Rayllianassa rudisulcus Komai, Fujita & Maenosono, 2014, n. sp.
Creators: name: Komai, Tomoyuki
name: Fujita, Yoshihisa
name: Maenosono, Tadafumi
Publisher: name: Zenodo
Year: 2014
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Callianassidae
Rayllianassa
Rayllianassa rudisulcus

description: Rayllianassa rudisulcus n. sp.
[New Japanese name: Ohura-futoude-sunamoguri] (Figs. 3–7)
Material examined. Holotype: ovigerous female (cl 3.6 mm), Ohura Bay, Okinawa Island, stn dredge 1, 3– 20 m (most probably 10–15 m), 22 June 2009, dredge, CBM-ZC 12361.
Description. Rostrum (Figs 4 A, B) broadly triangular, terminating in acute point, directed downward, far falling short of midlength of eyestalks. Carapace (Figs. 3 A, 4A) about 0.3 length of abdomen; orbital margins slightly concave; anterolateral projection blunt; excavation inferior to anterolateral projections moderately deep; dorsal oval absent, suture-like cervical groove across 0.8 length of carapace; linea thalassinica distinct.
Thoracic shield (plate on seventh thoracic sternite) (Fig. 4 C) subpentagonal with slightly produced anterior margin; ventral surface without median groove, posterior margin with faint median notch.
Length ratio of first pleomere to telson measured along midline 1.0: 1.3: 0.9: 0.9: 0.8: 1.2: 0.7 (Fig. 4 D–G). First pleomere (Figs. 3 B, 4D) gradually narrowing anteriorly in dorsal view; pleuron with poorly defined ventral margin. Second pleomere (Figs. 3 B, 4D) with pleuron bearing posterolateral margin slightly expanded, with tuft of long setae. Third to fifth pleomeres (Figs. 3 B, 4E, F) each with patch of soft plumose setae and tuft of long setae adjacent to posterior margin; posterolateral margins slightly expanded. Sixth pleomere (Figs. 3 B, 4G) about 1.2 times longer than wide, subrectangular, lacking ventrolateral projection; lateral margin without notch. Telson (Figs. 4 G, 5J) subtrapezoidal, narrowing posteriorly, 0.6 times as long as sixth pleomere and approximately as long as wide, broadest at anterior 0.2; dorsal surface gently convex transversely, with median tuft of long setae; lateral margin unarmed; 2 minute spiniform setae at each posterolateral angle; posterior margin regularly convex, unarmed, with row of sparse short setae and few lateral long setae.
Eyestalks (Figs. 3 A, 4B) slightly flattened dorsoventrally, tapering to bluntly pointed distal projection, contiguous, slightly reaching distal margin broadly rounded, unarmed, slightly exceeding beyond articulation to carpusdistal margin of first segment of antennular peduncle; dorsal surface narrowly separated from rostrum, sloping anteriorly; lateral margin convex. Cornea subterminal and lateral, darkly pigmented, its width greater than half of greatest width of eyestalk.
Antennular peduncle (Fig. 3 A) distinctly shorter than antennal peduncle; first segment short, hardly visible in dorsal and lateral views; second segment slightly longer than first segment; third segment about 2.5 times longer than second segment; second and third segments with longitudinal row of sparse long setae ventrally; antennular flagella both slightly shorter than peduncle; dorsal flagellum thicker and slightly shorter than ventral flagellum.
Antennal peduncle (Fig. 3 A) overreaching antennular peduncle by 0.9 length of fifth segment; distal two segments subcylindrical; fourth segment about 1.2 times longer than fifth segment; scaphocerite minute, subtriangular; flagellum broken.
Small process lateral to epistome bearing few long setae (Fig. 3 A).
Mandible and maxillule not dissected. First maxilliped (Fig. 5 A) with broad exopod. Second maxilliped (Fig. 5 B) with exopod slightly falling short of distal margin of merus. Third maxilliped (Fig. 5 C, D) without exopod; ischium-merus broadly operculiform, 1.2 times longer than wide; articulation between ischium and merus slightly oblique; ischium 1.4 times wider than long, crista dentata on mesial face consisting of row of minute spines; merus wider than and subequal in length to ischium, about 1.4 times wider than long, distal margin broadly rounded, unarmed, slightly exceeding beyond articulation to carpus; carpus cup-shaped, distinctly shorter than merus; propodus not narrowing distally, 1.5 times longer than high and subequal in length to carpus; dactylus stout, but not particularly expanded, about 0.8 times as long as propodus.
First pereopods (chelipeds) unequal in size but similar in general structure (Fig. 6 A, C). Major (left) cheliped (Fig. 6 A, B) stout, carpus-chela combined length 1.2 of carapace length. Ischium slightly widened distally, dorsal margin faintly sinuous, unarmed; lateral surface gently convex; ventral margin with row of 3 spinules. Merus subequal in length to ischium; dorsal and ventral margins convex, unarmed; lateral surface convex with midline slightly ridged; mesial surface generally flat distally. Carpus subsemicircular, about 1.5 times wider than long; dorsal and ventral margins sharply carinate, smooth, proximoventral margin broadly rounded; lateral surface smooth, convex; mesial surface nearly flat. Palm subrectangular, 1.4 times longer than wide; dorsal margin sharply carinate, with few long setae; lateral surface smooth, convex; mesial surface slightly convex generally, but with small shallow depression at base of fixed finger; ventral margin sharply carinate, with row of short to moderately long setae extending onto fixed finger; distolateral margin strongly produced. Fixed finger about 0.3 times as long as palm, slightly curving, terminating in acute tip; cutting edge with row of small blunt teeth in proximal half; lateral surface convex, with tuft of setae at midlength; mesial surface depressed along cutting edge. Dactylus about 0.6 times as long as palm, hooked distally, crossing fixed finger at midlength, terminating in acute tip; dorsal surface with blunt ridge laterally and with tufts of short to long setae; lateral surface glabrous; cutting edge sinuous, without conspicuous teeth; mesial surface slightly elevated in midline, with row of tufts of stiff setae along cutting edge.
Minor (right) cheliped (Fig. 6 C) stout, about 0.7 length of major cheliped, carpus-chela combined length subequal to carapace length. Ischium with 1 spinule on ventral margin. Merus wider than and subequal in length to ischium; dorsal and ventral margins convex, unarmed. Carpus subsemicircular, about 1.2 times wider than long; dorsal and ventral margins sharply carinate, smooth, proximoventral margin broadly rounded; lateral surface smooth, convex; mesial surface nearly flat. Palm subrectangular, 1.6 times longer than wide; dorsal margin sharply carinate, with few long setae; lateral surface smooth, convex; mesial surface slightly convex generally; ventral margin sharply carinate, with row of long setae extending onto fixed finger; distolateral margin with low convexity. Fixed finger about 0.6 times as long as palm, slightly curving, terminating in acute tip; cutting edge with 1 small tooth slightly distal to midlength and row of minute denticles proximally; lateral surface convex, with some tufts of long setae along cutting edge; mesial surface depressed along cutting edge. Dactylus about 0.8 times as long as palm, hooked distally, crossing fixed finger at distal to midlength, terminating in acute tip; dorsal surface rounded, with row of tufts of short to long setae; lateral surface with few tufts of setae; cutting edge concave, unarmed; mesial surface slightly elevated in midline, with row of tufts of stiff setae along cutting edge.
Second pereopod (Fig. 7 A) with ischium short. Merus with sinuous ventral margin; dorsal margin slightly convex. Carpus cup-shaped, about 1.7 times longer than wide. Chela subtriangular; palm 1.2 times wider than long; cutting edges of fingers bordered by thin corneous ridge; dactylus about 1.6 times longer than palm.
Third pereopod (Fig. 7 B, C) with carpus cup-shaped, about 2.2 times longer than wide. Propodus suboval, without heel; lateral face obtusely carinate medially; ventral margin gently convex, smooth, armed with relatively long movable spine subdistally. Dactylus slightly curved, 0.5 times as long as propodus.
Fourth pereopod (Fig. 7 D, E) with coxa (Fig. 4 C) somewhat flattened ventrally, immovable. Basis and ischium partially fused. Merus slightly longer than ischium. Carpus widened distally. Propodus strongly compressed, slightly shorter than carpus, with dense grooming setae and 1 distal movable spine on ventral margin. Dactylus slightly curving, about 0.3 times as long as propodus.
Fifth pereopod (Fig. 7 F, G) with chela shorter than carpus, stout, somewhat flattened; dactylus about 0.3 times as long as palm.
First pleopod (Figs. 3 B, 5E, F) uniramous, ramus subequal in length to protopod. Second pleopod (Figs 3 B, 5G) biramous; exopod subequal in length to endopod, both rami divided into 2 subequal articles. Third to fifth pleopods (Fig. 5 H) biramous, rami moderately broad. Each appendix interna (Fig. 5 I) distinctly longer than wide, digitiform, distinctly projecting beyond mesial margin of endopod, bearing coupling hooks on truncate apical margin.
Uropod (Figs. 3 B, 4G, 5K) with both endopod and exopod subovate, distinctly overreaching posterior margin of telson. Endopod about 1.7 times longer than wide and 1.3 times longer than telson; dorsal surface shallowly concave in mesial half; lateral margin convex, unarmed; mesial margin broadly convex. Exopod about 1.5 times longer than wide and 1.4 times longer than telson, exceeding beyond endopod by about 0.3 length; lateral margin slightly convex, unarmed; posterior and mesial margins rounded; dorsal surface with 2 faint longitudinal ridges; dorsal plate with distal row of spiniform setae distinctly separated from setal rows of posterior margin; setal rows on posterior margin consisting of mixture of spiniform setae and stout and thin setae.
Coloration in life. Not known.
Distribution. Known only from the type locality, Ohura Bay, Okinawa Island, shallow subtidal.
Habitat. The holotype of the new species was collected from soft sediment, clearly suggesting that it is a sediment burrower.
Remarks. The present new species is assigned to Rayllianassa because of the following features, although the morphology of the male first and second pleopods is unknown: rostrum broadly triangular, non-spiniform; posterior margin of telson broadly rounded, unarmed; third maxilliped with ischium-merus broadly operculiform; chelipeds unequal, but similar in general structure; cheliped meri unarmed on ventral margins; cheliped carpi much wider than long; propodus of third pereopod subovate, without proximal heel; appendices internae on third to fifth pleopods digitiform, entirely projecting from mesial margins of endopods. It is easily distinguished from the sole congeneric species, R. amboinensis, by the following characters: (1) the dorsal oval is absent in R. rudisulcus n. sp. (the cervical groove is merely suture-like and there is no transverse groove or depression behind the rostrum; Figs. 3 A, 4A), whereas it is present in R. amboinensis (the cervical groove is deep and there is a shallow transverse groove or depression behind the rostrum; Fig. 2 A); (2) the sixth pleomere is 1.2 times longer than wide in the new species (Fig. 4 G), while 0.8–1.0 times as long as wide in R. amboinensis (Fig. 2 B); (3) the posterior margin of the telson is regularly convex and unarmed in R. rudisulcus n. sp. (Fig. 5 J), rather than less convex, usually faintly bilobed, and armed with a minute median spine in R. amboinensis (Fig. 2 B); (4) the antennal peduncle is longer than the antennular peduncle in the new species (Fig. 3 A), whereas the former is shorter than the latter in R. amboinensis (Fig. 2 A); (5) the distolateral margin of the merus of the third maxilliped extends beyond the dorsodistal margin in R. rudisulcus n. sp. (Fig. 5 C), but not reaching or just reaching it in R. amboinensis (Fig. 2 C). Furthermore, the holotype of the new species was collected from soft sediments, suggesting that the species is a burrower, whereas the present study shows that R. amboinensis is associated with sponges or soft corals (see above). The habitat difference may support the recognition of the present new species.
Etymology. From the combination of the Latin, rudem (= rudimentary) and sulcus (groove), in reference to the rudimentary cervical groove of the carapace. Used as a noun in apposition.
description: Published as part of Komai, Tomoyuki, Fujita, Yoshihisa & Maenosono, Tadafumi, 2014, Additional record of Rayllianassa amboinensis (de Man, 1888) from Japan, and description of a new species from Okinawa Island, Ryukyu Islands (Crustacea: Decapoda: Axiidea: Callianassidae), pp. 549-563 in Zootaxa 3835 (4) on pages 554-560, DOI: 10.11646/zootaxa.3835.4.6, http://zenodo.org/record/229567