Hatschekia quadrata Hewitt, 1969

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 : 51-55

Hatschekia quadrata Hewitt, 1969

Material examined. 22 ♀♀ from gills of Tragulichthys jaculiferus (Cuvier, 1818) ( TC17076 ) collected off Green Island , Moreton Bay on 13 January 2016 , QM Reg. Nos. W55140 ; 8 ♀♀ and 9 juveniles from gills of T. jaculiferus ( TC17125 ) collected off Peel Island , Moreton Bay on 14 January 2016 ; 2 ♀♀ and 1 juvenile from gills of T. jaculiferus ( TC17023 ) collected off Green Island , Moreton Bay on 12 January 2016 ; 2 ♀♀ and 1♂ from gills of T. jaculiferus ( TC17409 ) collected off Green Island , Moreton Bay on 22 January 2016 ; 2 ♀♀ and 1 juvenile from gills of T. jaculiferus ( TC17935 ) collected at Wynnum North , Moreton Bay on 07 July 2016 ; NHMUK Reg. Nos. 2024.265-282 .

37 ♀♀ from gills of Dicotylichthys punctulatus Kaup, 1855 ( TC17008 ) collected off Green Island, Moreton Bay on 12 January 2016 , QM Reg. Nos. W55141 ; 23 ♀♀ from gills of D. punctulatus ( TC17402 ) collected off Mud Island, Moreton Bay on 22 January 2016 ; 10 ♀♀ and 1♂ from gills of D. punctulatus ( TC17693 ), collected off Green Island, Moreton Bay on 28 July 2016 ; 18 ♀♀ from gills of D. punctulatus ( TC16940 ) collected off Green Island, Moreton Bay on 08 December 2016 ; 7 ♀♀ from gills of D. punctulatus ( TC17751 ) collected off Wellington Point, Moreton Bay on 30 June 2016 ; 19 ♀♀ and 1♂ from gills of D. punctulatus ( TC17322 ) collected in the Port of Brisbane ( South of the port) on 20 January 2016 ; NHMUK Reg. Nos. 2024.283-329 .

Supplementary description of female.

Total body length of females from Tragulichthys jaculiferus excluding caudal rami ranging from 1.38 to 2.00 mm, with a mean of 1.77 mm (n = 25). Total body length of females from Dicotylichthys punctulatus excluding caudal rami ranging from 1.71 to 2.36 mm, with a mean of 2.05 mm (n = 28). Body ( Fig. 15A ) dorsoventrally depressed, comprising anterior cephalothorax and long trunk bearing minute genitoabdomen posteriorly. Cephalothorax heart-shaped in outline, about 1.3 times wider than long (378 x 505 μm), with medially indented frontal margin and flattened, mid-dorsal posterior expansion. Dorsal cephalothoracic shield supported by m-shaped subsurface chitinous frame. Trunk about 2.8 times longer than wide (1.39 x 0.493 mm), but ranging from 2.4 to 3.2 times longer; with greatest width about at level of insertion of third legs; tapering slightly from level of fourth legs towards posterior extremity; rear margin with rounded posterolateral angles and weak, rounded expansion dorsally in midline. Genitoabdomen ( Fig. 15B ) wider than long excluding caudal rami, comprising fused genital-double and abdominal somites; bearing paired genital apertures dorsally. Widest proximal part of genitoabdomen apparently telescoped within rear part of trunk. Caudal rami about 1.9 times longer than wide (26 x 14 μm); armed with 6 naked setae of different lengths; lateral seta located about at middle of lateral margin. Egg sacs linear: mean number of eggs per sac = 13.3 (range 9 to 17, n = 30) in females from T. jaculiferus compared with 18.1 (range 11 to 22, n = 22) in females from D. punctulatus .

Rostrum with concave posterior margin; lacking paired lateral rostral processes ( Fig. 15C ). Antennule ( Fig. 15C ) indistinctly 5-segmented: segmental setation pattern 10, 5, 4, 1, 12 + ae; posterior margin setae on segment 3 large and readily visible in undissected specimens.Antenna ( Fig. 15C ) 4-segmented, comprising very short unarmed coxa, robust tapering basis, and 2-segmented endopod forming subchela; surface of basis ornamented with minute pits; first endopodal segment armed with minute setule on knob-like process on inner margin; second endopodal segment forming curved claw armed with minute digitiform process proximally plus prominent process on midconcave margin. Mandible ( Fig. 15D ) stylet-like, bearing row of 5 minute, marginal teeth subapically. Maxillule bilobed ( Fig. 15E ): inner lobe armed with 2 short setae and outer lobe with 2 long enlarged setae. Maxilla ( Fig. 15F ) subchelate: coxobasis armed with single inner seta proximally on basal part; subchela comprising long segment armed with slender seta at inner extremity and distal claw with bifid tip.

Swimming legs 1 and 2 biramous; members of each leg pair joined by slender interpodal bars ( Fig. 15G ). Band of weakly sclerotized integument present between interpodal bars. Leg 1 ( Fig. 15G ) with fused sympod armed with outer and inner setae: exopod distinctly 2-segmented; proximal segment bearing slightly curved outer distal spine; distal segment bearing 3 long setal elements around apex and 1 reduced seta on inner margin: endopod distinctly 2-segmented; proximal segment unarmed; distal segment armed with short outer seta, 3 unequal setae around apex, and 2 reduced setae on inner margin. Leg ornamented with curved rows of minute spinules: 2 on sympod, and 2 each on exopodal segments 1 and 2, and endopodal segment 2. Leg 2 ( Fig. 15H ) with fused sympod bearing outer seta; exopod 2-segmented; with incomplete articulation between segments offset; proximal segment bearing long outer spine on extended outer distal tip of segment; distal segment bearing 2 unequal setal elements on apex and 3 reduced setae along inner margin: endopod distinctly 2-segmented; proximal segment with inner distal seta; distal segment armed with outer seta, 3 unequal setae around apex, and 1 inner seta. Leg ornamented with curved rows of minute spinules: 1 on sympod, and 3 on each exopodal segment. Leg 3 located laterally on trunk at about 30% of length ( Fig. 15A ), represented by two setae originating directly on trunk surface. Leg 4 located laterally on trunk at about 78% of length ( Fig. 15A ), represented by single seta originating directly on trunk surface.

Description of male.

Total body length excluding caudal rami 0.51 mm.Body ( Fig. 16A ) slightly dorsoventrally depressed, comprising anterior cephalothorax and slender trunk tapering posteriorly into incorporated urosome. Cephalothorax hexagonal in shape, about as wide as long (164 x 157 μm). Dorsal cephalothoracic shield supported by subsurface chitinous frame comprising anterior transverse bar and 3 longitudinal bars, median longitudinal bars with lateral extensions posteriorly aligned with medial extensions on each of lateral longitudinal bars. Trunk about 3.2 times longer than wide (348 X 108 μm); trunk with first two pedigerous somites defined by indentations anteriorly; greatest width of trunk about at level of insertion of third legs; tapering posteriorly to level of genital apertures. Genital apertures located ventrally ( Fig. 16B ); genital opercula each armed with single seta. Abdomen undivided, tapering slightly towards rear margin. Caudal rami elongate, about 2.8 times longer than wide (44 x 16 μm); armed with 6 naked setae of different lengths; primary seta fused to ramus and just longer than ramus; lateral seta located at about 40% of lateral margin.

Rostrum subtriangular with pointed posterior margin; lacking paired lateral rostral processes ( Fig. 16C ). Antennule ( Fig. 16C ) 5-segmented: segmental setation pattern 10, 5, 5, 1, 12 + ae; setae on segment 3 well developed but less conspicuously enlarged than in female.Antenna ( Fig. 16D ) comprising unarmed coxa, robust basis and distal subchela: basis bearing flattened chitinous process distally, projecting distally across base of subchela; subchela unsegmented but with incomplete transverse suture partially separating off proximal segment bearing 2 setae from recurved distal claw. Mandible as in female. Maxillule ( Fig. 16E ) bilobed as in female; inner lobe with 2 unequal slender setae and outer lobe with 2 long naked setae. Maxilla ( Fig. 16F ) as in female.

Swimming legs 1 and 2 biramous; members of each leg pair joined by slender interpodal bars ( Fig. 16G ). Vshaped band of weakly sclerotized integument present between interpodal bars. Leg 1 ( Fig. 16G ) with fused sympod armed with outer and inner setae: exopod distinctly 2-segmented; proximal segment bearing slightly curved outer distal spine; distal segment bearing total of 6 long setal elements around apex and along inner margin: endopod unsegmented; unarmed proximally; distally armed with 5 unequal setae around apex and along inner margin. Leg ornamented with curved rows of minute spinules: 4 on sympod, 1 on exopodal segment 1, and 2 on endopod. Leg 2 ( Fig. 16H ) with fused sympod bearing outer seta; exopod 2-segmented; with articulation between segments offset; proximal segment bearing long outer spine on extended outer distal tip of segment; distal segment bearing outer spiniform element on apex and 4 long pinnate setae along distal and inner margins: endopod indistinctly 2- segmented; proximal segment with pinnate inner seta; distal segment armed with naked outer setal element plus 1 naked and 3 pinnate setae around apical and inner margins. Leg 2 ornamented with curved rows of minute spinules: 3 on sympod, 2 each on exopodal segments, and 1 on each endopodal segment. Leg 3 located laterally on trunk, represented by two setae originating on small protrusion from trunk surface ( Fig. 16A , inset). Leg 4 located dorsally on trunk, represented by single seta originating directly on trunk surface.

Remarks

The original description of H. quadrata by Hewitt (1969) was based on female specimens collected in New Zealand waters from the diodontid fish Tragulichthys jaculiferus (as Allomycterus jaculiferus ), and Jones (1985) subsequently noted that H. quadrata was common on this host in the Cook Strait area between North and South Island. The present account is the first record of H. quadrata from Australian waters and its discovery on a second diodontid, Dicotylichthys punctulatus , is a new host record. It was common on both of these host fishes in Moreton Bay. A difference was noted in the number of eggs per egg sac in females from the two different hosts, with a mean of 13.3 per sac in the type host compared to 18.1 in D. punctulatus .

The Australian material closely resembles the New Zealand material in gross body morphology but there are some apparent differences in the appendages. The setation of the antennule illustrated by Hewitt (1969) is missing numerous setae from the first segment and 1 or more setae from each of the other segments. The missing setae are mostly small and easily overlooked. The antenna lacks the 2 reduced elements on the inner surface of the subchela and the ornamentation of minute pits on the surface of the basis was not mentioned by Hewitt. The mandible was not described by Hewitt (1969). The maxillule, referred to by Hewitt (1969) as the mandibular palp, was described as bilobed with 1 and 3 setae on the lobes whereas, like the vast majority of Hatschekia species, two setae are present on each lobe. The setation of leg 1 is the same in both sets of material except an additional reduced proximal seta is illustrated on the inner margin of the second exopodal segment in the original description. Leg 2 has identical setation on the exopod, including the unusually long outer spine on the proximal segment, but only 3 long distal setae are shown on the endopod whereas the new Australian material carries, in addition, 1 seta on the inner margin and 1 on the outer margin of the second segment, plus an inner seta on the first segment. These few differences involve reduced setae that are difficult to observe, and the key similarities are striking, such as the outer spine of the proximal exopodal segment of leg 2 extending well beyond the tip of the ramus.

The male is described here for the first time.The male is markedly smaller than the female and sexual dimorphism is apparent in general body morphology as well as in all of the appendages with the exception of the mandible and maxilla. The cephalothorax, trunk and abdomen all differ in shape between the sexes. The antennules exhibit the same numbers of setae per segment but some setae on the proximal three segments are more robust in the female (and are conspicuous even in whole mounts), while the subterminal aesthetasc on the apical segment is larger in the male. The dimorphism displayed by the antenna is remarkable: the basis carries a large spatulate process distally on the posterior surface in the male, which is absent in the female, and the distal subchela is provided with two long setae in the male whereas only setal vestiges are present in the female. In the male the outer lobe of the bilobed maxillule is armed with two long slender setae but in the female these setae are robust (cf. Figs 15E and 16E ). The most obvious sexual dimorphism in the swimming legs is the relative length of the setae on both rami: they are much better developed in the male and in leg 2 most of the setae on both rami are pinnate whereas those of the female are weakly developed and lack any ornamentation.

Figures

FIGURE 15. Hatschekia quadrata Hewitt, 1969, female.A, habitus, dorsal; B, posterior extremity of trunk and genitoabdomen, ventral; C, rostrum, right antennule and right antenna in situ, ventral; D, mandible; E, maxillule; F, maxilla; G, interpodal bars and left leg 1, with inset showing outer spine on first exopodal segment; H, leg 2. Scale bars: A, 500 μm, B, F, 50 μm, C, G, H, 100 μm, D, E, 25 μm.

FIGURE 16. Hatschekia quadrata Hewitt, 1969, male. A, habitus, dorsal view with inset showing leg 3; B, posterior extremity of trunk, showing paired genital apertures, and genitoabdomen bearing caudal rami, ventral; C, rostrum and right antennule, ventral; D, antenna; E, maxillule; F, maxilla; G, interpodal bars and left leg 1; H, leg 2. Scale bars: A, 200 μm, B, 100 μm, C, D, F–H, 50 μm, E, 25 μm.