Hatschekia cribbi, Boxshall & Bernot, 2025

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 : 30-36

Hatschekia cribbi new species

Type Material

Holotype ♀ and allotype ♂ from gills of Abudefduf bengalensis (Bloch, 1787) ( TC17269 ) collected off Amity , North Stradbroke Is., Moreton Bay on 19 January 2016; QM Reg. Nos. W55133 ( Holotype), W55134 ( Allotype); 1 paratype ♀ and 1 paratype ♂, NHMUK Reg. Nos. 2025.1423.

Differential diagnosis

Female with oval cephalothorax about 1.9 times wider than long. Dorsal cephalothoracic shield supported by m-shaped subsurface chitinous frame. Trunk about 3.3 times longer than wide; bearing prominent posterolateral processes. Genitoabdomen about as long as wide with more-or-less parallel sides. Rostrum with short lateral processes. Parabasal papilla with broad base and rounded apical lobes. Mandible stylet-like with 4 distal teeth. Legs 1 and 2 each joined by simple interpodal bar; endopods indistinctly 2-segmented and each armed with 2 apical setae, lacking inner seta on proximal segment. Leg 3 represented by 2 setae on small papilla.

Male with dorsal cephalothoracic shield ornamented dorsally with 3 pairs of posteriorly-directed spinous processes. Paired rostral processes present, longer than in female. Antenna with flattened process distally on basis. Interpodal bars joining members of legs 1 and 2, each with 2 pairs of posteriorly-directed spinous processes.

Description of female

Total body length excluding caudal rami 1.16 to 1.40 mm (n = 2). Body ( Fig. 6A ) dorsoventrally flattened, comprising anterior cephalothorax and broad subdivided trunk bearing minute genitoabdomen posteriorly. Cephalothorax oval, about 1.9 times wider than long (198 x 370 μm). Dorsal cephalothoracic shield supported by m-shaped subsurface chitinous frame ( Fig. 6A ) with long median longitudinal bar only slightly longer than lateral bars; lateral bars extending medially at tip, median bar with bilateral extensions at tip. Trunk with second pedigerous somite separated from rest of trunk by deep constriction. Trunk about 3.3 times longer than wide (1.19 x 0.36 mm); trunk with more-or-less parallel lateral margins, tapering slightly posterior to fourth legs; trunk with prominent posterolateral processes ( Fig. 6B ). Genitoabdomen just wider than long, bearing paired genital apertures dorsally and paired copulatory pores ventrally (with spermatophores attached in Fig. 6B ). Caudal rami about 1.4 times longer than wide (32 x 22 μm); armed with 5 naked setae of different lengths; lateral seta located about at 60% of lateral margin.

Rostrum with paired spinous expansions posteriorly near midline, and bearing small, digitiform, rostral processes laterally (arrowed in Fig. 6C ). Antennule ( Fig. 6C ) indistinctly 5-segmented: segmental setation pattern 10, 5, 4, 1, 13 + ae; 2 unequal setae located on antero-dorsal surface of first segment. Antenna ( Fig. 6D ) 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 fused with curved distal claw. Parabasal papilla lobate ( Figs. 6C, D ) with broad base and rounded apical lobes, located lateral to insertion of antenna. Mandible stylet-like ( Fig. 6E ) and bearing row of 4 marginal teeth subapically. Maxillule bilobed ( Fig. 6F ): both lobes armed with 2 setae; setae on outer lobe more robust and longer than on inner lobe. Maxilla ( Fig. 6G ) armed with single inner seta proximally on basal segment; subchela comprising long segment armed with slender seta at inner extremity and distal claw with bifid tip, plus minute slender seta midway along concave margin.

Swimming legs 1 and 2 biramous; members of each leg pair joined by slender interpodal bars ( Fig. 6H ). Trapezoidal box-shape of weakly sclerotized integument present between interpodal bars. Leg 1 ( Fig. 6I ) with fused sympod armed with outer and inner setae: exopod indistinctly 2-segmented; proximal segment with outer distal spine; distal segment bearing 3 long setal elements around apex: endopod unsegmented, armed with 2 unequal apical setae. Leg ornamented with curved rows of minute spinules: 5 on sympod, 1 on exopodal segment 1 and 3 on segment 2, and 2 distally on endopod. Leg 2 ( Fig. 6J ) with fused sympod bearing outer seta; exopod indistinctly 2-segmented; proximal segment armed with short outer spine on expanded margin; distal segment bearing 1 small and 1 large seta distally and 2 reduced setae on inner margin: endopod unsegmented, armed with short outer seta and long inner seta on apex. Leg ornamented with curved rows of minute spinules: 4 on sympod, 3 on each exopodal segment, and 2 on endopod. Leg 3 located laterally on trunk at 38% of length, represented by 2 long setae arising on trunk surface. Leg 4 located laterally on trunk at 73% of length, represented by single seta originating directly on trunk surface.

Description of male.

Total body length excluding caudal rami 0.44 mm. Body ( Figs. 7B–D , 8A ) comprising anterior cephalothorax and slender trunk showing traces of segmentation defined by marked constrictions anteriorly and incorporating urosome posteriorly. Cephalothorax about 1.15 times wider than long (160 x 185 μm); irregularly hexagonal with lateral margins longest. Dorsal cephalothoracic shield supported by subsurface chitinous frame ( Figs. 7C,D , 8A ) comprising anterior transverse bar and 3 longitudinal bars, median longitudinal bars with lateral extensions posteriorly joining with medial extensions from each of lateral longitudinal bars; 3 pairs of posteriorly-directed spinous processes present on dorsal surface of cephalothoracic shield ( Fig. 7C ). Trunk about 2.6 times longer than wide (412 X 160 μm); anteriorly trunk with first two pedigerous somites strongly defined by indentations; greatest width of trunk posterior to level of insertion of fourth legs. Genital apertures located ventrally ( Figs. 7B , 8B ); paired genital opercula each armed with single seta. Developing spermatophores about 130 μm in length, visible within posterior part of trunk ( Fig. 7C ). Abdomen wider than long ( Fig. 7D ), undivided. Caudal rami about 1.9 times longer than wide (45 x 24 μm); armed with large primary apical seta with flagellate tip plus 4 smaller naked setae; primary seta longer than ramus; lateral seta located about in middle of lateral margin.

Rostrum with medially indented posterior margin; bearing paired lateral rostral processes longer than in female (arrowed in Fig. 8C ). Antennule ( Fig. 8C ) indistinctly 5-segmented: segmental setation pattern 10, 5, 4, 1, 12 + ae. Antenna ( Figs. 7A , 8D ) comprising unarmed coxa, robust basis and distal subchela: basis bearing flattened chitinous process distally (arrowed in Fig. 7A ), projecting distally across base of subchela; subchela consisting of proximal segment, bearing 1 seta incompletely fused to recurved distal claw. Mandible and maxillule as in female. Maxilla ( Fig. 8E ) as in female but more slender.

Swimming legs 1 and 2 biramous; members of each leg pair joined by interpodal bars ( Figs. 7B , 8F ); interpodal bars each with 2 pairs of conspicuous, posteriorly-directed processes. U-shaped band of weakly sclerotized integument present between interpodal bars. Leg 1 ( Fig. 8F ) with fused sympod armed with outer and inner setae: exopod distinctly 2-segmented; proximal segment bearing outer distal spine; distal segment bearing 3 long setal elements around apex: endopod unsegmented; armed with 2 unequal setae on apex. Leg ornamented with curved rows of minute spinules: 3 on sympod, 2 on exopodal segment 1 and 3 on segment 2, and 3 on endopod. Leg 2 ( Fig. 8G ) with fused sympod bearing outer seta; exopod 2-segmented; proximal segment bearing long outer spine on outer distal tip of segment; distal segment bearing outer spiniform element and long apical seta distally plus 2 smaller setae on inner margin: endopod indistinctly segmented; ill-defined proximal segment unarmed; distal segment armed with 2 subequal apical setae. Leg 2 ornamented with curved rows of minute spinules: 6 on sympod, 3 on first exopodal segment, 2 on second segment, and 5 on endopod. Leg 3 located dorsolaterally on trunk at 40% of length ( Fig. 8A ), represented by two setae originating directly on trunk surface. Leg 4 located laterally on trunk at 60% of length ( Fig. 8A ), represented by single seta originating directly on trunk surface.

Etymology: This species is named in honour of Tom Cribb (University of Queensland) who has contributed enormously to our knowledge of metazoan parasites of marine fishes.

Remarks

The female of this species possesses a pair of well developed posterolateral lobes on the trunk. These lobes have a rounded distal margin and reach about to the posterior margin of the genitoabdomen. About 50 species of Hatschekia have various types of posterior lobes on the trunk ( Table 2). There are, for example, species with pairs of slender digitiform lobes either side of the genitoabdomen, such as H. bicaudata , and there are species with small hemispherical lobes on the postero-lateral margins, such as H. difficilis and H. albirubra Wilson, 1913 . However, there are only 20 described species that possess large well developed lobes with a broad rounded distal margin: H. amphiprocessa Castro-Romero & Baeza-Kuroki, 1986 , H. angulata Pearse, 1951 , H. boonah Uyeno & Nagasawa, 2013 , H. brotulae Cadenat, 1954 , H. ellipsocorpa Uyeno & Nagasawa, 2013 , H. delamarei Nuñes-Ruivo, 1954 , H. elliptica Pillai, 1968 , H. geniculata Uyeno & Nagasawa, 2013 , H. hippoglossi (Cuvier, 1830) , H. insolita Wilson, 1913 , H. ischnon Leigh-Sharpe, 1936 , H. khahajya Uyeno & Nagasawa, 2010 , H. legoulli Nuñes-Ruivo, 1954 , H. ostracii Yamaguti, 1953 , H. pholas (Wlson, 1906) , H. pinguis Wilson, 1908 , H. pygmaea T. Scott , in Scott & Scott, 1913, H. rhombocephalis Izawa, 2016 , H. thyrsitoidesi Izawa, 2016 and H. triannuli Uyeno & Nagasawa, 2012 . Separating the new species from these 20 species requires detailed comparison.

In both H. thyrsitoidesi and H. triannuli the rostral area in the middle of the frontal margin of the cephalothorax is crenulate and the subsurface chitinous frame supporting the dorsal cephalothoracic shield includes a rounded feature posteriorly ( Izawa, 2016c; Uyeno & Nagasawa, 2012). In the new species the frontal margin is smooth and the chitinous frame does not include a rounded posterior component. Hatschekia khahajya shares the same rounded posterior component in the subsurface chitinous frame supporting the dorsal cephalothoracic shield and also differs from the new species in possessing four spinous processes posteriorly on the bar-like interpodal bars of legs 1 and 2 in the female.

Hatschekia ellipsocorpa is a very short bodied species: according to Uyeno & Nagasawa (2010), it has “an ovate or ellipsoidal trunk”, which is widest at the base of leg 2 and tapers posteriorly, and it has a Y-shaped chitinous frame supporting the dorsal cephalothoracic shield. In contrast, in the new species the trunk is elongate and subequal in width along most of its length, and the dorsal cephalothoracic shield is supported by an m-shaped chitinous frame.

Both H. boonah and H. geniculata were described from pufferfish hosts ( Uyeno & Nagasawa, 2013). Hatschekia boonah is another short bodied form and can be distinguished from H. cribbi sp. nov. by its rounded triangular cephalothorax supported by a Y-shaped chitinous frame, in contrast to the wider than long cephalothorax supported by an m-shaped frame in the new species. Hatschekia geniculata is redescribed below (see Fig. 11 ) and is similar to H. cribbi sp. nov. These species differ in the extent of the posterolateral lobes on the trunk of the female, which is as long as the genitoabdomen in H cribbi sp. nov. but only half the length of the genitoabdomen in H. geniculata . In addition, the trunk of the female tapers posteriorly in the latter but retains more or less the same width in H. cribbi sp. nov.

The new species differs from H. pygmaea in having much better developed posterolateral lobes on the trunk of the female and in lacking the dorsal swelling present on the trunk just posterior to the cephalothorax in the latter species ( Kabata, 1979). There are numerous other differences including the shape of the parabasal papilla (small and conical in H. pygmaea versus bilobate in the new species), the number of teeth on the mandible ( 2 in H. pygmaea versus 4 in the new species), and the number of distal setae on the endopod of leg 1 ( 3 in H. pygmaea versus 2 in the new species).

Jones (1985) commented that H. delamarei was in need of redescription but Nuñes-Ruivo (1954) provided sufficient detail to distinguish between this species and the new species. In particular, the cephalothorax is rectangular in H. delamarei and the endopod of leg 2 carries 5 setae, compared to the ovoid cephalothorax and only 2 setae on this endopod exhibited by the new species.

In female H. ischnon the cephalothorax is about 1.2 times wider than long (Leigh-Sharpe, 1936), compared to 1.9 times in H. cribbi sp. nov. and the endopods of both legs 1 and 2 are armed with 4 setae, compared to only 2 in H. cribbi sp. nov.

In their redescription of H. legouli, Uyeno & Nagasawa (2009b) recorded the presence of 6 setae on the endopods of both legs 1 and 2 and noted the presence of broad, rounded expansions on the lateral margins of the rostrum. In contrast the new species has only 2 setae on the endopods of both legs and the rostrum bears small digitiform lateral processes.

Hatschekia pholas differs from the new species in possessing a greatly expanded dorsal cephalothoracic shield which extends posteriorly over the anterior part of the trunk. The short dorsal cephalothoracic shield of the new species is about 1.9 times wider than long and has no posterior expansion. The shape of the dorsal cephalothoracic shield also allows us to distinguish between H. ostracii and the new species. In H. ostracii the shield is just longer than wide and is supported by a T-shaped chitinous frame (Uyeno & Nagasawa, 2009), whereas in the new species the shield is distinctly wider than long and is supported by an m-shaped frame. Another major difference is that the female of H. ostracii possesses four posterior processes on the interpodal bars of legs 1 and 2, compared to the smooth interpodal bars in the female of the new species.

In H. amphiprocessa the posterolateral processes on the trunk are short (Castro-Romero & Baeza-Kuroki, 1986) and are more laterally directed than in the new species but this species is most readily distinguished by the presence of paired posterolateral processes on the dorsal cephalothoracic shield. The new species has no processes on the cephalothorax.

The original description of H. angulata lacked detail ( Pearse, 1951) but Jones (1985) re-examined the type material and noted that the antennules were short, only reaching just over half way towards the lateral margin of the dorsal cephalothoracic shield, and that the contracted trunk was subtriangular, tapering strongly posteriorly, so the anterior extremity was twice the width of the posterior end. The length of the antennule and the different shape of the trunk are sufficient to distinguish the new species from H. angulata . Jones (1985) also redescribed the types of H. insolita , noting that the dorsal cephalothoracic shield was supported by a T-shaped chitinous frame and that the caudal rami were more than 3.0 times longer than wide compared to about 1.3 times in the new species, which also has an m-shaped chitinous frame supporting the dorsal cephalothoracic shield.

The body proportions of H. elliptica differ from those of the new species. The trunk of H. elliptica is described as elliptical and nearly twice as long as wide ( Pillai, 1968), whereas, in contrast, the elongate trunk of the new species is linear and about 3.3 times longer than wide. However, small differences in trunk proportions are considered unreliable as a criterion for species discrimination in Hatschekia ( Jones, 1985; Kabata, 1991). The details of leg setation may also show some intraspecific variability but there are major differences between these species: in the new species the endopods of both legs 1 and 2 are armed with 2 setae whereas in H. elliptica there are 5 and 4 setae respectively. These differences are sufficient to distinguish between these species. Some of the other apparent differences, for example the segmentation and setation of the antennules, are generally unreliable as they were not accurately described in much of the older literature.

Hatschekia brotulae is similar to the new species: it has an m-shaped chitinous frame supporting the dorsal cephalothoracic shield and the trunk of the type specimen is about 2.8 times longer than wide ( Nuñes-Ruivo, 1954). Comparison with the illustrations of Nuñes-Ruivo (1954) suggests that the antenna is more slender and has a shorter terminal claw than in the new species, and that the caudal rami are just more than twice as long as wide, compared with only 1.3 times in the new species.

There are numerous detailed differences that serve to distinguish between H. rhombocephalis and the new species. Hatschekia rhombocephalis has caudal rami that are 2.2 times longer than wide, and the endopods of legs 1 and 2 are armed with 5 and 6 setal elements, respectively ( Izawa, 2016c). In contrast in the new species the caudal rami are only 1.3 times longer than wide and the endopods of legs 1 and 2 both carry only 2 apical setae.

Finally, the type species H. hippoglossi , is also characterized by the possession of paired posterolateral lobes and an elongate genitoabdomen that gives a trilobate appearance to the posterior end of the trunk ( Jones, 1985). Relative to most Hatschekia species, the type species is enormous, ranging from 2.6 to 9.3 mm in total length (Schram & Apsholm, 1997). This contrasts with a body length of about 2.4 mm in the new species. In addition, the endopods of both legs 1 and 2 are armed with 4 setae in H. hippoglossi (see Kabata, 1979) compared to 2 setae on this ramus of both legs in the new species. These differences from similar species are sufficient to justify the establishment of a new species.

The only species previously recorded from a species of Abudefduf Forsskål, 1775 is H. nahaensis Yamaguti, 1953 . This species was described from females collected in Okinawa, Japan, and Jones (1985) considered that it was in need of redescription. The new species differs from H. nahaensis in possessing large rounded posterolateral lobes on the trunk; the trunk of H. nahaensis has rounded posterolateral margins devoid of any lobes.

The male found on A. bengalensis and described above is treated as conspecific with the female despite two significant differences, here attributed to sexual dimorphism. The male possesses 6 (3 pairs) of spinous processes on the dorsal cephalothoracic shield whereas the female lacks such ornamentation. A similar sexual dimorphism has already been noted in H. couardi , in which the male only has 2 pairs of such processes (see Izawa, 2015a). More remarkable is the presence of unornamented, linear interpodal bars between the members of leg 1 and leg 2 in the female in contrast to the presence of 2 pairs of large spinous processes on the interpodal bars of both legs in the male. Spinous processes are reported from the females of 26 species of Hatschekia ( Table 3), but the only species known from both sexes, H. monacanthi Yamaguti, 1939 , has ornamented interpodal bars in both. Prior to this study, sexual dimorphism in the interpodal bars of legs 1 and 2 had not been reported in this family, although males are known for only a minority of hatschekiid species. This raises some uncertainty concerning the conspecificity of the two females and two males found on the same individual host fish in Moreton Bay. However, the holotype female of H. cribbi sp. nov. on this host carried a pair of spermatophores which must have been recently deposited by a male, and the only males present were those described above. This leads to the most parsimonious conclusion, that the male is conspecific with the fertilized female. Remarkably, the male of H. pholas is reported for the first time below and this species also displays sexual dimorphism in the interpodal bars, which are smooth in females but ornamented with 4 pairs of posteriorly-directed processes in males.

Figures

FIGURE 6. Hatschekia cribbi sp. nov., female. A, habitus, dorsal; B, posterior extremity of trunk and genitoabdomen, ventral view showing attached spermatophores; C, rostrum and antennule, ventral view with lateral rostral process arrowed; D, antenna and parabasal papilla in situ, ventral; E, mandible; F, right maxillule, ventral; G, maxilla; H, interpodal bars, ventral; I, leg 1; J, leg 2. Scale bars: A, 300 μm, B, D, 100 μm, C, G–J, 50 μm, E, F, 25 μm.

FIGURE 7. Hatschekia cribbi sp. nov., male, CLSM. A, Antennae in situ, with arrows showing process on basis on each antenna; B, habitus, ventral view showing spinous processes on interpodal bars; C, habitus, lateral view showing spinous ornamentation on surface of dorsal cephalothoracic shield; D, habitus, dorsal view showing subsurface chitinous frame and spinous ornamentation. Scale bars: A–D, 200 μm.

FIGURE 8. Hatschekia cribbi sp. nov., male. A, habitus, dorsal; B, posterior extremity of trunk, showing paired genital apertures, and urosome, ventral; C, rostrum and antennule, ventral view lateral rostral process arrowed; D, antenna; E, maxilla; F, interpodal bars and left leg 1 in situ, ventral; G, leg 2. Scale bars: A, 150 μm, B, 100 μm, C–G, 50 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.