Katianiridae is a taxonomic family erected by Svavarsson in 1987 to accommodate the genera Katianira and Natalianira. Before the study, it contained six species: five in Katianira and one in Natalianira. Natalianira was represented only by Natalianira spinosa, described from South Africa and known from depths of 550–850 metres. The Argentine material adds two recognized species to that genus, bringing the number of known Natalianira species to three. The authors amended the genus diagnosis and produced dichotomous keys for distinguishing the two genera within Katianiridae and the three species within Natalianira.

Records of Katianiridae are scattered, even in relatively well-sampled deep seas. Katianira has been reported from the North Atlantic, North Pacific, Arctic seas and Antarctica, as well as an undescribed occurrence in the Caiman Trench in the Caribbean. Its documented depth range extends from the sublittoral to 5,779 metres. Natalianira had been known only from the southern hemisphere and from a single species off South Africa. The new Argentine findings are consistent with the sporadic distribution reported for members of the family: N. bicornuta appeared in only three of 29 samples sorted from the Mar del Plata submarine canyon, while N. megalocera occurred in only two of 12 samples sorted from the Nunamcurá–Burdwood Bank marine protected area.

Specimens were collected with an epibenthic sledge fitted with a 1-millimetre mesh net during the Talud Continental I and II expeditions in 2012 and 2013 and the Bentos Banco Burdwood expedition in 2016. The sledge was towed from the research vessel Puerto Deseado. Material was sieved aboard ship with 300-micrometre mesh. Some specimens were initially fixed with 10% seawater-buffered formalin and later transferred to 70% ethanol in the laboratory, while other samples were preserved directly in 96% ethanol. For anatomical examination, researchers stained specimens with Chlorazole Black E, dissected the appendages and temporarily mounted them in glycerin.

The study combined habitus and appendage drawings with light microscopy and scanning electron microscopy. Habituses were drawn with a camera lucida attached to a Leica MZ8 dissecting microscope, while appendages were examined with a Carl Zeiss Axioskop compound microscope and rendered digitally. For scanning electron microscopy, specimens were cleaned with 0.5% nonionic detergent and ultrasound, dehydrated through an ethanol series and transferred into increasing concentrations of hexamethyldisilazane. They were then air-dried, mounted on aluminium stubs, coated with gold-palladium and examined with a Philips XL30 TMP microscope. Body length was measured dorsally from the frontal margin of the head to the tip of the pleotelson along the midline.

Natalianira bicornuta, the new species from the Mar del Plata submarine canyon, measures up to 2.8 millimetres in the reported male holotype. Its most conspicuous features are two cylindrical horn-like protuberances on top of the head, each carrying eight to 10 robust setae, and two pairs of large lateral processes on the pleotelson, the rear section of the segmented body. The lateral margins of pereonites 2–7 are divided into two lobes. The name bicornuta combines the Latin terms “bi,” meaning two, and “cornata,” meaning horn, referring to the paired dorsal projections. The species is known only from the canyon between 1,114 and 1,275 metres, with the type material collected at 1,144 metres.

The second species, N. megalocera, differs most clearly in its first antennula article, which is proportionally much larger than that of N. bicornuta and bears a greatly produced medial process extending beyond the fourth antennula article. The enlarged structure inspired the name megalocera, combining the Greek terms “mega,” meaning large, and “kerata,” meaning antenna, with an allusion to the resemblance of the projection to the antlers of the Irish elk, Megaloceros giganteus. Its head carries two low, rounded dorsal bumps rather than tall cylinders, and its pleotelson has one enlarged lateral process rather than two. Its antennal flagellum has two articles, whereas N. bicornuta has one.

Both new species share the basic body architecture used to characterize Natalianira. Robust setae line the lateral margins, each pereonite bears a midline dorsal bump, and the pleotelson carries one or two lateral processes. The first article of the antennula is greatly enlarged, while the antennal flagellum is short. The mandible has a denticulate incisor process and a spiniform molar process, and the maxillipedal palp has four articles in the new species rather than the five recorded for N. spinosa. The first pereopod forms a chela: the terminal claw of the dactylus opposes a particularly large ventral seta on the propodus. These features are reflected in the emended diagnosis of the genus.

The identification keys separate the genera and species using combinations of body and appendage characters. Katianira can be distinguished from Natalianira by the absence of dorsal bumps on the pereonites, a rounded pleotelson margin, a short and thin first antennula article and a first pereopod whose dactylus is longer than wide. Within Natalianira, N. spinosa has three dorsal bumps on each pereonite, one broad pleotelson process and a five-article maxillipedal palp. N. bicornuta and N. megalocera each have one dorsal bump per pereonite and four-article maxillipedal palps, but differ in head sculpture, pleotelson processes, antennule proportions and antennal flagellum structure.

The records document presence at discrete sampling localities rather than continuous distributions, population sizes or population trends. The new species were represented by small numbers of specimens in the material examined, and the available observations do not establish how widely either species occurs beyond the reported sites. Nevertheless, the specimens provide the first southwestern Atlantic record of Katianiridae and expand the known geographic range of Natalianira into Argentina. They also supply a revised anatomical framework for identifying additional records in deep-sea collections. Type and additional material of both species were deposited in the invertebrate collection of the Museo Argentino de Ciencias Naturales “Bernardino Rivadavia.”

Subject of Research: Taxonomic description of two new Katianiridae isopod species from the southwestern Atlantic off Argentina

Article Title: First record of the little-known family Katianiridae Svavarsson, 1987 ( Crustacea , Isopoda , Asellota ) from the Southwest Atlantic Ocean, with description of two new species

Article References: Calderón López, S., Roccatagliata, D., & Doti, B. (2026). First record of the little-known family Katianiridae Svavarsson, 1987 (Crustacea, Isopoda, Asellota) from the Southwest Atlantic Ocean, with description of two new species. ZooKeys, 1295, 111-128. https://doi.org/10.3897/zookeys.1295.205971

Image Credits: AI Generated

DOI: 10.3897/zookeys.1295.205971

Keywords: Katianiridae, Natalianira, deep-sea isopods, taxonomy, Southwest Atlantic, Argentina, submarine canyon, Burdwood Bank, new species, marine biology, First, record