Rayllianassa Komai and Tachikawa, 2008

Poore, Gary C. B., 2023, New records, one new genus and 21 new species of Callianassidae (Crustacea, Axiidea) from the Indo-West Pacific, Memoirs of Museum Victoria 82, pp. 167-255 : 222-223

Rayllianassa Komai and Tachikawa, 2008

Rayllianassa Komai and Tachikawa, 2008: 42–43 .—Komai et al., 2014a: 550–551.— Poore et al., 2019: 98, 143.— Robles et al., 2020: figs 1, 3, 6.— Poore and Ahyong, 2023: 213.

Diagnosis. Hermaphrodite. Rostrum obsolete or obtusely triangular, flat, not reaching cornea. Cervical groove deeply incised dorsally. Eyestalk distal lobes obliquely truncated, apices diverging. Antennular peduncle exceeding antennal peduncle by quarter to half length of article 3. Antennal scaphocerite simple, longer than wide, acute. Maxilliped 3 ischium-merus as wide as long or almost so; merus wider at ischium-merus suture than long; dactylus tapering, with scattered setae over upper margin, dense brush of short setae distally on lower margin. Major cheliped merus lower margin straight or widest at midpoint, with or without denticles. Minor cheliped half to two thirds width of major cheliped, both swollen; carpus upper margin shorter than propodus. Uropodal endopod ovoid, longer than wide, anterior margin straight, posterodistal margin evenly convex, usually with 2 facial spiniform setae on rib. Uropodal exopod about as long as wide, posterodistal margin with row of 6–8 long blade-like setae proximal to long setae on distal margin. Telson as long as or longer than wide, tapering from near base; posterior margin slightly concave, sometimes with medial spine.

Remarks. Rayllianassa was erected for Callianassa amboinensis De Man, 1888 by Komai and Tachikawa (2008). Komai et al. (2014b) later broadened the diagnosis to include a second species, R. rudisulcus Komai, Fujita and Maenosono, 2014 , but Poore et al. (2019) showed this to belong to another genus, Rudisullianassa . Rayllianassa has been diagnosed by the absence of a prominent proximal hook on the merus of the major cheliped (having at most a small tooth near the midpoint), the chelipedal carpi and propodi being swollen and the width of the minor propodus about 0.6 that of the major. The lobes on the eyestalks are truncate-oblique and the maxilliped 3 particularly broad (ischium-merus 1.5 times as long as wide) ( Poore et al., 2019).

Robles et al. (2020) found substantial genetic difference between eight individuals of “ Rayllianassa amboinensis ”, four from Papua New Guinea, two from the Philippines, one from the Line Islands and another from Vanuatu (mislabelled Papua New Guinea on Robles et al. [2020: fig. 3]), including within these localities. Five of these individuals plus another from Papua New Guinea were included in a reanalysis by Qi Kou (pers. comm., 7 July 2023), leading to the conclusion that at least five species are included in this complex. Estimates of interspecific evolutionary divergence ranged from 0.040 to 0.168 for 12S sequences and 0.047 to 0.143 for 16S sequences ( Table 2).

Subsequent morphological examination of the specimens contributing to these analyses revealed three species corroborated by the major clades in Robles et al.’s (2020) molecular analysis: R. amboinensis sensu stricto, R. aurora sp. nov. and R. bifida sp. nov., and another suggested by Kou’s analysis. One individual (tissue sample ULLZ 10127 from a female NHMW 25915) is included here as Rayllianassa sp.

The new species differ from R. amboinensis in some so-called generic features, necessitating the new generic diagnosis provided above, notably in the relative lengths of the antennular and antennal peduncles, armature of the major cheliped merus and shape of the pereopod 3 propodus.

Poore et al. (2019) included five species: R. amboinensis , R. bangensis ( Sakai, 2005) , R. lignicola (Alcock and Anderson, 1899) , R. parva (Edmondson, 1944) and R. sahul (Poore, 2008) . Only the first is so far well known. Rayllianassa bangensis ( Sakai, 2005) is known from a single male, cl. 3.8 mm, from 49 m in the Philippines. This record and Ngoc-Ho’s (1991) record of R. amboinensis are the only records of males in this genus – most are females, probably hermaphrodites. While the maxilliped 3 and major cheliped are typical of Rayllianassa , the antennal peduncle longer than the antennular peduncle is characteristic of Rudisullianassa . See further comment under R. aurora sp. nov. below. Rayllianassa lignicola was described from two females, tl. 11 mm, 14.8 mm, from “water-logged mangrove-twigs” at 185 fm (338 m) in the Andaman Sea. The chelipeds and relative lengths of the antennal peduncles, plus the association with wood, are evidence for placement in Rayllianassa . The generic placement of C. parva in Rayllianassa is doubtful. While the chelipeds and telson are Rayllianassa -like, the relative lengths of the antennal peduncles and maxilliped 3 are not typical. C. sahul Poore, 2008 is synonymised with R. amboinensis below.

Samadi et al. (2010) reported that “ Callianassa ” amboinensis is associated with deep-sea wood, having been collected in traps baited with wood sunk off New Caledonia and Vanuatu. Hoyoux (2006, 2010) studied the digestion of wood in this species from Papua New Guinea (MNHN SALOMON 2 stations). Callianassa amboinensis has been reported from 80 metres, scarcely the deep sea, of New Caledonia, but not specifically from wood ( Ngoc-Ho, 1991). The only available material from Vanuatu has been identified here as R. bifida sp. nov. and that from SALOMON 2 stations as R. aurora sp. nov., both from samples containing wood. Komai et al. (2014) summarised the depth distribution of R. amboinensis as 0.5 to 183 m, and cited literature showing that the species burrows in sponges or alcyonacean soft corals and suggested that the association with deep-sea wood involves species other than R. amboinensis . Species of another genus easily confused with Rayllianassa , Rudisullianassa rudisulcus (Komai, Fujita and Maenosono, 2014) and Rudisullianassa pandan sp. nov., are also from samples containing sunken wood.