Hatschekia monacanthi Yamaguti, 1939

Uyeno, Daisuke & Nagasawa, Kazuya, 2009, Redescription of four species of Hatschekia (Copepoda: Siphonostomatoida: Hatschekiidae) parasitic on tetraodontiform fishes from Japan, Zootaxa 2110, pp. 1-21 : 13-19

Hatschekia monacanthi Yamaguti, 1939

( Figs 38–64 )

Hatschekia monacanthi: Yamaguti 1939: 468 ; Jones 1985: 250.

Material examined. 6Ψ and 4ɗ (NSMT-Cr 20335), ex Thamnaconus modestus (Günther) , Sakaiminato (35°32΄N, 133°15΄E), Tottori, Sea of Japan, Japan, 19 June, 2002; 1Ψ (NSMT-Cr 20336), ex T. modestus, Osakikamishima (34°12΄N, 132°53΄E), Hiroshima, Seto Island Sea, Japan, 20 July, 2006.

Description of female. Body ( Figs 38–39 ) 1.44–1.66 (1.54 ± 0.09) long, excluding caudal rami (n = 7). Cephalothorax nearly elliptical, shorter than wide [0.39–0.45 (0.42 ± 0.03) × 0.48–0.54 (0.52 ± 0.02)], bears dorsal, T-shaped chitinous frame with complete ring at its posterior end. Trunk with posterior end being slightly swollen along the midline, longer than wide [1.05–1.27 (1.16 ± 0.09) × 0.44–0.58 (0.51 ± 0.06)]. Abdomen ( Fig. 40 ) shorter than wide [0.04–0.07 (0.05 ± 0.01) × 0.12–0.15 (0.13 ± 0.01)]. Caudal ramus ( Fig. 40 ) length 0.03–0.04 (0.03 ± 0); width 0.02–0.03 (0.02 ± 0); bears 5 naked setae.

Rostrum with 1 digitiform process on posterolateral corners ( Fig. 41 ). Antennule ( Fig. 41 ) indistinctly 5- segmented, 0.20–0.27 (0.23 ± 0.03) long; armature formula: 9, 5, 4, 1, 13 + 1 aesthetasc. Antenna ( Fig. 42 ) 3- segmented; proximal segment (coxa) unarmed; middle segment (basis) ornamented with surface pits; terminal segment, usually unarmed (1 specimen with 1 basal seta); proximal segment length 0.09–0.12 (0.10 ± 0.01); middle segment length 0.23–0.29 (0.26 ± 0.03); terminal segment length 0.04–0.08 (0.05 ± 0.01); total length 0.37–0.46 (0.42 ± 0.04). Parabasal papilla ( Fig. 43 ) shriveled, carrying apical process. Oral cone robust. Mandible ( Fig. 44 ) slender, with 4 sharp apical teeth. Maxillule ( Fig. 45 ) bilobate; both lobes armed with 2 tapering elements. Maxilla ( Fig. 46 ) 4-segmented; proximal segment unarmed; second segment rod-like, with 1 basal seta; third segment elongate, with 1 distal seta; terminal segment small, with 1 small seta and bifid claw. Maxilliped absent.

Legs 1 and 2 ( Figs 47–48 ) biramous, with 1-segmented rami; armature formula as follows:

Intercoxal sclerite of legs 1 and 2 ( Fig. 49 ) bears 2 short and 2 long processes plus 2 spinular rows. Protopods and rami, except leg 1 exopod, ornamented with rows of blunt spinules on anterior surface. Leg 1 ( Fig. 47 ) 0.12–0.14 (0.13 ± 0.01) long; protopod length 0.06–0.08 (0.07 ± 0.01); exopod length [0.05–0.06 (0.06 ± 0)] exceeding endopod length [0.02–0.03 (0.03 ± 0)]. Leg 2 ( Fig. 48 ) length 0.11–0.13 (0.12 ± 0.01); protopod length 0.05–0.07 (0.07 ± 0.01); exopod length 0.04–0.06 (0.05 ± 0.01); endopod length 0.02–0.03 (0.02 ± 0.01).

Leg 3 ( Figs 38 , 50 ) represented by 2 simple setae on mid-lateral surface of trunk. Leg 4 ( Figs 38 , 51 ) represented by 1 simple lateral seta on posterior ¾ of trunk.

Description of male. Body ( Fig. 52 ) 0.71–0.81 (0.77 ± 0.04) long, excluding caudal rami (n = 4). Cephalothorax subtriangular, 0.24–0.27 (0.25 ± 0.01) × 0.23–0.27 (0.25 ± 0.02), with 6 dorsal spines and dorsal chitinous frame constructed of 1 central, straight bar flanked by 2 curved bars. Trunk length longer than wide [0.50–0.55 (0.54 ± 0.02) × 0.19–0.22 (0.21 ± 0.01)]. Abdomen ( Fig. 53 ) shorter than wide [0.04–0.06 (0.05 ± 0.01) × 0.07–0.09 (0.08 ± 0.01)]. Caudal ramus ( Fig. 53 ) longer than wide [0.05–0.07 (0.06 ± 0.01) × 0.02–0.03 (0.02 ± 0)], bears 6 naked setae.

Rostral process absent. Antennule ( Fig. 54 ) incompletely 5-segmented, 0.19–0.22 (0.21 ± 0.01) long; armature formula: 9, 5, 4, 1, 13 + 1 aesthetasc. Antenna ( Fig. 55 ) 3-segmented; proximal segment (coxa) unarmed; middle segment (basis) robust, distally with 1 pointed and 1 globular processes, ornamented with surface pits; terminal segment pointed, claw-like, with 2 basal setae and 1 medial pointed process; proximal segment length 0.05–0.06 (0.06 ± 0.01); middle segment length 0.08–0.12 (0.10 ± 0.01); terminal segment length 0.05–0.08 (0.07 ± 0.01); total length 0.18–0.24 (0.22 ± 0.03). Parabasal papilla absent. Oral cone robust. Mandible ( Fig. 56 ) slender, with 4 sharp apical teeth. Maxillule ( Fig. 57 ) bilobate; both lobes armed with 2 tapering elements; outer lobe with 2 short rows of blunt spinules. Maxilla ( Fig. 58 ) 4-segmented; proximal segment unarmed; second segment rod-like, with 1 basal seta; third segment elongate, with 1 distal seta; terminal segment small, with 1 small seta and bifid claw. Maxilliped absent.

Legs 1 and 2 ( Figs 59–60 ) biramous, with 1-segmented rami; armature formula as follows:

Intercoxal sclerite of legs 1 and 2 ( Fig. 61 ) similar to those of female. Protopods and rami ornamented with rows of blunt spinules on anterior surface. General shape of legs 1 and 2 similar to those of female. Leg 1 ( Fig. 59 ) 0.09–0.11 (0.10 ± 0.01) long; protopod length 0.05–0.06 (0.06 ± 0.01); exopod length [0.04–0.05 (0.04 ± 0)] exceeding endopod length [0.02–0.03 (0.03 ± 0)]. Leg 2 ( Fig. 60 ) 0.09–0.11 (0.10 ± 0.01) long; protopod length 0.05–0.06 (0.05 ± 0.01); exopod length 0.04–0.05 (0.04 ± 0.01); endopod length 0.02–0.03 (0.02 ± 0).

Leg 3 ( Figs 52 , 62 ) represented by 2 simple lateral setae inserted slightly beyond anterior ½ of trunk. Leg 4 ( Figs 52 , 63 ) and leg 5 ( Figs 52 , 64 ) each represented by 1 simple seta (former inserted laterally on posterior ½ of trunk; latter inserted on posterior end of trunk).

Attachment site. Gill filaments.

Remarks. Hatschekia monacanthi was described originally by Yamaguti (1939) based on five female specimens removed from Stephanolepis cirrhifer (Temminck & Schlegel) collected in Toyama Bay, Japan, and was also reported in the same paper from Sebastiscus marmoratus (Cuvier) captured in Obama, Fukui (as Hukui), Japan. Jones (1985) subsequently redescribed the females of H. monacanthi that were collected from Thamnaconus modestus (Günther) [as Navodon modestus ] captured in Ogi, Ishikawa, Japan. As mentioned in the Remarks section of H. ostracii above, H. monacanthi , H. balistae and H. ostracii all have 4 processes on the intercoxal sclerite of legs 1 and 2. Hatschekia monacanthi can be differentiated easily from these other two species by having, as observed in our specimens, a complete ring at the posterior end of the dorsal chitinous frame on the cephalothorax ( Jones 1985).

Our female specimens of H. monacanthi collected from T. modestus vary slightly from those of Yamaguti (1939) and Jones (1985) with regard to the armature of the antennule and swimming legs 1 and 2. For example, there are four more setae on segments 1 and 5, as well as one more seta on segments 2 and 3, on the antennules of our specimens as compared to those of Jones’ specimens. The exopods of legs 1 and 2 bear seven and six setae, respectively, in our specimens as opposed to six and five in Yamaguti’s and Jones’ material. Although Jones (1985) illustrated a mid-lateral seta on the exopod of both legs 1 and 2, as shown in this paper, no such illustrations were made by Yamaguti (1939). Even in our specimens, it was difficult to observe these setae because they were each positioned immediately behind the outer margin of the exopod. It is thus probable that Yamaguti (1939) overlooked these setae. In the same vein, Jones may have overlooked the small, outer apical seta on the exopod of both legs, but other explanations are possible, such as geographical variation and abnormality of specimens. Yamaguti (1939, fig. 120) illustrated, but did not describe in the text, a protrusion near the insertion of the antennule. This protrusion was reconfirmed in our material ( Fig. 41 ). In addition, as reported by Jones (1985), we also found a parabasal papilla near the base of the antenna.

Males have been hitherto described for only seven species of the genus Hatschekia : H. conifera Yamaguti 1939 , H. hippoglossi , H. harkema Pearse, 1948 , H. iridescens , H. petiti Nuñes-Ruivo, 1954 , H. pinguis Wilson, 1908 , and H. prionoti Pearse, 1947 (see Schram & Aspholm 1997). This paper represents the first description of males of H. monacanthi , which demonstrated that females and males of this species differ in the shape of the cephalothorax, structure of the dorsal chitinous frame on the cephalothoracic shield, ornamentation of the maxillule and number of atrophied legs on the trunk surface.

Figures

FIGURES 38 – 43. Hatschekia monacanthi Yamaguti, 1939, female. 38, habitus, dorsal. 39, habitus with egg sacs, dorsal. 40, posterior part of body, dorsal. 41, antennule, ventral. 42, antenna, ventral. 43, antenna and parabasal papilla, medial. Scale bars: 38, 0.2 mm; 39, 0.4 mm; 40 – 42, 0.05 mm; 43, 0.1 mm.

FIGURES 44 – 51. Hatschekia monacanthi Yamaguti, 1939, female. 44, mandible, ventral. 45, maxillule, ventral. 46, maxilla, ventral. 47, leg 1, ventral. 48, leg 2, ventral. 49, intercoxal sclerite of leg 1 and 2, ventral. 50, leg 3, ventral. 51, leg 4, ventral. Scale bars: 44, 12.5 μm; 45, 47 – 48, 25 μm; 46, 49, 0.05 mm; 50 – 51, 13 μm.

FIGURES 52 – 57. Hatschekia monacanthi Yamaguti, 1939, male. 52, habitus, dorsal. 53, posterior part of body, ventral. 54, antennule, ventral. 55, antenna, ventral. 56, mandible, ventral. 57, maxillule, ventral. Scale bars: 52 – 53, 0.1 mm; 54 – 55, 0.05 mm; 56, 17 μm; 57, 25 μm.

FIGURES 58 – 64. Hatschekia monacanthi Yamaguti, 1939, male. 58, maxilla, ventral. 59, leg 1, ventral. 60, leg 2, ventral. 61, intercoxal sclerite of leg 1 and 2, ventral. 62, leg 3, ventral. 63, leg 4, ventral. 64, leg 5, ventral. Scale bars: 58, 0.05 mm; 59 – 61, 25 μm; 62 – 64, 13 μm.