Hatschekia cutmorei, 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 : 37-41

Hatschekia cutmorei new species

Type Material

Holotype ♀ and 12 paratype ♀♀ from gills of Glaucosoma scapulare Ramsay, 1881 ( TC18800 ) collected at Station 33S (offshore), Moreton Bay on 30 July 2017. QM Reg. No. W55135 ( Holotype), W55136 ( 6 paratype ♀♀), NHMUK 2025.1424 - 1429 ( 6 paratype ♀♀).

Differential diagnosis

Female body encased within transparent cuticle separated from underlying tissues. Cephalothorax about 1.4 times wider than long; dorsal cephalothoracic shield supported by m-shaped subsurface chitinous frame. Trunk about 3.7 times longer than wide; lacking any posterior processes. Genitoabdomen wider than long, tapering posteriorly from broad base. Rostrum lacking lateral processes. Parabasal papilla comprising single rounded lobe. Mandible stylet-like with 5 distal teeth. Legs 1 and 2 each joined by simple interpodal bar; first exopodal segment of both legs with long outer spine extending well beyond tip of ramus; endopods distinctly 2-segmented with 2 apical setae on both legs plus additional inner seta on second segment of leg 1; proximal segment unarmed in both. Leg 3 represented by 2 setae on small papilla.

Description of female

Total body length excluding caudal rami ranging from 1.33 to 1.62 mm, with a mean of 1.46 mm (n = 10). Body ( Fig. 9A ) comprising anterior cephalothorax and long cylindrical trunk fused with small conical genitoabdomen posteriorly; entire body encased in transparent cuticle separated from underlying tissues by distinct gap.Cephalothorax indistinctly defined from trunk; about 1.4 times wider than long (203 x 288 μm) and about 16% as long as trunk: dorsal cephalothoracic shield supported by m-shaped subsurface chitinous frame with median and paired lateral longitudinal bars similar in length. Trunk about 3.7 times longer than wide (1.24 x 0.32 mm); with maximum width about in middle, with rounded posterior margin. Genitoabdomen wider than long ( Fig. 9B ) comprising fused genital and abdominal somites; bearing paired genital apertures dorsally. Caudal rami more-or-less laterally-directed, about 2.0 times longer than wide (19 x 9 μm); armed with 5 naked setae of different lengths; proximal lateral seta located about at middle of lateral margin. Mean number of eggs per egg sac = 16 (range 13 to 23, n = 11).

Rostrum lacking lateral processes ( Fig. 9C ). Antennule ( Fig. 9C ) short, indistinctly 5-segmented: segmental setation pattern 9, 5, 4, 1, 12 + ae; 2 unequal setae located on antero-dorsal surface of first segment. Antenna ( Fig. 9D ) 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. 9D ) rounded, located lateral to insertion of antenna. Mandible stylet-like, bearing 5 minute marginal teeth subapically ( Fig. 9E ). Maxillule bilobed ( Fig. 9F ): inner lobe bearing single short seta, outer lobe armed with 2 large setae. Maxilla ( Fig. 9G ) armed with single inner seta proximally on first segment; 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. 9H ); short, paired cuticular thickenings present between interpodal bars, not meeting in midline. Leg 1 ( Fig. 9I ) with fused sympod armed with outer and inner setae: exopod distinctly 2-segmented; proximal segment with long curved outer distal spine extending beyond tip of apical setae on ramus; distal segment bearing 2 long setal elements on apex and 1 slightly shorter seta distally on inner margin: endopod 2-segmented; proximal segment unarmed; distal segment armed with 2 long setae on apex and 1 reduced seta at mid inner margin. Leg ornamented with curved rows of minute spinules: 1 on sympod, 2 on exopodal segment 2, and 3 each on exopodal segment 1 and endopodal segment 2. Leg 2 ( Fig. 9J ) with fused sympod bearing outer seta; exopod 2-segmented; proximal segment armed with long curved outer spine; distal segment bearing 2 apical setae: endopod 2-segmented, typically observed lying across exopod; proximal segment unarmed; distal segment armed with 1 small and 1 minute seta on apex. Leg ornamented with curved rows of minute spinules: 2 each on sympod, both exopodal segments and endopodal segment 2, and 1 row on endopodal segment 1. Leg 3 located laterally on trunk at 36% of length ( Fig. 9A ), represented by 2 setae arising directly from small knob-like vestige on trunk surface ( Fig. 9K ). Leg 4 located laterally on trunk at 80% of length ( Fig. 9A ), represented by single seta originating directly on trunk surface ( Fig. 9L ).

Etymology: This species is named in honour of Scott Cutmore (University of Queensland) who collected this material and made it available for study.

Remarks

This species is characterized by the marked separation of the external cuticle covering the body and its underlying tissue. This tissue separation is apparent in the illustrations of numerous other Hatschekia species but is typically only visible around the margins of the trunk. The taxonomic significance of this character state has rarely been discussed and is difficult to assess partly because of the possibility that the fixation or preservation of the maerial could be a causative factor in the tissue separation. For example, in H. hanguyenvani the tissue separation is extremely marked over both the cephalothorax and the trunk and has resulted in the formation of “funnel-shaped tubes” within the cuticle on the lateral and dorsal surfaces of the trunk ( Kazachenko et al., 2017). However, this material was collected in 1960 and not studied until 2017 and it seems possible that 57 years in preservative may have caused shrinkage of the inner tissues away from the trunk cuticle forming these tubular structures. Similarly, in species such as H. jorgei Nuñes-Ruivo, 1954 and H. pontini Nuñes-Ruivo, 1954 , the tissue separation is particularly well developed around the trunk but the illustrations of both species ( Nuñes-Ruivo, 1954: figs. 7 & 8) show females with inflated cylindrical trunks and, again, it seems likely that the fixation or state of preservation is contributing to this separation effect in these species. However, in other species such as H. cernae , the tissue separation in freshly collected specimens is continuous over the trunk and cephalothorax, and the specimen is dorsoventrally flattened rather than having become inflated ( Fig. 5A ). Other illustrations of H. cernae (e.g. Uma Devi & Shyamasundari, 1980) show the same tissue separation and it is inferred here that this is not a fixation artefact in this species.

Hatschekia cutmorei sp. nov. shows marked tissue separation externally over the cephalothorax and the trunk, as in H. siganicola El-Rashidy & Boxshall, 2011 , and these two species have similar body proportions. They differ, however, in numerous characters relating to legs 1 and 2: in H. siganicola the legs are visible in dorsal view but in the new species the legs are smaller and not visible in dorsal view; the outer margin spine on the first exopodal segment of legs 1 and 2 does not reach the tip of the ramus in H. siganicola but is unusually long in the new species and extends well beyond the tip of the ramus, and indeed, beyond the tips of the apical setae as well in leg 1; finally, the endopod of leg 1 is armed with 3 setae and that of leg 2 with 2 apical setae in H. cutmorei sp. nov. whereas in H. siganicola there is a total of 5 setae on the endopod of each of these legs.

There are 40 species of Hatschekia which have a short cephalothorax relative to the length of the trunk, i.e. the cephalothorax is less than 25% of the length of the trunk (listed in Table 5). Included in this list are the extremely elongate species, such as H. gracilis and H. pagrosomi , in which the cephalothorax comprises less than 10% of the length of the trunk. However, the majority of species in Table 5 have a cephalothorax that is between 10% and 24% as long as the trunk. The new species, with its cephalothorax comprising 16% of the trunk length, falls about in the middle of this range.

The setation of the endopod of leg 2 of the species in Table 5 falls into three categories: 27 species carry 4 or more setae on the distal segment of the endopod of leg 2; two species ( H. amplicapa and H. becuni ) are armed with 3 vestigial setal elements on the tip of the endopod of leg 2; H. ovalis has only 1 seta; and the remaining 8 species carry only 2 apical setae on the distal endopodal segment, as found in H. cutmorei sp. nov.

Detailed comparisons are presented here to distinguish the new species from these eight congeners: H. branchiostegi , H. caudata , H. crenulata , H. cylindrica , H. linearis , H. nahaensis , H. nemipteri , and H. pseudolabri . Only one of these species, H. nemipteri , retains the inner seta on the first endopodal segment of leg 2 ( Izawa, 2016a). All the other species, including H. cutmorei sp. nov., lack this inner seta. Hatschekia nemipteri also differs in the extent of the subsurface chitinous frame which is restricted to the anterior half of the dorsal cephalothoracic shield in the new species but extends well into the posterior half of the shield in H. nemipteri . There are numerous additional differences including the lengths of the outer spines on the first exopodal segments of legs 1 and 2.

The configuration of the rami of legs 1 and 2 of H. cutmorei sp. nov. is unusual for the genus. The first exopodal segment of leg 1 carries an elongate outer spine which reaches well beyond the tips of the apical setal elements on the second exopodal segment ( Fig. 9I ). Similarly, the outer spine on the first exopodal segment of leg 2 is robust and reaches well beyond the distal margin of the ramus ( Fig. 9J ). In addition, the endopod of leg 2 of H. cutmorei sp. nov. is 2-segmented and its 2 apical setae are markedly unequal in length. This combination of characters serves to distinguish H. cutmorei sp. nov. from H. crenulata , H. cylindrica , H. linearis , and H. nahaensis , all of which have short spines on the first exopodal segments of legs 1 and 2 that do not reach the tip of the ramus and have subsimilar apical setae on the endopod of leg 2. Hatschekia crenulata and H. nahaensis are both also distinguishable by having a strongly crenulate frontal margin of the cephalothorax ( Kabata, 1991; Yamaguti, 1953). According to Izawa’s (2016b) redescription of H. cylindrica , this species differs from H. cutmorei sp. nov. in having a longer median bar on the subsurface chitinous frame which reaches well into the posterior half of the cephalothoracic shield. It also differs in leg 3 which is represented by a single seta in H. cylindrica , compared with 2 setae in H. cutmorei sp. nov.

Hatschekia branchiostegi was redescribed in detail by Izawa (2018) based on material collected from Branchiostegus japonicus (Houttuyn, 1782) caught in Japanese waters. The subsurface chitinous frame is restricted to the anterior half of the dorsal cephalothoracic shield and comprises a simple median bar and paired lateral bars which are formed at their tips, as in H. cutmorei sp. nov. However, these species differ in the shape of the cephalothorax which is well defined posteriorly and is about 1.5 times wider than long in H. branchiostegi compared with ill-defined posteriorly and about 1.4 times wider.

Pillai (1985) established H. caudata to accommodate material from a Lutjanus species collected off Kerala, India. The trunk of H. caudata narrows markedly about at the level of leg 4 to produce a “tail-like” posterior region. In contrast, there is only a slight and very gradual narrowing of the trunk posteriorly in the new species. The endopod of leg 2 of H. caudata appears unsegmented and bears 2 long apical setae whereas the new species has a 2-segmented endopod bearing 1 reduced seta plus a vestigial seta apically.

In H. pseudolabri the cephalothorax is longer than wide and the subsurface chitinous frame comprises short lateral bars reaching to about the mid-level of the dorsal cephalothoracic shield plus a long median bar with a bifid tip that nearly reaches the rear margin of the shield (Yamaguti, 1953). This differs markedly from H. cutmorei sp. nov. in which the cephalothorax is wider than long and the chitinous frame is restricted to the anterior half of the shield.

The above comparisons demonstrate that there are sufficient distinguishing characters to justify the establishment of a new species to accommodate the material from Glaucosoma scapulare .

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