Caromiobenella hamatapex ( Grygier & Ohtsuka, 1995 )
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publication ID |
https://doi.org/10.11646/zootaxa.5576.1.1 |
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publication LSID |
lsid:zoobank.org:pub:7A65A968-EF09-4F1A-AF0D-470BDF2EE1DD |
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persistent identifier |
https://treatment.plazi.org/id/9D7DA92F-FFA9-8561-89AE-585292F9FECC |
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treatment provided by |
Plazi |
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scientific name |
Caromiobenella hamatapex ( Grygier & Ohtsuka, 1995 ) |
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Caromiobenella hamatapex ( Grygier & Ohtsuka, 1995) View in CoL
( Figs 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )
Material examined. Adult female, undissected, mounted on slide in glycerine, (ECO-CHZ-12525).
Type locality. Western Port Bay , Victoria, Australia (38°13.200’ S, 154°189.758’ E), coll. on 26 February 1985 .
Description of adult females. Body robust, wide.Total body length 1.34–1.37 mm in dorsal view.Cephalothorax almost 50% of total body length, with strongly convex ventral margin ( Fig. 1A View FIGURE 1 ); cephalothorax robust, bulletlike, with posterolateral expansions of incorporated first pediger reaching about half length of succeeding second pedigerous somite; preoral anterior surface strongly protuberant, with field of longitudinal integumental wrinkles and two pairs of nipple-like processes on ventral surface ( Figs. 1A View FIGURE 1 , 3C View FIGURE 3 ); dorsal surface with two pairs of integumental concave depressions on anterior half; depressions with adjacent field of integumental wrinkles ( Fig. 1B View FIGURE 1 ); with ventral oral papilla low, with adjacent pores, situated at about 45% of way back along ventral surface. First, second and third pedigerous somites with pit-setae sensu Grygier & Ohtsuka (1995). Eyes represented by two lateral cups and medial cup at anterior ¼ of cephalothorax, moderately developed, weakly pigmented ( Fig. 2B View FIGURE 2 ); medial eye cup positioned slightly anterior to lateral eye cups; lateral cups rounded, 60 µm in diameter, medial cup slightly smaller (45 µm in diameter) in dorsal view.
Urosome comprising fifth pedigerous somite, genital double-somite, free preanal somite, and anal somite holding pair of caudal rami. Fifth pedigerous somite longest, about 50% of urosome, carrying pair of fifth legs ventrally. Genital double-somite 22% length of urosome, incompletely divided, with dorsal and lateral suture ( Fig. 3D View FIGURE 3 ). Ovigerous spines arising from proximal ventral surface of somite ( Fig. 3B View FIGURE 3 ), reaching beyond distal end of caudal setae ( Fig. 1A View FIGURE 1 ), apical end of spines curved ( Fig. 2E View FIGURE 2 ). Succeeding preanal and anal somites subequally long (11% of urosome each) ( Fig. 2D View FIGURE 2 ). Anal somite carrying pair of caudal rami armed with 6 caudal setae (setae I–VI); setae I–V subequal in length and width; reduced seta VI slightly shorter than caudal ramus ( Fig. 1E View FIGURE 1 ).
Antennules ( Figs 2A, B View FIGURE 2 , 3A View FIGURE 3 ) 0.43–0.45 mm long, 5-segmented, proximal segment 1 separated from remaining antennulary segments 2–5, represented by long compound segment (65% of antennule length) ( Figs 2A View FIGURE 2 , 3A View FIGURE 3 ). Following antennule armature nomenclature by Grygier & Ohtsuka (1995), proximal 2d 2 seta setose; all distal bsetae unbranched and sparsely setulose; distal 5-seta and apical 6 2 -setal element modified, with small apical hook (arrowheads in Figs. 2A View FIGURE 2 , 3A View FIGURE 3 ).
Swimming legs 1–4 ( Fig. 1E–H View FIGURE 1 ) biramous, with three-segmented rami; endopods slightly smaller than exopods. Outer basipodal seta present in all legs, subequally long. Outer spines on first and third exopodal segments of legs 1–4 almost as long as bearing segment. Outer margin of outer apical exopodal seta of legs 1–4 with short, sparse setules and tight row of denticles. Apical spiniform seta on third exopodal segment spinulose along outer margin, inner margin setulose. Armature of swimming legs 1–4 as:
Leg 5 ( Fig. 1D View FIGURE 1 ) uniramous, symmetrical, with obliquely directed cylindrical lobe slightly shorter than proximal protopod; legs medially joined by short protopod. Exopodal ramus elongate, carrying two subequally long setae on distal half; one of them apical, the other subapical, both slightly plumose, subequally long and wide. Inner margin of exopodal lobe with unarmed rounded protuberance, likely a reduced endopodal lobe.
Remarks. The genus Caromiobenella was described based solely on males (Jeon et al. 2018) and consists of about 10 species. Some of the species were originally described as members of Monstrilla , e.g. C. hamatapex , one of the few species of the genus for which the female is known, as well as the widespread C. helgolandica ( Zavarzin & Suárez-Morales 2024) and the Brazilian C. brasiliensis (Dias & Suárez-Morales, 2000) (see Cruz Lopes et al. 2021). Caromiobenella hamatapex was originally described from Japan ( Grygier & Ohtsuka, 1995) and then recorded from South Korea ( Chang 2014). This record from Australian waters is the first documented report of this species from outside Japan or Korea.
As already recognized by other authors ( Sekiguchi 1982; Grygier & Ohtsuka 1995), C. hamatapex closely resembles C. helgolandica . The Australian specimen reported here has the distinctive characters of C. hamatapex as described by Grygier and Ohtsuka (1995) including: (1) bullet-shaped cephalothorax longer than wide (Grygier & Ohtsuka 1996, fig. 5A; Fig. 1B View FIGURE 1 ), (2) genital double-somite divided; an almost complete suture is observed in the Australian specimen ( Fig. 1C View FIGURE 1 ), (3) long ovigerous spines reaching well beyond caudal setae ( Grygier &Ohtsuka 1995, fig. 5A; Fig. 1A View FIGURE 1 ), 4) setal elements 5 and 6 2 apically hooked ( Grygier & Ohtsuka 1995, fig. 6; Figs. 2A View FIGURE 2 , 3A View FIGURE 3 ), 5) outer basipodal seta on swimming leg 3 as long as corresponding seta on other swimming legs ( Grygier & Ohtsuka 1995, fig. 7C; Fig. 1G View FIGURE 1 ); basipodal seta of leg 3 in most monstrillids is usually longer and broader than that on the other legs ( Suárez-Morales 2011).
The assumed worldwide distribution of C. helgolandica could be the result of inaccurate or incomplete local or regional records of distinct, closely related species ( Grygier & Ohtsuka 1995). This situation is not unusual among the Monstrilloida , with several nominal species with a presumed wide distribution comprising of different species with a restricted distribution, e.g. Cymbasoma rigidum (see Suárez-Morales & Mercado-Salas 2023), C. longispinosum Bourne, 1890 ( Suárez-Morales 2011, 2018; Suárez-Morales & Grygier 2021), and M. grandis Giesbrecht, 1891 ( Suárez-Morales et al. 2013). The actual diversity of these species, now including C. helgolandica , is still being reviewed ( Suárez-Morales & Grygier 2021; Suárez-Morales et al. 2020 a, b). In this account of the Australian Monstrilla , we included a comparative analysis of the two previous records of this genus in Australian waters viz., Dakin & Colefax (1940) and Nicholls (1944). In our opinion, the incomplete illustrations provided by these two authors clearly correspond to C. helgolandica , as discussed in the taxonomic remarks of these records. So, considering the possibility that C. helgolandica was for decades present in Australian coastal systems, it was important to compare our specimens of C. hamatapex with C. helgolandica to confirm that the females examined in our material are C. hamatapex .
The females of most species of Caromiobenella remain unknown (Jeon et al. 2018), while the male of C. hamatapex is undescribed. It is therefore possible that the male of C. hamatapex , or the females of other members of Caromiobenella , has already been described but with true identity undetermined. Similarly, based on morphological and distributional evidence, Suárez-Morales et al. (2008) designated the male of M. patagonica Suárez-Morales, Ramírez & Derisio, 2008 from the Beagle Channel as the male of C. helgolandica , something that only additional morphological and molecular data could confirm.
Our material of C. hamatapex from Australia is compared with females from other two geographic areas including the holotype specimen from Japan ( Grygier & Ohtsuka 1995) and a set of females from South Korean waters examined by Chang (2014). The Australian specimen diverges from the holotype from Japan and the Korean population in the shape of the cephalothorax; the anteriormost 1/3, particularly the preoral margin, is strongly protuberant in lateral view, thus differing from the other two Asian populations, in which this part of the cephalic surface is not strongly expanded ( Grygier & Ohtsuka 1995, fig. 5A; Chang 2014, fig. 3B). In the original description of C. hamatapex ( Grygier & Ohtsuka 1995, fig. 5B) the occurrence and distribution of numerous pit setae on the dorsal surface of the cephalothorax were described, while a similar pattern was reported in the Korean specimens ( Chang 2014, figs 3A, B). In the Australian specimen we were able to observe only a reduced number of pit setae.
Additionally, we observed three pairs of nipple-like processes on the perioral ventral surface in the Australian specimen, which is similar in the holotype from Japan ( Grygier & Ohtsuka 1995, fig. 5C), but not in the Korean specimens ( Chang 2014, fig. 3B). The crater-like integumental structures on the dorsal surface of the cephalothorax that are usual in members of the genus (see Jeon et al. 2018) were not described in the holotype from Japan, but similar processes were depicted by Chang (2014, fig. 3A) and observed in the Australian individual. The division of the genital double-somite is incomplete in both the Australian specimen ( Fig. 1C View FIGURE 1 ) and in the Japanese holotype ( Grygier & Ohtsuka 1995, fig. 5A), whereas the genital somite has a complete suture in the Korean specimens ( Chang 2014, fig. 3B).
The relative length of the antennule is different in the three populations. It represents 15% of total body length in the holotype from Japan, 19% in the Korean specimens ( Chang 2014), and 29% in the Australian female, thus exhibiting the longest antennule. The apically hooked antennulary setal elements 5 and 6 2, a distinctive character of C. hamatapex , is shared by the Japanese, Korean, and Australian populations ( Grygier & Ohtsuka 1995, fig. 5D; Chang 2014, fig. 4B). In the three groups, the setae of the “ b ”-group (sensu Grygier & Ohtsuka 1995) are unbranched.
In reference to the structure and armature of the fifth leg, the original description shows the presence of a short inner “aberrant” seta on the exopodal ramus ( Grygier & Ohtsuka 1995, fig. 7H) which was not observed by Chang (2014, fig. 4F) from the Korean specimens, and is absent in the Australian specimen. Additionally, the Australian specimen shows the narrowest rami of the fifth leg amongst the populations compared while the inner (endopodal) protuberance is poorly defined in both C. hamatapex and C. helgolandica . In the three populations compared, the outer basipodal seta of leg 3 is as long as that of the other swimming legs ( Grygier & Ohtsuka 1995, fig.7A–D; Chang 2014, fig.4C, D). The Japanese, Korean, and Australian populations lack the spinules on the outer margin of the fifth legs, reported only in the North American specimens of C. helgolandica (see Park, 1967).
The reduced caudal seta VI is 1.3 times as long as the caudal ramus in the Korean population, but 1.4 times as long as the ramus in the holotype from Japan. This seta is relatively shorter (0.9 times as long as the ramus) in the Australian specimen. The Australian specimen is the smallest of the three groups compared; the holotype female from Japan is more than 2 mm long (2.08 mm) in dorsal view ( Grygier & Ohtsuka 1995); the Korean specimens range between 1.3 and 1.6 mm, whereas the Australian female is 1.3 mm long in dorsal view. Thus, the Australian female specimen is easily assignable to C. hamatapex .
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Mykotektet, National Veterinary Institute |
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