A new species of Calaxius Sakai & de Saint Laurent, 1989, from the Galapagos Islands (Crustacea: Decapoda: Axiidae)

-Calaxius galapagensis, a new species, is described on the basis of two ovigerous females from coral rubble in shallow water at North Plaza off Isla Santa Cruz, Galapagos Islands. The species is compared with the eight previously described species of Calaxius Sakai & de Saint Laurent, 1989, and characterized by a strongly tridentate rostral apex, and by rows of corneous spine-like setae on pereopods 3 and 4. While engaged in an ongoing survey of the crustacean fauna of the Galapagos Islands in August 1997, one of us (CPH) collected two female specimens of a creamyyellow axiid shrimp bearing robust chelipeds fringed with long setae. The shrimp were at first identified as Neaxius vivesi (Bouvier, 1895), which they superficially resemble, but a more careful examination revealed that they were an undescribed species of the axiid genus Calaxius Sakai & de Saint Laurent, 1989. The specimens were collected by hand at a depth of approximately 6 meters along the western end of North Plaza (Plaza Norte), one of a pair of small islets lying off the east side of Isla Santa Cruz. Both specimens were found beneath rocks in coral rubble where they had built burrows. This habitat parallels that ofAxiopsis baronae Squires, 1977, an axiid shrimp that we have collected throughout the archipelago, (and also known from Pacific Colombia, Peru and Mexico). The specimens were photographed immediately after the dive, then preserved in 70% ethanol. The only other axiids known from the Galapagos are Eiconaxius cristagalli (Faxon, 1893), a sponge inquiline known from deep water (717 m) between Isla Santa Cruz and Isla San Cristobal, and Coralaxius galapagensis Kensley, 1994, recorded from Sullivan Bay, Isla San Salvador. USNM National Museum of Natural History, Smithsonian Institution. Carapace length is measured from posterior margin of orbit to posterior margin of carapace. Family Axiidae Huxley, 1879 Calaxius Sakai & de Saint Laurent, 1989 Calaxius galapagensis, new species Fig. 1 Material examined.-Holotype, USNM 308977, ovigerous female, carapace length 11.9 mm, sta 97-384, west end of North Plaza, 6 m, colI. C. P. Hickman, Jr., 28 Aug 1997. Paratype, Charles Darwin Research Station 97-385, ovigerous female, carapace length 11.0 mm, same data as holotype. Description of holotype.-Integument hard, brittle, with numerous scattered clumps of setae. Carapace (Fig. lA) with posterodorsal region faintly rugose/pitted; rostrum (Fig. IB) twice length of eyes, apically tridentate, with median spine set at lower level than 2 subterminal spines; strong supra-ocular spine; lateral carina extending posteriorly, bearing 2 strong spines posterior to orbit, plus row of 5 spines decreasing in size posteriorly; submedian carina of 5 small spines; median carina having 3 strong spines anterior to tubercle, 5 small spines posterior to tubercle; 3 small spines between anterior median and submedian carinae. Abdominal somite 1 with triangular pleura ventrally subacute; pleura 2-6 (Fig. lA) ventrally broadly rounded, bearing fringe of setae. Telson (Fig. Ie) as long as basal width, lateral margin with 2 or 3 serrations, posterior margin evenly convex, with 3 articulating spines posterolaterally (spines sometimes lost); dorsal surface bearing 2 pairs of fixed spines. Rostrum reaching beyond antennular peduncle; flagella subequal in length to carapace. Antennal flagellum missing on both sides; acicle slender, crescent-shaped, reaching about midway along peduncle article 4; peduncle article 3 with strong dorsal and ventral spine. Maxilliped 3 (Fig. IF), basis with strong posterodistal spine; merus with 2 strong spines in distal half of posterior margin, latter bearing elongate setae; carpus with small posterodistal spine; carpus, propodus and dactylus bearing strong clumps of setae. Pereopod 1, chelipeds (Fig. ID, E) similar in length and spination, with right slightly more robust than left; ischium having 4 spines on lower margin; merus with row of 7-10 spines on lower margin, 2 distalmost spines strongest, 2 or 3 spines on distal part of upper margin; carpus having single strong spine distally on upper surface, flattened spine on flange of ventrolateral surface; propodus strongly setose, especially dorsally, with row of 5 strong curved spines along upper margin, dorsolateral surface granular, strong spine on lateral surface at base of fixed finger; fixed finger and dactylus with irregular tubercles on cutting edges. Pereopod 2 (Fig. IG), merus with 3 spines on lower margin; dactylus, propodus and carpus setose along upper and lower margins; cutting edges of chela bearing fine spine-like setae. Pereopod 3 (Fig. IH), merus with 3 or 4 spines on lower margin; propodus with 5 ventrolateral rows of spine-like setae, 3 rows near upper margin; dactylus with 3 spines on lateral surface. Pereopod 4 (Fig. 11), merus with 3 spines on lower margin; propodus with 7 rows of spine-like setae along posterior margin, 4 rows near anterior lateral margin; dactylus with double row of fine spine-like setae. Pereopod 5 (Fig. 11), propodus with 3 spine-like setae on posterodistal margin, row of spine-like setae along distal margin, plus strongly setose patch in distal half; dactylus ventrally hollowed. Pleopod 1 consisting of single slender ramus. Uropodallateral ramus (Fig. Ie) bearing 6 serrations along lateral margin, 10 spines along transverse suture, 6 spines on dorsal surface; mesial ramus with 4 serrations along lateral margin, row of 5 strong spines on middorsal rounded ridge, distalmost reaching well beyond margin. Color.-Body overall creamy yellow-orange, with diffuse red patches on dorsal carapace, anterior and posterior margins of pleura, mesial and lateral surface of pereopod 1 propodal palm, especially at base of fingers, margins of pereopodal articles, uropodal and telsonic spines. Tips of pereopod 1 chela fingers white. Strong red patch on epistome. Eggs yellow. Variation.-Paratype: slight differences in spination from holotype. Rostrum (Fig. lK) damaged, with apical and left subapical teeth fused. Foraminiferan on dorsal base of rostrum. Four pairs of small spines between median and submedian carinae of carapace (3 in holotype). Eight small spines on dorsal surface of uropodal lateral ramus (6 in holotype) (Fig. 1L); 7 serrations on lateral margin of mesial uropodal ramus (4 in holotype). Telson with 3 articulating spines posterolaterally on each side; tubes of 2 newly settled spirorbid polychaetes present on dorsal surface. Remarks.-Sakai & de Saint Laurent (1989) included eight species in their new genus Calaxius, with C. acutirostris Sakai & de Saint Laurent, 1989, designated as the type species. These include three species from the western Atlantic and five from the Fig. I. Calaxius galapagensis, new species. A-J, holotype, USNM 308977; K-L, paratype, Charles Darwin Research Station no. 97-384. A, carapace and abdomen in lateral view, scale = 5 mm; B, anterior carapace in dorsal view; C, telson and right uropod; D, right pereopod I; E, left pereopod 1; F, maxilliped 3; G, pereopod 2; H, pereopod 3; I, pereopod 4; J, pereopod 5; K, anterior carapace in dorsal view (with foraminiferan on rostrum); L, telson (with 2 spirorbid polychaete tubes) and right uropod.