Lepeophtheirus acutus Heegaard 1943
Creators: name: Tang, Danny
name: Maran, B. A. Venmathi
name: Matsumoto, Yousuke
name: Nagasawa, Kazuya
Publisher: name: Zenodo
Year: 2012
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Hexanauplia
Siphonostomatoida
Caligidae
Lepeophtheirus
Lepeophtheirus acutus

description: Lepeophtheirus acutus Heegaard, 1943   
(Figures 1–4)  
 Lepeophtheirus acutus Heegaard, 1943: 4; Yamaguti, 1963: 71; Kik et al., 2011: 797.    Material examined   
 From M. alfredi: nine adult females (two immature) and one adult male, ex no. 16, 29 October 2006; 21 immature adult females and 10 adult males, ex no. 10-3-1, 20 September 2009; seven adult females, ex no. 10-3-1, 18 June 2010. From R. typus: 49 adult females (one immature), ex no. 27, 10 January 2010; one adult female, ex no. 28, 30 April 2008; seven adult females, ex no. 32, 2 October 2009; 15 adult females, ex no. 32, 28 April 2010; 23 adult females, ex no. 33, 30 October 2009; 207 adult females (one immature) and three adult males (NSMT-Cr 21848), ex no. 33, 27 January 2010. Syntypes (Type-656): three immature adult females, one mature adult male and one late chalimus female, Apamama, Gilbert Islands, Kiribati, 24 November 1917.    Description   
 Adult female. Body (Figure 1A) 4.22 (3.77–4.59) mm long (excluding caudal setae) (n = 10). Cephalothoracic shield subcircular, slightly longer than wide [1.99 (1.80–2.12) × 1.92 (1.70–2.17) mm], with well-developed paired frontal plates and posterior margin of thoracic zone extending beyond posterior limit of lateral zone. Free fourth pedigerous somite wider than long [208 (175–225) × 409 (350–475) µm] and indistinctly separated from genital complex. Genital complex longer than wide [1.39 (1.25–1.57) × 1.08 (0.95–1.22) mm], with oblique margins at anterior half, parallel margins at posterior half, slightly protruded posterolateral corners and genital apertures (Figure 1B) situated ventrally near junction of abdomen. Abdomen composed of one somite, longer than wide [616 (550–675) × 350 (300–375) µm] and indistinctly separated from genital complex. Caudal ramus (Figure 1C) longer than wide [91 (65–100) × 69 (60–80) µm], with six plumose setae (seta I absent), mid-dorsal sensillum and short row of setules along distomedial margin. Egg sacs (Figure 1A) uniseriate.   
Antennule (Figure 1D) two-segmented; proximal segment longer than distal segment, bearing two posterodistal processes and 27 setae (25 plumose, two naked); distal segment slim, bearing 12 setae (two setae near posterodistal corner share a common base) and two aesthetascs. Antenna (Figure 1E) three-segmented, comprising coxa, basis and one-segmented endopod incorporating distal claw; coxa with long spiniform process on posterolateral corner; basis stout, with dorsolateral adhesion pad; terminal segment long, uncinate, bearing two setae. Postantennal process (Figure 1F) slightly curved, with two inner setulose papillae at wide base and another setulose papilla adjacent to base. Mandible (Figure 1G) modified into elongated stylet bearing distolateral hyaline membrane and 12 distomedial teeth. Maxillule (Figure 1H) composed of trisetose papilla and long, slender dentiform process; latter with minute hyaline structure on ventral surface; sclerite anterior to papilla with triangular process that distally projects over base of dentiform process. Maxilla (Figure 2A), brachiform, two-segmented, composed of elongate, unarmed syncoxa and slender basis; latter with long, curved flabellum and long apical calamus and short apical canna; calamus and canna each furnished with finely serrated membranes. Maxilliped (Figure 2B) large, subchelate, three-segmented, comprising long protopod (corpus) and subchela consisting of free endopodal segment (shaft) and claw; protopod unarmed; shaft with minute pore proximally and minute hyaline element subapically; claw with long basal seta and fine surface striations distally. Tines of sternal furca (Figure 2C) slightly shorter than box, divergent, apically pointed, ornamented with hyaline marginal membranes and overlying bow-shaped sclerite.  
Roman numerals indicate spines; Arabic numerals indicate setae.  
 ∗ Although the coxa and basis are fused to form a protopod in this leg, these segments are treated separately in the table.   
Armature on rami of legs 1–4 is shown in Table 2.  
Leg 1 (Figure 2D) intercoxal sclerite naked and elongate. Protopod with one outer and one inner plumose seta, one proximolateral setulose papilla, one mid-lateral pore and patch of minute spinules near insertion of inner seta. First exopodal segment with small pectinate membrane at base of small outer spine and row of setules along inner margin. Second exopodal segment with pectinate membrane at base of each apical denticulate spine; middle and inner apical spines each with accessory process; apical seta short, with row of spinules along inner margin; three inner setae plumose. Endopod cylindrical, bearing apically bifurcate element. Leg 2 (Figure 2E) intercoxal sclerite subquadrate, with hyaline membrane along distal margin. Coxa with one inner plumose seta and one small sensillum and two minute pores on anterior surface. Basis with one outer short, naked seta, one minute pore near outer margin, one small inner sensillum and hyaline membrane along dorsolateral and posterior margins. Exopod three-segmented, with large hyaline membrane covering dorsal surface of ramus. First segment with one inner plumose seta, row of setules along inner margin and pectinate membrane at base of outer serrate spine. Second segment with one inner plumose seta, short row of setules along proximomedial margin, one outer serrate spine and one minute pore on anterior surface. Third segment with five inner plumose setae, few setules along proximomedial margin, pectinate membrane at base of outermost naked spine, row of spinules along inner margin of outer apical spine and finely serrate membrane along outer margin and row of setules along inner margin of apical spine. Endopod three-segmented. First segment with one inner plumose seta, row of setules along most of outer margin and row of large denticles on distolateral corner. Second segment with two inner plumose setae, spiniform projection on distolateral corner and row of setules along inner and outer margins. Third segment with spinules at base of three outermost plumose setae and row of setules along proximolateral and proximomedial margins.  
Leg 3 (Figure 3A) protopod with one outer naked and one inner plumose setae, velum between rami, corrugated patch on dorsolateral surface, three marginal membranes, minute pores scattered on ventral surface, two short sensilla along posterior margin and patch of fine spinules between pair of short sensilla on ventromedian surface. Exopod two-segmented. First segment with one inner plumose seta and one outer spinulate spine; latter straight, with hyaline membrane at base. Second segment with five plumose setae, four spinulate spines, one minute pore and setules along outer margin. Endopod two-segmented. First segment with one inner plumose seta. Second segment with six plumose setae and setules along outer margin. Leg 4 (Figure 3B) uniramous, composed of protopod and two-segmented exopod. Protopod with one distolateral pinnate seta. First exopodal segment with pectinate membrane at base of outer spinulate spine. Second exopodal segment with three apical spinulate spines, one distal pore and pectinate membrane at base of innermost spine; outer and middle spines subequal, about one-third length of inner spine; middle spine typically reflexed over inner spine. Leg 5 (Figure 3C) vestigial, situated near posterolateral corners of genital complex, composed of two setiferous lobes (anterior lobe with one plumose seta; posterior lobe with one pore and three plumose setae). Leg 6 (not figured) rudimentary, represented by unarmed genital operculum at gonopore opening.  
 Adult male. Body (Figure 3D) 1.92 (1.76–2.32) mm long (excluding caudal setae) (n = 7). Cephalothoracic shield slightly longer than wide [1.21 (1.10–1.45) × 1.11 (1.04–1.27) mm]. Free fourth pedigerous somite wider than long [113 (100–140) × 209 (190–260) µm]. Genital complex slightly wider than long [344 (310–390) × 357 (330–400) µm]. Abdomen composed of one somite, longer than wide [210 (190–275) × 192 (180–210 µm]. Caudal ramus longer than wide [95 (90–110) × 65 (60–75) µm], armed as in female.   
All limbs as in female, except for the following. Antenna (Figure 3E) threesegmented, comprising coxa, basis, and one-segmented endopod incorporating distal claw; coxa with corrugate structure along inner margin; basis with one large and two small corrugate structures; terminal segment forming short claw and bearing two setae, outer surface striations, one corrugate, linguiform structure and round process. Maxillule (Figure 3F) with corrugate surface and one stout hyaline structure on dentiform process. Postoral process (Figure 3F) elongate, with corrugate surface. Maxilliped (Figure 3G) similar to that of female, except protopod with small hyaline structure on myxal area and claw without surface ornamentation. Tines of sternal furca (Figure 4A) noticeably shorter than box and unornamented.  
Leg 5 (Figure 4B) vestigial, situated mid-laterally on genital complex and bearing four plumose setae. Leg 6 (Figure 4B) forming genital operculum, with one seta and two subequal, spiniform processes on distolateral corner.   Variability   
Some females with two apical elements on leg 1 endopod (Figure 4C). One immature adult female syntype with one bifurcate tine on sternal furca (Figure 4D). One male with an abnormal distal endopodal segment of left leg 3 (Figure 4E). One male with very long spiniform process on leg 6 (Figure 4F).   Attachment sites   
 Lepeophtheirus acutus individuals were found attached around the eyes and mouth, on the cephalic fins, on and around the pelvic fins and on the dorsal body surface of M. alfredi (Figures 5 and 6) and on the eyes and dorsal body surface of R. typus (Figure 7).
description: Published as part of Tang, Danny, Maran, B. A. Venmathi, Matsumoto, Yousuke & Nagasawa, Kazuya, 2013, Redescription of Lepeophtheirus acutus Heegaard, 1943 (Copepoda: Caligidae) parasitic on two elasmobranch hosts off Okinawa-jima Island, Japan, pp. 581-596 in Journal of Natural History 47 (5 - 12) on pages 583-589, DOI: 10.1080/00222933.2012.738832, http://zenodo.org/record/5198477