Hatschekia amyemmarum, 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 : 18-25

Hatschekia amyemmarum new species

Type Material

Holotype ♀, plus 6 paratype ♀♀ from gills of Arothron hispidus (Linnaeus, 1758) ( TC17119 ) caught off Peel Island , Moreton Bay on 14 January 2016, QM Reg. Nos. W55129 ( Holotype), W55130 ( paratypes); 5 paratype ♀♀ from gills of A. hispidus ( TC17325 ) caught off Mud Island, Moreton Bay on 20 January 2016, NHMUK Reg. Nos. 2024.333-337.

Other material examined: 1♀ from gills of A. nigropunctatus (Bloch & Schneider, 1801) ( TC17278 ) caught off Amity , North Stradbroke Is., Moreton Bay on 19 January 2016, NHMUK Reg. No. 2024.338 .

Differential diagnosis

Female with broad cephalothorax about 1.7 times wider than long and about 1.6 times wider than trunk. Dorsal cephalothoracic shield supported by m-shaped subsurface chitinous frame. Trunk about 2.3 times longer than wide; lacking posterior processes. Genitoabdomen longer than wide with more-or-less parallel sides. Rostrum with short lateral processes. Parabasal papilla comprising 2 rounded lobes located lateral to antenna. 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.

Description of female

Total body length excluding caudal rami ranging from 1.07 to 1.29 mm, with a mean of 1.18 mm (n = 10). Body ( Fig. 3A ) comprising broad anterior cephalothorax and cylindrical trunk with small rectangular genitoabdomen posteriorly. Cephalothorax about 1.7 times wider than long (range 1.5 to 1.9 times) and 1.6 times wider than trunk: dorsal cephalothoracic shield supported by m-shaped subsurface chitinous frame with long median longitudinal bar and pair of shorter lateral bars, with short tapering bar just medial to lateral bars. Surface of dorsal cephalothoracic shield densely sculptured with rounded pits. Cephalothorax length comprising about 39% of trunk length (range 33 to 45%). Trunk about 2.3 times longer than wide (range 1.5 to 2.9; with maximum width about in middle; posterior margin transverse with rounded posterolateral corners. Surface of trunk ornamented with rounded flattened knobs from level of second legs posteriorly to rear margin of trunk ( Fig. 3B ). Genitoabdomen longer than wide ( Fig. 3B ) comprising fused genital and abdominal somites; bearing paired genital apertures dorsally and paired copulatory pores ventrally. Caudal rami about 1.4 times longer than wide (30 x 21 μm); armed with 6 naked setae of different lengths; proximal lateral seta located about at middle of lateral margin. Mean number of eggs per egg sac = 15 (range 13 to 18, n = 8).

Rostrum ( Fig. 3C ) broad, bearing short rostral processes laterally. Antennule ( Fig. 3D ) indistinctly 5-segmented but with compound second segment showing bands of thickened cuticle: segmental setation pattern 10, 5, 4, 1, 11 + ae; 2 unequal setae located on antero-dorsal surface of first segment. Antenna ( Fig. 3E ) 3-segmented, comprising short unarmed coxa, robust tapering basis, and distal subchela: surface of basis ornamented with minute pits; subchela large with swollen and thickened base plus long curved distal claw. Parabasal papilla ( Fig. 3F ) comprising 2 rounded lobes located lateral to insertion of antenna. Mandible ( Fig. 3G ) stylet-like, bearing 4 minute marginal teeth subapically. Maxillule bilobed ( Fig. 3H ): both inner and outer lobes bearing 2 setae, with outer seta on outer lobe longer than others. Maxilla ( Fig. 3I ) armed with single inner seta proximally on first segment; subchela comprising long segment armed with slender seta at inner extremity and distal claw with minute seta at mid-length and bifid tip.

Swimming legs 1 and 2 biramous; members of each leg pair joined by slender interpodal bars ( Fig. 3J ); U-shaped cuticular thickening with lateral extensions present between interpodal bars. Leg 1 ( Fig. 3J ) with fused sympod armed with outer and inner setae: exopod distinctly 2-segmented; proximal segment with short outer distal spine; distal segment bearing short outer and long inner setae on apex and 4 shorter setae distributed along inner margin: endopod indistinctly segmented; unarmed proximally; distally bearing 2 unequal setae on apex. Leg ornamented with curved rows of minute spinules: 1 on sympod, 2 on exopodal segment 1 and 1 each on both endopodal segments. Leg 2 ( Fig. 3K ) with fused sympod bearing outer seta; exopod 2-segmented; proximal segment armed with curved outer spine; distal segment bearing 2 unequal apical setae plus 3 short setae on inner margin: endopod 2-segmented; proximal segment unarmed; distal segment armed with 1 long and 1 short seta on apex. Leg ornamented with curved rows of minute spinules: 2 each on sympod and proximal exopodal segment, and 1 row on each endopodal segment. Leg 3 located dorsolaterally on trunk at 43% of length ( Fig. 3A ), represented by 2 medially-directed setae arising directly from small knob-like vestige on trunk surface. Leg 4 located dorsally on trunk at 72% of length ( Fig. 3A ), represented by single seta originating directly on trunk surface.

Etymology: This species is named after Amy Boxshall-Collar and Emma Kiernan (nee Ridley) who compiled a database of records of parasitic copepods, including many hatschekiids, from Indo-Pacific fishes during work placement at the NHM, London.

Remarks

This species can be characterized by its short, broad cephalothorax combined with the relatively short, narrow trunk. Interpreting the posterior region is more problematic: the figured specimen ( Fig. 3A ) shows the genitoabdomen partly telescoped up inside the trunk but in a second specimen the genitoabdomen ( Fig. 3B ) was fully extended so the dorsal oviduct openings and the paired ventral copulatory pores were readily visible. Any attempt to use the length: width proportions of the genitoabdomen is problematic as a taxonomic character given the variable degree of telescoping of fixed specimens. This simply reinforces the need for caution in making habitus comparisons between female hatschekiids.

The new species lacks any kind of posterior processes or lobes on the trunk of the female which distinguished it from the 50 species listed in Table 2. Similarly, in possessing unornamented interpodal bars it can be distinguished from the 26 species which possess posteriorly-directed spinous processes on the interpodal bars of legs 1 and 2 ( Table 3). [Six species have both posterolateral lobes on the trunk plus spinous processes on the interpodal bars of legs 1 and 2 and are therefore listed in both Tables 2 and 3.] Eliminating these 70 species from the total of 150 listed in the World of Copepods ( Walter & Boxshall, 2025) leaves another 80 Hatschekia species which share rounded posterolateral corners on the trunk and smooth interpodal bars. The new species has a large cephalothorax combined with a short trunk, i.e., the length of the cephalothorax is just over a third (39%) of the length of the trunk. Given that the proportions of the trunk are known to vary markedly with the state of contraction/preservation of Hatschekia specimens, it is necessary to allow for this potential artefactual variation when making comparisons. Here we focus on making detailed comparisons with the 22 species which share the possession of a large cephalothorax combined with a short trunk, i.e., a cephalothorax that is between 25% and 50% of the length of the trunk ( Table 4). Effectively this applies a filter which excludes another 44 species in which the cephalothorax is less than 25% of the length of the trunk and four other species in which the cephalothorax is more than 50% of the length of the trunk.

The new species plus nine other species listed in Table 4 are characterized by the reduction in the setation of the endopod of leg 2, so that the distal endopodal segment carries only 2 setae (cf. 4 or 5) and endopodal segment 1 lacks the inner seta (cf. present). The presence-absence of this latter seta was regarded as an important and reliable morphological character in Hatschekia by Uyeno & Nagasawa (2013). In addition to the new species, these species are: H. affluens Castro Romero & Baeza-Kurocki, 1986 , H. cadenati Nuñes-Ruivo, 1954 , H. fuscoguttatus Lee, Lee & Boxshall, 2013 , H. hanguyenvani Kazachenko, Kovalev, Nguyen & Ngo, 2017 , H. laeopsi Izawa, 2018 , H. nohu Villalba, 1986 , H. papillifera Kabata, 1991 , H. sphyraeni Pillai, 1964 , and H. synagris Yamaguti, 1954 .

The cephalothorax of H. affluens is wider in its posterior half than anteriorly and the subsurface chitinous frame comprises a long median bar plus long lateral bars which curve inwards to almost meet the median bar distally ( Uyeno & Nagasawa, 2013). In contrast, the cephalothorax of the new species is widest about at mid-length and the lateral bars of the chitinous frame are straight and extend only about half the length of the median bar.

The new species shares many characters with H. cadenati but differs in the form of the subsurface chitinous frame of the dorsal cephalothoracic shield. In H. amyemmarum sp. nov. the lateral bars are straight and only about half as long as the median bar whereas in H. cadenati they are long and curve inwards, almost meeting the tip of the median bar. Hatschekia cadenati also has a unique setation feature in leg 1 as the second exopodal segment carries 2 large setae originating very close together on the inner margin ( Lee et al., 2013), whereas in the new species the inner setae on this segment are all reduced and are spaced out along the inner margin of the segment ( Fig. 3J ).

The new species differs from H. fuscoguttatus in the shape of the cephalothorax and in the configuration of its subsurface chitinous frame. The lateral margins of the cephalothorax are much more angular in H. fuscoguttatus than in H. amyemmarum sp. nov. and in the former the chitinous frame has lateral bars that are as long as the median bar and continue medially to almost meet the small side branches near the tip of the median bar. The very long apical setae on both rami of leg 2 are a unique feature of H. fuscoguttatus ( Lee et al., 2013) . In the new species the setae on leg 2 are all shorter than the rami.

The description of H. hanguyenvani is difficult to compare because the style of the drawings obscures important details but the rear margin of the dorsal cephalothoracic shield is produced posteriorly into a rounded median lobe ( Kazachenko et al., 2017: Figs 3a, 3k ), as found in H. pagellibognarei for example, whereas in H. amyemmarum sp. nov. this posterior margin is straight.

In H. laeopsi the subsurface chitinous frame of the cephalothorax comprises a long median bar plus long lateral bars which curve inwards to almost meet the median bar ( Izawa, 2018) whereas in the new species the lateral bars are straight and extend only about half the length of the median bar. Izawa (2018) also figures the rostrum of the female but does not show any lateral rostral processes which are present in the new species ( Fig. 3C ).

The frontal margin of the cephalothorax of female H. nohu protrudes medially between the antennules ( Villalba, 1986) whereas in the new species the frontal margin is straight. In addition, the genitoabdomen of H. nohu has strongly convex lateral margins and is about 1.5 times wider than long. In contrast, the genitoabdomen of H. amyemmarum sp. nov. has parallel to weakly convex lateral margins and is about as long as wide (depending on the degree of telescoping of the genitoabdomen within the trunk).

The new species can be readily distinguished from H. papillifera by the shape of the cephalothorax which is 1.24 times longer than wide in the latter, compared to about 1.7 times wider than long in H. amyemmarum sp. nov. The parabasal papillae are unusually large in H. papillifera and are often visible in dorsal view extending beyond the margins of the dorsal cephalothoracic shield in some specimens ( Kabata, 1991). They are small and rounded in the new species.

In H. sphyraeni the subsurface chitinous frame has large lateral bars that curve medially to meet the median bar. It also has only 1 seta on the tip of the endopod of leg 1 (Pillai, 1964), rather than 2 setae as in the new species.

Hatschekia synagris shares with H. papillifera the possession of unusually large parabasal papillae which extend beyond the lateral margins of the cephalothorax, as shown in Yamaguti’s dorsal habitus view (Yamaguti, 1954: Fig. 55). The presence of these papillae, plus the shape of the cephalothorax of H. synagris , which is just longer than wide compared to 1.7 times wider than long in H. amyemmarum sp. nov., is sufficient to distinguish between these two species.

Given the differences between these species outlined above, the establishment of a new species to accommodate the material from Arothron hispidus and A. nigropunctatus in Moreton Bay is fully justified.

Figures

FIGURE 3. Hatschekia amyemmarum sp. nov., female.A, habitus, dorsal view with arrows showing positions of legs 3 and 4; B, posterior extremity of trunk and genitoabdomen, ventral; C, rostrum, ventral view showing paired lateral rostral processes; D, antennule; E, antenna; F, antenna and parabasal papilla in situ, G, mandible; H, left maxillule, ventral; I, maxilla; J, interpodal bars and leg 1 in situ, ventral; K, leg 2. Scale bars: A, 300 μm, B–D, F, J, 100 μm, E, K, 50 μm, G, H, 25 μm