Hatschekia bifurcata Yamaguti & Yamasu, 1959

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 : 25-26

Hatschekia bifurcata Yamaguti & Yamasu, 1959

Material examined: 4 ♀♀ from gills of Diploprion bifasciatum Cuvier, 1828 ( TC17917 ) collected off Amity, North Stradbroke Is., Moreton Bay on 03 July 2016 , QM Reg. Nos. W55131 ; 3 ♀♀ from gills of D. bifasciatum ( TC17838 ) collected off Amity, North Stradbroke Is., Moreton Bay on 05 July 2016 ; 1♀ from gills of D. bifasciatum ( TC17918 ) collected off Amity, North Stradbroke Is., Moreton Bay on 05 July 2016 ; 3 ♀♀ from gills of D. bifasciatum ( TC18252 ) collected at North Wistari, Heron Island , Queensland on 04 February 2017 ; NHMUK Reg. Nos. 2022.209-212 .

Supplementary description of female

Total body length excluding caudal rami ranging from 0.86 to 1.33 mm, with a mean of 1.07 mm (n = 9). Body ( Fig. 4A ) dorsoventrally flattened, comprising anterior cephalothorax and broad trunk bearing minute genitoabdomen posteriorly. Cephalothorax oval, about 1.4 times wider than long (225 x 520 μm). Dorsal cephalothoracic shield supported by m-shaped subsurface chitinous frame with long median longitudinal bar only slightly longer than lateral bars. Trunk about 2.4 times longer than wide (range 2.0 to 3.1, n = 9), (0.88 x 0.37 mm); trunk tapering slightly towards transverse posterior margin, with rounded posterolateral corners. Surface of trunk with irregular wrinkles posteriorly ( Fig. 4B ). Genitoabdomen fused with trunk and comprising fused genital-double and abdominal somites; bearing paired genital apertures dorsally. Caudal rami about 2.0 times longer than wide (30 x 15 μm); armed with 6 naked setae of different lengths; lateral seta located about at middle of lateral margin. Mean number of eggs per egg sac = 11.8 (range 9 to 15, n = 11).

Rostrum lacking lateral processes ( Fig. 4C ). Antennule ( Fig. 4C ) short, indistinctly 5-segmented: segmental setation pattern 10, 6, 4, 1, 12 + ae; 2 unequal setae located on antero-dorsal surface of first segment. Antenna ( Fig. 4C ) 3-segmented, comprising short unarmed coxa, robust tapering basis, and distal subchela: surface of basis ornamented with minute pits; subchela with swollen and thickened base bearing tiny blunt setal vestige, plus curved distal claw. Parabasal papilla ( Fig. 4C ) with broad base and rounded apical lobe, located lateral to insertion of antenna. Mandible stylet-like, bearing row of 4 marginal teeth subapically. Maxillule bilobed ( Fig. 4D ): both lobes armed with 2 setae; setae on outer lobe more robust and slightly longer than on inner lobe; innermost seta on inner lobe overlying oral cone. Maxilla ( Fig. 4E ) comprising basal segment armed with single inner seta proximally; subchela comprising long segment armed with slender seta at inner extremity and distal claw with minute seta and bifid tip.

Swimming legs 1 and 2 biramous; members of each leg pair joined by slender interpodal bars ( Fig. 4F ). Transverse band of weakly sclerotized integument present between interpodal bars. Leg 1 ( Fig. 4G ) with fused sympod armed with outer and inner setae: exopod distinctly 2-segmented; proximal segment with thickened outer margin bearing outer spine distally; distal segment bearing 3 long setal elements around apex and 2 shorter setae along inner margin: endopod indistinctly segmented; proximal segment bearing inner seta; distal segment armed with 3 unequal setae around apex and 2 reduced setae on inner margin. Leg ornamented with curved rows of minute spinules: 1 on sympod and on exopodal segment 1, and 2 on distal exopodal segment. Leg 2 ( Fig. 4H ) with fused sympod bearing outer seta; exopod 2-segmented; proximal segment longer than distal, armed with short outer spine; distal segment bearing 3 setae around apex and 1 reduced seta distally on inner margin: endopod indistinctly 2-segmented; proximal segment armed with reduced inner seta; distal segment armed with short outer seta, 1 long and 2 small setae around apex, and 1 inner seta. Leg ornamented with curved rows of minute spinules: 1 on sympod, and 2 each on exopodal segment 1 and endopodal segment 2. Leg 3 located laterally on trunk at about 35% of length ( Fig. 4A ), represented by small lobe armed with 1 minute and 2 long setae ( Fig. 4I ). Leg 4 located laterally on trunk at about 77% of length ( Fig. 4A ), represented by single seta originating directly on trunk surface ( Fig. 4J ).

Remarks

The species name, H. bifurcata , alludes to the “bifurcate” state of the antennule, as interpreted by Yamaguti & Yamasu (1959), a feature considered unique within the genus by Jones (1985). According to Yamaguti & Yamasu (1959), the antennule of the female carries a posteriorly directed “digitiform process with a rudimentary seta at tip” on the distal end of the compound second segment. In his recent redescription of female H. bifurcata, Izawa (2015a) referred to this structure as a “hook-like ventral process tipped with setiform sensillum” but in his subsequent description of the complete developmental series of this species, Izawa (2015b) demonstrated that this structure is simply a modified seta with a flagellate tip, with the setal modification taking place at the moult from Copepodid IV to Co V in the female. The homologous seta is not modified in males.

This species was originally described based on females collected from the gills of a grammistine serranid, Diploprion bifasciatum , caught in the Inland Sea of Japan (Yamaguti & Yamasu, 1959). There were no additional records until Izawa (2015a) reported a single ovigerous female collected from a new host, the scorpaenid Pterois lunulata Temminck & Schlegel, 1843 , caught off Seto, Wakayama Prefecture, Japan. Izawa (2015b) subsequently reported on abundant material, including developmental stages of both sexes, collected at the same locality, both from the original host ( D. bifasciatum ) and from Aulacocephalus temmincki Bleeker, 1855 , another member of the serranid subfamily Grammistinae .

The Australian material was collected from the type host and closely resembles the type material in gross morphology. The female ranges in body length from 0.86 to 1.33 mm, which is a wider range than the original Japanese material: the body length was given as 0.95 to 1.1 mm in the type material from D. bifasciatum (Yamaguti & Yamasu, 1959) . However, Izawa (2015a, b) subsequently reported a body length of 0.78 mm for a single female from Pterois lunulata , and 0.66 to 0.98 mm for material from D. bifasciatum and A. temmincki . Unfortunately, the host species of the measured females was not specified by Izawa (2015b). Despite this variation in body size, the Australian material conforms closely to the original description in most other respects.

The most interesting difference is the unmodified state of the distal seta on the compound second segment of the female antennule (comprising the second and third segments of most other Hatschekia species). The name of the species is actually based on the misinterpretation of this modified seta by Yamaguti & Yamasu (1959), but Izawa (2015b) has shown that this modification takes place at the moult from Copepodid IV to Co V. In the Moreton Bay material this seta is enlarged but lacks the distinctive flagellate tip. This difference is interpreted here as due to geographical variation.

Figures

FIGURE 4. Hatschekia bifurcata Yamaguti & Yamasu, 1959, female. A, habitus, dorsal; B, posterior extremity of trunk and genitoabdomen, ventral; C, antennule, antenna and parabasal papilla in situ, ventral; D, right maxillule, ventral; E, maxilla; F, interpodal bars, ventral; G, leg 1; H, leg 2, I, leg 3; J, leg 4. Scale bars: A, 300 μm, B, C, E–H, 50 μm, D, I, J, 25 μm.