Haplomesus celticensis, Kavanagh, Fiona A., Wilson, George D. F. & Power, Anne Marie, 2006

Kavanagh, Fiona A., Wilson, George D. F. & Power, Anne Marie, 2006, Heterochrony in Haplomesus (Crustacea: Isopoda: Ischnomesidae): revision of two species and description of two new species, Zootaxa 1120, pp. 1-33 : 14-21

Haplomesus celticensis sp. nov. ( Figs 8–12 )

Etymology. Named from the type locality of the Celtic Sea, Ireland.

Material examined. Holotype female, 4.1 mm, AM P64985, RV Chain cruise 106, J.F. Grassle and party, WHOI stn 313, 17 August 1972, Celtic Sea, off west coast of Ireland 51°32.2'N, 12°35.9'W, 1491–1500 m, epibenthic sled. Paratypes: male 4 mm, AM P.71659; juvenile male, 3.7 mm, AM P.71660 manca male 3 mm, AM P.71661, paratype male mouthparts slide and carcass AM P.71667, paratype male pleopods slide and carcass AM P.71666, same station; additional paratypes 49 ind., paratype adults, 2 males, 2 females, AM P.71662, paratype adults AM P.71663, paratype juveniles AM P.71664, paratype mancas AM P.71665, same locality as holotype.

Diagnosis. Male with spines on pereonites 1 and 4. Female with anterolateral spines on pereonite 1 only, shorter than spines observed on pereonite 1 of males. Pleotelson posterolateral margin anterior to uropods with pedestal spines: in female length approximately half uropod length, in male subequal to uropod length. Antennula with 3 distal flagellar articles. Pereopod I carpus ventral margin with 1 proximal robust seta and 1 distal robust seta on palm. Pleopod I of male without setae. Pleopod II female operculum without plumose setae.

Description of female. Body length 4.0– 4.4 mm; pereonite 7 reduced. Head length 0.7 width; lobe on ventrolateral margin absent in lateral view; dorsal cuticle densely covered with fine granules. Pereonite 1 width 0.16 total body length. Pereonite 1 anterolateral simple spines, short, length projecting dorsally, somewhat anteriorly curved. Pereonite 5 length 3.2 width, 0.4 total body length. Pleotelson length 1.3 width; dorsal surface axial ridge weakly vaulted, separated from lateral fields only by shallow elongate concavities; posterolateral margin adjacent to uropods convex.

Antennula and antenna. Antennula with 5 articles altogether, article 2 length 0.7 head width, inserting on article 1 dorsally, with 2 elongate ventromedial setae; distal articles short, in total shorter than article 2; article 3 length similar to article 4; article 3 elongate and tubular, much longer than wide; terminal article longer than penultimate article; aesthetascs absent. Antenna article 3 length 0.2 anterior body length, length 3 width, cuticle smooth.

Mouthparts. Maxillula with 10 robust setae on lateral lobe; medial lobe with 1 robust medially­projecting dentate seta. Maxilla with 2 long (approximately as long as lateral lobes) medially­projecting pectinate setae on medial lobe. Maxilliped palp article 2 wider than 3.

Pereopods. Pereopod I propodus ventral margin with 1 robust seta. Pereopod VII absent in adults.

Pleopods and uropods. Pleopod II female operculum with narrow proximal neck, laterally convex, broadening posteriorly to rounded angles, posterior margin weakly convex. Uropods extending near posterior margin of pleotelson; length 0.1 length of pleotelson.

Description of male. Body length 3.9–4.0 mm. Head length 0.7 width. Pereonite 1 width 0.15 total body length. Pereonite 1 spines projecting dorsally, elongate, length near width of pereonite 1. Pereonite 4 anterolateral simple spines, projecting dorsally, short, length near pereonite 1 length. Pereonite 5 length 3.9 width, 0.47 total body length. Pleotelson length 1.2 width.

Antennula and antenna. Antennula article 2 length 0.6 head width. Antenna article 3 length 3.1 width.

Pleopods and uropods. Pleopod I distal tip with lateral horns. Pleopod II stylet not extending to distal margin of protopod. Pleopod III exopod with plumose setae, with fringe of fine setae on lateral margin. Pleopod V present. Uropods extending near posterior margin of pleotelson, length 0.1 length of pleotelson.

Distribution. North Atlantic Ocean: Celtic Sea, South West of Ireland, 1491–1500 m.

Remarks. H. celticensis sp. nov. can be immediately identified by the combination of spination pattern: male with spines on pereonites 1 & 4, female with spines on pereonite 1 only, 3 articled antennular flagellum and the lack of distal setae on male pleopod I, as discussed in the remarks for H. hanseni .

Figures

FIGURE 8. Haplomesus celticensis (female holotype AM P. 64985). A, antenna and antennula; B, pereopod I; C, D, body dorsal and lateral; E, pleotelson ventral (scale bars C, D, 1 mm; E, 0.5 mm).

FIGURE 9. Haplomesus celticensis (male paratype AM P. 71659). A, dorsal view; B, antennula; C, head ventral; D, lateral view E, pereopod I; F, uropod; G, pleotelson ventral (scale bar 1 mm).

FIGURE 10. Haplomesus celticensis (male paratype mouthparts AM P. 71667). A, maxilliped; B, maxilliped palp; C, maxilliped endite; D, maxillula; E, maxillula detail; F, paragnaths; G, H, maxillae; I, left mandible, J, left mandible detail; K, right mandible; L, right mandible detail (scale bars 0.1 mm).

FIGURE 11. Haplomesus celticensis (paratype male pleopods AM P. 71666). A, pleopod I ventral; B, pleopod I ventral detail; C, pleopod I dorsal; D, pleopod II; E, pleopod II stylet; F, pleopod III; G, pleopod IV; H, pleopod V (scale bar 0.1 mm).

FIGURE 12. Haplomesus celticensis (male paratypes juvenile AM P. 71660, manca 3 AM P. 71661). A, juvenile male body lateral; B, manca 3 male dorsal view; C, manca 3 male lateral view; D, juvenile male pleotelson ventral; E, manca 3 male pleotelson ventral (scale bar 0.5 mm).