Ischnomesus harrietae, Kavanagh, Fiona A., Frutos, Inmaculada & Sorbe, Jean Claude, 2015

Kavanagh, Fiona A., Frutos, Inmaculada & Sorbe, Jean Claude, 2015, Ischnomesus harrietae sp. nov., a new benthic asellote (Crustacea: Isopoda: Ischnomesidae) from bathyal bottoms of the southern Bay of Biscay, Zootaxa 3911 (2), pp. 201-217 : 204-210

publication ID	https://doi.org/ 10.11646/zootaxa.3911.2.3
publication LSID	lsid:zoobank.org:pub:EDF19A15-6C94-49EB-A9F0-AC321C347F13
DOI	https://doi.org/10.5281/zenodo.5674667
persistent identifier	https://treatment.plazi.org/id/1A6C8B7B-FFAF-9805-FF18-FF6FFDF7FBAD
treatment provided by	Plazi
scientific name	Ischnomesus harrietae
status	sp. nov.

Treatment

Ischnomesus harrietae View in CoL sp. nov.

( Figs 2–6 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Etymology. The species is named for Harriet Richardson in recognition of her contribution to the knowledge of Isopoda (see Damkaer 2000).

Material examined. Holotype: post-brooding female (BL = 8.4 mm), MNHN-IU-2014-10127 ( Fig. 2 View FIGURE 2 ); ESSAIS II, RV Côte d’Aquitaine, 18 May 1989, ‘Roscoff’ suprabenthic sled, Arcachon Plateau, sample reference TS11-R-N1, 44°32.89’N 2°14.24’W, 923–924 m, muddy bottom (SUPRABAT XV cruise, 25 January 1992, sediment sample FLU92004; median grain size: 7.6 µm; particles <63 µm: 97.6%; particulate organic carbon content: 1.36%), inferred water temperature, salinity and oxygen concentration at 923 m depth above bottom: 9.9°C, 35.75 and 3.61 ml l -1, respectively (ECOFER III cruise, 15 October 1990, CTD data from the water column above a 3000 m depth bottom in the Cap Ferret Canyon).

Paratypes: 1 copulatory male MNHN-IU-2014-10128 (BL = 4.7 mm), used for fully body illustration ( Fig. 4 View FIGURE 4 ); 1 preparatory female MNHN-IU-2014-10129 (BL = 5.8 mm) used for uropod illustration ( Fig. 2 View FIGURE 2 ); 1 post-brooding female MNHN-IU-2014-10130 (BL = 6.4 mm), not illustrated; 1 post-brooding female MNHN-IU-2014-10131 (BL = 6.1 mm), used for description of pereopods ( Fig. 3 View FIGURE 3 ); 1 post-brooding female MNHN-IU-2014-10132 (BL = 6.9 mm), not illustrated; data as for holotype. 1 copulatory male, MNHN-IU-2014-10133 (BL = 4.5 mm), used for description of mouthparts and pleopods ( Figs 5 View FIGURE 5 & 6 View FIGURE 6 ); 1 aberrant precopulatory male MNHN-IU-2014-10134 (BL = 5.5 mm), used to illustrate pleotelson ( Fig. 4 View FIGURE 4 ); 1 manca 3 male MNHN-IU-2014-10135 (BL = 3.6 mm), not illustrated; ECOFER I, RV Le Noroît, 1 July 1989, Arcachon Plateau, ‘Roscoff’ suprabenthic sled, sample reference TS02-R-N1, 44°36.21’N 2°12.84’W, 714– 708 m, muddy bottom (ECOFER 5 cruise, August 1991, sediment sample KTB154; median grain size: 22.6 µm; particles <63 µm: 76.5%; particulate organic carbon content: 0.67%), inferred water temperature and salinity at 711 m depth above bottom: 10.2°C and 35.75, respectively (PRECOMAT II cruise, 23 April 1985, CTD data from the water column above a 800 m depth bottom on the Arcachon Plateau). 1 manca 2 MNHN-IU-2014-10136 (BL = 2.7 mm), not illustrated; OXYBENT 10, RV Côtes de la Manche, 1 May 2000, Aquitanian slope, ‘Roscoff’ suprabenthic sled, sample reference TS13-R-N1, 44°09.18’N 2°20.05’W, 991– 990 m, oxygen concentration at sediment-water interface (multitube boxcorer sample OB10-A-MT14, 1008 m): 4.43 ml l -1.

Additional deposited material. 2 manca 3 females, 1 female (anterior fragment), 1 manca 2, MNCN 20.04/ 9520; RV Vizconde de Eza, ECOMARG 0 3, 20 October 2003, ‘Arcachon’ suprabenthic sled, sample reference TS8-A, 44º01.59'N 5º09.93'W, 817– 816 m, mud, near-bottom water temperature and salinity: 10.3°C and 35.8 (CTD data). 1 preparatory female ( MNCN 20.04/9521); RV Vizconde de Eza, ECOMARG 0 4, 13 April 2004, ‘Arcachon’ suprabenthic sled, sample reference TS1-A, 44º00.78'N 5º08.86'W, 829– 828 m, mud, near-bottom water temperature and salinity: 10.3°C and 35.8 (CTD data). 1 precopulatory male, 1 manca 3 male ( MNCN 20.04/ 9522); RV Vizconde de Eza, ECOMARG 0 4, 15 April 2004, ‘Arcachon’ suprabenthic sled, sample reference TS3- A, 43º51.11'N 5º05.64'W, 620– 619 m, muddy fine sand, near-bottom water temperature and salinity: 10.5°C and 35.7 (CTD data). 2 manca 3 males, 1 preparatory female, 1 manca 3 female, 1 manca 2 ( MNCN 20.04/9523); RV Vizconde de Eza, ECOMARG 0 4, 16 April 2004, ‘Arcachon’ suprabenthic sled, sample reference TS4-A, 43º55.26'N 4º53.97'W, 1049–1062 m, mud, near-bottom water temperature and salinity: 9.7°C and 35.8 (CTD data). 1 male (posterior fragment), 1 female (posterior fragment), 1 manca 2, 2 anterior fragments ( MNCN 20.04/ 9524); RV Cornide de Saavedra, ECOMARG 0 8, 10 July 2008, ‘Coruña’ suprabenthic sled, sample reference TS3- C, 44º02.98'N 5º15.09'W, 954– 951 m, muddy fine sand.

Diagnosis. Mandible palp absent. Antenna article 2 with pedestal setae. Pereonites 1–4 and 6–7 with at least one pair of dorsal pedestal setae in adults. Pereonite 5 covered with many pedestal setae, arranged in longitudinal rows. Pleotelson of adults with at least one pair of dorsal pedestal setae. Uropods biarticulate. Lateral margins and ventral face of copulatory male pleopod I with numerous short clusters of simple setae. Mesial margin of pleopod II protopod with fringe of short setae. Distal margin of adult female pleopod II with simple setae (no plumose setae).

Description of female holotype ( Fig. 2 View FIGURE 2 ) (MNHN-IU-2014-10127; BL = 8.4 mm)

Dorsal cuticle covered with coarse projections (pedestal setae). Head length 0.8 width, dorsal surface without protuberances. Pereonite 1 width 0.18 BL. Pereonite 4 length 1.0 width. Pereonite 5 length 2.0 width, 0.3 BL, 1.5 pereonite 4 length. Pleotelson length 1.1 width. Pereonites 1–2 with 1 pair of dorsal pedestal setae. Pereonite 1 with 1 pair of anterolateral and 1 pair of lateral pedestal setae. Pereonite 2 with four pairs of short (length less than twice width) lateral pedestal setae. Pereonite 3 with 2 pairs of dorsal pedestal setae and with 2 pairs of short lateral setae. Pereonite 4 with 4 pairs of short anterolateral pedestal setae, with 10 pairs of lateral pedestal setae and 8 pairs of dorsal pedestal setae. Pereonite 5 with 17–18 pairs of lateral pedestal setae, 1 pair of posterolateral pedestal setae and 10 pairs of dorsal pedestal setae. Pereonite 6 with 1 pair of lateral pedestal setae, 1 pair of dorsolateral pedestal setae and 2 pairs of dorsal pedestal setae. Pereonite 7 with 1 pair of dorsolateral pedestal setae and 1 pair of dorsal pedestal setae. Pleonite 1 with 1 pair of simple lateral setae. Pleotelson with 1 pair of anterolateral pedestal setae, 3 pairs of dorsal pedestal setae, numerous lateral simple setae and 4 distal setae.

Antennula with 6 articles. Article 1 squat and globular, with 2 simple setae. Article 2 length 10.2 article 1 length, 0.73 head width, 0.1BL; inserting dorsally on article 1, curved at proximal insertion, with 12 ventromedial setae and 8 lateral setae. Articles 3–6 altogether shorter than article 2; article 3 elongate and tubular, much longer than wide, longer than article 4; articles 4 and 5 subequal in length, each one longer than article 6; article 6 longer than wide, with 2 terminal setae.

Antenna article 2 with 4 pedestal setae; article 3 length 2.3 width, 0.08 BL. Flagellum missing.

Pereopod I weakly carposubchelate. Basis with 5 anterior simple setae. Ischium with 4 anterior and 3 posterior simple setae. Merus with 2 anterior, 2 posterior and 2 mesial simple setae. Carpus with 4 anterior simple setae, with weakly expanded posterior palm, with 6 short sensillate robust setae and 4 simple setae proximally. Propodus with 10 anterior simple setae and 8 posterior simple setae and 2 short sensillate robust setae. Dactylus with 3 anterior simple setae, 1 posterior simple seta and 1 mesial simple seta.

Pereopods II–VII all broken at basis/ischium articulation.

Pleopod II (operculum) neck 0.54 width of operculum, laterally convex, broadening posteriorly to rounded corners, posterior margin concave, with 4 simple distal setae (no plumose setae).

Description of female pereopods ( Fig. 3 View FIGURE 3 ) (paratype MNHN-10131, BL = 6.1 mm)

Pereopods I-VII all present, although pereopods V and VII broken on both sides and therefore not illustrated.

Pereopods increasing in length from anterior to posterior (PI / PII / PIII / PIV / PVI length ratios: 1 / 1.4 / 1.5/ 1.7 / 1.8).

Pereopod II (left), basis / ischium / merus / carpus / propodus / dactylus length ratios: 1 / 0.9 / 0.5 / 1.1 / 0.5 / 0.3. Basis with 3 anterior and 6 posterior setae; ischium with 6 anterior and 6 posterior setae; merus with 4 anterior, 4 posterior and 1 distal setae; carpus with 7 anterior and 13 posterior setae; propodus with 3 anterior, 2 lateral, 8 posterior and 2 distal setae; dactylus with 3 lateral and 2 posterior setae.

Pereopod III (left), basis / ischium / merus / carpus / propodus / dactylus length ratios: 1 / 0.9 / 0.5 / 1.3 / 0.7 / 0.3. Basis with 1 anterior and 5 posterior setae; ischium with 1 anterior and 5 lateral setae; merus with 4 anterior and 5 posterior setae; carpus with 6 anterior, 11 posterior and 3 distal setae; propodus with 5 anterior, 4 posterior, 3 distal and 1 lateral setae; dactylus with 3 lateral setae and 1 posterior seta.

Pereopod IV (left), basis / ischium / merus / carpus / propodus / dactylus length ratios: 1 / 0.9 / 0.3 / 1.1 / 0.7 / 0.3. Basis with 3 anterior, and 6 mesial setae located distally; ischium with 7 anterior, 7 posterior and 2 mesial setae; merus with 3 scattered mesial setae and 3 mesial setae on distal margin; carpus with 9 anterior, 7 posterior and 2 distal setae; propodus with 6 anterior, 3 posterior and 4 distal setae; dactylus with 3 mesial setae.

Pereopod VI (right), basis / ischium / merus / carpus / propodus / dactylus length ratios: 1 / 0.8 / 0.3 / 1.0 / 0.7 / 0.4. Basis with 5 anterior and 12 posterior setae; ischium with 12 anterior and 10 posterior setae; merus with 2 mesial and 5 anterior setae; carpus with 4 anterior, 7 posterior and 2 mesial setae; propodus with 8 anterior and 6 posterior setae; dactylus with 3 mesial setae and 2 anterior setae.

Description of female uropods ( Fig. 2 View FIGURE 2 ) (paratype MNHN-IU-2014-10129; BL = 5.8 mm)

Uropods uniramous and biarticulate, length 9.5 width, 0.6 length of pleotelson. Proximal article 0.6 length of distal article, with 5 simple setae. Distal article with 4 simple setae.

Description of male ( Figs 4 View FIGURE 4 , 5 View FIGURE 5 & 6 View FIGURE 6 ) (paratypes MNHN-IU-2014-10128, BL = 4.7 mm, MNHN-IU-2014- 10133, BL = 4.5 mm and MNHN-IU-2014-10134, BL = 5.5 mm).

Head length 0.56 width. Pereonite 1 width 0.2 BL. Pereonite 4 length 1.2 width. Pereonite 5 length 1.8 width, 0.3 BL. Pleotelson length 1.1 width.

Pereonite 1 with 1 pair of anterolateral pedestal setae. Pereonites 1–3 with 1 pair of dorsal pedestal setae. Pereonites 1–4 with 1 pair of lateral pedestal setae. Pereonite 4 with 3 pairs of dorsal pedestal setae and 4 pairs of lateral pedestal setae. Pereonite 5 with 6–8 pairs of lateral pedestal setae, 4 pairs of dorsal pedestal setae and with 1 pair of posterolateral pedestal setae. Pereonite 6 with 1 pair of posterolateral pedestal setae and 1 pair of dorsal pedestal setae. Pereonite 7 with 1 pair of dorsal pedestal setae. Pleotelson with 2 pairs of dorsal pedestal setae and numerous lateral simple setae.

Antennula article 2 length 0.53 head width, 0.11 BL.

Antenna article 2 with 3 pedestal setae; article 3 length 2.5 width, 0.08 BL. Flagellum missing.

Mouthparts. Mandible palp absent. Maxillula with 12 robust setae on lateral lobe, 1 robust medially projecting dentate seta on medial lobe. Maxilla with 2 medially projecting pectinate setae, numerous dorsal short and long setae on mesial lobe, 2 distal pectinate setae on lateral lobes. Maxilliped with 3 receptaculi on basal endite; palp narrower and shorter than basal endite, articles 1–3 expanded, wider than long, with numerous simple setae, article 2 wider than article 1 and 3, articles 4 and 5 longer than wide. Epipod without spines.

Pleopods. Pleopod I length more than twice proximal width, distal tip with lateral horns, distal margin and ventral face with long simple setae, lateral margins and ventral face with numerous short clusters of simple setae. Pleopod II stylet with pointed tip, length of stylet related to sexual maturity, not reaching (paratype male MNHN- IU-2014-10133) or reaching well beyond (allotype male MNHN-IU-2014-10128) end of protopod in copulatory males. Pleopod II protopod tapering toward distal margin, mesial margin with fringe of short setae, apex rounded with long simple setae, ventral face with clusters of short simple setae. Pleopod III exopod length more than half endopod length, apex with 1 long plumose seta, lateral margin fringed with fine setae and 7 elongate simple setae, mesial margin fringed with fine setae; endopod with 3 plumose setae on distal margin, one lost during dissection in drawn specimen but actually observed in other ones. Pleopod IV without setae on margins.

Remarks. Within the genus Ischnomesus , four species bear numerous projections on their body surface, in a pattern more or less similar to those observed in I. harrietae sp. nov.: I. spaercki (Kermadec Trench, 6660–7000 m), I. birsteini (Kermadec Trench, 4410 m), I. antarcticus (W Antarctic Peninsula, ~ 274 m) and I. tasmanensis (E Bass Strait, 1750–1840 m). However, all four species bear lateral spines on their pleotelson, not observed in I. harrietae sp. nov. Furthermore, in comparison with I. harrietae sp. nov., the body dorsal projections are smaller (spines and tubercles), more numerous and irregularly arranged in I. spaercki , and absent on pereonites 5–7 and pleotelson in I. tasmanensis . I. birsteini can be distinguished from I. harrietae sp. nov. by the presence of a long hair-like seta on many of its dorsal body spines. I. antarcticus (male) can be distinguished from I. harrietae sp. nov. by the more numerous, highly calcified dorsal body spines, distinct from the pedestal setae observed on I. harrietae sp. nov. I. antarcticus can also be identified by the distinct morphology of pleopod I (about 30 long plumose setae between two long distolateral extensions in the former).

The paratype male MNHN-IU-2014-10134 displays an unusual morphology. According to its dorsal ornamentation and shape of pereopod I, it undoubtedly belongs to the new species I. harrietae sp. nov. herein described. Furthermore, due to its size (BL = 5.5 mm), fully developed pereopods VII (pereopods VI and VII with subequal basis) and large pleopod II stylet (reaching well beyond protopod, but not yet functional), it could be classified as a precopulatory male. However, its pleopods I are not as developed as expected for this developmental stage (pleopods I with reduced length, as typically observed in manca 3 males). Such contradictory morphological features suggest that it is an aberrant male.