Aphanodactylus loimiae Konishi & Noda, 1999

Ng, Peter K. L., Ahyong, Shane T. & Komai, Tomoyuki, 2010, On The Male Of Aphanodactylus Loimiae Konishi & Noda, 1999 (Crustacea: Brachyura: Pinnotheroidea: Aphanodactylidae), Raffles Bulletin of Zoology 58 (1), pp. 75-78 : 75-78

Aphanodactylus loimiae Konishi & Noda, 1999

Aphanodactylus loimiae Konishi & Noda, 1999: 223–227 , Figs. 1 , 2 [type locality: Kuroshima Island, Yaeyama Islands, Japan, in tube of Loimia ingens Grube, 1878 (Polychaeta) ]; Ng et al., 2008: 247 (list); Ng & Naruse, 2009: 284; Ahyong & Ng, 2009: 36, Figs. 1 , 2 .

Material examined. – 1 male (10.3 × 7.4 mm), 1 ovigerous female (13.9 × 8.6 mm) ( CBM 5341 ), Kyan , Kuroshima Island , Yaeyama Islands, Ryukyus, Japan, 10 m deep, coral reef, in tube of Loimia ingens , 10 Oct. 1999, coll. K. Nomura on SCUBA ; 1 ovigerous female (15.3 × 9.1 mm) ( CBM 5443 ), Ahra Beach , Kume-jima Island , Okinawa Islands, Ryukyus, Japan, 10 m deep, coral reef, inhabited in tube of Loimia ingens , 15 Jun. 1995, coll. K. Nomura on SCUBA .

Comparative specimens of Aphanodactylus edmondsoni . – 1 male (11.5 × 8.2 mm), 1 female (16.9 × 10.2 mm) ( ZRC 2000.0542 ), Oahu, Hawaii, coll. C. H. Edmondson.

Remarks. – Discovery of a male specimen of Aphanodactylus loimiae permits documentation of sexual dimorphism in this species. As in other species of Aphanodactylus , the carapace of A. loimiae is proportionally narrower in the male than females (width: length ratio 1.39 versus 1.62–1.76); the front is more distinctly concave medially; the male chelipeds are more robust than in females; and the male abdomen is narrowly triangular and tapering to a rounded apex. Perhaps the most significant differences between male and female A. loimiae , however, are in the shape of the cornea and thoracic sternal structures. The cornea of female A. loimiae is a simple oval shape in anterior view, but in males, the cornea is strongly constricted medially, forming a distal bulb. As far as is known for Aphanodactylus species , this corneal dimorphism is unique to A. loimiae , being neither present in A. edmondsoni nor A. sibogae (based on Tesch [1918]). Thoracic sternites 5–7 of male A. loimiae are separated by deep, wide grooves, whereas in females, the sternites are demarcated by narrow, shallow grooves. As with the corneal dimorphism, the sternal dimorphism in A. loimiae is apparently unique in the genus. This sternal differentiation is similar in both sexes in A. edmondsoni (present observation), and presumably also in A. sibogae , based on Tesch’s (1918) lack of comment on sternal differences. Thus, the unusual corneal shape and deep sternal grooves will immediately distinguish A. loimiae from A. edmondsoni and A. sibogae .

Availability of additional females of A. loimiae also permits documentation of intraspecific variation. The carapace width to length ratio of the present females is 1.62–1.68, which is slightly lower than that recorded for the holotype (1.76), and the frontal margin is slightly sinuous rather than straight as recorded by Konishi & Noda (1999). All three specimens examined in this study also differ from the type description of A. loimiae in the ventral armature of the meri of the walking legs. Konishi & Noda (1999) recorded 4–6 ventral teeth on the posterior margins of the meri of P2–4 and one prominent tooth and two vestigial ventral teeth on the posterior margins of the merus of P5. The present specimens bear 3–5 ventral teeth on the posterior margins of the meri of P2–4, none of which are prominently enlarged, and no ventral teeth on the merus of P5. These variations in the ambulatory meral armature are presently interpreted as intraspecific variation.

Features used by Konishi & Noda (1999) to distinguish species of Aphanodactylus were the width to length ratio of the carapace, dorsal punctuation of the carapace, shape of the frontal margin (straight or concave), the number of antennular segments, and the ventral armature of the meri of P2–5. Most of the characters used by Konishi & Noda (1999) to distinguish species of Aphanodactylus are invalid, though other features are available for species identification. The width to length ratios of the carapace of A. loimiae , A. edmondsoni and A. sibogae are similar to each other in males, and overlap in females (Table 1). The shape of the carapace front, presence or absence of dorsal pits on the carapace, and antennular segmentation appear to be similar in A. loimiae , A. edmondsoni and A. sibogae . The front is slightly sinuous in females and distinctly sinuous in males of all three species. Similarly, the presence of dorsal pits on the carapace, cited as diagnostic of A. sibogae by Konishi & Noda (1999) appears to be unreliable — both A. loimiae and A. edmondsoni have similar, pits, but were probably overlooked in the original accounts because the pits are not very deep and can be difficult to observe unless the carapace surface is dried. The carapace pits of A. sibogae , as depicted by Tesch (1918), are deeper and more prominent than they actually are. A female syntype of A. sibogae (RMNH D2162, cw. 8.8 mm, cl. 5.4 mm) in the Nationaal Natuurhistorisch Museum, Leiden, examined by T. Naruse (National University of Singapore) at our request has very shallow carapace pits, as presently observed in A. loimiae and A. edmondsoni . The antennular flagellum in all three species appears to number about seven segments. Tesch (1918) cited three segments for female and seven for male A. sibogae , but, the low female number is likely to be the result of damage. The differences in meral armature of P2–4 appears to be a useful distinguishing feature, at least for A. edmondsoni (1–3 teeth) and A. loimiae (4–6 teeth).

Cases & Storch (1981) reported A. sibogae from Poro, Camotes Islands, Cebu, Philippines. Although the size and sex of the Cebu specimen was not specifically stated, it appears to be a male with carapace proportions (width: length ratio 1.45) similar to that of male A. sibogae reported by Tesch (1918). Notably, Cases & Storch (1918: Fig. 9) did not show dorsal carapace pits, suggesting that if present, the dorsal pits were probably shallow and therefore overlooked. The identity of the Philippines specimen will need to be checked to see if they are really A. sibogae or perhaps even A. loimiae . Attempts to locate the specimen(s), supposedly in the zoological museum of the University of San Carlos, Cebu City, Philippines, were unsuccessful. The material appears to be lost.

The present specimens of A. loimiae were all found to inhabit the tubes of a large polychaete, Loimia ingens , as with the holotype (see Konishi & Noda, 1999). The heterosexual pair (CBM-ZC 5341) was collected from the same tube (K. Nomura, pers. comm.). It is still unclear if Aphanodactylus loimiae is only found with Loimia ingens .

Figures

Fig. 1. Aphanodactylus loimiae Konishi & Noda, 1999 (CBM 5341). A, C, dorsal views. B, D, ventral views. A, B, male (10.3 × 7.4 mm); C, D, female (13.9 × 8.6 mm).

Fig. 2. Aphanodactylus loimiae Konishi & Noda, 1999, male (10.3 × 7.4 mm) (CBM 5341). A, left anterior of carapace; B, right P5; C, abdomen; D, E, left G1, abdominal and sternal view, respectively. Scales: A–B = 1.5 mm, C = 3.0 mm, D–E = 1.0 mm.