A redescription of the type species of Oedicerina Stephensen, 1931 (Crustacea, Amphipoda, Oedicerotidae) and the description of two new species

The poorly known species Oedicerina ingolfi Stephensen, 1931 (Crustacea: Amphipoda: Oedicerotidae) is redescribed, based on new material from the Norwegian Sea. Oedicerina vaderi sp. n. from the northeast Atlantic Ocean and Oedicerina loerzae sp. n. from New Zealand waters are described raising the number of species in the genus to five. The three species treated here together with Oedicerina megalopoda Ledoyer, 1986 and Oedicerina denticulata Hendrycks & Conlan, 2003 are separated by characters of the rostrum, maxilliped, gnathopods, epimera, and by the dorsal armature of pleonites and urosomites. The genus is recorded from the Atlantic, Indian and Pacific Oceans, mainly at bathyal depths.


Introduction
Participants in a workshop organised by Professor Wim Vader at the University of Tromsø field station at Skibotn in 2009 sorted and identified amphipods from the Natural History Collections of the University Museum of Bergen collected from the Norwegian Sea.Among the extensive material in these collections were specimens of the poorly known oedicerotid genus Oedicerina Stephensen, 1931.The genus was based on a single individual collected from the Norwegian Sea by The Danish-Ingolf Expedition (Stephensen 1931).Although the specimen consisted of just the head and pereonites 1-4 and was lacking gnathopods, the new genus was created for O. ingolfi Stephensen, 1931 to recognise the unique nature of the huge posterior lobe of coxa 4. The genus remained monotypic and unreported until Ledoyer (1986) described ?Oedicerina megalopoda from the Mozambique Channel, western Indian Ocean, also based on a single anterior fragment.This species was defined by the characteristic shape of coxa 4 and by the strongly developed carpal articles of gnathopods 1 and 2. The description of a third species, O. denticulata Hendrycks & Conlan, 2003 from the northeast Pacific Ocean, was the first to record complete specimens and was accompanied by a more detailed appraisal of the genus.
The new material from the Bergen Museum has made possible a re-description of O. ingolfi.Specimens belonging to Oedicerina from the northeast Atlantic Ocean and

Material and methods
Norwegian Sea material assigned to O. ingolfi from the Natural History Collection of the University Museum of Bergen (ZMBN) was collected with an RP sledge (Rothlisberg and Pearcy 1977) by Torleiv Brattegard (Brattegard and Fosså 1991) in the period 1981-1986.Additional material from the Norwegian and Greenland Seas from the Museum of Zoology, Lund University was collected during the NORBI expedition (Dahl et al. 1976) using an epibenthic sledge (drague Sanders) (Guennegan and Martin 1985).
Specimens from the Discovery Collections at the National Oceanography Centre, Southampton were obtained in the East Iceland Basin on an RRS Discovery cruise that contributed to the Institute of Oceanographic Sciences investigations of mid-water and benthic faunas in the eastern North Atlantic Ocean (1965)(1966)(1967)(1968)(1969)(1970)(1971)(1972)(1973)(1974)(1975)(1976)(1977).The material, from an epibenthid sledge, was fixed in 4% formaldehyde and later transferred to 70% Industrial Methylated Spirits.These specimens have been deposited in the Amphipoda collections at The Natural History Museum, London.
The New Zealand material was collected during the Ocean Survey 2020 expeditions with RV Tangaroa to the Chatham Rise and the Challenger Plateau (Knox et al. 2012) by means of a "Brenke" epibenthic sledge (Brenke 2005).The material was sorted on board, fixed in 96% ethanol and later transferred into 70% ethanol.It has been deposited in the National Institute of Water and Atmosphere Research (NIWA) Marine Invertebrate Collection in Wellington, New Zealand.
For habitus drawings the specimens were transferred into glycerol on a cavity slide.Specimens were then dissected under a stereomicroscope (Leica M205 or Wild M5) using dissecting needles.Mouthparts and appendages were mounted temporarily in glycerol on slides for microscopic examination and drawing.Appendages were later mounted as permanent slides with glycerol jelly, or transferred into small glass microvials.Microvials were stoppered with a cotton ball wrapped in Japan paper to avoid the appendages being entangled in the cotton fibres.
After dissection, mouthparts and appendages of Discovery Collection material were made directly into permanent mounts using Polyvinyl-lactophenol stained with lignin-pink.Drawings of habitus and appendages were made using a camera lucida attached to a compound microscope (Leica DMLB or Wild M20).Pencil drawings were scanned, inked digitally and arranged to plates using the methods described in Coleman (2003Coleman ( , 2009)).
Body lengths were measured along the dorsal outline from the tip of the rostrum to the end of the telson.Lengths of individual articles of gnathopods and pereopods measured along anterior or posterior margins can vary depending on the degree of flexure of the appendage.All articulations except those between coxae and tergites and between merus and carpus of gnathopods are bicondylar.Measurements made between condyles gives a length that is not affected by limb flexure.Length ratios herein have been derived using this principle.

Sexual dimorphism.
Male antenna 1 with shorter peduncle articles in the ratio 1:0.7:0.3 and more numerous flagellum articles compared to female.Article 1 of the flagellum is elongate, about as long as peduncle article 3. Subsequent proximal articles are shorter than wide.The 1-articulate slender accessory flagellum is about 1/3 as long as article 1 of the primary flagellum.
Remarks.Stephensen's (1931) specimen was damaged and incomplete.Only the head and pereonites 1-4, pereopods 3-4 and coxae and bases of pereonites 1-2 on one side were available for study.The material from the Bergen Museum used for this description consists of numerous specimens of all sizes, both female and male, and was col-lected relatively close to the type locality of O. ingolfi, but nevertheless we cannot be absolutely sure that our material represents Stephensen's species (see discussion below).Etymology.The specific name vaderi recognises the important contributions to amphipod studies made by Professor Wim Vader.
Variability.The paratypes bear a small posteriorly directed tooth on pleonite 3. It may be that this process has been present and is worn down in the holotype.Antenna 1 of the female (Fig. 6b) has a longer and more slender peduncle and fewer and more elongate flagellum articles compared to the male.Etymology.The species is named for Dr. Anne-Nina Lörz to acknowledge her significant contributions to amphipod systematics.
Distribution.Chatham Rise, east of New Zealand.

Remarks.
The female specimen has the same antenna 1 morphology as the male: short peduncle articles and numerous flagellum articles.The proximal articles of the flagellum are shorter than wide.Remarks.Only the head and pereonites 1-2 are present.Coxae 1-2 bear long setae along the distal margins.The animal appears similar to O. ingolfi, but as a result of incompleteness it is impossible to attribute it to any species.

Discussion
The three species described herein are morphologically very similar.Mouthparts and appendages show only minor and subtle differences and the species are best discriminated by habitus characters.Two of the species, O. ingolfi and O. loerzae sp.n. have mid-dorsal carinae on pleonites 1-2.Oedicerina ingolfi differs from O. loerzae sp.n. in having a small, slender, acute, upright tooth on pleonite 3 and a small pointed process on the posterior margin of urosomite 3 both of which are absent in O. loerzae sp.n.Oedicerina vaderi sp.n. has a small pointed process on the posterior margin of urosomite 3, as found in O. ingolfi, but pleonites 1-2 are evenly vaulted lacking any trace of a carina.Pleonite 3 of the holotype of O. vaderi sp.n. appears to be dorsally unarmed, but the paratypes have a small acute process (see female paratype, 6.3 mm in Fig. 10e).Coxa 5 of O. ingolfi is longer than wide, that of O. vaderi sp.n. is about as wide as long, and that of O. loerzae sp.n. much wider than long.
Oedicerina sp.indet.was collected from the warm-temperate east Atlantic Ocean off Western Sahara.The unique specimen is incomplete, only the head and pereonites 1 and 2 are present, preventing a full identification.
Apart from the type species O. ingolfi, two other species had been described in the genus prior to this study: Oedicerina megalopoda Ledoyer, 1986, collected close to Mayotte, Mozambique Channel, western Indian Ocean (200-500 m) and Oedicerina denticulata Hendrycks & Conlan, 2003 from the northeast Pacific Ocean off California (4050 m).Knowledge of O. megalopoda is limited as the unique specimen is incomplete, but the massive rostrum of this species differs markedly from all other species of the genus.The palm of gnathopod 2 of O. megalopoda is straight, similar to that of O. loerzae sp.n., and thus different from the convex pattern seen in both North Atlantic species.In Oedicerina denticulata pleonite 1 is smooth and pleonites 2 and 3 have a posteromarginal process.The process on pleonite 3 is directed posteriorly and is reminiscent of that seen in paratype material of O. vaderi sp.n. thus contrasting with the upright condition found in O. ingolfi.The posterior margin of urosomite 3 bears a small process (as do all species except for O. loerzae sp.n.) and urosomite 1 has a small upright process in the male but not the female, a character unique within the genus.Coxa 5 appears to be longer than wide, as in O. ingolfi.
The mouthparts and appendages of all species of this genus are remarkably similar to each other.Examination of the extensive Norwegian Sea material which we attribute to O. ingolfi indicates that intraspecific variability is minimal, except for sexual dimorphism in antenna 1.In females of both Atlantic species peduncle articles of antenna 1 are longer and more slender than in males.Flagellum articles in females are uniformly much longer than wide and relatively few in number, whereas in males they are more numerous and proximally wider than long, forming an incipient callynophore.This sexual dimorphism is not apparent in O. loerzae sp.n.where the structure of antenna 1 is very similar in males and the one ovigerous female paratype.
Because of minimal differences among appendages and mouthparts in Oedicerina species, differentiation within the genus relies significantly on patterns of ornamentation of pleonites and urosomites.As the posterior segments of the type material of O. ingolfi are missing, the question remains as to which of the two Atlantic species represents the species that Stephensen described.We allocate the material from the museums in Bergen and Lund studied herein to O. ingolfi on geographical grounds in that it was collected much closer to the type locality of that species, and on the morphological grounds of the dense fringe of setae on the distal margins of coxae 1 and 2 and the shape of the rostrum that our material shares with Stephensen's original description.