Macrophthalmus (Macrophthalmus) microfylacas, Nagai & Watanabe & Naruse, 2006

Nagai, Takashi, Watanabe, Tetsuya & Naruse, Tohru, 2006, Macrophthalmus (Macrophthalmus) microfylacas, a new species of sentinel crab (Decapoda: Brachyura: Ocypodidae) from western Japan, Zootaxa 1171 (1), pp. 1-16 : 2-13

Macrophthalmus (Macrophthalmus) microfylacas sp. nov.

( Figs. 1–3 , 4a, b )

Macrophthalmus telescopicus — Sakai, 1939: 623 (part?), pl. 73, fig. 1.

Macrophthalmus (Macrophthalmus) verreauxi — Sakai, 1976: 610 (part).

Macrophthalmus telescopicus — Marumura & Kosaka, 2003: 70.

Material examined

Male holotype (6.5/ 10.4 mm), RUMF­ZC­257, Awase, Nakagusuku Bay , Okinawa I., Ryukyus (26°18.145' N, 127°50.653' E), coll. H. Oku & T. Masumoto, 21 Aug. 2005 .

Paratypes. Three females (5.7/9.7–6.2/ 10.6 mm), 1 ovig. female (5.8/ 10.1 mm), RUMF­ZC­258, same data as holotype ; 1 male (6.0/ 10.2 mm), 1 ovig. female (5.7/ 9.6 mm), OMNH Ar 7116, same data as holotype ; 3 males (5.5/9.4–4.4/7.0 mm), 2 females (2.7/4.3, 2.9/ 4.7 mm), 3 ovig. females (4.7/7.7–5.8/ 9.8 mm), ZRC 2005.0147 , Awase, Nakagusuku Bay, Okinawa I., Ryukyus , coll. H. Oku, T. Inoue & T. Higuchi, 25, 26 Aug. 2005 ; 1 female (3.1/ 4.9 mm), RUMF­ZC­259, north of Sea Road, Kin Bay, Okinawa I., Ryukyus (26°20.313' N, 127°55.817' E), coll. M. Kubo, K. Nonaka, T. Nagai & T. Naruse, 28 Sep. 2005 ; 5 males (2.4/3.8–3.9/ 6.4 mm), 6 females (2.3/3.3–3.5/ 5.6 mm), 3 ovig. females (4.1/6.6–4.8/ 8.8 mm), RUMF­ZC­260, western breakwater, off Awase, Nakagusuku Bay, Okinawa I., Ryukyus (26°18.691' N, 127°51.755' E), coll. K. Nonaka, M. Kubo, T. Nagai & T. Naruse, 28 Sep. 2005 ; 1 female (3.5/ 5.6 mm), RUMF­ZC­261, Atsuta, Nakagusuku Bay, Okinawa I., Ryukyus (26°16.620' N, 127°49.217' E), coll. K. Nonaka, M. Kubo, T. Nagai & T. Naruse, 29 Sep. 2005 ; 1 male (2.5/ 3.7 mm), 1 female (3.0/ 4.8 mm), RUMF­ZC­262, Hamaya, Nakagusuku Bay, Okinawa I., Ryukyus (26°19.253' N, 127°52.740' E), coll. K. Nonaka, M. Kubo, T. Nagai & T. Naruse, 29 Sep. 2005 ; 2 females (3.1/4.8, 3.3/ 5.2 mm), RUMF­ZC­263, northwest of White Beach, Nakagusuku Bay, Okinawa I., Ryukyus (26°18.567' N, 127°53.299' E), coll. K. Nonaka, M. Kubo, T. Nagai & T. Naruse, 29 Sep. 2005 ; 1 male (3.3/ 4.7 mm), 1 female (4.2/ 6.9 mm), RUMF­ZC­264, Nakagusuku Bay , Okinawa I., Ryukyus, coll. Tokyo Kyuei Co. Ltd .; 1 male (2.6/ 3.8 mm), RUMF­ZC­265, Nakagusuku Bay , Okinawa I., Ryukyus, coll. Tokyo Kyuei Co. Ltd .; 1 male (6.2/ 10.5 mm), 4 ovig. females (5.7/9.3–6.0/ 10.4 mm), OMNH Ar 7117, Satoura, Oniki , Ushibuka City, Kumamoto Prefecture, Kyushu, coll. T. Watanabe, 20 Jun. 2004 ; 2 males (3.4/5.4, 5.4/ 8.9 mm), 1 ovig. female (5.4/ 8.9 mm), RUMF­ZC­266, Satoura, Oniki, Ushibuka City , Kumamoto Prefecture, Kyushu, coll. T. Watanabe, 7 Apr. 2004 ; 1 male (3.9/ 6.3 mm), 3 females (5.7/9.6–6.3/ 10.9 mm), 1 ovig. female (5.8/ 9.8 mm), ZRC 2005.0148 , Satoura, Oniki, Ushibuka City , Kumamoto Prefecture, Kyushu, coll. T. Watanabe, 31. Aug. 2004 , 2 ovig. females (5.1/8.6, 5.7/ 9.8 mm), RUMF­ZC­267, Satoura, Oniki, Ushibuka City , Kumamoto Prefecture, Kyushu , coll. T. Watanabe, 24. Jul. 2005 ; 1 female (4.8/ 7.8 mm), RUMF­ZC­268, Matsushima Watering Place, Kamiamakusa City, Kumamoto Prefecture, Kyushu , coll. T. Watanabe, 20 Jul. 2005 ; 1 female (6.2/ 10.7 mm), WMNH­Na­Cr 1205, Takahama , Ehime Prefecture, Seto Inland Sea coast of Shikoku I., 21 July 1990 ; 2 females (5.8/9.7, 6.8/ 11.6 mm), WMNH­Na­Cr 1205, Kamiura, Kushimoto, Kii Peninsula , Pacific Ocean coast of Kii Peninsula, 10 m, Dec. 1979 .

Comparative material: Macrophthalmus telescopicus ( Owen, 1839) : 1 male (11.7/ 18.5 mm), 2 females (7.8/12.3, 11.1/ 18.2 mm), RUMF­ZC­269, Awase, Nakagusuku Bay , Okinawa I. (26°18.145' N, 127°50.653' E), coll. H. Oku & T. Masumoto, 21 Aug. 2005 ; 1 female (11.2/ 17.8 mm), RUMF­ZC­270, Awase, Nakagusuku Bay, Okinawa I., coll. H. Oku, T. Inoue & T. Higuchi , 25, 26 Aug. 2005 ; 2 males (10.3/15.4, 11.1/ 16.5 mm), 1 female (12.0/ 18.5 mm), 1 ovig. female (12.1/ 19.5 mm), ZRC 2005.0149 , east of Cape Oh­ Misaki, Nakagusuku Bay , Okinawa I. (26°18.104' N, 127°50.605' E), coll. M. Kubo & K. Nonaka, 24 Aug. 2005 ; 1 female (11.1/ 17.3 mm), RUMF­ZC­271, north of Sea Road, Kin Bay , Okinawa I. (26°20.313' N, 127°55.817' E), coll. M. Kubo, K. Nonaka, T. Nagai & T. Naruse, 28 Sep. 2005 ; 1 male (9.6/ 14.5 mm), RUMF­ZC­272, Hamaya, Nakagusuku Bay , Okinawa I. (26°19.253' N, 127°52.740' E), coll. T. Nagai, M. Kubo, K. Nonaka & T. Naruse, 29 Sep. 2005 ; 1 male (6.6/10.0 mm), WMNH­Na­Cr 1206 (labelled as M. serenei ), Mikawa Bay , Pacific Ocean coast of Honshu, coll. Kimura, Nov. 1997 . Macrophthalmus serenei Takeda & Komai, 1991: 1 male (11.3/ 18.8 mm), RUMF­ZC­273, Hisamatsu, Yonaha Bay, Miyako I., coll. T. Naruse , J. Nawa & H. Osada, 26 May 2005; 3 males (10.8/18.0–11.4/ 18.8 mm), 1 female (9.6/ 15.5 mm), ZRC 2005.0150 , Hisamatsu, Yonaha Bay, Miyako I., coll. T. Naruse , J. Nawa & H. Osada, 26 May 2005 ; 7 males (4.5/ 6.8–9.8/15.8), 4 females (5.3/8.2–9.6/16.0 mm), RUMF­ZC­274, Awase, Nakagusuku Bay , Okinawa I. (26°18.145' N, 127°50.653' E), coll. H. Oku & T. Masumoto, 21 Aug. 2005 ; 1 female (7.9/ 12.8 mm), RUMF­ZC­275, Awase, Nakagusuku Bay, Okinawa I., coll. H. Oku, T. Inoue & T. Higuchi , 25, 26 Aug. 2005 ; 2 males (9.8/14.8, 11.7/ 18.7 mm), WMNH­Na­Cr 1206 (labelled as M. serenei ), Kamiura, Kushimoto, Wakayama Prefecture, Jun. 1985 . Macrophthalmus milloti Crosnier, 1965: 2 ovig. females (8.4/14.3, 10.2/ 17.4 mm), RUMF­ZC­276, Shirahama, Iriomote I., coll. T. Naruse & T. Nagai , 24 Mar. 2005 ; 1 male (5.7/ 9.3 mm), 1 female (7.9/ 12.7 mm), 1 ovig. female (8.6/ 14.7 mm), RUMF­ZC­277, intertidal flat of north of Motonagura, Ishigaki I., coll. T. Naruse , 13 Apr. 2005 ; 7 males (4.1/6.2–8.1/ 13.7 mm), 2 females (6.9/11.0, 9.6/­ mm), ZRC 2005.0151 , Motonagura intertidal flat, Ishigaki I., coll. T. Naruse , 22 May 2005 ; 1 female (5.1/ 8.3 mm), RUMF­ZC­278, Awase, Nakagusuku Bay , Okinawa I. (26°18.145' N, 127°50.653' E), coll. H. Oku & T. Masumoto, 21 Aug. 2005 ; 2 males (8.1/13.7, 9.6/ 15.8 mm), RUMF­ ZC­279, Awase, Nakagusuku Bay, Okinawa I., coll. H. Oku, T. Inoue & T. Higuchi , 25, 26 Aug. 2005 ; 2 females (7.9/13.3, 10.3/ 18.3 mm), WMNH­Na­Cr 1206 (labelled as M. serenei ), Yakata, Onna Village , Okinawa I., 25 Feb. 1993 ; 1 male (4.9/7.0 mm), 1 female (4.7/ 7.1 mm), WMNH­Na­Cr 1209 (labelled as M. philippinensis ), Nakagusuku Bay , Okinawa I., coll. Kubo, 7 Dec. 1992 ; 1 male (6.3/ 9.9 mm), WMNH­Na­Cr 1218 (labelled as Macrophthalmus sp. 1 ), Yakata, Onna Village , Okinawa I., Nov. 1991 .

Description

Carapace rectangular, moderately wide, CW 1.43–1.84 (mean 1.62, n = 41) times CL; dorsal surface smooth, shiny, regions ill­defined. Front relatively wide, with strong constriction across bases of ocular peduncles; frontal margin thinly rimmed. Supraorbital margin rimmed, gently sinuous; infraorbital margin cristate, granulated, granules set closer in inner, sparsely in outer, outer extreme of margin interrupted as wide as ocular peduncle. Epistome with posterior margin medially convex, submedially concave. Anterolateral margin with 3 teeth including external orbital angle, first tooth acute, largest, disconnected from second tooth by deep U­shaped notch, second, third teeth indistinct, lamellar, never spiniform, maximum width of carapace across first or following teeth in males, while across third teeth in females; anterolateral region with short transverse ridge behind supraorbital margin; posterolateral margin granulated, posterolateral region with few granules.

Eyes with extremely slender peduncle, peduncle reaching beyond external orbital angle by its 44.1–58.6% length (mean = 51.8 %, n = 30).

Third maxilliped rectangular, with narrow rhomboidal hiatus when closed; exopod narrow, with long flagellum.

Male chelipeds equal; merus with granular dorsal surface, ventral surface with granular, laterally convex margins, with mat of pubescence, inner surface without horny ridge; chela with flat manus, outer surface shiny, but covered with microscopic granules, single row of small granules from proximal lower part to immovable finger; immovable finger shorter than movable finger, tip pointed, lower margin concave near base, cutting edge with differentiated, distally directed tooth, top of tooth placed on distal third of margin, followed proximally by small granules; movable finger curved downwards, backwards, tip pointed, with differentiated, quadrate tooth, distal margin of tooth placed on proximal third of edge; inner surfaces of fingers with mats of pubescence from bases of fingers to distal third of immovable, distal quarter of movable fingers, pubescence extending to outer surface of cutting edge in movable finger, so subproximal tooth hidden in outer view.

Female chelipeds feeble; merus short, lower surface glabrous, with granular, foliaceous small projection on distal inner margin; carpus with row of setae along inner margin; chela very flat, with row of tiny granules along lower margin, extending from base of manus to immovable finger; fingers curved backwards, tips slightly scoop­shaped.

of manus to immovable finger; fingers curved backwards, tips slightly scoop­shaped.

Ambulatory legs slender; meri sparsely fringed with long setae on anterior, posterior margins, but without black, stiff setae; male with slender meri, length to width ratio 3.15–4.31 (mean = 3.63, n = 11), 2.71–3.47 (mean = 3.09, n = 13) in female, anterior three legs with meri with subdistal sharp tooth on anterior margin; dactyli spiniform, slightly incurved; propodi, dactyli sparsely lined with long setae on inner margin of third leg, inner, outer margins of fourth legs

Telson, abdominal segment bell­shaped, base of sixth abdominal segment projected laterally.

G1 slender, straight; distal end corneous, stout, abruptly curved outwardly.

Colouration

Okinawa specimens of M. microfylacas sp. nov. are slightly pink­ivory with black irregular patterns on the branchial and gastric regions, distal half of the ambulatory meri, outer part of the third maxilliped meri, pterygostomial region, and other regions ( Fig. 1a–c ). In contrast, specimens from Amakusa are yellowish grey with white spots ( Fig. 1d ). These colour variations are corresponding to the substratum colour (see habitat section below). Colouration of the ocular peduncles is similar in specimens of both localities: black patches and blue spots scattered throughout their lengths, subproximal to distal 1/3 of the peduncles transparent in life ( Fig. 1d ).

Habitat

Macrophthalmus microfylacas sp. nov. occurs mostly at depths of 2–4 m in bays with canescent sandy or small coral­rubble bottoms in Okinawa. Some substrates have Thalassia hemprichii seagrass beds. Macrophthalmus telescopicus and M. serenei were also collected from the same habitat. In Amakusa the new species is found in lower littoral zone of bays with relatively solid, dark, and sandy to muddy substrates, with seagrasses absent.

Etymology

The name of the new species derives from the Greek micros (small) and fylakas (watchman), alluding to its small size and the common name for the species of Macrophthalmus , the sentinel crabs. The name is used as a noun in apposition.

Distribution

Okinawa I., Ryukyu Islands; Amakusa , Kumamoto, Kyushu; Shimabara , Nagasaki, Kyushu; Takahama , Ehime, Seto Inland Sea coast of Shikoku I.; Kushimoto, Kii Peninsula, Pacific Ocean coast of Honshu; Shimoda, Izu Peninsula, Pacific Ocean coast of Honshu .

Remarks

The taxonomy of M. telescopicus ( Owen, 1839) , M. serenei Takeda & Komai, 1991 (= M. verreauxi sensu Serène, 1973 = M. kempi sensu Serène, 1981 ), and M. milloti Crosnier, 1965 was unclear until their revision by Serène (1973) (also see Serène, 1981; Takeda & Komai, 1991). Macrophthalmus microfylacas sp. nov. shares with these three species their extremely long ocular peduncles (cornea distinctly reaching beyond external orbital angle), the presence of three anterolateral teeth, and the smooth dorsal and ventral margins of the manus. Macrophthalmus microfylacas sp. nov. is distinguished from these three species ( Table 1) by the blunt second and third anterolateral teeth ( Fig. 2a, b ), the Ushaped notch between the first and second teeth ( Fig. 2a, b ), the convex lower margin of the cheliped immovable finger of males ( Figs. 2f , 4a ), the shape of the mats of pubescence of the cheliped fingers of males ( Figs. 4b ), and the small body size (see below). Furthermore, M. microfylacas sp. nov. can be differentiated from M. serenei and M. milloti by the smaller subproximal tooth on the cutting edge of the movable finger of the cheliped ( Fig. 2f ) [vs. distinct and rectangular ( Fig. 4e, g ; Crosnier, 1965: 126 (part), figs. 220, 227)], while M. microfylacas sp. nov. differs from M. telescopicus by the short distal projection of the G1 which is abruptly curved outwards ( Fig. 3c–e ) [vs. moderately long and slender ( Fig. 5g )].

Several authors have focused on the ocular peduncle length and body size to characterize the M. telescopicus complex (e.g. Serène, 1973; Barnes, 1976; Takeda, 1981). Macrophthalmus microfylacas sp. nov. tends to have a larger percentage of the extraorbital ocular peduncle length as a portion of total peduncle length, ranging from 44.1 to 58.6 % length (mean = 51.8 %, n = 30) ( Fig. 6 ). In contrast, the percentage in M. milloti is low; it never overlaps with those of the other three species (26.3–35.7 %, mean = 30.6 %, n = 16). The ranges of M. telescopicus (43.3–50.6, mean = 47.2, n = 11) and M. serenei (38.3–49.1 %, mean = 44.0 %, n = 17) largely overlap, but M. telescopicus tends to have a larger percentage than in M. serenei when specimens of similar body sizes are compared.

The new species is also characterised by its small body size, minimum size in ovigerous female being 6.6 mm CW (RUMF­ZC­260). In M. microfylacas sp. nov., the width of the female fifth abdominal segment begins to exceed that of the third segment by an individual with CL/CW 3.1/ 4.9 mm ( Fig. 7 ). In contrast, individuals with a wider fifth segment are much larger in M. serenei (7.7/12.1– mm) and M. milloti (7.9/12.7– mm). Small individuals of M. telescopicus could not be examined, but M. telescopicus is a clearly larger than M. microfylacas sp. nov.

Sakai (1939) recorded M. telescopicus from Shimoda (Pacific coast of Honshu), Nagasaki (Kyushu), and Loo Choo (= the Ryukyu Is.), and he recognized it as a small­size species (e.g. a male with CL/CW 6.5/ 10.5 mm). Serène (1973) concluded that Sakai’s (1939) material belonged to an undescribed species not only because of their small size but of the high manus of males, the wide gape between fingers, and the absence of a tooth on the cutting edge of the dactylus. Sakai (1976), however, identified the material from Shimoda and Nagasaki, together with specimens from Noto Peninsula ( Japan Sea coast of Honshu) and Wakayama (Pacific coast of Honshu), as M. verreauxi sensu Serène, 1973 (= M. serenei ). Macrophthalmus microfylacas sp. nov. indeed fits Sakai’s (1939) M. telescopicus except for the absence of the tooth on the cutting edge of the cheliped dactylus of males in the Shimoda specimens. The tooth of M. microfylacas sp. nov. is covered by dense pubescence and hidden from outer view which was probably missed by Sakai (1939). The Shimoda and Nagasaki specimens are most probably M. microfylacas sp. nov. Sakai’s (1976: fig. 334) material from Noto Peninsula clearly belongs to M. serenei (= M. verreauxi sensu Serène, 1973 ), while the identity of his specimens from the Ryukyus and Wakayama remains unconfirmed.

The third author could examine the late Mr. Seiji Nagai’s crab collection, which was catalogued by Marumura & Kosaka (2003). The specimens identified as M. telescopicus (WMNH­Na­Cr 1205) from Kushimoto, Kii Peninsula and Takahama, Shikoku I. are M. microfylacas sp. nov. The identities of the M. telescopicus complex listed in the catalogue were corrected in the material examined section above.

Figures

FIGURE 1. Macrophthalmus microfylacas sp. nov. a, Specimen from Okinawa I., Ryukyu Is., Japan, holotype, male, RUMF­ZC­257, CL/CW 6.5/10.4 mm; b, holotype; c, specimen from Okinawa I., paratype, male, RUMF­ZC­258, CL/CW 5.7/9.7 mm; d, specimens from Amakusa, Japan, paratype, female, RUMF­ZC­268, CL/CW 4.8/7.8 mm.

FIGURE 2. Macrophthalmus microfylacas sp. nov. a, male carapace and eyes; b, female anterolateral margin; c, epistome; d, third maxilliped; e, male cheliped, upper view; f, male chela, outer view (setae of movable finger are partially removed); g, female chela, outer view. a, c–f, holotype, male, RUMF­ZC­257, CL/CW 6.5/10.4 mm; b, g, paratype, female, RUMF­ZC­258, CL/ CW 5.9/10.3 mm. Scales, 1 mm.

FIGURE 3. Macrophthalmus microfylacas sp. nov. a, male abdomen and telson; b, female abdomen and telson; c, G1, dorsal view; d, distal end of G1, dorsal view; e, distal end of G1, ventral view; f, G2. a, c–f, holotype, male, RUMF­ZC­257, CL/CW 6.5/10.4 mm; b, paratype, female, RUMF­ZC­258, CL/CW 5.9/10.3 mm. Scales, a–c, f, 1 mm; d, e, 0.5 mm.

FIGURE 4. Male left chelae of Macrophthalmus microfylacas sp. nov. and allied species. a, b, M. microfylacas sp. nov., paratype, RUMF­ZC­258, CL/CW 5.7/9.7 mm; c, d, M. telescopicus (Owen, 1839), ZRC 2005.0149, CL/CW 10.3/15.4 mm; e, f, M. serenei Takeda & Komai, 1991, ZRC 2005.0150, CL/CW 11.2/18.9 mm; g, h, M. milloti Crosnier, 1965, ZRC 2005.0151, CL/CW 8.1/ 13.7 mm. a, c, e, g, outer view; b, d, f, h, inner view.

FIGURE 5. Anterolateral margins of carapace and G1s of Macrophthalmus telescopicus (Owen, 1839), M. serenei Takeda & Komai, 1989, and M. milloti Crosnier, 1965. a, g, M. telescopicus, male, ZRC 2005.0149, CL/CW 10.3/15.4 mm; b, M. telescopicus, female, ZRC 2005.0149, CL/CW 12.0/18.5 mm; c, h, M. serenei, male, ZRC 2005.0150, CL/CW 11.2/18.9 mm; d, M. serenei, female, RUMF­ZC­274, CL/CW 7.7/12.1 mm; e, i, M. milloti, male, ZRC 2005.0151, CL/CW 8.1/ 13.7 mm; f, M. milloti, female, RUMF­ZC­276, CL/CW 10.2/17.4 mm. Scales, 1 mm.

FIGURE 6. Percentage of the extra­orbital ocular peduncle length in the total ocular peduncle length of Macrophthalmus microfylacas sp. nov. and allied species.

FIGURE 7. Third and fifth female abdominal segments widths of Macrophthalmus microfylacas sp. nov. and allied species.