Thor marguitae Bruce, 1978

Komai, Tomoyuki, Okuno, Junji & Minemizu, Ryo, 2015, New records of two species of the coral reef shrimp genus Thor Kingsley, 1878 (Crustacea: Decapoda: Thoridae) from the Ryukyu Islands, Japan, Zootaxa 4013 (3), pp. 399-412 : 406-407

Thor marguitae Bruce, 1978

[New Japanese name: Daruma-hime-sango-moebi] Figs. 5A , 6 , 7

Thor marguitae Bruce, 1978: 159 , figs. 1–6 (type locality: Heron Island, Capricorn Islands, Queensland, Australia; 1983: 9 (key).— Chace 1997: 99 (key).— De Grave & Fransen 2011: 434.

Material examined. Off Ginowan, Okinawa Island, 16 m, associated with fungiid coral, 22 June 2011, coll. R. Minemizu, SCUBA diving, 1 ovigerous female (cl 2.7 mm), CBM-ZC 11889.

Description. See Bruce (1978).

Colouration in life. Carapace mottled milky white, pleon semitransparent with faint white markings, caudal fan (telson + uropods) with proximal and distal white bands, intermediate part speckled with brown. Appendages also generally milky white. Ultimate segment of third maxilliped proximally with grayish brown ring. Propodi of third to fifth pereopods each with grayish brown bands distally and proximally, meri also with grayish brown markings.

Distribution. Previously known only from the type locality in Queensland, Australia. The discovery of the present specimen from Okinawa Island greatly extends the known geographical range of the species and suggests a wide distribution in the tropical and subtropical western Pacific.

Habitat. The present specimen was found under the solitary fungiid coral, Fungia repanda Dana, 1846 .

Remarks. The present ovigerous female specimen agrees generally with the original description of Thor marguitae by Bruce (1978), particularly in the following characteristics: body moderately robust for genus ( Fig. 6 A); rostrum deep, subtruncate terminally, ventral margin sinuous ( Fig. 6 C); carapace without supraorbital or pterygostomial teeth ( Fig. 6 B); telson bearing three pairs of dorsolateral spines, posterior margin convex, medially not acute, armed with two pairs of spines and one mesial pair of plumose spine ( Fig. 6 D); stylocerite of antennular peduncle with small erect tooth near proximal end ( Fig. 6 C); third maxilliped and pereopods relatively slender for genus ( Fig. 7 A–H); chela of first pereopod tapered and clearly compressed ( Fig. 7 B, C); dactyli of third to fifth pereopods relatively slender with penultimate unguis weaker than ultimate unguis ( Fig. 7 F). Nevertheless, minor differences are seen in the extension of the distolateral tooth of the antennal scale and the number of the carpal articles of the second pereopod. Bruce (1978) specifically stated that the distolateral tooth of the antennal scale slightly overreaches the distal margin of the lamella, but in the present specimen, the distolateral tooth falls slightly short of the distal margin of the lamella ( Fig. 6 C). In his identification key to the species of Thor, Chace (1997) used the extension of the distolateral tooth of the antennal scale in differentiating T. amboinensis and T. marguitae , but this character might not be so reliable. The carpal articles number is six in the type series, but there are only five articles in the present specimen ( Fig. 7 D). In Thor , carpal articles of the second pereopod are normally six, but Kemp (1914) recorded a single specimen of T. paschalis having seven carpal articles. The present specimen seems to represent a new example of aberrant variation of the carpal division of the second pereopod in the genus. Furthermore, the living coloration of the present specimen seems to be somewhat different from the description given by Bruce (1983), particularly in the lack of red speckles on the pleura of the pleon. The apparent lack of red speckles in the present specimen may be due to contraction of chromatophores.

Bruce (1978) reported on the variation in the number of meral spines of the third to fifth pereopods in T. marguitae : two to five in the third, one to four in the fourth, and one (rarely zero) in the fifth. In the present specimen, the numbers of the meral spines are two-one-one, falling within the reported range of variation.

Association with the fungiid coral was already reported by Bruce (1978). As noted above, the present specimen was found in association with Fungia repanda .

With the discovery of the two species in the present study, five species of Thor are now known from Japanese waters. Future study may eventually reveal the presence of the other three Indo-West Pacific species ( T. hainanensis , T. intermedius , and T. spinipes ) in the Japanese Archipelago.

In addition to the 15 formally named species of Thor, Miyake & Hayashi (1966) reported on an unidentified specimen ( Thor sp.) on the basis of a tiny single female specimen from Amami-oshima Island, the Ryukyu Archipelago. The specific status of this unidentified specimen has not been settled. We have found that Miyake & Hayashi’s (1967) specimen is generally similar to T. marguitae in many diagnostic aspects cited above, in particular, the characteristic shape of the chela of the first pereopod ( Miyake & Hayashi 1966: Fig. 8d). The rostrum of the specimen used by Miyake & Hayashi differs from that of typical T. marguitae in having an acute tip and a single ventral tooth extending as far as the rostral tip. However, Bruce (1973) reported on a wide range of variation in the shape and armature of the rostrum in T. marguitae . It is likely that Miyake & Hayashi’s (1966) specimen actually represent young T. marguitae .

Figures

FIGURE 6. Thor marguitae Bruce, 1978, ovigerous female (cl 2.7 mm), CBM-ZC 11889. A, habitus, lateral view; B, carapace and cephalic appendages, dorsal view; C, anterior part of carapace and cephalic appendages, lateral view (left eye removed); D, telson, dorsal view. Scale bars: 2 mm for A; 1 mm for B, C; 0.5 mm for D.

FIGURE 7. Thor marguitae Bruce, 1978, ovigerous female (cl 2.7 mm), CBM-ZC 11889. Left appendages. A, third maxilliped, lateral view; B, first pereopod, lateral view; C, same, chela, flexor view; D, second pereopod, lateral view; E, third pereopod, lateral view; F, same, dactylus and distal part of propodus, lateral view; G, fourth pereopod, lateral view; H, fifth pereopod, lateral view. Scale bars: 0.5 mm for A – E, G, H; 0.25 mm for F.

FIGURE 5. A, Thor leptochelus (Xu & Li, 2015) n. comb., ovigerous female (cl 2.3 mm), CBM-ZC 13091, in situ; B, Thor marguitae Bruce, 1978, ovigerous female (cl 2.7 mm), CBM-ZC 11889, in situ, attaching to solitary fungiid coral Fungia repanda. Photography by R. Minemizu.