Rayllianassa bifida, Poore, 2023

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 : 230-232

Rayllianassa bifida sp. nov.

http://zoobank.org/urn:lsid:zoobank.org:act:DF11C5CD-E6EF-

4C09-9952-44505A84A984

Figures 1g , 42 , 43

Rayllianassa cf. amboinensis .— Robles et al., 2020: figs 1, 3, 6 (part).

Material examined. Holotype. Vanuatu. NW of Malo I., 15° 38' S, 167° 04' E, 114–132 m (Santo 2006 stn AT05 ), MNHN IU-2013-7137 * (female, 4.4 mm) . Paratype, collected with holotype, MNHN IU-2017- 1357 (ovigerous female, 4.7 mm) .

Diagnosis. Antennular peduncle about as long as antennal peduncle. Major cheliped merus with large proximal bifid tooth on lower margin; carpus upper and lower margins carinate, directed mesially to form parallel depressions above and below swollen mesial face; palm upper margin with narrow rounded keel, without tubercles and ridges on distal mesial and lateral margins at the base of fingers; dactylus with blade along cutting edge, apex simple. Pereopod 3 propodus oval, not wider proximally. Uropodal exopod widest near midpoint, 1.8 times as long as wide.

Description of holotype. Hermaphrodite. Rostrum broadly triangular, apically depressed, situated below level of dorsal carapace, one quarter length of eyestalks. Carapace dorsally convex in lateral view, as long as pleomeres 1–2 combined; orbital margin almost transverse; anterolateral angle blunt; subanterolateral margin almost horizontal; anterior margin of branchiostegite convex; cervical groove deeply incised, across 0.8 length of carapace, reaching linea thalassinica. Thoracic sternite 7 wider than long, posterior margin deeply incised between pair of lobes. Pleomere 1 tergite with shallow transverse groove. Pleomere 2 twice as long as pleomere 1. Pleomere 6 about as long as wide.

Eyestalk little longer than wide, with dorsal face close to rostrum, with sharp ventrolateral margin, anterolateral margin oblique, anteromedial angle rounded in dorsal view, not reaching distal margin of antennular peduncle article 1. Cornea densely pigmented, occupying anterolateral margin of eyestalk.

Antennular peduncle about as long as antennal peduncle (neither individual with both); article 1 visible in dorsal view; article 3 about as long as articles 1 and 2 combined; articles 2 and 3 with longitudinal ventral row of long setae. Antennal peduncle article 5 0.75 length of article 4; scaphocerite minute, triangular (paratype).

Maxilliped 3 ischium dilating distally, 1.2 times as long as wide, crista dentata consisting of row of about 20 small, well-spaced irregular teeth; merus about half as long as ischium measured along outer margin, about 1.4 times as wide as long, wider than ischium, with mesiodistal margin produced as convex lobe beyond base of carpus; carpus about as long as merus outer margin; propodus ovoid-tapering, 1.6 times as long as wide; dactylus digitiform, 0.8 times length of propodus.

Pereopods 1 (chelipeds) unequal, dissimilar. Major cheliped massive, carpus-palm upper margin 1.5 times carapace length. Ischium expanding distally, upper margin almost straight, unarmed; lower margin with row of 7 similar spines. Merus as long as ischium, 1.8 times as long as wide (tooth excluded), ovate; upper margin convex, unarmed; lower margin with subproximal bicuspid spine, with small blunt teeth over distal three quarters. Carpus 0.85 as long as wide; upper and lower margins carinate, directed mesially to form parallel depressions above and below swollen mesial face. Propodus upper margin 1.2 times as long as carpus; palm widest subproximally, as wide as carpus, tapering, as long as wide; upper margin with narrow rounded keel; lateral surface smooth, convex; mesial surface convex, with obtuse angle set back from distolateral margin; lower margin carinate, with row of setae extending onto fixed finger; fixed finger 0.4 length of palm, distally directed; cutting edge lateral, blade-like. Dactylus as long as fixed finger, hooked distally, with acute tip and mesial accessory tooth; upper margin ridged, with tufts of long setae; lateral surface with few tufts of long setae along cutting edge; cutting edge unarmed.

Minor cheliped carpus-palm upper margin as long as carapace length. Ischium upper margin smooth, lower margin with row of 6 teeth. Merus about as long as ischium; lower margin with tooth about one quarter along. Carpus wider distally, little shorter than merus, as long as wide, upper and lower margins carinate as in major cheliped. Palm slightly swollen, 1.2 times as long as wide; upper margin convex, with narrow rounded keel; lower margin carinate, with row of long setae extending onto fixed finger; mesial face with small tubercle at base of fixed finger. Fixed finger deep, triangular, half as long as palm, cutting edge lateral, with tooth at midpoint. Dactylus as long as palm, curved, with subapical mesial accessory tooth; cutting edge smooth.

Pereopod 2 merus lower margin slightly sinusoidal, 2.5 times as long as wide; carpus about 1.8 times as long as wide; chela subtriangular; palm about 1.6 times as wide as upper margin; dactylus twice as long as palm upper margin. Pereopod 3 merus 2.4 times as long as wide; carpus subtriangular, 1.7 times as long as wide; propodus suboval-angular, upper margin 1.2 times greatest width, lower margin with distinct corner between straight proximal half and concave distal half, marginal setae with 2 clear gaps along distal half, with 1 slender spiniform seta subdistally; dactylus about 0.7 length of propodus upper margin. Pereopod 4 coxa flattened ventrally, otherwise unknown. Pereopod 5 chelate.

Pleopod 1 of 2 articles at right angles; ramus 1.2 times as long as peduncle; setose. Pleopod 2 biramous; endopod slightly shorter than exopod. Pleopods 3–5 biramous, endopod 2.3 times as long as wide; appendix interna slender, rod-like, projecting well beyond mesial margin of endopod.

Uropod endopod and exopod overreaching posterior margin of telson. Endopod oval-tapering, widest over proximal half, about 1.5 times as long as wide; upper surface with 2 spiniform setae on dorsal rib, 3 others more anteriorly; anterior margin almost straight; anterodistal margin with 4 short spiniform setae; distal margin convex, with fringe of setae; posterior margin setose. Exopod widest near midpoint, 1.5 times as long as wide, exceeding endopod by one quarter its length; anterior margin almost straight; all margins with numerous slender setae, with more than 20 blade-like setae on posterior margin indistinguishably merged with distal margin; dorsal plate apparent on distal margin as row of about 12 stiff setae merging anteriorly with similar setae on anterior margin.

Telson trapezoidal, 1.2 times as wide as long, broadest at anterior fifth, narrowing posteriorly; greatest width 1.4 times posterior width; posterolateral angle each with spiniform setae; posterior margin medially excavate, with median tooth; dorsal surface with few medial setae.

Variation. The two individuals are similar; the meral tooth on the paratype is not so obviously bicuspid as in the smaller holotype.

Etymology. bifida (Latin) , describing the tips of the cheliped dactyli.

Distribution. Tropical Southwestern Pacific ( Vanuatu); 114– 132 m.

Remarks. Rayllianassa bifida is represented by MNHN IU-2013-7137, one of two individuals on the smaller primary clade in the molecular phylogram of Robles et al. (2020: fig. 3 [mislabelled PNG]).

Rayllianassa bifida shares with R. amboinensis a broad angular propodus of pereopod 3, a broad oval maxilliped 3, prominent mesial lobes on the eyestalks, large cornea, a large major cheliped relative to the carapace, spiniform setae along the uropodal endopod ridge, and hermaphrodism. The new species differs in having a proximal tooth on the major cheliped merus (never seen in R. amboinensis ), a feature shared with R. huonensis sp. nov. Whereas the upper margin of the cheliped of R. amboinensis has a dull ridge visible only mesially as a shadow under suitable lighting, R. bifida has a prominent ridge on the upper margin of the carpus and propodus (fig. 42f, n); on the carpus this ridge and the one on the lower margin are directed mesially as carinae, creating shallow mesial concavities parallel to the margins (fig. 42i). The third article of the antennule is much shorter and thicker than that of R. amboinensis figured by De Man (1928a) and Komai et al. (2014a), making the antennular and antennal peduncles of similar lengths.

Figures

Figure 1. Dactylus of maxilliped 3 of representatives of two callianassoid families. Eucalliacidae. a, Calliaxina kensleyi (Dworschak, 2005), MNHN IU-2016-8084. Callianassidae. b, Caviallianassa moorea sp. nov., UF 28875; c, Paratrypaea sp, MNHN IU-2013-7035; d, Praedatrypaea lobetobensis sp. nov., MNHN IU-2015-109; e, Praedatrypaea orientalis (Bate, 1888), AM P.74473; f, Rayllianassa amboinensis (De Man, 1888), UF 8700; g, Rayllianassa bifida sp. nov., MNHN IU-2013-7137; h, Rudisullianassa pandan sp. nov., MNHN IU-2013-7063; i, Rudisullianassa rudisulcus Komai, Fujita and Maenosono, 2014, MNHN IU-2013-7121; j, Scallasis amboinae Bate, 1888, MNHN IU-2013-12303; k, Spinicallianassa spinicauda (Komai, Maenosono and Fujita, 2014), MNHN IU-2014-2778; l, Spinicallianassa papetoai sp. nov., UF 29280.

Figure 42. Rayllianassa bifida sp. nov. Vanuatu. MNHN IU-2013-7137, holotype female, 4.4 mm: a, carapace, pleomeres 1, 2 tergites, eyestalk; b, c, carapace, eyestalks, antennular peduncle, antennal peduncle articles 1–3 (lateral, dorsal); d, pleomere 6, telson, left uropod; e, major cheliped (left, mesial); f, major cheliped, carpus–dactylus (upper view); g, major cheliped fingers (lateral); h, major cheliped finger tips (apical view); i, major cheliped carpus cross-section (upper margin topmost, inner face left); j, minor cheliped (right, mesial); k, minor cheliped fingers (lateral); l, minor cheliped dactylus (apical view). MNHN IU-2017-1357, paratype ovigerous female, 4.7 mm: m, anterior carapace, eyestalk, antennular peduncle article 2, antennal peduncle; n, major cheliped, carpus–dactylus (upper view). Scale bars = 1 mm.

Figure 43. Rayllianassa bifida sp. nov. Vanuatu. MNHN IU-2013-7137, holotype female, 4.4 mm: a, b, maxilliped 3 (left, inner, outer views); c–e, pleopods 1–3; f, pereopod 3; g, pereopod 5 coxa (mesial view); h, thoracic sternite 7, pereopodal coxae 3, 4. MNHN IU-2017-1357, paratype ovigerous female, 4.7 mm: i, pereopod 2. Scale bar = 1 mm.