Elasmopus thalyae, Gouillieux, Benoit & Sorbe, Jean Claude, 2015

Gouillieux, Benoit & Sorbe, Jean Claude, 2015, Elasmopus thalyae sp. nov. (Crustacea: Amphipoda: Maeridae), a new benthic species from soft and hard bottoms of Arcachon Bay (SE Bay of Biscay), Zootaxa 3905 (1), pp. 107-118 : 109-115

Elasmopus thalyae sp. nov.

Elasmopus rapax . ― Chevreux and Fage, 1925: 244, figs 255, 256 (in part).

Type material. Holotype, male, 9.45 mm (BL), (MNHN-IU-2013-15778), Arcachon Bay (SW France), station ‛Stn. 11’ (44° 39.16N –1° 12.09W), depth: 2.4 m. Collected during scuba diving with a hand-manipulated Eckman grab. Sediment characteristics: median particles size: 334.6 µm, silt and clay: 12.3%, fine sand: 14.5%, medium sand: 55.1%, coarse sand: 14.2%, gravel: 3.9%, organic content: 3.8%. 23 November 2011, coll. X. de Montaudouin.

Paratype, male, 7.49 mm (BL), (MNHN-IU-2013-15779), Arcachon Bay (SW France), station ‛Comprian’ (44° 40.41N –1° 06.10W), depth: 8.2 m, near-bottom temperature: 18.7 °C. Collected with van Veen grab. Sediment characteristics: median particles size: 221.6 µm, silt and clay: 3.3%, fine sand: 35.8%, medium sand: 51.4%, coarse sand: 9.5%, gravel: 0.0%, organic content: 0.4%. 27 April 2011, coll. B. Gouillieux. Dissected specimen (13 slides).

Additional material examined. Arcachon Bay: 50 males (MNHN-IU-2013-15780), 40 brooding females (MNHN-IU-2013-15781), 17 females with oostegites (MNHN-IU-2013-15782), 50 juveniles (MNHN-IU-2013- 15783), 1 aberrant brooding female (MNHN-IU-2013-15784), Arcachon Bay (SW France), station ‛B13’ (44° 38.12N –1° 14.11W). On mussels hand-collected at 2 m depth on the immerged part of a navigation buoy. 3 July 2013, coll. B. Gouillieux.

Chevreux Elasmopus ‘rapax’ collection: MNHN-IU-2009-5425, Guéthary, France, in algae: 1 male, 1 brooding female and 1 juvenile; MNHN-IU-2009-5427, Trébeurden, France, St. 771, in Saccorhiza bulbs, August 1919: 17 males, 12 brooding females, 5 females with oostegites; MNHN-IU-2009-5430, Le Croisic, France, on the decapod Majidae Maja brachydactyla Balss, 1922 (initially mentioned as Maia sp.): 1 male, 5 females with oostegites; MNHN-IU-2009-5431, Locquirec, France, St. 773, in Saccorhiza bulbs, September 1919: 2 males, 2 brooding females, 2 females with oostegites; MNHN-IU-2009-5432, Guéthary, France, in algae: 1 male, 1 brooding female; MNHN-IU-2009-5433, Trébeurden, France: 1 male, 1 female with oostegites; MNHN-IU-2009- 5434, Le Croisic, France, on Maja brachydactyla (initially mentioned as Maia squinado ): 31 males, 25 brooding females, 40 females with oostegites, 4 juveniles; MNHN-IU-2009-5437, Iles Glénans, France, St.197, 0 2 July 1887: 3 males, 2 brooding females; MNHN-IU-2009-5439, Guéthary, France, St. 734, in Laminaria bulbs, August–September 1905: 9 males, 11 brooding females; 3 females with oostegites; MNHN-IU-2009-5440, Saint Jean-de-Luz, France, in Saccorhiza bulbs, 14 September 1920: 1 male, 2 brooding females.

Type locality. Station ‘Stn. 11’ (44° 39.16N –1° 12.09W), Arcachon Bay (SW France).

Etymology. The name is dedicated to the daughter of the first author (GB).

Description. Based on male paratype MNHN-IU-2013-15779.

Head ( Figs 2 , 3 ). Eyes subovoid; lateral cephalic lobe broad, truncated, anteroventral margin notched, anteroventral corner subquadrate. Antenna 1 longer than antenna 2; peduncular article 1 subequal in length to article 2, with 1 robust seta on posterodistal margin; article 3 shorter; accessory flagellum short, 3-articulate, distal article tiny; flagellum with 28 articles. Antenna 2 peduncular article 2 cone gland slightly reaching beyond distal end of article 3, article 4 slightly longer than article 5; flagellum with 11 articles. Upper lip distally rounded with many setules. Mandible incisor asymmetrical, with smooth cutting edge and 2 apicomedial cusps; accessory setal row with 4 serrulate setae; molar well developed, triturative; palp well developed, 3-articulate; article 1 about twice as long as broad, shorter than article 2; article 2 slightly shorter than article 3, inner margin with long and short setae; article 3 falcate, 3 x as long as broad, distal half with comb-like row of setae, increasing in length distally, with 3 long distal setae. Lower lip with many small setae on apical and inner margins of inner and outer plates; tube-like structure on distomesial margin of outer plates, extending into plate as thin tapering channel; mandibular lobes elongated and pointed. Maxilla 1 inner plate tapering distally, with 2 apical long plumose setae and many lateral simple setae; outer plate with 8 distal stout setae (difficult to observe), inner one simple with setules, other ones multicuspidate; palp 2-articulate, article 2 with long simple setae on distal half. Maxilla 2 with both plates equally thin; inner plate with short simple setae, 2 subapical long plumose setae and many shorter plumose setae in facial and marginal apical rows; outer plate with long plumose setae in facial and marginal apical rows. Maxilliped palp article 3 with small distal protuberance apically covered with many setules.

Pereon ( Figs 4 , 5 ). Gnathopod 1 subchelate; coxa anteroventral corner slightly produced, rounded, anterior margin slightly concave; basis with 2 median stout curved setae on outer face, long setae on posterior margin and a subdistal tuft of setae on posterodistal corner; ischium with subdistal tuft of setae on posterodistal corner; merus with 2 subdistal rows of long and short setae; carpus about 1.6 x as long as broad, slightly shorter to propodus, with clusters of setae on distal half of inner face and along posterior margin; propodus palm acute, slightly convex, entire, limited posteriorly by 4 robust sensory setae (2 short and 2 long ones), clusters of setae along anterior and posterior margins as well as on inner face. Gnathopod 2 subchelate; coxa regularly convex distally; basis with short and long setae along posterior margin; ischium with two setae on posterodistal corner; merus produced posterodistally, with 2 clusters of setae along distal half of posterior margin; carpus compressed, lobate, broader than long, with many clusters of setae on posterior projection and 1 cluster on anterodistal corner; propodus expanded, with many clusters of setae all along anterior and posterior margins as well on inner face, palm slightly concave and sculptured, 0.42 x length of propodus, with weak excavation in which dactylus rests, subquadrate distomedial shelf with rows of 4 medial and 4 lateral sensory robust setae, palmar margin without robust setae, subpalmar area with two subacute inner teeth, mid and distal palm respectively; dactylus closing along and reaching end of palm, with one setae on proximal anterior margin, apically blunt. Pereopds 3 and 4 similar, except coxae; coxa 3 regularly convex distally, posterior margin slightly concave; coxa 4 posterodistal lobe slightly developed, with rounded posteromedial corner, ventral margin with many small setae and 7 long setae. Pereopods 5–7 broadly expanded; basis posterior margin with short setae (P5) or with short setae and few long slender setae (P6–P7). Pereopod 5 basis expanded; posterior margin convex, posterodistal corner rounded; carpus and propodus with robust and slender setae on anterior margin. Pereopod 6 basis posterior margin convex, minutely serrate, posterodistal corner rounded; carpus and propodus with robust and slender setae on anterior margin; propodus not expanded posterodistally. Pereopod 7 basis posterior margin convex, minutely serrate, posteroventral corner broadly rounded; propodus not expanded posterodistally.

Pleon ( Figs 2 , 6 ). Pleonites 1–3 dorsally smooth. Epimera 1–3 with short and long setae along distal margin, some arranged in clusters; posterodistal corner with small tooth. Epimeron 3 posterior margin serrated on distal part. Urosomites 1–3 dorsally smooth. Uropod 1 peduncle longer than rami, with robust basofacial seta; inner ramus longer than outer ramus. Uropod 2 peduncle about as long as outer ramus, inner ramus longer than outer ramus. Uropod 3 peduncle shorter than rami; rami distally truncated, apical robust setae long and short; inner ramus slightly shorter than outer ramus, distal end just reaching tip of outer ramus; rami long (length 2.5–2.6 x breadth), 1-articulate. Telson cleft 0.84 x telson length, longer than broad, outer margin with two short pappose setae; each lobe with long inner and short outer apical cusps, both apically acute; distal indentation with 2 subapical robust setae, one short and one long (the last one 0.5 x telson length).

Female (sexually dimorphic characters). Gnathopod 2 less powerful than in male ( Fig. 4 ). Palm not excavate, regularly convex, without shelf and teeth, but with a row of short sensory robust setae both on mesial and lateral margins; proximal end of palm limited by 3 submarginal sensory robust setae. Uropod 3 inner ramus distinctly shorter than outer ramus, distal end clearly not reaching tip of outer ramus. Telson lobes with distal indentation most frequently bearing 3 subapical robust setae, shortening from outer to inner; inner cusp less acute than in male.

Morphological variations. In the biggest males (BL> 11 mm), the accessory flagellum of antenna 1 is 4- articulate, the shelf of gnathopod 2 palm can bears up to 5 medial and 5 lateral sensory robust setae.

The number of long setae along the ventral margin of coxa 4 ranges between 5 and 8 in males, between 2 and 8 in females. The apical setation of telson lobes shows a great variability both in males and females, with the following observed formula: 2+2 (as in the male paratype), 2+3, 3+2, 3+3. When present on telson lobes, the third robust seta in inner position is shorter than the other ones.

Remarks. Vader and Krapp-Schickel (2012) published a world key of Elasmopus species, established on adult males. According to this key, E. thalyae sp. nov. is discriminated by couplet 35 (uropod 3 rami subequal versus uropod 3 rami very unequal in E. hooheno Barnard, 1970 ). However, the subsequent couplet 36 is not discriminant because the new species shows a mix of characters between the two propositions: gnathopod 2 with 3 protuberances (shelf and 2 teeth) in E. mayo Barnard, 1979 and coxa 4 with more than 5 setae on ventral margin in E. rapax Costa, 1853 , E. lecroyae García-Madrigal, 2010 and E. bampo Barnard, 1979 . Elasmopus thalyae sp. nov. can be easily distinguished from these close species by its telson ornamentation, characterized by distal robust setae clearly reaching beyond telson tip. Furthermore, additional distinguishing characters can be used: telson lobes regularly rounded distally in E. lecroyae (versus distally acute); article 3 of mandibular palp deeply falcate in E. bampo (versus falcate); posterior margin of epimeron 3 with only 1–2 notches in E. mayo (versus distally serrate).

In Arcachon Bay, E. thalyae sp. nov. has probably been confused with E. rapax in past studies on benthic communities (de Montaudouin et al. 2006). However, the new species can be distinguished from Hughes and Lowry’s neotype by the following characters: cone gland of antenna 2 peduncle article 2 slightly reaching beyond distal end of peduncle article 3 (versus not reaching to end of peduncular article 3); antenna 2 article 4 slightly longer than article 5 (versus subequal to article 5); mandibular palp article 2 slightly shorter than article 3 (versus longer than article 3), gnathopod 2 shelf with rows of 4–5 medial and 4–5 lateral sensory robust setae (versus 2 medial and 4 lateral robust setae); gnathopod 2 propodus palmar with 2 subacute inner teeth (versus 3 subacute teeth); coxa 4 with rounded posteromedial corner (versus subrectangular corner); pereopod 5 basis with only short setae (versus long setae); pereopods 5–6 basis posterior margin convex (versus straight margin); uropod 1 inner ramus longer than outer ramus (versus subequal in length); uropod 2 inner ramus longer than outer ramus (versus subequal to outer ramus); uropod 3 with long and short apical robust setae (versus only short apical robust setae); telson with acute inner apical lobes (versus broadly rounded lobes), each lobe with one short and one long subapical robust setae (versus 2 subapical short robust setae).

Eleven Elasmopus species were not included in the identification key of Vader and Krapp-Schickel (2012) for different reasons: insufficiently detailed descriptions ( E. erythraeus ( Kossmann, 1880) , E. dentipalmus Walker, 1916 , E. barbatus Schellenberg, 1925 , E. caprai Maccagno, 1936 , E. fusimanus Oliveira, 1951 , E. perditus Reid, 1951 , E. rishikondiensis Kanakadurga, Rao and Shyamashundari, 1981 , E. spinipes Mateus and Mateus, 1986 ), subsequent description of new species ( E. atollicus Myers, 2014 , E. ora Myers, 2014 ). Morphological comparisons between E. thalyae sp. nov. and each of these species (male specimens; male not known in E. caprai ) has been carried out according to literature data. All these species differs from E. thalyae sp. nov. by the following characters: pleon sparsely setose in E. erythraeus versus smooth ( Kossmann, 1880); 2 distal protuberances on gnathopod 2 palm in E. dentipalmus versus one mid and one distal protuberance on palm ( Walker, 1916); distally rounded inner lobe of telson in E. barbatus versus distally acute ( Schellenberg, 1925); uropod 1 without robust setae on inner ramus and telson apex truncated in E. fusimanus versus robust setae on uropod and telson distally acute ( Oliveira, 1951); carpus of gnathopod 1 as long as broad, palm limited by 1 small robust seta in E. perditus versus carpus longer than broad, palm limited by 4 robust setae ( Reid, 1951); uropod 3 outer ramus with 2 transverse rows of setae in E. rishikondiensis versus 3 transverse rows of setae ( Kanakadurga et al., 1981); posterodistal corner of pereopods 3–4 propodus with 1 large striated seta in E. spinipes versus without striated seta ( Mateus et al. 1986); rami of uropod 3 unequal in E. atollicus versus subequal rami ( Myers, 2014); hind margin of pereopod 7 basis with only short setae in E. ora versus long and short setae ( Myers, 2014).

A female (Fig. 7) with aberrant morphology (MNHN-IU-2013-15784) was collected in Arcachon Bay (station ‘B13’ 03/07/2013, mussel fouling, BL: 8.56 mm), characterized by a supernumerary antenna inserted outside right antenna 2. This appendage is clearly shorter than antenna 2 and with an intermediate morphology between antenna 1 and antenna 2 (bi-articulate peduncle distally bearing two small flagella, the longer one with 8 articles and the shorter one with 6 articles). This aberrant female also showed an unusual telson with 4 subapical robust setae (short external one) on the left lobe.

The E. ‘rapax’ from the MNHN collection (English Channel and Atlantic coast of France) contained 67 males, 112 females and 5 juveniles. According to our morphological observations, all the males actually belong to the new species E. thalyae sp. nov. herein described. Such a conclusion is strengthened by gnathopod 2 ornamentation of these specimens, characterized by a subquadrate shelf and 2 teeth along palmar margin. However, when compared to the Arcachon specimens, the telson structure shows some variability in the shape of inner cusp (from acute to rounded) and in the relative length of subapical robust setae (longer or shorter than inner lobe).

Figures

FIGURE 2. Elasmopus thalyae sp. nov. A) holotype, male, BL = 9.45 mm, MNHN-IU- 2013 - 15778, habitus in lateral view. B) paratype, male, BL = 7.49 mm, MNHN-IU- 2013 - 15779, accessory flagellum. Scale bars: A: 1 mm; B: 0.1 mm.

FIGURE 3. Elasmopus thalyae sp. nov., paratype, male, BL = 7.49 mm, MNHN-IU- 2013 - 15779. A) right mandible, posterior view; B) right maxilliped, anterior face; C) left maxilla 2, anterior face; D) left maxilla 1, anterior face; E) upper lip; F) lower lip, anterior face. Scale bars: 0.1 mm.

FIGURE 4. Elasmopus thalyae sp. nov., paratype, male, BL = 7.49 mm, MNHN-IU- 2013 - 15779. A) right gnathopod 1, outer face; B) right gnathopod 2, outer face; C) right gnathopod 2, detail of shelf. Additional material collected at station ‛ B 13 ’, used for SEM. D) male, BL = 9.45 mm, gnathopod 2 dactylus and propodus, inner face showing ornamentation of palm; E) female, BL = 7.73 mm, gnathopod 2 dactylus and propodus, inner face. Scale bars: A, B, D, E: 0.5 mm; C: 0.1 mm.

FIGURE 5. Elasmopus thalyae sp. nov., paratype, male, BL = 7.49 mm, MNHN-IU- 2013 - 15779. A – E) outer face of right pereopods 3 – 7 and corresponding coxae. Scale bars: 0.5 mm.

FIGURE 6. Elasmopus thalyae sp. nov., paratype, male, BL = 7.49 mm, MNHN-IU- 2013 - 15779. A – C) outer view of right uropods 1 – 3; D) outer view of left epimeral plates 1 – 3; E) dorsal view of telson. Scale bars: A – C, E: 0.2 mm; D: 0.5 mm.