Pilumnopeus kimorum sp. nov.

urn:lsid:zoobank.org:act: BEB8C18C-8E85-4CDA-9D55-47035CA1A31E

(Figures 3, 4, 6E–F, 7E–I)

Pilumnopeus granulatus — Takeda & Miyake 1969: 127 (part), fig. 12c–f.— Garth & Kim 1983: 704.— Ko & Takeda 2000: 34.— Marumura & Kosaka 2003: 60.— Ko & Lee 2012: 26, fig. 7A, B.

Pilumnopeus serratifrons granulatus — Sakai 1976: 501.

Pilumnopeus granulata — Ko 1997: 31, figs. 1–5.

(not Pilumnopeus serratifrons granulatus Balss, 1933).

Material examined. Holotype: male (15.0 mm × 11.2 mm) (ZRC 2023.0379), Korea, coll. S.Y. Hong, ca. 2002 . Paratypes: 1 male (8.3 mm × 5.8 mm), 1 ovigerous female (16.6 mm × 11.6 mm) (ZRC 2024.0692), same data as holotype; 1 male (14.9 mm × 10.8 mm) (Ben.Ar.Cr. 2412.01), Gimnyeong, Jeju-si, Jejudo Island, Korea, coll. S.- k. Lee, 27 October 2005 ; 1 male (10.2 mm × 8.3 mm) (Ben.Ar.Cr. 2412.02), Hamo-ri, Daejung-eup, Seogwipo-si, Jejudo Island, Korea, 33°12’39.5″N 126°15’37.4″E, coll. S.H. Lee, 19 June 2012 ; 1 male (12.8 mm × 9.0 mm) (Ben. Ar.Cr. 2412.03), Seodo-ri, Samsan-myeon, Yeosu-si, Jeollanam-do, Korea, 34°02’48.3″N 127°17’37.7″E, coll. S.H. Lee, 23 July 2024 ; 1 ovigerous female (11.2 mm × 9.3 mm) (Ben.Ar.Cr. 2412.04), Hamo-ri, Daejung-eup, Seogwipo-si, Jejudo Island, Korea, 33°12’39.5″N 126°15’37.4″E, coll. S.H. Lee, 12 June 2014 ; 1 male (14.6 mm × 10.2 mm) (NIBR IV0000245898), Jocheon-eup, Jeju-si, Jejudo Island, Korea, 33°30’51″N 126°58’0″E, coll. H.S. Ko, 15 June 2011 ; 2 females (12.3 mm × 9.0 mm, 12.8 mm × 9.3 mm) (MABIK CR00241039), Hagosudong Beach, Yeonpyeongri, Udo-myeon, Jeju-si, Jejudo Island, Korea, 33°33’54.3″N 126°57’42.6″E, coll. S.-k. Lee, 31 May 2007 .

Comparative material examined. Pilumnopeus serratifrons (Kinahan, 1856): 1 male (19.9 mm × 14.8 mm), 1 female (14.0 mm × 10.1 mm) (ZRC 1995.0972), Cudgera Creek, Hastings Point, New South Wales, Australia, coll. P.J.F. Davie, 15 May 1988 ; 1 female (7.4 mm × 5.6 mm) (ZRC 2023.0378), near mouth of Brisbane River, Brisbane, Queensland, Australia, coll. Zoology Department , Queensland University; 1 female (13.0 mm × 9.6 mm) (ZRC 2008.0114), near lighthouse, low tide, under boulders, Lowly Point, Whyalla, South Australia, coll. S. T. Ahyong, 9 May 2005 . Pilumnopeus marginatus (Stimpson, 1858): 1 female (15.3 mm × 11.7 mm) (ZRC 2023.0380), Ohura River, Okinawa Island, Ryukyus, Japan, coll. M. Irei, 16 November 1990 ; 1 female (15.4 mm × 11.7 mm) (ZRC 2013.0160), Naha City, Okinawa Island, Ryukyus, Japan, coll. T. Maenosono, 9 April 2007 .

Diagnosis. Dorsal surface of carapace relatively smooth, regions well demarcated, with only scattered setae, with low, sometimes flattened granules mainly on the gastric regions and the mesobranchial crest; posterior half of carapace smooth (Fig. 3A, B); frontal margin lined with rounded granules (Fig. 3D); posterior margin of epistome relatively less wide with median lobe acutely triangular, protruding slightly obliquely outwards (Fig. 3E); outer surfaces of male cheliped with numerous low to flattened granules and denser setae, especially on ventral and proximal parts (Fig. 3G); male pleon relatively wide, triangular, somite 6 distinctly wider than long, trapezoidal (Fig. 6F); overall G1 relatively shorter, stouter (Fig. 7E); G1 distal part gently curved with the tip not reaching main stem; distal inner margin with 22–25 straight or gently curved spines (Figs. 4H, I, 7E–H).

Variation. The dorsal surface of the new species is generally quite smooth with the low granules concentrated on the gastric and mesobranchial cristae (Fig. 3A, B), although in some specimens, these granules are even lower and fewer (Fig. 4A). In the holotype and most of the paratypes, the frontal lobes protrude anteriorly and are gently convex (Figs. 3D, 4C, D, J), but in one specimen (Ben.Ar.Cr.2412), the front is relatively lower, appearing more flattened (Fig. 4A, E). The anteroexternal angle of the merus of the third maxilliped of the holotype male is relatively more rounded (Fig. 3C) whereas it is gently but visibly auriculiform in P. serratifrons (Fig. 1C). This feature, however, is not always reliable as one paratype male of P. kimorum sp. nov. is slightly expanded (Fig. 4B). The granules on the cheliped surface are always distinct, varying between relatively lower (Fig. 3G) to strong (Fig. 4F, G). In addition to the loss of setae through normal wear and tear in the live animal, the variation in setation may be due to how thoroughly the specimen was originally cleaned. As has been noted for some pilumnids (see Ng et al. 2024: 326), the setae on the carapace can easily be removed if they are brushed too strongly, with the short and plumose setae easily detached. In P. kimorum sp. nov., freshly obtained specimens have a relatively thicker coat of setae on their chelipeds and numerous tufts on the carapace (Fig. 4C, D, J), but when brushed, they appear more glabrous (Figs. 3A, B, 4A, E). For the G1, the number of strong spines on the inner distal margin varies slightly; there are 22 setae on the holotype (Fig. 7E–H), but the paratypes have 23–25 such spines (Fig. 4H, I).

Etymology. The species honours the late Hoon Soo Kim (1923–2015), the father of carcinology in Korea, and his son, Won Kim, who took the science to new heights. The first author had the privilege to be friends with both men, and the second author was a student of Won Kim.

Remarks. Pilumnopeus kimorum sp. nov. superficially resembles P. serratifrons, but can easily be distinguished by its distinctly smoother and less granulated dorsal carapace surface (Fig. 3A, B) (versus rougher, with more granules and uneven surface in P. serratifrons; Fig. 1A, B); the frontal margin is lined with rounded granules (Fig. 3D) (versus with sharp granules in P. serratifrons; Fig. 1D); the posterior margin of the epistome is less wide with the median lobe acutely triangular and protruding out (Fig. 3E) (versus posterior epistomal margin distinctly wider with a lower obtusely triangular median lobe in P. serratifrons; Fig. 1E); the outer surfaces of the cheliped are covered with numerous low to flattened granules and denser setae on the ventral and proximal parts (Fig. 3G) (versus with some low granules and may be uneven, but is generally smooth and glabrous in P. serratifrons; Fig. 1G); the male pleon is proportionately wider, with somite 6 distinctly wider than long and trapezoidal (Fig. 6F) (versus pleon narrower, with somite 6 as long as broad and quadrate in P. serratifrons; Fig. 6B); and the distal part of the G1 is less strongly curved with the tip not reaching the main stem (Fig. 7E–H) (versus tip longer and overlaps the main G1 stem in P. serratifrons; cf. Davie 1989: fig. 5E, F).

The strong granulation of the dorsal carapace surfaces of P. granulatus and P. marginatus (Figs. 2A, B, 4A, B) easily distinguish them from the smooth condition in P. kimorum sp. nov. (Fig. 3A, B). Although the outer surfaces of the chelipeds of P. kimorum sp. nov. are also granulated, the granules present are relatively more flattened and less dense than in P. granulatus and P. marginatus (Fig. 3G versus Figs. 2G, 4F).

The relatively smooth carapace of P. kimorum sp. nov. is similar to the condition seen in P. pearsei (Rathbun, 1932), a species also known only from Japan and Korea (Patel et al. 2024). Pilumnopeus pearsei, however, is a relatively smaller species with the carapace width only reaching 10.5 mm (Patel et al. 2024: 386) (versus carapace width reaches 16.6 mm in P. kimorum sp. nov.); the dorsal carapace surface is distinctly more convex with the anterolateral teeth more acutely triangular (Patel et al. 2024: fig. 6A–D) (versus surface less convex with the anterolateral teeth distinctly wider in P. kimorum sp. nov.; Fig. 3A, B); the outer surfaces of the chelipeds are completely smooth (Patel et al. 2024: fig. 6A–E) (versus surfaces granulated with setae in P. kimorum sp. nov.; Fig. 3G); and the distal part of the G1 is less strongly bent (Patel et al. 2024: fig. 7A–C) (versus distal part distinctly recurved in P. kimorum sp. nov.; Fig. 7E–H).

The G 1 in the type of P. kimorum sp. nov. appears more strongly recurved (Fig. 7E–H) than that figured in Takeda & Miyake (1969: fig. 12c–f) but this may be a consequence of size (although the size of their male examined was not indicated in their text). The length of the distal part of the G1, however, is known to vary to some degree in several pilumnid species (see Ng et al. 2018).

The description of the species by Takeda & Miyake (1969) of “ P. granulatus ” from Japan indicates that it is probably the same species as what is here regarded as P. kimorum sp. nov. That being said, Takeda & Miyake (1969: 128–129) did have one female specimen from Fiji and they noted that it “is the largest of the specimens examined, and its dorsal surface is more strongly sculptured and granulated than in the specimens from the Ryukyu Islands.” They, however, did not see other differences and regarded the stronger granulation on this specimen only as variation. In any case, all the published records of “ P. granulatus ” from Korea and Japan should be re-examined to confirm if they are also P. kimorum sp. nov.; it is certainly possible that P. granulatus s. str. may also be present in Japan. It is noteworthy that P. kimorum sp. nov. has not been reported elsewhere around the Yellow Sea or Sea of Japan. The record by Garth & Kim (1983) of “ P. granulatus ” is interesting as the specimens (2 males: 6.1 mm × 4.5 mm, 8.0 mm × 5.9 mm; 1 ovigerous female: 6.2 mm × 4.5 mm) were collected from Negros Island in the Philippines, and their record follows the prognosis by Takeda & Miyake (1969). Their record is provisionally placed with P. kimorum sp. nov. and will need to be re-examined. If confirmed, it would be the most southerly record of the species.