Heterochrony in Haplomesus (Crustacea: Isopoda: Ischnomesidae): revision of two species and description of two new species Author Kavanagh, Fiona A. Author Wilson, George D. F. Author Power, Anne Marie text Zootaxa 2006 1120 1 33 journal article 50778 10.5281/zenodo.171687 7f252475-feaa-41c9-b25b-30fd000477db 1175­5326 171687 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. 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). 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 .