The Eurycope producta Sars, 1868 Species Complex (Isopoda, Munnopsidae) at the Transition of the Northern North Atlantic and the Nordic Seas—Including Descriptions of Six New Species and a Key "2279

Eurycope producta Sars, 1868 is a highly abundant and widely distributed munnopsid species complex within Icelandic waters. The complex differs from all other Eurycope Sars, 1864 species by having a broad and long rostrum with serrated margins, which is subequal in length and width to article 1 of antenna I. Previous molecular evidence to disentangle the E. producta species complex forms the base for the herein-presented taxonomic description of six new species belonging to the genus Eurycope. Additionally, descriptions of specimens of E. producta sensu stricto and E. dahli Svavarsson, 1987, which were included in the analyses, are presented herein for morphological comparison with the new species. The studied species can be divided in two subgroups: (1) E. producta sensu stricto, E. dahli, E. mishkai sp. nov., and E. nikitai sp. nov. and (2) E. gordeyi sp. nov., E. emmae sp. nov., E. jakobi sp. nov., and E. mathiasi sp. nov. Additionally, a key to the eight studied species of the complex

Eurycope producta sensu stricto was revealed later to be highly abundant and widely distributed within Icelandic waters [26,27] and was presumed to be a species complex [27,28]. Figure 1 shows the thus far known distribution of the unresolved E. producta complex specimens within Icelandic Waters based on data of the BIOICE project (Benthic Invertebrates of Icelandic Waters) [27] and the IceAGE project (Icelandic Marine Animals: Genetics and Ecology [28]. Environmental conditions around Iceland are shaped by the Greenland-Scotland Ridge (GSR), extending across the North Atlantic in an east-west direction. This submarine ridge system, with a mean depth of 500 m, separates the deep-sea basins of the North Atlantic from deep-sea basins of the Nordic Seas (Greenland, Iceland, and Norwegian Seas) and the Arctic Mediterranean. Water exchanges of cold and dense water masses occur at depth through channels in the Faroe Bank Channel (840 m), Denmark Strait (620 m) and across the Iceland-Faroe Ridge (480 m) [29]. Major temperature differences of near-bottom water masses could be observed within the area, ranging from −1 to up to 12-14 • C [30]. Thus, this highly variable environment, with such a unique mixture of abiotic factors, is predestined to be studied regarding species' distributional patterns and limits.
Examination and close investigation with a focus on species complexes within this area become highly interesting, since one would expect that species occupy smaller ecological niches than species complexes. For instance, the documented bathymetric depth range of the E. producta complex was, prior to Schnurr et al. [28], 103-2029 m depth.
Schnurr et al. [28] examined specimens of E. producta within Icelandic waters (see Figure 1 and Table 1 for sampling locations). The authors included not only specimens of the E. producta complex, but also some specimens of E. dahli, a species closely related to E. producta. Schnurr et al. [28] showed that the species clades were geographically and bathymetrically much more restricted than previously assumed. Further, Schnurr et al. [28] revealed that the observed molecular species clades ( Figure 2) coincide with morphological findings. The mainly molecular-based study identified eight potential species clades (including an E. producta sensu stricto clade and an E. dahli clade). Specimens from all clades, including six potentially new species clades, were available for a thorough morphological investigation of this species complex, whereas only a short summary of morphological characters was presented in Schnurr et al. [28]. The current study is a follow-up of this project and aims to elucidate the species clades further by providing illustrations and thorough morphological species descriptions of: Eurycope producta sensu stricto, E. dahli, E. mishkai sp. nov., E. nikitai sp. nov., E. gordeyi sp. nov., E. emmae sp. nov., E. jakobi sp. nov., and E. mathiasi sp. nov. along with a key to the species of the complex. 1 Figure 2. Consensus Bayesian tree for E. producta of the concatenated four gene loci dataset (16S, COI, 18S, and H3) of Schnurr et al. [28]. The branch lengths are proportional to the number of substitutions per site considering the models of nucleotide substitution estimated by MrAIC for the respective loci or partition. Posterior probabilities (>0.9) from Bayesian analyses and bootstrap percentages (>70) from maximum likelihood trees are indicated at the nodes. The names of the species are indicated next to the respective clade: E. producta sensu stricto, E. dahli, E. mishkai sp. nov., E. nikitai sp. nov., E. gordeyi sp. nov., E. emmae sp. nov., E. jakobi sp. nov., and E. mathiasi sp. nov. The figure was reprinted and adapted from [28] by permission from Springer Nature, Marine Biodiversity (2018). Table 1. Voucher specimen information with reference to voucher name; clade names of Schnurr et al. [28]; species names; type status (H, holotype; P, paratype; d, dissected), sex (F, female; M, male; J, juvenile), German Centre for Marine Biodiversity Research numbers (DZMB HH), Zoological Museum of Hamburg collection numbers (ZMH K), cruise name (Ice1, IceAGE1 cruise; Ice2, IceAGE2 cruise), station number, sampling coordinates, sampling depth, and GenBank Accession numbers of COI, 16S, 18S, and H3. The table was reprinted and adapted from [28] by permission from Springer Nature, Marine Biodiversity (2018).

Materials and Methods
All 83 E. producta complex specimens of the current study were sampled during the IceAGE1 and IceAGE2 (Icelandic marine Animals: Genetics and Ecology) expeditions in 2011 and 2013 onboard the RVs Meteor and Poseidon, respectively, using three different types of epibenthic sleds [31][32][33]. Cooling and fixation in 96% nondenatured ethanol of bulk samples was immediately conducted on deck. Cooled subsamples were already sorted on board and also fixed in 96% nondenatured ethanol. Samples were handled according to Riehl, et al. [34] and kept cool throughout the whole sorting process. A semi-destructive approach of dissection for tissue digestion and DNA amplification was executed, considering that specimens will be needed for further taxonomic investigation. Thus, only one to three posterior pereopods (depending on the size of the individual) were dissected.
The molecular methods applied in order to obtain sequences for 18S, 16S, COI, and H3 gene fragments and the methods used for the conducted analyses were described in detail in Schnurr et al. [28] and are thus not repeated herein. Eurycope complanata was chosen as an outgroup for the tree. All sequences can be retrieved from GenBank (see Table 1 for accession numbers). We only present the tree of the concatenated analyses. Further details and a thorough discussion on tree topologies and species delimitation results can be retrieved from Schnurr et al. [28].
Morphological analyses of the specimens were conducted with a Leica M125 binocular microscope and a Leica DM2500 compound microscope, both equipped with a camera lucida. The pencil drawings were inked by hand and finalized using Adobe Photoshop 7. The drawings were created following the guidelines of Hessler [35] and Wilson [36] and the terminology of eurycopid structures follows Wilson and Hessler [37] and Wilson [38]. Measurement of the total body length was conducted medially from the anterior edge of the cephalon to the posterior tip of the pleotelson. Body segment length was measured medially from the anterior margin to the posterior margin. If the body was voluminous and the pleotelson was tucked up, its length was measured in the lateral view.
All specimens were deposited in the collections of the Zoological Museum of Hamburg (see Table 1 for accession numbers).

Description of characters common for all species of the complex:
Body about twice as long as wide. Cephalon behind antennulae shorter than pereonite 1. Rostrum width about one third of cephalon width. Anterolateral margin of pereonites acute; coxae of pereopods I-IV visible in dorsal view, subequal in length and in shape, with acute anterior lobe and rounded posterior lobe. Pleotelson broader than long, about 0.3 times body length.
Antenna II squama of article 3 half as long as article 4. Mandibular molar process distally truncate, denticulate; palp stout, subequal to mandibular body in length; article 3 slightly broader than article 2, twisted; distal seta longest.
Maxilla I mesial endite width about 0.7 times lateral endite width, with fine distal setae and one stout long distomedial seta; lateral endite with 12 robust differently serrated setae.
Maxilla II middle endite shortest, lateral endite longest; mesial endite with tuft of distal setae; distomedial setulated seta longest, middle and lateral endites with two long and two shorter comb-like distal setae.
Maxilliped basis length about three times width; endite width about half basis width; distal margin slightly concave, with several small fan setae and numerous fine small setae. Basis acute lateral projection near palp insertion subequal in length to lateral projection of article 1. Palp article 2 longest, equal in width to basis. Article 3 almost as wide as article 2; medial margin subequal in length to article 2, rounded. Article 4 equal to article 3 in lateral length; medial lobe subequal to article 5. Epipod length about twice width, 0.9 times basis length, width 1.3 times basis width tip narrow rounded, lateral margin projected midlength.
Bases of pereopods I-IV subequal in length, basis V shortest among all bases. Pereopod I broadest on basis-merus, dactylus < 0.3 times propodus length. Pereopods V-VII dactyli elongate, slightly bent, subequal in length to propodi; two setae proximal to claws, dorsal claw twice broader and longer than ventral one, two setae between claws. Pereopods V-VII carpi semirounded; propodi drop-like, broadened distally, about half as broad as carpi; dorsal margin serrated.
Male pleopod I and female pleopod II longer than branchial cavity of pleotelson, overlapping anterior part of anal. Male pleopod II protopod distolateral margin with several plumose setae; endopod and exopod inserted in middle of medial side, Pleopod III endopod with three or more plumose distal setae exopod with one distal seta. Pleopods V embraced laterally pleopods IV and III.

Remarks:
The complex differs from all Eurycope species by having a broad and long rostrum, which is subequal in length and width to article 1 of antenna I. The combination of the other characters mentioned in the diagnosis distinguishes the species complex as well. The broad and long-almost rectangular-rostrum with lateral keels of the E. producta complex is similar to that of the genus Disconectes. Some species of Disconectes also have the pronounced distomedial lobes of male pleopod I. However, Disconectes differ in having the pereonites 5 and 6 dorsally fused, which are free in Eurycope.
As already noted by Svavarsson [21], E. gaussi from the Indian sector of the Southern Ocean and the two northwest Pacific species E. linearis and E. spinifrons are closely related species to the E. producta complex. We may also include to the similar and related species E. septentrionalis Malyutina and Kussakin, 1996 [41] from the Canadian Basin of the North Polar Ocean as well as E. andreyi Malyutina and Golovan, 2022 [42]. All these mentioned species have a large rostrum, though not as notable as in the studied North Atlantic ones. All of them also possess similar morphological features to the male pleopods I and the maxillipeds. The North Pacific species differ from the studied species of the complex by a reduced distomedial lobe of antenna I article 1, which is shorter than article 2, in contrast to the long lobe of the species of the E. producta complex.
Mandible (male, ZMH K-45592, Figure 4B,C) incisors of both mandibles with four cusps; lacinia mobilis of left mandible almost as long as incisor, with seven small distal teeth; spine row with eight and nine spines on left and right mandibles, respectively; molar process distally with six small setae on base of denticles. Palp length 1.1 times mandible body length; article 2 with row of small simple lateral setae and two stout setulated distal setae; articles 2 and 3 length 2.15 and 1.05 times article 1 length, respectively. Article 3 distal seta length 2.1 times other marginal setae length and 0.55 times article 3 length.
Maxilliped (male, ZMH K-45592, Figure 5C) basis length 2.95 times width, lateral margin setulated; endite width 0.55 times basis width, with three coupling hooks; distal margin with five narrow fan setae. Basis acute lateral projection near palp insertion length 1.2 times article 1 lateral length. Palp length 2.25 times width, 0.75 times basis length. Article 2 length 0.8 times width, as wide as basis, lateral length 1.2 times medial length, each distal angle with small seta; article 3 almost as wide as article 2, medial length equal to article 2 medial length, lateral length 0.4 times article 2 lateral length, medial margin rounded, denticulate, few small setae distally; article 4 equal to article 3 in lateral length, medial lobe slightly shorter than article 5, with three long distal setae, article 5 with four long distal setae. Epipod length 2.0 times width, 0.9 times basis length, width 1.3 times basis width; tip narrow, with three setae. Pereopod I (male, ZMH K-45592, Figure 6C) as long as body, length ratios of ischium-dactylus to basis: 0.4, 0.3, 0.8, 0.65, 0.15. Basis length 7.1 times width, dorsal margin with nine small simple setae and one broom proximal seta, ventral margin with five small simple setae and three longer simple distoventral setae. Ischium length 4.0 times width, with three small simple distal setae. Merus with three simple distal setae. Carpus 0.6 times basis width, length 9.65 times width; with three dorsal and seven ventral simple setae. Propodus with six ventral simple setae and six distal simple setae; dactylus almost straight, claw length 0.4 times dactylus length.
Pereopod II (male, ZMH K-45592, Figure 6D) length 1.9 times pereopod I length. Length ratios of ischium-dactylus to basis: 0.45, 0.4, 1.4, 1.7, 0.5. Basis stout, length 7.7 times width, with scattered small setae along basis, one broom dorsal seta and few distal setae. Ischium with two strong and five small simple ventral setae. Merus with five dorsal and five ventral simple setae. Carpus with 12 simple dorsal setae, seven small simple and 17 UB ventral setae; distal margin with one broom, one long and six small UB setae. Propodus with 17 simple dorsal setae, one broom seta, and one small UB seta distodorsally and 25 UB ventral setae. Dactylar claw length 0.25 times dactylus length.  Pereopod V (male, ZMH K-45592, Figure 7A) propodus and dactylus broken off, length ratios of ischium-carpus to basis: 1.4, 0.6, 2.0. Basis length 1.8 times width, with one long whip and five broom dorsal setae and four small simple ventral setae. Ischium and merus visibly narrower than basis; ischium with eight plumose dorsal setae and three simple ventral setae. Merus with one dorsal plumose seta and five simple ventral setae. Carpus length 1.6 times width, with 24 dorsal and 18 ventral plumose setae, one broom, one UB, and three simple setae distally.  Pereopod VI (male, ZMH K-45592, Figure 7B) propodus and dactylus broken off, length ratios of ischium-carpus to basis: 0.4, 0.5, 1.4. Basis length 2.7 times width, with three long distal setae. Ischium as wide as basis, with nine plumose dorsal setae and 14 simple ventral setae. Merus with one plumose dorsal seta and five simple ventral setae. Carpus length 1.5 times width, with 22 dorsal and 15 ventral plumose setae, one broom and three simple setae distoventrally.
Pleopod II (male, ZMH K-45592, Figure 8B,C) protopod length 1.65 times width, 0.9 times pleopod I length; distal margin with five simple setae, distomedial notch weak, length 0.4 times medial margin length. Stylet length 0.8 times protopod length, tip reaching behind pleopod I tip; sperm duct opening at 0.3 times length from proximal margin. Exopod distal article half as wide and 0.8 times as long as basal article.
Uropod (male, ZMH K-45592, Figure 7D) length 0.3 times pleotelson length; protopod length 1.0 times width, with one UB distolateral seta and one broom seta and six UB distomedial setae. Endopod length 1.25 times protopod length, width 0.5 times protopod width, with four broom and seven UB distal setae and three simple medial setae. Exopod length 0.95 times endopod length, width 0.5 times endopod width, with seven UB and two broom distal setae.
Remarks: Our specimens were identified as E. producta G.O. Sars, 1868 sensu stricto as they fit the original descriptions and illustrations in G.O. Sars [43], though the male pleopod I in Sars's Pl. 65 has more pronounced distomedial lobes than our specimens.
Distribution: Eurycope producta occurs according to G.O. Sars [43] along the Norwegian coast from Christiania Fjord (Oslo), Skagerrak in the South to Vadsø in the North at a depth range of 60-400 fathoms (109.7-731.5 m). The species was recorded in many further publications west of Ireland, off the Faroe Islands, south of Iceland, near eastern, southern and southwestern Greenland, and in the southern part of the Davis Strait, featuring a depth range of 72-2087 m [44] (pp. 56-59). The herein-studied specimens of E. producta sensu stricto were sampled in the Denmark Strait, the Norwegian Sea, the Iceland-Faroe Ridge, and the Iceland Basin, featuring a depth range of 316-1385 m.   Svavarsson, 1987 Material examined: Male (ZMH K-45598), 5.7 mm length; male (ZMH K-45609), used for dissection; female (ZMH K-45612), 4.6 mm length; juvenile (ZMH K-45606); and 19 further specimens (see Table 1 for specimen information).  Antenna I (male, ZMH K-45609, Figure 11A) broken off on article 3; article 1 length 1.15 times width with two distal and two dorsal broom setae; article 2 length 0.35 times article 1 length, not reaching tip of distomedial lobe of article 1, with one distal broom seta; article 3 broken, width 0.4 times article 2 width. Antenna II (male, ZMH K-45598, Figure 12A) broken off after article 4; articles 1-4 subequal in length; squama on article 3 reaching midlength of article 4. Mandible (male, ZMH K-45609, Figure 12B) incisors of left mandible with six cusps, lacinia mobilis almost as long as incisor, with seven distal teeth; spine row with 11 spines; molar process distodorsally acute, with 11 small setae on base of denticles; condyle length 0.15 times mandibular body length. Palp length 1.05 times mandibular body length; article 2 with nine thin medial setae and one long distal seta; articles 2 and 3's lengths 2.1 times and 0.85 times article 1 length, respectively. Article 3 distal seta length 3.5 times other marginal setae length and as long as article 3.
Maxilla II (male, ZMH K-45609, Figure 11C) mesial and lateral endites subequal in length, middle endite shortest; mesial endite with tuft of distal setae, one long setulated seta distomedially, middle and lateral endites with two long and two shorter comb-like distal setae.
Maxilliped (male, ZMH K-45609, Figure 11D) basis length 2.85 times width; endite width 0.55 times basis width, with four coupling hooks, distal margin slightly concave, with six small fan setae. Basis acute lateral projection near palp insertion length 1.2 times article 1 lateral length. Palp length 2.6 times width, 0.75 times basis length. Article 2 length 1.05 times width, width 0.85 times basis width, lateral length 1.4 times medial length. Article 3 almost equal to article 2 in width and medial length, lateral length 0.3 times article 2 lateral length; medial margin rounded, denticulate, with small setae. Article 4 lateral length 1.45 times article 3 lateral length, medial lobe slightly shorter that article 5, with six long distal setae. Article 5 as long as article 4 laterally, with seven long distal setae. Epipod length 2.2 times width, 0.85 times basis length, width 1.2 times basis width.
Pleopod II (male, ZMH K-45609, Figure 13B) protopod length 1.6 times width, 0.9 times pleopod I length; distal margin with eight simple setae, distomedial notch well defined, length 0.3 times medial margin length. Stylet length 0.7 times protopod length, tip reaching slightly behind pleopod II tip; sperm duct opening at 0.4 times length from proximal margin. Exopod distal article half as wide and almost as long as basal article.
Remarks: The species differs from other species of the complex by its rostrum, which is shorter (0.8 times) than antenna I article I (in all other species the rostrum is equal in length or longer than antenna I article I) and narrower (0.75 times) than antenna I article I. It is the only species of the complex which has six distal plumose setae on the endopod of pleopod III (all others have only three setae).   Paratypes: female (ZMH K-45626), 3.1 mm length; female (ZMH K-45625), used for dissection; male (ZMH K-45624), used for dissection; and 2 further specimens (see Table 1 for specimen information).
Mandible (male paratype, ZMH K-45624, Figure 15B) incisors of left mandible with four cusps; lacinia mobilis almost as long as incisor, with four distal teeth; spine row with eight spines; molar process distodorsal margin acute, with four small setae on base of denticles; condyle length 0.15 times mandibular body length. Palp length 0.85 times mandibular body length; article 2 with two long distal setae; articles 2 and 3 lengths 1.95 times and 0.95 times article 1 length, respectively. Article 3 distal seta length 1.65 times other marginal setae and 0.85 times article 3 length.
Maxilliped (male paratype, ZMH K-45624, Figure 15E) basis length 2.9 times width; endite width 0.5 times basis width, with three coupling hooks; distal margin slightly concave, with five small fan setae and numerous fine small setae. Basis acute lateral projection near palp insertion as long as article 1. Palp length 2.0 times width, 0.7 times basis length. Article 2 length 0.85 times width, as wide as basis; lateral length 1.05 times medial length. Article 3 almost equal to article 2 in width; medial length 0.7 times medial length of article 2; medial margin rounded, denticulate, with small setae; lateral length 0.3 times article 2 lateral length. Article 4 lateral length equal to article 3 lateral length; medial lobe length 1.1 times article 5 length, with three long distal setae; article 5 with three long distal setae. Epipod length 2.35 times width, 0.95 times basis length, width 1.2 times basis width. Pereopods broken off. Pleopod I (male paratype, ZMH K-45624, Figure 16A) length 2.5 times basal width, distal width 0.5 times basal width; distal margin truncated; medial and lateral lobes not separated. Distolateral and distomedial angles with small setulae.
Diagnosis: Pereonites 5-7 equal in medial length. Cephalon rostrum length 1.0 times basal width, subequal to antenna I basal width. Maxilliped endite with two coupling hooks. Basis lateral projection near palp insertion as long as article 1. Article 4 medial lobe length 0.6 times article 5 length. Epipod length 2.1 times width, 0.9 times basis length, width 1.35 times basis width. Pleopod I length 2.8 times basal width; distal margin with light rounded notch between distomedial and distolateral lobes. Male pleopod II protopod distomedial notch length 0.25 times medial margin length. Uropod protopod length 0.95 times width; endopod length 1.3 times protopod length, width 0.75 times protopod width; exopod as long as endopod.
Description of male (holotype, ZMH K-45627, Figure  Antenna I (male paratype, ZMH K-45633, Figure 18A) article 1 length 1.0 times width, with one broom dorsal seta, one UB seta and one simple seta distomedially. Article 2 length 0.45 times article 1 length, reaching tip of distomedial lobe of article, with two broom and two simple distal setae. Article 3 and flagellum broken off.
Antenna II (male paratype, ZMH K-45633, Figure 17E) twice longer than BL; article 5 length 0.5 times total body length, article 6 1.2 times article 5 length and slightly narrower than article 5; flagellum length 0.7 times peduncle length.  Mandible (male paratype, ZMH K-45633, Figure 18B) incisors of right mandible with four cusps, spine row with eight spines, molar process with two small distal setae on base of denticles; condyle length 0.15 times mandibular body length. Palp length 1.05 times mandible body length; article 2 with two distal setae; articles 2 and 3 lengths 1.85 times and 0.95 times article 1 length, respectively. Article 3 distal seta length 1.65 times other marginal setae and 0.5 times article 3 length.
Maxilla II (male paratype, ZMH K-45633, Figure 18D) middle endite visibly shorter than mesial and lateral endites which subequal in length; mesial endite with row of distal setae, middle and lateral endites with two long and two shorter distal setae.
Maxilliped (male paratype, ZMH K-45633, Figure 18E) basis length 3.1 times width; endite width 0.5 times basis width, with two coupling hooks, distal margin narrow, straight, with one small fan seta. Basis acute lateral projection near palp insertion as long as article 1 laterally. Palp length 2.25 times width, 0.7 times basis length. Article 2 length 0.9 times width, as wide as basis; lateral length 1.15 times medial length; one long distomedial seta. Article 3 almost equal to article 2 in width; medial length 0.9 times article 2 medial length, lateral length 0.35 times article 2 lateral length; medial margin rounded, denticulate, with small setae. Articles 4 and 5 lateral lengths 1.2 times and 1.4 times article 3 lateral length, respectively, medial lobe slightly shorter than article 5, with three simple distal setae; article 5 with three simple distal setae. Epipod length 2.1 times width, 0.9 times basis length, width 1.35 times basis width.
Left mandible (male paratype, ZMH K-45646, Figure 23B) incisor and lacinia mobilis with five cusps; spine row with nine spines; molar process distodorsally acute, with four thin setae on base of denticles. Condyle length 0.2 times mandibular body length. Palp length subequal to mandible body length; article 2 with three small simple lateral setae and three strong serrated distal setae; articles 2 and 3 lengths 2.2 times and 1.1 times article 1 length, respectively. Article 3 distal seta length 2.65 times other marginal setae length and 0.8 times article 3 length.
Maxilliped (male paratype, ZMH K-45645, Figure 23E) basis length 3.2 times width; endite width 0.5 times basis width, with five coupling hooks; distal margin with four fan setae. Basis acute lateral projection near palp insertion length 0.9 times article 1 lateral length. Palp length 2.2 times width, 0.7 times basis length. Article 2 length 1.2 times width, width 1.05 times basis width; lateral length 1.1 times medial length; two small setae distolaterally. Article 3 width 0.8 times article 2 width; medial length 0.8 times article 2 medial length; lateral length 0.35 times article 2 lateral length; medial margin denticulate, with seven small setae. Article 4 equal to article 3 in lateral length; medial lobe slightly shorter than article 5, with three distal setae. Article 5 with five long distal setae. Epipod length 2.5 times width, 0.95 times basis length; width 1.2 times basis width, tip narrow and rounded with one small simple seta.
Mandible (male paratype, ZMH K-45654, Figure 27B,C) incisor with five and four cusps and spine row with nine and eight spines on right and left mandibles, respectively; lacinia mobilis of left mandible slightly shorter than incisor, with four distal teeth. Molar process distodorsally acute, with two thin setae on base of denticles. Palp length subequal to mandible body length; article 2 with three distal setae; articles 2 and 3 lengths 2.2 times and 1.1 times article 1 length, respectively. Article 3 distal seta length 1.45 times other marginal setae length and 0.5 times article 3 length.
Maxilla II (male paratype, ZMH K-45654, Figure 28B) middle endite shortest, lateral endite longest; mesial endite with tuft of distal setae, middle and lateral endites with two long and two shorter distal setae.   Maxilliped (male paratype, ZMH K-45654, Figure 28C) basis length 3.0 times width; endite width 0.5 times basis width, with two coupling hooks; distal margin with three fan setae. Basis acute lateral projection near palp insertion length 0.9 times article 1 lateral length. Palp length 2.2 times width, 0.95 times basis length. Article 2 length 0.95 times width, slightly wider than basis; lateral length 1.1 times medial length, one small distolateral seta. Article 3 width 0.9 times article 2 width; medial length 0.85 times article 2 medial length; lateral length 0.3 times article 2 lateral length; medial margin denticulate, with few small setae. Article 4 lateral length 1.35 times article 3 lateral length; medial lobe as long as article 5, with four setae. Article 5 with two lateral and three distal setae. Epipod length 2.4 times width, 0.95 times basis length; width 1.2 times basis width.
Pleopod III (male holotype, ZMH K-45652, Figure 30C) protopod length 0.65 times width, endopod length 1.3 times width, length of three distal plumose setae 0.6 times pleopod III length. Exopod subequal in length to protopod and endopod together and 0.4 times as wide as endopod, with row of fine simple marginal setae; plumose distal seta slightly shorter than endopod distal setae.
Remarks. The new species differs from other species of the complex by its broad and long rostrum in comparison to the size of antenna I article 1-it is 1.7 times longer than article 1 of antenna I.   Paratypes: female (ZMH K-45658), 2.2 mm length, used for dissection; (ZMH K-45657), used for dissection; and 1 further specimen (see Table 1  Antenna II (male holotype, ZMH K-45656, Figure 31C) broken off after article 4; articles 1-4 subequal in length; squama on article 3 reaching midlength of article 4.
Pleopod II (male holotype, ZMH K-45656, Figure 32B) protopod length 1.55 times width, 0.95 times pleopod I length; lateral margin with one simple seta; distomedial notch length 0.25 times medial margin length. Stylet length 0.6 times protopod length, tip reaching behind protopod tip; sperm duct opening at 0.3 times length from proximal margin. Exopod distal article half as long and wide as basal article.
Pleopod III (male holotype, ZMH K-45656, Figure 32C) protopod length 0.7 times width; endopod length 1.35 times width; three distal plumose setae length 0.3 times pleopod III length; exopod as long as protopod and endopod together and 0.3 times as wide as endopod, with row of fine simple lateral setae; simple distal seta slightly shorter than endopod distal setae.
Antenna I (female paratype, ZMH K-45658, Figure 33C) broken off after article 2. Article 1 length 1.15 times width; distomedial lobe tapering distally, with one broom medial and two small medial and three small UB distal setae; one broom seta on distolateral angle. Article 2 length 1.3 times width, with one long broom and two simple small distal setae.
Antenna II (female paratype, ZMH K-45657, Figure 33A) length 1.7 times body length; articles 1-4 subequal in length; squama on article 3 half of article 4 length. Article 5 length 2.3 times articles 1-4 length, width 1.5 times article 4 width; article 6 length 1.05 times article 5 length, width 0.6 times article 5 width; flagellum as long as previous part of antenna II, of about 30 articles.   Mandible (female paratype, ZMH K-45658, Figure 34A,B) incisor with four and three cusps and spine row with nine and eight spines on right and left mandibles, respectively; lacinia mobilis of left mandible visibly shorter than incisor, with three distal teeth; molar process distodorsally acute, with four thin setae on base of denticles. Proximoventral margin and lateral margin of palp article 1 denticulated. Palp length subequal to mandible body length; article 2 with three distal setae; articles 2 and 3 lengths 1.9 times and 1.0 times article 1 length, respectively. Article 3 distal seta length 2.5 times other marginal setae and 0.7 times article 3 length. Maxilla I (female paratype, ZMH K-45658, Figure 34C) mesial endite width 0.6 times lateral endite width, with fine distal setae and stout long distomedial seta; lateral endite with 12 robust differently serrated setae.
Maxilliped (female paratype, ZMH K-45658, Figure 34E) basis length 3.4 times width; endite width 0.5 times basis width, with three coupling hooks; distal margin with four fan setae. Basis acute lateral projection near palp insertion as long as lateral projection on article 1. Palp length 2.1 times width, 0.7 times basis length. Article 2 length 0.8 times width; width 1.1 times basis width; lateral length equal to medial length; three small distal setae laterally and medially. Article 3 width 0.9 times article 2 width; medial length 0.95 times article 2 medial length; lateral length 0.4 times article 2 lateral length; medial margin denticulate, with few small setae. Article 4 equal to article 3 in lateral length, with two lateral setae; medial lobe length 0.8 times article 5 length, with three distal setae. Article 5 with four lateral and five long distal setae. Epipod length 2.4 times width, 0.8 times basis length; width 1.2 times basis width.
Etymology: The name honors Sarah Schnurr's son, Jakob Lutz. Distribution: Known only from the type locality in the Iceland Basin and the Irminger Basin, featuring a depth range of 1385-1588 m. Paratypes: female (ZMH K-45662), used for dissection; female (ZMH K-45663), used for dissection; and 2 further specimens (see Table 1   Antenna I (female paratype, ZMH K-45662, Figure 36A) broken off, article 1 length 1.2 times width, with two broom dorsal setae, one small UB seta, and one small simple seta distomedially; article 2 length 1.4 times width, 0.45 times article 1 length, tip not reaching tip of distomedial lobe of article 1; two broom and three UB distal setae; articles 3 broken off. Antenna II (female holotype, ZMH K-45660, Figure 35B) broken off after article 4; articles 1-4 subequal in length; squama on article 3 reaching midlength of article 4.
Maxilliped (female paratype, ZMH K-45663, Figure 36B) basis length 2.9 times width; endite width 0.6 times basis width, with three coupling hooks; distal margin straight, with three fan setae. Basis acute lateral projection near palp insertion length 1.1 times article 1 lateral length. Palp length 2.1 times width, 0.8 times basis length. Article 2 as long as wide, slightly wider than basis; lateral length 1.15 times medial length; lateral and medial margins with four small setae each. Article 3 almost as wide as article 2; medial margin denticulate, with 10 small setae; medial length 0.85 times article 2 medial length; lateral margin with two small simple setae, length 0.35 times article 2 lateral length. Article 4 equal lateral length 0.8 times article 3 length; medial lobe length 1.2 times article 5 length, with four long distal setae. Article 5 with four lateral and five long distal setae. Epipod length 2.1 times width, 0.9 times basis length; width 1.2 times basis width.
Etymology: The name honors Sarah Schnurr's husband, Mathias Lutz. Distribution: Known only from the type locality in the Irminger Basin, featuring a depth range of 214-698 m.

Molecular Taxonomy
Taxonomists, evolutionary biologists, ecologists, and conservationists rely on a solid knowledge on species [45,46]. Underestimation of biodiversity due to morphologically similar species and cryptic species is a known issue [47], especially in the deep sea. Thus, a solid backbone of taxonomy is needed. An integrative approach combining molecular and morphological data has shown to help to reveal diversity and "unknowns" within benthic samples. However, formal descriptions of species are a time-consuming process and must be conducted by taxonomic experts of the field. The current study disentangles the morphological diversity of the E. producta complex within Icelandic waters. However, the type specimens of E. producta and E. dahli were not suitable for genetic studies. Thus, genetic data rely only on newly collected specimens of the IceAGE1 and IceAGE2 expeditions, since those samples were fixed in 96% nondenatured ethanol, which makes them suitable for genetic analyses.
Maximum likelihood and Bayesian inference tree construction of the different Eurycope producta species complex datasets by Schnurr et al. [28] revealed identical tree topologies, each clade being well-supported by high posterior probabilities and bootstrap support (see Figure 2 for tree topologies of the concatenated dataset. Single gene trees can be retrieved from Schnurr et al. [28]). It has been shown previously that the eight potential genetic species clades are also well-supported by species delimitation methods and hence, further repetition of molecular evidence will be avoided. However, the previous molecular analyses strongly support the distinct species clades of E. producta sensu stricto and E. dahli, as well as the six herein newly described species E. mishkai sp. nov., E. nikitai sp. nov., E. gordeyi sp. nov., E. emmae sp. nov., E. jakobi sp. nov., and E. mathiasi sp. nov. Thus, the evaluated specimens of the E. producta complex represent eight not only genetically, but also morphologically different species.

Taxonomy
The species of the E. producta complex differ from all Eurycope species by having a broad and long rostrum, which is subequal in length and width to article 1 of antenna I, with a medial groove, lateral keels are serrated anteriorly. The large, almost rectangular rostrum of the E. producta complex is similar in the genus Disconectes, though Disconectes differs in having pereonites 5 and 6 dorsally fused, which are free in all Eurycope species. The above-described elaborate species diagnoses of the eight species of the E. producta complex feature specific morphological characters, serving to distinguish them from each other.
Our morphological evaluation shows that the species of the E. producta complex can be divided into two subgroups. The first subgroup consists of the species: E. producta sensu stricto, E. dahli, E. mishkai sp. nov., and E. nikitai sp. nov., whereas the second subgroup includes: E. gordeyi sp. nov., E. emmae sp. nov., E. jakobi sp. nov., and E. mathiasi sp. nov.
The first group is characterized by a relatively narrow tapering rostrum, which is not broader than article 1 of antenna I, a truncate distal margin of the male pleopod I, with distomedial and distolateral lobes of equal length. The species of the second group have a rostrum which is longer than the distomedial lobe of antenna I article 1 and broader than antenna I article 1; in this group the male pleopod I tapers distally and distomedial lobes are elongated, much protruded beyond tiny distolateral lobes.
The most useful diagnostic characters for distinguishing species were revealed. These are the relative size and shape of the rostrum, the correlation between length and width of the rostrum and of article 1 of antenna I, as well as the shape of the distal margin of the male pleopod I. Maxilliped and its palp articles proportions -especially the relation of article 4 distomedial lobe and article 5-can also be used to separate the species from each other.

Distribution
The elucidated species of the herein-evaluated dataset are geographically much more restricted than previously assumed (see Figure 1 for the assumed distribution prior to Schnurr et al. [28] and also for distribution maps of each resolved species). The resolved species feature much smaller ecological niches than the complex. Eurycope dahli was the only species restricted to the deep areas north of the GSR, whereas E. mishkai, E. nikitai, E. jakobi, and E. mathiasi were restricted to the deep areas south of the GSR. Eurycope emmae occurred along the northern side of the GSR and across the Iceland-Faroe Ridge, whereas E. gordeyi occurred only across the Iceland-Faroe Ridge. Thus, the GSR or factors related to this massive submarine ridge system seem to have an effect on the distribution of most of the herein-evaluated species, except for E. producta sensu stricto. Eurycope producta sensu stricto is the only species, which occurred on both sides of the GSR, showing a trans-GSR distribution and a depth range of over 1000 m. (3) Rostrum visibly shorter than article 1 of antenna I, pleopod III with six distal plumose setae. E. dahli Svavarsson, 1987 3.
(2) Rostrum equal or longer than antenna I article I, pleopod III with three distal plumose setae 4.
(1) Rostrum broader than article 1 of antenna I, distal margin of male pleopod I tapering; distomedial lobes elongated, protruding significantly beyond tiny distolateral lobes