Pentaceration rihothalassa Just, 2011, sp. nov.
Creators: name: Just, Jean
Publisher: name: Zenodo
Year: 2011
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Paramunnidae
Pentaceration
Pentaceration rihothalassa

description: Pentaceration rihothalassa sp. nov.
Figures 21–24
Type fixation. Holotype, male, here designated.
Etymology. The epithet combines the Greek ρηχός (rihos = shallow) and θάλασσα (thalassa = sea) thus ‘of the shallow sea’ denoting that this species can be found at a few meters depth.
Material examine. Holotype, terminal 3, 1.23 mm, Australia, New South Wales, Port Jackson, North Harbour, Sydney, North side of Cannae Point, 33°49'S, 151°17'E, 7 m, sand, shell fragments, much detritus, scattered algae and Posidonia sea grass, hand dredge, SCUBA, J. Just, P.B. Berents, R.T. Springthorpe, 26 September 1984, stn AU 60, NMV J20076 (2 slides).
Paratypes (15 specimens). Same data as holotype, NMV J60997 (ƤA, 1.62 mm, illustrated). Same data as holotype, NMV J20074 (7 3, 6 Ƥ). Same data as holotype, NMV J20075, (1 Ƥ cleared in lactic acid).
Additional material (25 specimens). Yakka Bay, Montague Island, New South Wales, Australia, 36°14.979'S, 150°13.369'E, 15 m, mixed algae: Pterocladia capillacea, Cystophora sp., Plocamium microcladioides, Sargassum sp. (minor amount), by hand on SCUBA, A. Millar & G. Wilson, 23 March 2001, stn NSW 1774, AM P83766 (2 Ƥ). ‘Northwest Trench’, Montague Island, New South Wales, Australia, 36°14.55'S, 150°13.45'E, 33 m, lacy bryozoan colonies at base of trench wall growing in rubble and detritus, by hand on SCUBA, G. Wilson, 24 March 2001, NSW 1775, AM P83767 (12 spms). ‘Northwest Trench’, Montague Island, New South Wales, Australia, 36°14.55'S, 150°13.45'E, 33 m, red algae Spyridia filamentosa and Zonaria diesingiana, by hand on SCUBA, A. Millar & N. Yee, 24 March 2001, NSW 1777, AM P83769 (9 spms, inclusive 3A, 1.38 mm, and ƤA, 1.45 mm). ‘Northwest Trench’ at Montague Island, New South Wales, Australia, 36°14.55'S, 150°13.45'E, 33 m, Lobophora variegata with a little Sargassum, from ‘bommie’ in trench floor, by hand on SCUBA, A. Millar & N. Yee, 24 March 2001, NSW 1781, AM P83768 (1 Ƥ). North side of Burrewarra Point, south of Batemans Bay, New South Wales, Australia, 35°49.776'S, 150°13.955'E, 15 m, under stones with small stones, very little sediment, airlift on SCUBA, RV Baragula and Sula, stn NSW 2540, AM P83770 (1 Ƥ).
Description (male, terminal). Body tapering from pereonite 1 towards pleon; width 0.46 length, widest between pereonites 1 and 2. Head length 0.32 width; length posterior to eyestalks 1.8 anterior length. Frontal margin middle spine length equals width of lateral spines; lateral spines as long as pereonite 1 midlength, straight with marginal denticles, diverging at 80°; all 3 spines with flattened, slightly splayed apex. Eyestalks barely reaching widest lateral point of pereonite 1, pointing forwards at 10º, with broadly rounded apex and few small ocelli.
Pereonite 1 lateral parts strongly expanded, margins concave in distal 2/3, convex proximally; pereonites 2 and 3 lateral spines diverging at 20°; pereonite 2 with flat-tipped marginally denticulate lateral spines as long as 1/3 pereonite width; pereonite 3 spines pointed, half length of pereonite 2 spines; pereonite 4 spines with short point approximately half length of pereonite 3 spine; pereonites 5 and 6 lateral spines subequal, length equal to pereonite 2 spines, but with broader base and posterior lobes overlapping succeeding pereonite: pereonite 7 lateral spine about as long as pereonite 3 spines, pointing backwards at 45º. Tumaculae present on pereonites 6 and 7 (Fig. 21 tum).
Pleon length 0.9 width. Pleonite 1 width 0.5 distance between uropods, length 0.18 width. Pleotelson with slight neck, proximal and lateral margins evenly merging, lateral margins nearly straight, diverging distally, with 16–17 denticles, distolateral corners curved inwards in acute hook-like denticle; distal projection triangular at 60°, apex broadly rounded, 0.23 length of entire pleotelson.
Antennula articles 1 and 2 combined reaching to apex of eyestalks; articles 1 and 2 of equal length, 1 wider than 2, tubular; 3 and 4 of equal length, both 2/3 length of subequal 5 and 6.
Antenna article 2 in ventral view approximately four times length of 1; 3 width 0.27 length, with small denticle laterally in distal half; 5 length 1.6 times 4; 6 twice length of 5; flagellum with 9 articles, first articles 1.25 length of 2, all articles slender.
Pereopod I basis length 3.75 times width; ischium length half length of basis, anterior margin with single acute spine; merus with single acute spine on anterior margin; carpus irregularly rectangular, margin distal to robust setae strongly concave with rounded translucent flange in front of distal robust seta, propodus narrowing distally to insertion of dactylus, with 1 robust seta on opposing margin. Pereopods II–VII slender; propodus with 2 slender robust setae on posterior margin.
Pleopod I lateral sublobes rounded, similar, partly overlapping, width 0.3 distance to midline; distal projection length 0.25 pleopod total length, forming acute angle of 75º, with bluntly pointed apices. Pleopod II protopod rounded distally, lateral margin with simple setae; endopod article 2 (stylet) forming 130° curve.
Uropods recessed into low protruding cuticle tube with medial projection, protopod hidden, exopod vestigial, hidden, with single seta protruding; endopod length 2.5 width.
Female (paratype ƤA). Head and pleon configuration similar to male; lateral head spines diverging at 100°. Pereonite 1 similar to male but smaller; pereonites 2 and 3 lateral spines shorter and broader than in male, diverging at 20°. Pereopod I carpus oval, distal margin straight. Pleopod II (operculum) ovoid with concave distal margins, apex broadly rounded, width 0.7 length.
Size. Largest female, 1.54 mm; largest male, 1.46 mm.
Distribution. Australia, New South Wales, Port Jackson, 7 m.
Remarks. Specimens from Montague Island and Burrewarra Point, south of Batemans Bay (Other material) differ from the population at the type locality Port Jackson as follows: head front margin spines are broader, the middle spine slightly longer relative to the lateral ones. Head and pereonite spine margins are more heavily denticulate. The medial cuticle projection at uropod insertion is longer and spiny. These differences are consistent, also in small specimens. In all other respects these specimens share diagnostic characters with the type material.
Considering the generally greater level of difference among Pentaceration species, it does not seem justified, at present, to create a separate species for the Montague Island and Burrewarra Point specimens. Additional material from several places in the presently large distributional gap between the two forms may resolve this issue.
description: Published as part of Just, Jean, 2011, Remarkable Australasian marine diversity: 18 new species in Pentaceration Just, 2009 (Crustacea, Isopoda, Paramunnidae), pp. 1-54 in Zootaxa 2813 on pages 32-35, DOI: 10.5281/zenodo.203856