Actaeodes ogasawaraensis, Tune & Zachrison & Pines & Zheng & Hayden, 2024

Actaeodes ogasawaraensis View in CoL sp. nov. [New Jn: Ogasawara-awatsubu-ougigani]

( Figs. 3–4 View Fig View Fig ) urn:lsid:zoobank.org:act:907AB301-A12D-4304-A7EE-130E7C392D21

? Actaeodes quadriareolata Takeda and Miyake, 1968 : Takeda & Kurata, 1977a, p. 108.

? Paractaea quadriareolata (Takeda and Miyake, 1968) View in CoL : Takeda & Kurata, 1977b, p. 143.

Material examined. Haha-jima Is. —Diving site Blue Ribbon (26°34′03″N, 142°12′48″E), Imoto-jima I., 12–14 m, 1 ♂ (Holotype, NSMTCr 31668; cb 7.3×cl 4.7 mm), 14-VII-2016, H. Komatsu leg.; Diving site Shihon-iwa South (26°38′49″N, 142°08′36″E), Haha-jima I., 1 ♂ (Paratype, NSMT-Cr 31669; cb 4.9×cl 3.8 mm), 6-VII-2015, H. Komatsu leg.

Diagnosis. Small species, generally close to Actaeodes consobrinus (A. Milne-Edwards, 1873) . Carapace evenly convex, with deeply sculptured dorsal surface; each protogastric region (2M) subdivided into four subequal parts; each anterolateral margin with four subequal, obtuse, equidistant teeth behind small external orbital angle; posterior three teeth arranged almost longitudinally; carapace posterolateral margin shorter than anterolateral margin, strongly convergent toward lateral end of carapace posterior margin. Chelipeds short, with chelae and carpi provided with some nodules; dark color of fingers extended back onto most part of outer surface of palm except for place close to basal part of movable finger. Ambulatory legs short; anterior margins of meri and carpi narrowly ridged throughout lengths, regularly serrated with minute sharp granules; each carpus and propodus inflated dorsally, dorsal surface roughly sculptured with longitudinal furrows and depressions.

Description of holotype male. Carapace ( Fig. 3A–C View Fig ) evenly convex in both directions, distinctly divided into regions by wide furrows, without hairs; regions raised, more or less nodular, thickly covered with small granules ( Fig. 3B–C View Fig ); interregional furrows with sparse indistinct granules of variable sizes; frontal regions (1F and 2F) fused, low, but distinct; epigastric region (1M) of good size, widely separated from 2F, protogastric region (2M) and supraorbital margin; each 2M subdivided into four nodular subequal parts by longitudinal and transverse furrows; metagastric region (3M) indistinctly subdivided into three parts, with short median anterior extension attaining median part of 2M; main part of 3M as large as 2M, with a deep furrow as boundary from inner branchial region (6L); urogastric region (4M) not formed, with a deep transverse furrow between 3M and cardiac region (1P); 1P prominent, with anterior margin rather raised, ridged; intestinal region (2P) marked with a pair of weak ridges along carapace posterior margin; hepatic region (1L) flattened, without granules or nodules; branchial regions (2–4L) nodular, subequal to 2M nodules; 4L subequal to 3L; 5L prominent, as wide as 3M, with two small nodules along furrow between 5L and 4L, shallowly separated from 6L.

Front ( Fig. 3B–C View Fig ) about one third as wide as carapace, divided into two by a median distinct notch; each lobe strongly convex along inner half, deeply concave along outer half both in dorsal and frontal views; lateral end of each lobe directed downward, not directly continuous with supraorbital angle. Orbit ( Fig. 3B–C View Fig ) orbicular, deep, supraorbital margin weakly raised, with shallow marginal depression; two small interruptions at median part, external orbital tooth not prominent, forming only a part of supraorbital margin; infraorbital margin concave for most of length, with both ends obtusely angulated.

Anterolateral margin ( Fig. 3A–B View Fig ) 1.5 times as long as posterolateral margin, prominent in dorsal view, but not strongly arched as a whole, being cut into four stout, subequal, equidistant teeth; first tooth obtuse at tip, nodular, distinctly isolated from external orbital angle; posterior three teeth more or less nodular dorsally, obtusely angulated at tip, isolated from carapace dorsal regions by submarginal furrow, being arranged almost longitudinally. Posterolateral margin ( Fig. 3B View Fig ) nearly straight, with posterior dorsal surface shallowly concave.

Third maxilliped ( Fig. 4A View Fig ) smooth, wide, with breadth of exopod about half of ischium; merus weakly angulated at antero-external angle.

Both chelipeds ( Fig. 3A–D View Fig ) equal in size and shape, comparatively short; merus short, small, almost disguised under carapace; carpus prominent, with several obtuse tubercles, but carpus margin not developed outward; inner angle not formed. Palm ( Fig. 3D View Fig ) with three large, obtuse nodules on upper surface, with small granules on outer lower surface; small granules roughly arranged in some longitudinal rows extending onto immovable finger; dark color of movable finger extended onto more than half of outer surface of palm, except for base of movable finger; both fingers obtusely toothed throughout lengths on cutting edges, leaving no space between them.

Ambulatory legs ( Figs. 3A–B View Fig , 4B View Fig ) short, stout, meri of second and third pairs in situ attaining just at level of last tooth of carapace anterolateral margin; anterior margins of meri and carpi narrowly ridged throughout lengths, regularly serrated with minute sharp granules; anterior margins of propodi and dactyli not distinctly ridged, but similarly serrated; carpi and propodi weakly inflated dorsally, dorsal surface roughly sculptured with longitudinal furrows and depressions; dorsal surfaces of carpus and propodus of first pair with longitudinal thick ridges and nodules.

Pleon ( Fig. 4C View Fig ) seven-segmented, not markedly narrow, with a longitudinal shallow furrow along each lateral margin; surfaces weakly roughened, but not granulated; third to fifth somites fused, with traces of sutures. G1 ( Fig. 4D View Fig ) curved at subdistal part, with a bundle of several long hairs, similar to those of most of actaeinae relatives.

Notes on paratype male. The paratype (cb 4.9 mm) ( Fig. 3E–F View Fig ) is smaller than the holotype (cb 7.3 mm), and the right cheliped is missing. However, the outline of the carapace, the sculpture of the carapace dorsal surface, the development of the frontal margin, four anterolateral teeth of the carapace, and the pleon are close to those of the holotype. The tubercles of the carpus and palm of the left cheliped are similar to those of the holotype, but not so prominent as in the holotype.

The pterygostomial regions and thoracic sternum are provided with longish club-shaped hairs. The G1 is not so strongly curved at the subterminal part probably due to the smaller size of the specimen, though it seems to be fully developed.

Remarks. The new species is most characteristic in the subfamily Actaeinae in having each protogastric region (2M) subdivided into four; this character is only known in Paractaeopsis quadriareolatus (Takeda and Miyake, 1968) , the type species of the genus Paractaeopsis established by Serène (1984) together with Actaea tumulosa Odhner, 1925 . In P. quadriareolatus , the carapace seems to be narrowly elliptical in outline, with the regularly convex anterolateral margins, the carapace dorsal surface is strongly convex in both directions, and all of the regions including the subdivided 2M are distinctly nodular, as seen in the photographs ( Takeda and Miyake, 1968a, pl. 8 fig. A; Peyrot-Clausade and Serène, 1976, pl. 3 fig. B; Serène, 1984, pl. 17 fig. E).

The carapace, chelipeds and ambulatory legs of the new species are generally similar to Actaeodes consobrinus (A. Milne-Edwards, 1873) , which is somewhat doubtful in its affiliation to the genus Actaeodes , but in addition to the difference in the contour of the carapace and the shape of 2M mentioned above, the other differences between A. consobrinus and new species are remarked in the following lines (cf. Fig. 1F View Fig for A. consobrinus , and Fig. 3 View Fig for the new species).

1) In the new species, the carapace anterolateral margin is strongly developed, but not regularly convex, and longer than the posterolateral margin, with its posterior two-thirds from the first to fourth teeth being almost longitudinal as a whole.

2) In the new species, the carapace posterolateral margin is nearly straight, but weakly concave dorsally, and shorter than the anterolateral margin.

3) In the new species, the inner half of each frontal lobe is developed and strongly convex forward in dorsal view.

4) In the new species, the first anterolateral lobe is similar to the following three teeth, with its anterior margin deeply isolated from the external orbital angle. In A. consobrinus , the first lobe is almost obsolete, and the carapace anterolateral margin is weakly directed toward the infraorbital margin.

5) The color in life is distinctly different from each other ( Fig. 3A, E View Fig in the new species vs. Fig. 1F View Fig in A. consobrinus ). It may be remarkable that in both of the color photographs of the holotype and paratype of the new species ( Fig. 3A, E View Fig ), each 2M is seen to be longitudinally subdivided into two, not four, but in the same specimens preserved in 70 % ethyl alcohol, the 2M is shown to be clearly subdivided into four, not two. This difference may be the results of lighting to take the photographs of the fresh specimens in water.

The carapace contour of the new species, with strongly arched and long anterolateral margin armed with four teeth, is somewhat similar to some Euxanthus species such as E. herdmani Laurie, 1906 ( Laurie, 1906, pl. 1 fig. 9; Serène, 1984, pl. 11 fig. A; Mendoza and Ng, 2010, fig. 1D; Maenosono, 2021c, figs. 1D, 2C) and Euxanthus sp. ( Iwasa-Arai et al., 2015, figs. 1C, 2A), but the small size, the chelipeds without outward projection of the carpus, the short and stout ambulatory legs and the G1 having a tuft of subterminal long hairs show the systematic position in the subfamily Actaeinae rather than the Euxanthinae .

Takeda and Kurata (1977a) recorded Actaeodes quadriareolata from the vicinity of new volcanic island, Nishino-shima-shinto, based on the anterior half of the carapace, both chelipeds and two ambulatory legs found in stomach of the slender emperor [Jn: Hoso-fuefuki], Lethrinus variegatus Valenciennes , and also Takeda and Kurata (1977b) recorded Paractaea quadriareolata from Minami-fukurozawa, Chichi-jima Island, with the carapace found in stomach of the striped large-eye bream [Jn: Nokogiridai], Gnathodentex aureolineatus (Lacèpedé) . However, unfortunately, it is impossible, at present, to confirm the identification with Paractaeopsis quadriareolatus , as the voucher specimens obtained from stomach contents of fishes were not kept in the laboratory.