Hatschekia geniculata Uyeno & Nagasawa, 2013

Boxshall, Geoffrey A. & Bernot, James P., 2025, The Hatschekiidae (Copepoda: Siphonostomatoida) of Moreton Bay, Queensland, Australia, with a key to species reported from Australian waters, Zootaxa 5716 (1), pp. 11-65 : 44-46

Hatschekia geniculata Uyeno & Nagasawa, 2013

Material examined

5 ♀♀ from gills of Arothron hispidus ( TC17325 ) collected off Mud Island , Moreton Bay on 20 January 2016, QM Reg. Nos. W55138 ; 1 ♀ from gills of A. hispidus ( TC17119 ) collected off Peel Island , Moreton Bay on 14 January 2016 ; 2 ♀♀ from gills of Arothron nigropunctatus ( TC17278 ) collected off Amity , North Stradbroke Is., Moreton Bay on 07 January 2016; NHMUK Reg. Nos. 2024.331-332 .

Supplementary description of female

Total body length excluding caudal rami 1.26 to 1.54 mm, with a mean of 1.42 mm (n = 5). Body ( Fig. 11A ) comprising anterior cephalothorax and long cylindrical trunk bearing pyriform genitoabdomen posteriorly. Cephalothorax rhomboidal with angular lateral margins; about 1.5 times wider than long (245 x 373 μm). Dorsal cephalothoracic shield supported by m-shaped subsurface chitinous frame with median and paired lateral longitudinal bars of similar length, incomplete transverse bars located at posterior ends of longitudinal bars. Trunk about 2.9 times longer than wide (1.18 x 0.40 mm); with maximum width just anterior to level of third legs; median chitinous bar present dorsally just posterior to cephalothoracic shield; posterolateral corners forming broadly rounded processes and posterior margin of trunk projecting in dorsal midline and overlapping base of genitoabdomen ( Fig. 11B ). Genitoabdomen wider than long ( Fig. 11C ) comprising fused genital and abdominal somites; bearing paired genital apertures dorsally. Caudal rami about 1.5 times longer than wide (28 x 19 μm); armed with 5 naked setae of different lengths; lateral seta located about at 58% of lateral margin. Mean number of eggs per egg sac = 15.7 (range 10 to 21, n = 9).

Rostrum bearing paired spinous processes posteriorly and small lateral processes (arrowed in Fig. 11D ). Antennule ( Fig. 11D ) short, indistinctly 4-segmented: segmental setation pattern 10, 5, 5, 12 + ae; 2 unequal setae located on antero-dorsal surface of first segment. Antenna ( Fig. 11E ) 3-segmented, comprising short unarmed coxa, tapering basis, and distal subchela: surface of basis ornamented with minute pits; subchela with swollen and thickened base plus curved distal claw. Parabasal papilla small and rounded, located lateral to insertion of antenna. Mandible stylet-like, bearing 4 marginal teeth subapically. Maxillule bilobed; both lobes armed with 2 unequal setae. Maxilla ( Fig. 11F ) slender, coxobasis armed with single inner seta proximally; subchela comprising long segment armed with slender seta at inner extremity and distal claw armed with minute seta and with bifid tip.

Swimming legs 1 and 2 biramous; members of each leg pair joined by slender interpodal bars ( Fig. 11G ). Leg 1 ( Fig. 11H ) with fused sympod armed with outer and inner setae: exopod distinctly 2-segmented; proximal segment with outer distal spine; distal segment bearing 3 long setal elements around apex and 1 short seta distally on inner margin: endopod unsegmented, armed with 2 long apical setae plus 1 setal vestige on inner margin. Leg ornamented with curved rows of minute spinules: 2 on sympod and exopodal segment 1, and 3 each on exopodal segment 1 and on endopod. Leg 2 ( Fig. 11I ) with fused sympod bearing outer seta; exopod 2-segmented; proximal segment armed with outer spine; distal segment bearing 2 long setae on apex plus small seta distally on inner margin: endopod indistinctly 2-segmented; proximal segment unarmed; distal segment armed with 3 unequal setae around apex. Leg ornamented with curved rows of minute spinules on both rami: 3 each on exopodal segments, 1 row on endopodal segment 1 and 3 on endopodal segment 2. Leg 3 located laterally on trunk at 34% of length ( Fig. 11A ), represented by 2 setae arising directly from trunk surface. Leg 4 located laterally on trunk at 64% of length ( Fig. 11A ), represented by single seta originating directly on trunk surface.

Remarks

This species was established by Uyeno & Nagasawa (2013) to accommodate material collected from two species of Arothron Müller, 1841 , A. hispidus and A. stellatus , caught off the Ryukyu Islands. Interestingly, both of these two hosts were sampled in Moreton Bay but only A. hispidus hosted H. geniculata . The other host in Moreton Bay was A. nigropunctatus , a new host record for this copepod.

This species was named after its “bent urosome” which was described as bent ventrally and bearing a dorsal protrusion ( Uyeno & Nagasawa, 2013). We interpret this feature slightly differently in our Australian material: the posterior end of the trunk forms distinctive paired posterolateral lobes in the Australian material ( Fig. 11A–B ) while in the Japanese material these lobes are figured ( Uyeno & Nagasawa, 2013: Fig. 5B ) but appear less well developed. Also the median lobe that extends dorsally over the proximal part of the genitoabdomen ( Fig. 11B ) is interpreted here as part of the trunk rather than as a “bent abdomen with a dorsal protrusion” ( Uyeno & Nagasawa, 2013: 67). The telescoping of the genitoabdomen up into the trunk has not previously been discussed in Hatschekia but this appears to be the explanation for the much longer genitoabdomen in Uyeno & Nagasawa’s (2013) figure 5B, compared with their figure 5A. In dorsal view the genitoabdomen of the Australian material seems partly telescoped within the trunk as in Uyeno & Nagasawa’s figure 5A. The degree of telescoping of the genitoabdomen can influence perceptions of the relative length of the genitoabdomen and posterolateral trunk lobes, so this possibility needs to be considered when assessing the morphology of the female.

The Australian material is very similar to H. geniculata as described by Uyeno & Nagasawa (2013). They share, for example: the rhomboidal dorsal cephalothoracic shield and the shape of its subsurface chitinous frame, the presence of small lateral processes on the rostrum (arrowed in Fig. 11D ), the setal formula of the antennule is the same, and the antenna and mouthparts are the same (mandible and maxillule not figured here), and there is only a single difference in the setation of legs 1 and 2: the endopod of leg 2 in the original description carries 2 unequal apical setae whereas in the Australian material an additional small inner seta in present on the apex of this ramus. This minor difference is not regarded as significant because such small setae on the legs are difficult to observe and hard to to distinguish from ornamentation elements, and because leg setation has been interpreted as variable in Hatschekia (see Jones, 1985; Kabata, 1991).

Figures

FIGURE 5. Hatschekia cernae Goggio, 1905, female. A, habitus, dorsal view with arrows indicating inset enlargements of legs 3 and 4 on trunk; B, posterior extremity of trunk and genitoabdomen, ventral; C, antennule in situ, ventral; D, antenna; E, mandible; F, maxillule; G, maxilla; H, anterior part of trunk showing interpodal bars and legs 1 and 2 in situ, ventral. Scale bars: A, 250 μm, B–D, G, 50 μm, E, F, 25 μm, H, 100 μm.

FIGURE 11. Hatschekia geniculata Uyeno & Nagasawa, 2013, female. A, habitus, dorsal view with arrows showing positions of legs 3 and 4 on trunk; B, posterior extremity of trunk and genitoabdomen, lateral view; C, posterior extremity of trunk and genitoabdomen, ventral; D, rostrum and left antennule, ventral view with arrows showing lateral rostral processes; E, antenna; F, maxilla; G, interpodal bars in situ, ventral; H, leg 1; I, leg 2. Scale bars: A, 300 μm, B, 100 μm, C–I, 50 μm.