INTRODUCTION
The genus Mysidopsis Sars, Reference Sars1864 presently contains a heterogeneous group of 46 living species (Anderson, Reference Anderson2010), showing a wide variety of morphological characters (Bacescu, Reference Bacescu1968a; Brattegard, Reference Brattegard1969; Tattersall, Reference Tattersall1969; Bacescu & Gleye, Reference Bacescu and Gleye1979; Mauchline, Reference Mauchline1980).
Since Sars’ generic diagnosis (1864) based on the description of two European species, many distantly related species have been included in this genus, thus excessively broadening its morphological limits. However, as commented by Price et al. (Reference Price, Heard and Stuck1994), some Mysidopsis species were subsequently transferred to other genera (Australomysis W.M. Tattersall, 1927; Metamysidopsis W.M. Tattersall, Reference Tattersall1951; Brasilomysis Bacescu, 1968; Parvimysis Brattegard, Reference Brattegard1969; and Americamysis Price et al., Reference Price, Heard and Stuck1994) according to the divergent structure of their antennal scale, eye peduncle, mandibule, maxillae, thoracopod endopods and telson. Tattersall (Reference Tattersall1969) proposed a detailed diagnosis of the genus Mysidopsis and Price et al. (Reference Price, Heard and Stuck1994) presented a listing of the nominal species currently retained within this genus with information on their geographical distribution (most of them from the western Atlantic Ocean). Mysidopis lata Bravo & Murano, Reference Bravo and Murano1996 is the latest species to be described from Japanese specimens.
The first three species described in genus Mysidopsis―M. didelphys (Norman, 1863), M. angusta Sars, Reference Sars1864 and M. gibbosa Sars, 1864―are until now the only species known from the north-eastern Atlantic and the Mediterranean. Within their respective distributional areas, all of them have been reported in numerous studies such as Sars (Reference Sars1872), Colosi (Reference Colosi1929), Bacescu (Reference Bacescu1941), Tattersall & Tattersall (Reference Tattersall and Tattersall1951), Mauchline (Reference Mauchline1970), Mauchline & Murano (Reference Mauchline and Murano1977), Lagardère & Nouvel (Reference Lagardère and Nouvel1980), Sorbe (Reference Sorbe1982), Müller (Reference Müller1993), Cunha et al. (Reference Cunha, Sorbe and Bernardes1997) and San Vicente (Reference San Vicente and Barrientos2004). Despite the confused status of this genus, these European species are morphologically well described and easy to identify (Sars, Reference Sars1872; Tattersall & Tattersall, Reference Tattersall and Tattersall1951; Tattersall, Reference Tattersall1969; Mauchline, Reference Mauchline1971).
During a multidisciplinary survey of the deep seamount-like ‘Le Danois' Bank in the southern Bay of Biscay (nowadays the first off-shore Spanish ‘El Cachucho' Marine Protected Area; see Heredia et al., Reference Heredia, Pantoja, Tejedor and Sánchez2008), many suprabenthic Mysida were sampled on its southern flank, including the Boreomysinae Boreomysis tridens G.O. Sars, 1870, the Erythropinae Amblyops spinifera Nouvel & Lagardère, 1976, A. tenuicauda W.M. Tattersall, 1911, A. trisetosa Nouvel & Lagardère, 1976, Dactylamblyops goniops W.M. Tattersall, 1907, Dactylerythrops dimorpha Nouvel & Lagardère, 1976, Paramblyops rostrata Holt & W.M. Tattersall, 1905, Parapseudomma calloplura (Holt & W.M. Tattersall, 1905), Pseudomma kruppi W.M. Tattersall, Reference Tattersall1909, the Heteromysinae Mysidetes farrani (Holt & W.M. Tattersall, 1905) and the Mysidellinae Mysidella biscayensis Lagardère & Nouvel, Reference Lagardère and Nouvel1980 as well as two females ascribed to a new species within the genus Mysidopsis (Leptomysinae). This paper deals with the morphological description of this new taxon and provides an updated identification key to the known European Mysidopsis. Furthermore, some ecological data on the new species are also given.
MATERIALS AND METHODS
Within the ECOMARG project framework (see www.ecomarg.net), two multidisciplinary surveys ECOMARG 03 (October 2003) and ECOMARG 04 (April 2004) were carried out at the ‘Le Danois' Bank (Figure 1). During these surveys, the suprabenthic fauna was quantitatively sampled with a sled equipped with superimposed nets (0.5 mm mesh size), an opening–closing system activated by contact with the sea floor and a TSK flowmeter for haul length estimations (see Sorbe, Reference Sorbe1983). On-board, samples were fixed with a solution of 4% formalin in seawater. At the laboratory, the Mysidopsis specimens were sorted and stored separately in 70% ethanol for later examination.
Fig. 1. Location of stations sampled with a suprabenthic sled at the Le Danois Bank (‘El Cachucho' Marine Protected Area) during ECOMARG 03 (squares) and ECOMARG 04 cruises (circles). Solid symbol: samples including Mysidopsis cachuchoensis sp. nov. Isobaths in metres.
The specimens examined in the present study were recorded only during ECOMARG 04 cruise at E04-TS2 station located at 828 m depth (Figure 1). The total body length of individuals (TL) was measured from the apex of the rostrum to the posterior end of the telson, excluding spines. Buccal, thoracic and abdominal appendages were dissected, temporarily mounted on slides and drawn with the aid of a camera lucida mounted on a Zeiss Axioscop 20 microscope. The terminology for cuticle projections (setae) follows that of Garm (Reference Garm2004).
The type specimens are deposited in the Museo Nacional de Ciencias Naturales (MNCN), Madrid.
RESULTS
SYSTEMATICS
(modified from Meland & Willassen, Reference Meland and Willassen2007)
Order MYSIDA Boas, 1883
Family MYSIDAE Haworth, 1825
Subfamily LEPTOMYSINAE Norman, 1892*
Genus Mysidopsis G.O. Sars, Reference Sars1864
Mysidopsis cachuchoensis sp. nov.
(Figures 2–4)
*In disagreement with Norman's classification, Hansen (Reference Hansen1910) created the tribe Leptomysini, at present an obsolete item according to Meland & Willassen (Reference Meland and Willassen2007).
Fig. 2. Mysidopsis cachuchoensis sp. nov.: (A) holotype, mature female (MNCN 20.04/1178); (B–I) paratype, immature female (MNCN 20.04/1179); (A) habitus in dorsal view; (B) antenna in ventral view; (C) labrum; (D) posterior margin of labrum; (E) right mandible; (F) left mandible; (G) incisor to molar process of left mandible; (H) maxillule; (I) maxilla.
Fig. 3. Mysidopsis cachuchoensis sp. nov.: (A, H–I) holotype, mature female (MNCN 20.04/1178); (B–G) paratype, immature female (MNCN 20.04/1179); (A) 1st thoracopod; (B) distal articles of endopod of 1st thoracopod; (C) 2nd thoracopod; (D) distal articles of endopod of 2nd thoracopod; (E) 3rd thoracopod; (F) 4th thoracopod; (G) distal articles of endopod of 4th thoracopod; (H) 6th thoracopod; (I) 7th thoracopod.
Fig. 4. Mysidopsis cachuchoensis sp. nov.: (A–H) holotype mature female (MNCN 20.04/1178); (I) paratype immature female (MNCN 20.04/1179); (A) 1st pleopod; (B) 2nd pleopod; (C) 3rd pleopod; (D) 4th pleopod; (E) 5th pleopod; (F) telson and uropods in dorsal view; (G) distal end of telson; (H, I) right uropods in ventral view.
TYPE MATERIAL
Holotype: 1 mature female, 14.1 mm TL, MNCN 20.04/1178, north-eastern Atlantic Ocean, Le Danois Bank, RV ‘Vizconde de Eza', ECOMARG 04 cruise, 14 April 2004, Arcachon suprabenthic sled, haul E04-TS2, 43°57.76′N 5°09.34′W (haul beginning), 828 m depth, 0–50 cm near-bottom water layer, haul length: 458 m; dissected, one vial.
Paratype: 1 immature female, 8.6 mm TL, MNCN 20.04/1179, data as for holotype; dissected, one vial.
DIAGNOSIS
Carapace without dorsal median nodules; anterior margin evenly rounded. Antennal scale without distal article. Telson linguiform and entire; proximal half unarmed; distal half armed with 19–20 graduated cuspidate setae, increasing in size towards apex; apex with a median pair of cuspidate setae half length of adjacent ones. Uropodal endopod armed with 34–36 short cuspidate setae along inner margin, from statocyst to sub-apex.
DESCRIPTION
The following morphological characteristics only refer to females (male unknown).
Carapace (Figure 2A) with anterior margin slightly produced and evenly rounded; posterior margin dorsally emarginate, leaving last thoracic somite partially uncovered; posterolateral lobe covering anterior abdominal somite.
Eyes (Figure 2A) large, globular, broader than eyestalk, laterally extending slightly beyond carapace limits; eyestalk without dorsal finger-like papilla; ommatidial pigment yellow (in preserved specimens).
Antennular peduncle (Figure 2A) slightly shorter than antennal scale. First article longer than wide; second article short, half as long as broad; third article longer than broad, armed with three simple setae near distal end of inner margin.
Antennal sympod (Figure 2B) with outer distal angle rounded. Peduncle extending to half scale length; first article short, as long as broad, inner margin rounded; second article twice as long as broad, inner distal margin armed with two simple setae; third article slightly shorter than second one, distal inner margin armed with one simple seta.
Antennal scale (Figure 2A, B) three times longer than maximum width, extending slightly beyond antennular peduncle; margins convex, setose all around and without apical suture.
Labrum (Figure 2C, D) symmetrical, without frontal spiniform process, posterior margin with two distinct areas consisting of a cluster of short irregularly distributed thin simple setae and a reduced area covered with small scale-like projections.
Mandibles (Figure 2E–G) well developed. Three-segmented palp, second article bottle-shaped, about twice as long as third, with pappose setae on both margins; third article armed on distal third of inner margin with 7–8 ventral serrate setae and one distal large conspicuous pappose seta. Setal row with two setae and molar process reduced.
Maxillule (Figure 2H) apex of outer lobe armed with six strong cuspidate setae and two rows of three and five pappose setae on ventral surface. Inner lobe with eight pappose setae, proximal anterior margin with a row of small pappose setae.
Maxilla (Figure 2I) with distal article of endopod oval, longer than wide, margins densely setose on inner distal two-thirds. Exopod relatively broad, extending to distal margin of proximal article of endopod, with 25 short pappose setae. Inner margin of coxal endite armed with a row of pappose setae, medial one longer than others. Inner margin of bilobulate basal endites also armed with setae.
First thoracopod (Figure 3A, B) short and robust, with unarmed epipodite. Inconspicuous articulation between basis and preischium. Endopod with preischium and ischium fused; merus longer than carpopropodus; dactylus bearing distal serrate nail. Exopod longer than endopod, with 9-segmented flagellum.
Second thoracopod (Figure 3C, D) slightly longer than first one, with small endite on the basis. Inconspicuous articulation between basis and preischium. Endopod with preischium and ischium fused; merus subequal to carpopropodus; dactylus densely setose, armed with 4 terminal serrate setae with basal septum and about 12 pappose setae. Exopod shorter than endopod, with 7-segmented flagellum.
Third to eighth thoracopods (Figure 3E–I) with endopod longer than exopod; ischium and merus subequal in length; carpopropodus 3-segmented, shorter than merus; dactylus with a strong distal simple nail. Exopod with a 9–10-segmented flagellum. Sixth to eighth thoracic appendages with a pair of developed oostegites, first pair smaller than posterior ones.
Pleopods (Figure 4A–E) uniramous, unjointed, increasing in length towards posterior pairs.
Uropod (Figure 4F, H, I) endopod slender, extending beyond apex of telson for 1/3 of its length, armed along inner margin with 34–36 short cuspidate setae not extending to apex. Exopod longer than endopod; outer and inner margin almost parallel. Probably reflecting a teratological condition, the right exopod of the holotype female is broader and larger than the left one (Figure 4F).
Telson (Figure 4F, G) linguiform, 1.7 times longer than maximal width; distal half of lateral margins armed with 19–20 cuspidate setae, increasing in size towards apex; apex armed with two median cuspidate setae, half length of adjacent ones.
ETYMOLOGY
This species is named after the ‘El Cachucho' Marine Protected Area (Cantabrian Sea) where it was discovered.
DISTRIBUTION
The known distributional area of the new Mysidopsis species is at present restricted to the Le Danois Bank (southern Bay of Biscay).
REMARKS
According to Mauchline's identification key to Mysidae (1980), the two females herein examined belong to subfamilies Leptomysinae/Mysinae (previously tribe Leptomysini/Mysini; see Meland & Willassen, Reference Meland and Willassen2007), as demonstrated by the following diagnostic characters: statocyst present, exopod of uropod undivided, outer margin of uropod exopod without spines, labrum normal and symmetrical, third thoracopod similar to the posterior ones. Unfortunately, due to the absence of males in our collection, there is actually no possibility to use this key furthermore after couplet 22 of Mauchline's key. Using the modern list of genera presented in the World Register of Marine Species (WoRMS) website (Mees, Reference Mees2012) for both subfamilies, our females were compared to all recognized genera, using original diagnoses. The Appendix shows the results of these comparisons, related to the structure of antennal scale and telson. As in the case of our females, many genera of both subfamilies are characterized by a telson entire. However, all of them in subfamily Mysinae also show a 2-jointed antennal scale (subdistal suture) as well as some of them in subfamily Leptomysinae (Antichthomysis Fenton, 1991, Brasilomysis Bacescu, 1968, Leptomysis G.O. Sars, 1869, Megalopsis Panampunnayil, Reference Panampunnayil1987, Metamysidopsis W. Tattersall, Reference Tattersall1951, Mysideis G.O. Sars, 1869, Paraleptomysis Liu & Wang, Reference Liu and Wang1983 and Pyroleptomysis Wittmann, Reference Wittmann1985). In consequence, our females (without distal joint on their antennal scales) do not belong to these genera. Furthermore, the genus Calyptoma W. Tattersall, Reference Tattersall1909 can be easily discarded due to the peculiar aspect of its antennal scales (outer margin naked and distally pointed). Finally, only two genera from subfamily Leptomysinae show both a telson entire and a 1-jointed antennal scale: Americamysis, Price, Heard & Stuck, Reference Price, Heard and Stuck1994 and Mysidopsis G.O. Sars, Reference Sars1864. According to Price et al. (Reference Price, Heard and Stuck1994), the genus Americamysis was created to receive six American Mysidopsis species with two articles in the carpopropodus of thoracic endopods 3–8. As our females have 3 articles in the carpopropodus of thoracic endopods 3–8, they do not belong to genus Americamysis. Finally, according to the genus diagnosis of Tattersall (Reference Tattersall1969), they are assigned to genus Mysidopsis, considering the structure of their antennal scale (distal article absent), of their maxilla (exopodite present), of their thoracopod endopods (first thoracopod with preischium and ischium fused; third to eighth thoracopods with carpopropodus subdivided in 3 articles) as well as the armature of their uropod endopods and telson.
According to the morphological criteria used by Tattersall (Reference Tattersall1969) to construct an identification key for the known species, M. cachuchoensis sp. nov. shows the closest morphological similarity to M. hellvillensis Nouvel, Reference Nouvel1964, a littoral mysid captured in night-time subsuperficial plankton hauls at Nosy-Bé, north-west Madagascar (Nouvel, Reference Nouvel1964). However, this Indian Ocean species can be distinguished by the following discriminating characters: frontal plate triangular, antennal scale with distal article, endopod of maxilla with distal article elongate, inner margin of uropodal endopod armed from statocyst to sub-apex with cuspidate setae arranged in series, telson armed with two cuspidate setae on each side near its base and with a median pair of cuspidate setae longer than the adjacent ones at its apex.
Mysidopsis cachuchoensis sp. nov. is the fourth species of this genus to be discovered in European waters (north-eastern Atlantic and western Mediterranean), after M. didelphys (Norman, 1863)―the type species of this genus― M. angusta Sars, Reference Sars1864 and M. gibbosa Sars, Reference Sars1864. It can be easily distinguished from these species by the ornamentation of its eyestalk (without dorsal finger-like papilla), the structure of its antennal scale (without distal article), the armature of the inner margin of its uropodal endopods (more than 30 graduated cuspidate setae from statocyst to sub-apex), the armature of the lateral margins of its telson (proximal half naked). Furthemore, its carapace shows no dorsal ornamentation (presence of two nodules in the median line in M. gibbosa ―however, as mentioned by Bacescu (Reference Bacescu1941) and Ariani (Reference Ariani1967), these nodules are sometimes poorly visible or even absent in Mediterranean specimens) and its telson apex is entire and rounded (unarmed small wedge-shaped incision in M. angusta). It is noteworthy to point out that the telson apex of M. cachuchoensis sp. nov. has two median cuspidate setae half shorter than the adjacent ones, a morphological peculiarity in contrast with the case of many Mysidopsis species in which the median apical pair is the longest. Adapted from Tattersall & Tattersall (Reference Tattersall and Tattersall1951), an identification key is proposed to include the new European species herein described.
KEY TO SPECIES OF MYSIDOPSIS G.O. SARS, 1864 RECORDED IN EUROPEAN WATERS
(Modified from Tattersall & Tattersall, Reference Tattersall and Tattersall1951; ecological data according to Tattersall & Tattersall, Reference Tattersall and Tattersall1951; Furnestin, Reference Furnestin1959; Tattersall, Reference Tattersall1969; Mauchline, Reference Mauchline1971; Lagardère & Nouvel, Reference Lagardère and Nouvel1980; Sorbe, Reference Sorbe1984; Cunha et al., Reference Cunha, Sorbe and Bernardes1997.)
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1. Apex of telson with small median V-shaped cleft………M. angusta G.O. Sars, Reference Sars1864
north-eastern Atlantic, from Norway to Portugal; western Mediterranean, Adriatic Sea……… Shelf and upper slope, 2–400 m
―Apex of telson entire………2
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2. Eyes with a finger-like papilla on the inner dorsal side of the eyestalk. Antennal scale with distal article. Inner margin of uropodal endopod with no more than 5 cuspidate setae near statocyst. Proximal lateral margin of telson with cuspidate setae………3
―Eyestalk without dorsal finger-like papilla. Antennal scale without distal article. Uropodal endopod with a row of more than 30 cuspidate setae along inner margin. Proximal lateral margin of telson unarmed……… M. cachuchoensis sp. nov. Le Danois Bank (southern Bay of Biscay)
Upper slope, 828 m
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3. Rostrum well produced, broadly triangular and acutely pointed. Telson triangular with narrow truncate apex, armed with a pair of large median cuspidate setae……… M. didelphys (Norman, 1863) north-eastern Atlantic, from Norway to Portugal; western Mediterranean
Shelf and upper slope, 20–435 m
―Rostrum small, obtusely triangular. Telson linguiform, apex with outer corners rounded and naked, only armed with a pair of median cuspidate setae……… M. gibbosa G.O. Sars, Reference Sars1864 north-eastern Atlantic, from Norway to Morocco; western and eastern Mediterranean Shelf, from river outflow areas down to 179 m
ECOLOGICAL NOTES
Mysidopsis cachuchoensis sp. nov. is a very rare species in the Le Danois Bank area. Despite a two-year monitoring survey of this bank including its top plateau and southern flank (9 suprabenthic hauls), only two females were sampled at one station (abundance: 0.3 ind./100 m2 in the 0–50 cm near-bottom water layer sampled by the sled; 0.1% of the total suprabenthic fauna collected in the haul). According to the habitat classification proposed by Sánchez et al. (Reference Sánchez, Serrano, Parra, Ballesteros and Cartes2008), this mysid belongs to the demersal Pheronema placenta–Deania calcea community of the inner basin (between the bank and the adjacent Cantabrian shelf), where the bathyal suprabenthic fauna is dominated by euphausiid larvae and cumaceans (unpublished observations). According to available environmental data (Parra & Sánchez, personal communication), it lives over muddy bottoms (median grain size: 21.6 µm; particles <62 µm: 69.58%; particles 62–500 µm: 29.07%; particles >500 µm: 1.34%; sediment organic content: 7.00%) where near-bottom water temperatures and salinities were 10.2°C and 35.8, respectively (conductivity–temperature–depth data at 14 m above bottom). In conclusion, M. cachuchoensis sp. nov. is a strict suprabenthic inhabitant of upper bathyal bottoms (endemic to the Le Danois Bank?), in contrast to the other European Mysidopsis species known to occur more abundantly in inner shelf areas (Tattersall & Tattersall, Reference Tattersall and Tattersall1951; Tattersall, Reference Tattersall1969; Mauchline, Reference Mauchline1970, Reference Mauchline1971, Reference Mauchline1980).
ACKNOWLEDGEMENTS
We thank the crew of the RV ‘Vizconde de Eza' and all participants on the ECOMARG cruises for their assistance at sea during sampling. Special thanks to Dr F. Sánchez (IEO, Santander) and Dr S. Parra (IEO, Coruña) for the communication of environmental data, to Dr W. Price (University of Tampa) for his help with old literature and critical review of the manuscript, an anonymous referee for useful comments on our work, and to Z. Sorbe for help in material sorting. This study was funded by the Spanish Science and Technology Ministry (ECOMARG project, REN2002-00916/MAR). I. Frutos is grateful to J. and P. Cathalàa for their hospitality during her Arcachon stoys.
APPENDIX
Comparison of morphological characters in genera of Leptomysinae and Mysinae:
