Leonardsaxius amurensis ( Kobjakova, 1937 )

Marin, Ivan, 2015, Complete morphological re-description of mud-dwelling axiid Leonardsaxius amurensis (Kobjakova, 1937) with remarks on Axiidae (Crustacea: Decapoda: Axiidea) from the Russian coast of the Sea of Japan, Zootaxa 3937 (3), pp. 549-563 : 550-557

Leonardsaxius amurensis ( Kobjakova, 1937)

( Figures 1–5 , 8 f, g)

Axius spinulicauda amurensis Kobjakova, 1937: 142 , pl. 2 fig. 9 [type locality: Amur Bay, the Sea of Japan]. Axiopsis spinulicauda amurensis .— Vinogradov, 1950: 223, pl. 24, fig. 102.

Leonardsaxius amurensis .— Sakai, 2011: 125.

Material examined. Holotype: the sex is unknown because of poor condition of the specimen, possibly male (dissected, ZMMU), Sea of Japan, Russia, Peter the Great Bay, Amur Bay, st. 201, depth 31 m, muddy bottom, bottom-grab “Ocean”, coll. N. Tarasova, 0 1 Sept. 1932.

Freshly collected material: 1 non-ovigerous female (dissected, LEMMI), Russia, Sea of Japan, Peter the Great Bay, Vostok Bay, near scientific station “Vostok”, 42°51′14.48″ N 132°46′ 47.24″E, depth 6 m, deep mud bottom, pumped with yabby-pump, coll. I. Marin, 12 July 2011; 2 non-ovigerous females and 2 males ( MIMB, LEMMI), same locality, depth 5–10 m, pumped with yabby-pump, coll. K. Dudka, 14–20 July 2012.

Description. Carapace ( Fig. 2 a, b) smooth, with simple setae on dorsal surface; gastric region weakly convex, with distinct cardiac notch; median carina well marked, with several rounded teeth, extending from base of rostrum to about midlength of gastric region; submedian carinae short and unarmed; anterolateral margin ( Fig. 2 b) bluntly produced at infraorbital position, unarmed; pterygostomian angle produced anteriorly, broadly rounded. Rostrum ( Fig. 2 a, b) broad, about 0.3 times as long as carapace, slightly turned forward, gradually tapering to acute, with upturned apex; dorsal surface concave, lateral margin with 4-5 teeth; ventral surface unarmed; lateral rostral carinae unarmed, not reaching level of posterior end of median carina.

Pleon ( Fig. 2 d) smooth, with tufts of long simple setae on dorsal surface of each somite; pleura of second to sixth somites unarmed ( Fig. 2 c); ventral margin of sixth somite rounded, with prominent, sharp process at posteroventral comer.

Telson ( Fig. 2 d) subrectangular, about 1.2 times as long as proximal width, dorsal surface with shallow median depression, with 2 sharp submedian teeth at 0.4 length and 2 sublateral carina armed with 2 sharp teeth at 0.4 and 0.7 length; lateral margins with 1 movable spine (or spiniform setae) and 2–3 fixed teeth ( Fig. 2 c); posterior margin broadly rounded, with sharply produced apex.

Eyes well developed ( Fig. 2 a, b); cornea rounded; eyestalk broad, equal to cornea.

Antennula ( Fig. 2 b) with peduncle shorter than antennal, basal segment about 2 times as long as next segment, with small spine on lateral surface of statocyst lobe; Penultimate and ultimate segments as long as wide, unarmed; dorsal and ventral flagella about as long as carapace, bearing short setae on distal margin of each article.

Antenna ( Fig. 2 a, b) with basal segment armed with 2 small teeth on ventrodistal margin; second segment with dorsolateral distal angle produced in strong tooth, overreaching midlenght of the next segment, and smaller sharp distoventral tooth; third segment with distinct tooth at ventromesial distal angle, reaching to the distal margin of the next segment; fourth segment unarmed, slender, about 3 times as long as wide; fifth segment less than half length of fourth segment, unarmed. Antennal flagellum much longer than ventral antennular flagellum, with several short to long setae on each article.

Third maxilliped ( Fig. 3 a) overreaching distal margin of antennal peduncle; coxa about 1.3 times as long as wide, with arthrobranch-podobranch and epipod; basis about as long as wide, with sharp tooth medially, with long segmented exopod, overreaching distal margin of merus; ischium unarmed, about 3 times as long as wide, with straight margins; crista dentate composed of acute teeth noticeably enlarged distally; merus short, about 2 times as long as wide, with 3 long sharp teeth on distal half of ventral margin; carpus stout, about 1.5 times as long as wide, with robust sharp tooth on ventrodistal margin; propodus nearly as long as carpus, unarmed, with straight margins; dactyls shorter than propodus, tapering distally.

First pereiopod ( Fig. 1 , 3 b, c, 4g –j) equal in shape and slightly dissimilar in size. Major first pereiopod ( Fig. 3 b) with smooth segments covered with long simple setae; coxa about 1.3 times as long as wide, bearing small spine distoventrally; basis almost quadrate, unarmed; ischium short, about as long as wide, with small acute spine distoventrally; merus subcylindrical, with smooth surface, becoming concave in its mesial part; dorsal surface almost straight, ventral surface convex, armed with 4–6 sharp spine in proximal half, prominent subdistal spine; carpus short, triangular, about 0.4 times as long as merus, unarmed, inflated ventrolaterally; propodus smooth, compressed laterally, about 1.5 times as long as wide, equal to merus, slightly concave in its mesial part; dorsal margin sharply carinate, terminating in small subdistal spine; ventral surface carinate, with 1 subdistal sharp teeth in males, sometimes absent in females; fingers equal, simple, about 0.7 times as long as palm; pollex (fixed finger) tapering distally in acute apex, about 2.5 times as long as proximal width, with straight cutting edge, armed with sharp mesial tooth; dactyl about 2.5 times as long as wide, gradually tapering distally in acute apex; dorsal margin concave, distinctly carinate; lateral surface with median carina becoming obsolete in distal half, cutting edge straight, without teeth. Minor first pereiopod ( Fig. 3 c) generally similar to major, slightly smaller in size, sometimes with 2 subdistal teeth along ventral margin of palm (propodus) in males and smooth, with 1 tooth or unarmed in females, fingers more slender, with unarmed cutting margins.

Second pereiopod ( Fig. 3 d) chelate; coxa unarmed, about as long as wide; basis quadrate, as long as wide; ischium unarmed, about 1.3 times as long as wide, with concave ventral margin; merus about 6 times as long as wide, compressed laterally, dorsal margin straight, unarmed, ventral margin slightly convex, armed with 3–4 sharp teeth, situated a proximal half, and tufts of long setae; carpus widening distally, about 2.5 times s long as distal width, unarmed, with sparse row of long setae over entire length; propodus about as long as carpus, slightly compressed, unarmed, with straight dorsal and ventral margins, armed with tufts of long simple setae; fingers (polex and dactylus) similar, about 0.5 times as long as propodus, with straight cutting margins tapering with sharp tips.

Third pereiopod ( Fig. 4 m) with simple unarmed segments; coxa unarmed, about as long as wide, basis about as long as wide, unarmed; ischium slender, about 2 times as long as wide, slightly widening distally, with straight unarmed margins; merus about 5.5 times as long as wide, with straight unarmed margins; carpus about 4 times as long as wide, about 0.5 times as long as merus, and about 0.8 times as long as propodus, slightly widening distally, with straight margins armed with tufts of long simple setae; propodus about 6 times as long as wide; dactyl simple, about 0.2 times as long as propodus, 0.37 times as long as propodus, curved, paddle-like, sharp distally.

Fourth and fifth pereiopods ( Fig. 1 ) generally similar to third, with slightly slender segments; coxa unarmed, about as long as wide; basis about as long as wide, unarmed; ischium slender, about 2 times as long as wide, slightly widening distally, with straight unarmed margins; merus about 5 times as long as wide, with straight unarmed margins; carpus about 6 times as long as wide, about 0.5 times as long as merus, and about 0.8 times as long as propodus, slightly widening distally, with straight margins armed with tufts of long simple setae; propodus about 8 times as long as wide, with straight margins; dactyl simple, about 0.2 times as long as propodus, curved, paddle-like, sharp distally.

Branchial formula is similar to that given by Kensley (1996) for the genus Calocarides Wollebaek, 1908 . Two trichobranchiate arthrobranchs and epipod on each third maxilliped to fourth pereiopod. Reduced podobranch present on each third maxilliped to third pereiopods. Pleurobranchs absent.

Uropod ( Fig. 2 c) with unarmed protopodite; endopod with lateral margin slightly convex, with two large sharp teeth at 0.5 and 0.9 length; submedian carina on dorsal surface feebly developed, short and unarmed; exopod with lateral margin slightly convex, armed with medium teeth terminating in tooth posteriorly; distal margin rounded, overreaching distolateral spine, unarmed; lateral carina on dorsal surface unarmed, submedian carina with 1 small distal tooth; uropodal suture distinct, armed with numerous medium teeth.

Coloration. Body and appendages generally reddish-orange, eyes cornea white ( Fig. 1 c–e, 4).

Measurements. Holotype specimen has TL 55 mm, PCL is about 24 mm. Largest freshly collected male has TL 75 mm, CL is about 28 mm, female—TL 70 mm, CL is about 30 mm.

Habitats. The species was found living at the depth of 5–10 meters, inside deep silty or muddy bottom, probably, making deep burrows in the substratum. All specimens were collected with the help of a bait suction pump (yabby-pump) separately suggesting that the species inhabits each burrow solitary.

Distribution. The species presently is presently known only from two localities, Vostok Bay near biological scientific station “Vostok” of IBM FEB RAS (42°53'02"N 132°43'38"E), 5–10 meters (the present paper) and the type locality, Amur Bay at the depth of 31 meters (Kobyakova, 1937). Both localities are parts of large Peter the Great Bay bounded east by the Cape Gamov (42°33′27.97″N, 131°13′4.85″E) and west by the Cape Povorotnyy (42°40′46.13″N, 133°2′30.28″E).

Taxonomic position. Presently, Leonardsaxius amurensis is placed into the genus Leonardsaxius Sakai, 2011 that includes two further species, Leonardsaxius spinulicauda ( Rathbun, 1902) and L. werribee (Poore & Griffin, 1979) (the type species of the genus) ( Sakai, 2011). Leonardsaxius werribee is known from Port Philips, Victoria, Australia (the type locality) and Tasmania; Leonardsaxius spinulicauda is known from Pacific coasts of North America from Vancouver to California (the type locality) ( Hart, 1982; Sakai, 2011). Leonardsaxius amurensis is morphologically similar to L. spinulicauda but can be separated by straight rostrum and long median carina reaching almost to cervical groove. Leonardsaxius spinulicauda possesses rostrum curved downward, submedian carinae short and curved anteriorly, and not merging with the median one ( Sakai, 2011). The other specific feature is the coloration of cornea—it is white in L. amurensis ( Fig. 1 , 4 a–d) and black in L. spinulicauda (after Hart, 1982). At the same time, all species of the genus can be clearly separated geographically.

Figures

FIGURE 1. Leonardsaxius amurensis (Kobjakova, 1937), general lateral view: a — adult male (LEMMI), b — subadult specimen, probably male (MIMB); c, d — adult male.

FIGURE 2. Leonardsaxius amurensis (Kobjakova, 1937), male (LEMMI): a — front of carapace, lateral; b — front of carapace, dorsal; c — sixth pleomere, telson and uropods, lateral; d — telson and uropods, dorsal.

FIGURE 3. Leonardsaxius amurensis (Kobjakova, 1937), male (LEMMI): a — third maxilliped; b — larger first pereiopod (cheliped); c — smaller first pereiopod (cheliped); d — second pereiopod.

FIGURE 4. Leonardsaxius amurensis (Kobjakova, 1937), color photos, large adult male (LEMMI) (a, d, g) — non-ovigerous female (MIMB) (b, c, e, f, h – m): a, b — front of carapace, lateral view; c, d — carapace, dorsal view; e — sixth pleomere, telson and uropods, lateral view; f — same, dorsal view; g, h, i — first major pereiopod; j, k — first minor pereiopod; l — second pereiopod; m — third pereiopod.

FIGURE 5. Leonardsaxius amurensis (Kobjakova, 1937), holotype (ZMMU): a — front of carapace, lateral view; b — front of carapace, dorsal view; c — telson and uropods, dorsal view; d — first major pereiopod; e — first minor pereiopod; f — second pereiopod.

FIGURE 8. Alive coloration of Boasaxius princeps (Boas, 1880) (a – e) and Leonardsaxius amurensis (Kobjakova, 1937) (f, g).