ml/L), and organic carbon (3.0-7.2%). The type material and original descriptions of Notomastus species with hooks in thoracic chaetigers were examined; an identification key and tables with morphological distinctive characteristics, methyl green staining patterns, and geographic distribution of these close species are provided.

A new genus and species, Lissaclita melaniae (Tetraclitidae), is described from the Gulf of California, Baja California Sur, Mexico. Lissaclita has a secondarily divided single row of parietal tubes without septa, lack of tubes in the radii, diametric shell growth, and a membranous basis. This combination of characters does not agree with any currently described subfamily within the Tetraclitidae. Lacking a detailed phylogenetic analysis of the entire family, we place the new genus in the Tetraclitidae without assigning it to a subfamily.

Summ.ary- Material collected from intersegmental spaces beneath the dorsal plates (pereonites) of beach hoppers from the Pacifie Coast of North America is herein referred to RhabdiLis (CruslOrhabdiLis) SlO.Si!eonovi (Belogurov, 1977) Sudhaus & Nirnrich, 1989 (Rhabditida; Rhabditidae). This species, hitherto known only on the basis of female anatomy, was described from beach wrack in the Commander Islands by Belogurov (1977) who proposed a new genus, Marispelodera, for il. Sudhaus and Nimrich (1989) reported the species from beach wrack on Vancouver Island but referred the species to the subgenus RhabdiLis (CruslOrhabdiLis). Females are exceptional in that the tail is extremely short and rounded. Males described herein agree in all essential respects to the subgenus RhabdiLis (Cruslorhabdilis) and therefore corroborate Sudhaus and Nirnrich's (1989) interpretation. Adult and larval worms were collected from intersegmental spaces of MegalorchesLia cah/omiana, M. benediai and Trasko...