Review of the subfamily Cleonardopsinae Lowry, 2006 (Crustacea: Amphipoda: Amathillopsidae) with description of a new genus and species from Japan

Abstract The amathillopsid subfamily Cleonardopsinae Lowry, 2006 is reviewed. The only species of the subfamily, Cleonardopsis carinata K.H. Barnard, 1916, should be regarded as a species-complex. A new genus and species of the subfamily, Carinocleonardopsis seisuiae gen. et sp. nov., is described from the Sea of Kumano, Japan as the second species of the subfamily Cleonardopsinae as well as the first record of the subfamily from the North Pacific. This new genus can be easily distinguished from Cleonardopsis by the presence of distinct large eyes and the dorsal carination on head, pereonites and pleonites.


Introduction
The monotypic amphipod subfamily Cleonardopsinae Lowry, 2006 has a complex taxonomic history. The only current genus of the subfamily, Cleonardopsis Barnard, 1916 was originally established in the family Eusiridae, however, it has been frequently placed in other families such as Amathillopsidae or Pleustidae by various authors (e.g. Pirlot, 1936;Barnard & Karaman, 1991a, 1991bColeman, 1998;Lowry, 2006).
The only species of the genus, Cleonardopsis carinata Barnard, 1916, also has a complex taxonomic history. This species was originally described from off South Africa (Barnard, 1916). Since then, several authors have reported the species from various localities (e.g. Schellenberg, 1926;Pirlot, 1934Pirlot, , 1936Stephensen, 1944). However, these reports sometimes lacked descriptions or illustrations, and moreover, sometimes showed different morphologies from each other. Lowry (2006) implied that the material of 'Cl. carinata' from different localities could be separate species.
During a survey of the deep-sea benthic fauna in the Sea of Kumano and off Tanabe Bay by TRV 'Seisui-maru', Mie University (research cruise no. 1803; Kimura et al., 2019), an amphipod species attributed to the subfamily Cleonardopsinae was collected. The present study provides a review of the subfamily Cleonardopsinae and compares our material with the description of Cleonardopsis carinata in previous studies. As a result, our specimens clearly revealed distinct characters from the genus Cleonardopsis, and therefore, we herein describe and illustrate the present species as Carinocleonardopsis seisuiae gen. et sp. nov.

Remarks
Several authors reported the occurrence of this species, however, only Barnard (1916) and Pirlot (1934) provided morphological description and illustration (Figures 2-4). Detailed taxonomic history of this species is reviewed below (see Review and discussion of the subfamily Cleonardopsinae).

Remarks
The present new genus is distinctively different from the genus Cleonardopsis in many morphological characters, especially in the (1) presence of large distinct eyes, (2) presence of a large dorsal carination on the head, pereonites and pleonites and (3) presence of a row of slender setae on the ventromedial margin of uropod 3 inner ramus.

Etymology
The generic name is derived from the combination of 'Carino-' after the large dorsal carination and 'Cleonardopsis' after the type genus of the subfamily Cleonardopsinae. The gender is feminine, as the generic name is ending in '-opsis' ( Kimura et al., 2019). Paratype: NSMT-Cr 29001, male(?), 7.3 mm, same data as holotype.

Description
Based on holotype, except for maxilla 1 inner plate being based on paratype (both left and right maxilla 1 inner plates unfortunately broken in holotype). BODY ( Figure 5A) with distinct carination on head, pereonites, pleonites, but not on urosomites, each carina located on mid-dorsal part of each segment. HEAD ( Figure 5A, B) about as long as pereonites 1-2 combined; carina on head rounded, larger than that on pereonite 1; eyes distinct, large, reniform, located along antennal sinus of antenna 1; lateral cephalic lobes small, not beyond apex of rostrum, rounded distally; antennal sinus of antenna 2 present, small, deep; rostrum short, curved downward, pointed apically, reaching proximal 0.1-0.2 of peduncular article 1 of antenna 1. Antenna 1 ( Figure 5C1) slender, setose ventrally; length ratio of peduncular articles 1-3 about 5:3:1; flagellum much longer than peduncle, consisting of numerous short articles, first flagellar article longer than others with callynophore, with endosomatic transverse-stripe pattern (?vestige of fused articles); accessory flagellum slender, consisting of 1 article, shorter than first flagellar  article, with several slender setae distally; calceoli present ( Figure 5C2). Antenna 2 ( Figure 5D) slender; peduncle setose, article 2 with produced gland cone; flagellum much longer than peduncle, consisting of numerous short articles; calceoli present.
Gnathopod 1 (Figure 7A1, 2) subchelate; coxa produced anteroventrally, anterior margin concave, proximal to distal margin rounded; basis, medial face with row of short setae, posterior margin with row of short robust (or sometimes slender) setae, posterodistal lobe weak having short robust setae; carpus broad, subequal or slightly broader than propodus, with strongly dense setae posteriorly and medially, posterior margin convex with subdistal excavation; propodus, medial face setose, palm convex with dense slender setae and robust setae; dactylus, posterior margin without teeth, with several short simple setae. Gnathopod 2 ( Figure 7B) similar to gnathopod 2 in shape, but larger than gnathopod 1; coxa produced anteroventrally, rounded ventrally to distally, ventral margin with 2 or 3 very small teeth, each tooth with short simple setae; carpus broader than that of gnathopod 1, posterodistal excavation on carpus deeper than that on gnathopod 1; propodus slightly more slender than that of gnathopod 1.

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Masafumi Kodama and Tomohiko Kawamura Pereopods 3 ( Figure 8A) simple, longer than gnathopod 2; coxa subrectangular, slightly tapering distally, rounded ventrally; basis with row of short robust setae posteriorly, anterior margin with dense long and short setae on distal half; merus expanded posterodistally; merus-propodus, weakly curved posteriorly, with several groups of robust setae anteriorly, posteriorly; dactylus falcate, distally acute, with several short setae anteriorly. Pereopods 4 ( Figure 8B) simple, slightly longer than pereopod 3; coxa enlarged, deeper than coxa 3, anterior margin slightly convex, posterior margin with triangular projection, posterior margin from posteroproximal corner to the projection excavated almost fitting anterior margin of coxa 5, posterior margin from the projection to distal end slightly concave, distal area subrounded, not acute or pointed; basis-dactylus similar to those of pereopod 3, but slightly longer than those of pereopod 3.

Colouration in life
Body generally reddish orange ( Figure 11A); appendages and urosomites partly whitish to colourless; eyes red. These colours on body faded in preservation over time; eyes changed to white ( Figure 11B, C).

Distribution
Known only from Sea of Kumano, Japan (Figure 1).

Etymology
The new species is named after TRV 'Seisui-maru'. The specific name is a noun in the genitive case.

Remarks
See the Remarks section of the genus and Review and discussion of the subfamily Cleonardopsinae.

Discussion
Review and discussion of the subfamily Cleonardopsinae The subfamily Cleonardospinae has a complex taxonomic history. The hitherto only genus of the subfamily, Cleonardopsis, was originally established in the family Eusiridae by Barnard (1916). Soon after that, Schellenberg (1926) reported Cl. carinata near the type locality, treating it in the family Eusiridae. Pirlot (1934) established the new family Amathillopsidae and the new genus Amathillopleustes, however, Pirlot (1936) subsequently synonymized Amathillopleustes with Cleonardopsis, and placed the genus in the family Amathillopsidae. Stephensen (1944) reported Cl. carinata from off Greenland, treating it as the family Amathillopsidae. After that, however, Barnard (1969), Griffiths (1975) and Ledoyer (1986) placed Cleonardopsis in the family Eusiridae. The biggest monograph of marine gammaridean amphipods by Barnard & Karaman (1991a, 1991b placed Cleonardopsis in the two families, Eusiridae and Pleustidae. Coleman (1998) again transferred Cleonardopsis to the family Amathillopsidae based on several characters such as dorsal carination and outline of gnathopod morphology. Lowry (2006) recently revised the family Amathillopsidae. He established a new subfamily Cleonardopsinae in the family Amathillopsidae and placed Cleonardopsis in this subfamily. The genus Cleonardopsis is, therefore, currently treated as a member of the Amathillopsidae. The genus is distinguished from the other amathillopsids by the ventrally rounded coxae 3 and 4 and the slightly cleft telson. The hitherto only species of the subfamily, Cl. carinata, also has a complex taxonomic history. This species was originally described from the Cape Peninsula area of South Africa (Barnard, 1916). However, in the original description, Barnard (1916) only illustrated the coxae 5-6, pleosomites 2-3 and telson ( Figure 2). Soon after the original description, Schellenberg (1926) reported Cl. carinata near the type locality, however, no illustrations or descriptions were provided. Pirlot (1934) described Amathillopleustes alticoxa from off the Moluccas in eastern Indonesia with detailed description and illustrations (Figures 3,  4), and subsequently synonymized A. alticoxa with Cl. carinata (see Pirlot, 1936). Stephensen (1944) reported Cl. carinata from 'Ingolf' station 27 off western coast of Greenland and 'Thor' station 78 in North Atlantic without any illustrations or descriptions. Lowry (2006) recently mentioned the synonymization of A. alticoxa with Cl. carinata made by Stephensen (it seems he possibly overlooked Pirlot (1936)) as 'risky business based on unsubstantiated evidence'. Lowry (2006) also mentioned that it is difficult to accept that the material reported by Stephensen (1944) from eastern Greenland is synonymous with either of these species. We basically agree with his opinion. Indeed, illustrations in Barnard's (1916) original description ( Figure 2) show a clearly different morphology from those of Pirlot's (1934) material ( Figure 4F, G, I2); the anterior lobe of coxae 5 and 6 of Barnard's material are more acutely falcate than that of Pirlot's material; the lateral margins of the telson are sinuous in Barnard's material (proximally convex and distally concave), whereas those in Pirlot's material are rather rounded (entirely convex). Therefore, we concluded that Cl. carinata should be regarded as a species-complex. More material, especially topotype material, would need to be examined in future studies to solve the Cl. carinata species-complex problem.
The recent IceAGE expeditions (Icelandic marine Animals: Genetics and Ecology) reported 46 specimens of Cleonardopsis around Iceland (Iceland Basin and Irminger Basin; Brix et al., 2018). Five individuals of these were subsequently DNA-barcoded . These specimens from Iceland were identified to the genus-level pending further investigation.
In this study, we described Carinocleonardopsis seisuiae gen. et sp. nov. This is the second genus and species of the subfamily as well as the first record of the subfamily from the North Pacific. We have placed the present new genus and species in the subfamily Cleonardopsinae based on the enlarged and ventrally rounded coxae 3 and 4, the short flagellar articles 2 and 3 of antenna 1 (both of them are distinctively shorter than the article 1), the subchelate gnathopods 1 and 2, and the cleft telson. This new genus is also somewhat similar in habitus with the family Pleustidae, especially the carinate pleustid genus Neopleustes. However, pleustids have an entire telson (or weakly notched telson in some species), whereas the present new genus has the distinctively cleft telson. Moreover, the outline of the gnathopods clearly shows amathillopsid characters (see Coleman, 1998): row of short spine-like setae on posterior margin of basis, carpal lobes, almond-shaped propodi, slender dactyli with microtrichs in inner curvature. Therefore, we concluded that this new genus should be placed in the amathillopsid subfamily Cleonardopsinae. In the Cleonardopsinae, the present new genus is also distinctively different from the genus Cleonardopsis in many characters such as (1) presence of large distinct eyes, (2) presence of a large dorsal carination on the head, pereonites and pleonites and (3) presence of a row of dense slender setae on the ventromedial margin of uropod 3 inner ramus. Museum, Sydney), for their careful reading, helpful comments on our manuscript, and recommendation for establishing the present new genus.