Pseudacanthocanthopsis secunda ( Yamaguti and Yamasu, 1960 )

Pseudacanthocanthopsis secunda ( Yamaguti and Yamasu, 1960)

( Figures 1–4 View Figure 1 View Figure 2 View Figure 3 View Figure 4 )

Pseudacanthopsis secunda Yamaguti and Yamasu, 1960: 137 .

Pseudacanthocanthopsis secunda: Yamaguti, 1963: 293 ; Ho, 1970: 192; Ho and Kim, 1995: 42; Østergaard, 2003: 144.

Material examined

Thirty adult females and two adult males (each male attached to the egg sac of a separate female) [only 20 females deposited from this collection (NSMT-Cr 21844)], ex gill filaments of 10 A. lineatus, Seto Inland Sea , off Osakikami-jima Island , Hiroshima Prefecture, Japan, 16 September 2010 ; 103 adult females (75 mature, 28 immature) and 25 adult males ( 19 males each attached to genito-abdomen of a mature adult female; two males each attached to genito-abdomen of an immature adult female; two males each attached to the egg sac of a separate female; two detached males stored in a separate vial) (NSMT-Cr 21845), ex branchial cavity wall of six A. lineatus , northern East China Sea, off Kyushu, Japan, 23–24 August 1982 ; six adult females (NIBRIV0000244191), ex gill filaments of three A. lineatus , northern East China Sea, off Yeosu Dolsan, Jeollanam Province, Korea, 30 August 2011 ; two adult females (NSMT-Cr 21846), ex gill filaments of two T. poecilonotus, Seto Inland Sea , off Osakikami-jima Island , Hiroshima Prefecture, Japan, 16 September 2010 ; one adult female (NSMT-Cr 21847), ex gill filament of P. major, Seto Inland Sea , Hiroshima Bay , Hiroshima Prefecture, Japan, 15 July 2008 .

Description

Adult female. Body ( Figure 1A,B View Figure 1 ) 1.28 (1.17–1.36) mm long (from anterior margin of head to distal end of posterior processes on trunk) ( n = 4), divided into head, neck and trunk. Head composed of cephalothorax (incorporating first pediger), wider than long [379 (350–400) × 729 (687–750) µm], with two pairs of rounded processes along anterior margin and another pair lateral to oral appendages. Neck region short, composed of second pediger. Trunk large, reniform, wider than long [0.86 (0.80–0.92) × 1.13 (1.05–1.18) mm], with pair of posterolateral processes. Genito-abdomen ( Figure 1C View Figure 1 ) divisible as two tagmata; anterior tagma (genital somite) longer than posterior tagma (abdominal somite), with ventral pair of genital apertures; posterior tagma wider than long, with pair of caudal rami; latter wider proximally, bearing four setae (usual inner knob not observed).

Antennule ( Figure 1D View Figure 1 ) unsegmented, elongated, with basal group of minute setae, four setae at distal two-thirds, three subapical setae and eight apical setae. Antenna ( Figure 2A View Figure 2 ) three-segmented, composed of coxobasis and two-segmented endopod; coxobasis short, unarmed but ornamented with surface pits along medial margin; proximal endopodal segment forming powerful uncinate claw and ornamented with surface pits along two-thirds of claw and fine striations near tip; atrophied tip (distal endopodal segment) with four unequal apical setae. Labrum ( Figure 2B View Figure 2 ) wider than long, naked. Mandible ( Figure 2C View Figure 2 ) one-segmented, with apical falcate blade armed with 13–17 teeth along convex margin and double row of teeth (four to six inner teeth and three to six outer teeth) along concave margin ( n = 5). Paragnath not observed. Maxillule ( Figure 2D View Figure 2 ) unilobate, sigmoid, with one inner and two apical elements. Maxilla ( Figure 2E View Figure 2 ) two-segmented, composed of syncoxa and basis; syncoxa robust, unarmed; basis forming claw-like process, armed with two unequal basal setae. Maxilliped ( Figure 2F View Figure 2 ) three-segmented, composed of short syncoxa, elongate basis and short terminal claw (endopod); all three segments unarmed.

Leg 1 ( Figure 2G View Figure 2 ) large, modified, biramous, with rami fused proximally to protopod; latter laterally inflated, with outer naked seta; exopod one-segmented, rounded, with five to six naked setae ( n = 6); endopod one-segmented, subquadrate, with three or four naked apical setae ( n = 6). Leg 2 ( Figure 2H View Figure 2 ) minute, biramous; protopod with outer naked seta; exopod one-segmented, with four or five naked setae ( n = 4); endopod one-segmented, with three or four naked setae ( n = 4).

Adult male. Body ( Figure 3A,B View Figure 3 ) 303 (280–330) µm long (excluding caudal setae) and 110 (105–115) µm wide ( n = 3), divided into large cephalothorax (incorporating first pediger), short second pediger and long genito-abdomen; latter with pair of opercula, each covering genital aperture and bearing two minute lateral setae ( Figure 3B View Figure 3 ). Caudal ramus ( Figure 3C View Figure 3 ) subquadrate, bearing two outer, one apical and two inner setae (usual small inner knob not observed).

Antennule ( Figure 3D View Figure 3 ) three-segmented; first segment longest, bearing 10 setae; second segment shortest, bearing four setae; third segment bearing eight setae and two aesthetascs (seta and aesthetasc on anterodistal corner shares common base). Antenna ( Figure 3E View Figure 3 ) three-segmented, composed of coxobasis and two-segmented endopod; coxobasis short, with small digitiform element along inner margin; proximal endopodal segment forming powerful uncinate claw, bearing two spiniform setae and one digitiform element along inner margin; atrophied tip (distal endopodal segment) with one large claw, one small seta and one small claw apically. Labrum (not figured) similar to that of female. Mandible ( Figure 3F View Figure 3 ) with 12–13 teeth on convex side and no teeth on concave side ( n = 2) of blade. Maxillule ( Figure 3G View Figure 3 ) lobate, with two apical elements. Maxilla ( Figure 3H View Figure 3 ) as in female, except with larger setae and three or four apical teeth ( n = 4) on basis. Maxilliped ( Figure 3I View Figure 3 ) three-segmented; first two segments elongate and naked; third segment forming uncinate claw.

Leg 1 ( Figure 4A View Figure 4 ) biramous, with unimerous exopod and bimerous endopod; protopod with outer naked seta; exopod with five spines (each with accessory flagellum at tip) and three naked setae; first endopodal segment unarmed; second endopodal segment with four apical naked setae. Leg 2 ( Figure 4B View Figure 4 ) biramous, with one-segmented rami; protopod with one outer naked seta; exopod with three spines (each with accessory flagellum at tip) and four naked setae; endopod with four apical naked setae.