Synalpheus maxillispinus, Anker, Arthur & Pachelle, Paulo P. G., 2014

Anker, Arthur & Pachelle, Paulo P. G., 2014, Taxonomic notes on some Brazilian species of Synalpheus Spence Bate, 1888, with new records and description of a new species (Decapoda, Alpheidae), Zootaxa 3815 (2), pp. 215-232 : 218-221

Synalpheus maxillispinus sp. nov.

( Figs. 2 , 3 )

Material examined. Holotype: female (cl 3.0 mm), Brazil, Abrolhos Bank off southern Bahia and northern Espírito Santo, REVIZEE—Comissão Central: 2, R/V Astro Garoupa, station 17C, 18°34’00”S 38°04’00”W, depth: 55 m, 22.XI.1997 [ MZUSP 30093]. Paratypes: 1 male (cl 2.6 mm), same collection data as for holotype [ MZUSP 30094]; 1 male (cl 3.5 mm), Brazil, Espírito Santo, off Rio Doce, TAAF MD-55/ Brasil 1987, station 51/ DC–87, 19°39’S 39°42’W, depth: 15 m, 29.V.1987 [ MZUSP 30095].

Description. Rostrum slightly lower than orbital hoods, triangular, distinctly longer than wide at base, subequal or slightly longer than orbital teeth, subacute distally; orbital teeth triangular, subacute, longer than wide at base; frontal margin between orbital teeth and rostrum deeply concave, forming with rostrum V- to U-shaped notches, adjacent rostro-orbital area slightly depressed ( Fig. 2 A, B, L).

Pleuron of first abdominal somite rounded posteroventrally, without hook; pleura of third to fifth somites also rounded, fifth slightly more angular ( Fig. 2 C). Telson moderately broad, about 1.5 times as long as anterior width, tapering distally; dorsal surface with broad, longitudinal, median depression and two pairs of strong spiniform setae inserted at about 0.4 and 0.7 length of telson, respectively; posterior margin rounded, less than half-length of anterior width, with two stout spiniform setae, mesial much longer than lateral ( Fig. 2 D).

Antennular peduncle with second article 1.3–1.6 times as long as wide; stylocerite falling short of distal margin of first article, with blunt or subacute tip ( Fig. 2 A, L). Antennal basicerite with blunt, non-projecting distodorsal tooth, and strong distolateral tooth reaching at least to middle of second article of antennular peduncle; scaphocerite with strong broad distolateral tooth reaching beyond end of antennular peduncle; blade always present, slender, not reaching mid-length of scaphocerite, slightly overreaching distolateral tooth of basicerite, fringed with short setae ( Fig. 2 A, B, L).

Mouthparts typical for genus. Third maxilliped with ultimate article bearing one dorsal row of six short spiniform setae, one ventral row of three longer spiniform setae and crown of seven or so stouter spiniform setae on apex ( Fig. 2 E, F).

Major cheliped with palm 2.5–2.8 as long as dactylus; distodorsal tooth on palm not greatly protruding, ending blunt distally, without acute point; dactylus reaching distinctly beyond pollex ( Fig. 3 A–E). Minor cheliped with palm about 1.3 times as long as fingers, latter with cutting surfaces excavated and bidentate tips; dactylus with very few tufts of setae not organised in rows ( Fig. 3 F, G).

Second pereiopod with five-articulated carpus, first carpal article about four times length of second, about as long as sum of second to fifth articles ( Fig. 2 G). Third pereiopod with merus about three times as long as wide; propodus with six spiniform setae on ventral margin and one pair of spiniform setae on distoventral margin; dactylus biunguiculate, moderately stout, secondary unguis subparallel to and shorter than terminal unguis ( Fig. 2 H, I). Fifth pereiopod with propodus armed with five spiniform setae on ventral margin; grooming brush well developed ( Fig. 2 J).

Uropodal exopod with distolateral margin bearing two strong teeth (including lateral tooth of diaeresis) and one or two spiniform seta(e) ( Fig. 2 K, M).

Colour in life unknown.

Type locality. Brazil: Abrolhos Bank off southern Bahia / northern Espírito Santo (holotype and first paratype) and off Rio Doce, Espírito Santo (second paratype).

Distribution. Southwestern Atlantic: presently known only from two localities off eastern Brazil (southern Bahia and Espírito Santo).

Etymology. The specific name refers to the presence of the characteristic spiniform setae on the ultimate article of the third maxilliped; used as an adjective.

Ecology. The type specimens were dredged from moderate depths of 15–50 m, without records of their sponge hosts.

Remarks. Synalpheus maxillispinus sp. nov. plainly belongs to the Synalpheus paraneptunus species complex recently revised by Anker & Tóth (2008) and with one additional species subsequently added by Hultgren et al. (2011). The S. paraneptunus species complex was originally defined by three morphological characters: (1) the relatively long stylocerite, almost reaching or overreaching the distal margin of the first article of the antennular peduncle; (2) the minor chela fingers broadened and spoon-shaped, i.e. with hollowed cutting surfaces; and (3) the minor chela dactylus with dorsal and lateral setae not organised in rows forming a dense brush, usually forming a single row of scarce setae. Anker & Tóth (2008) recognised additional five species in the complex: Synalpheus duffyi Anker & Tóth, 2008 ; Synalpheus riosi Anker & Tóth, 2008 ; Synalpheus brevidactylus Anker & Tóth, 2008 ; Synalpheus bocas Anker & Tóth, 2008 ; and Synalpheus belizensis Anker & Tóth, 2008 , all from the Caribbean Sea ( Panama, Belize, Dominica). Hultgren et al. (2011) added a seventh species, Synalpheus microneptunus Hultgren, Macdonald & Duffy, 2011 , from Barbados. The S. paraneptunus complex was shown to form a well-supported clade within the S. gambarelloides group in the combined molecular-morphological analysis of Hultgren & Duffy (2011). However, and interestingly, this clade also contained a morphologically more distinctive Synalpheus kensleyi ( Ríos & Duffy, 2007) , which unlike other species of the S. paraneptunus complex is characterised by a rather well-developed brush of gambarelloid setae and a strong acute tooth projecting from the dorsal margin of the antennal basicerite.

Synalpheus maxillispinus sp. nov. is morphologically closest to S. bocas and S. belizensis , sharing with them the presence of two teeth on the distolateral margin of the uropodal exopod, adjacent to spiniform seta. The new species can be separated from S. bocas and S. belizensis by the shorter stylocerite, not reaching (vs. overreaching) distal margin of the first article of the antennular peduncle; the major chela with a short, bluntly ending (vs. more projecting and sharply pointed) distodorsal tooth; specifically from S. bocas by the scaphocerite having (vs. not having) a blade1; and the shorter dorsal spiniform setae on the telson; and specifically from S. belizensis by the more slender third pereiopod, with merus about three (vs. 2.5) times as long as wide (cf. Anker & Tóth 2008).

The presence of two teeth on the distolateral margin of the uropodal exopod separates Synalpheus maxillispinus sp. nov. from S. paraneptunus , S. duffyi , S. riosi , S. brevidactylus , S. microneptunus and S. kensleyi , which all have three teeth. In addition, S. maxillispinus sp. nov. can be separated from S. microneptunus by the presence of five (vs. four) articles in the carpus of the second pereiopod; from S. kensleyi by the minor chela without setae organised in rows (vs. with distinct gambarelloid setae) and the antennal basicerite without (vs. with) acutely projecting dorsal tooth; from S. duffyi and S. brevidactylus by the moderately slender, distally blunter (vs. more slender and acute) orbital teeth and the major chela palm with a bluntly ending (vs. sharply pointed) distodorsal tooth; from S. riosi by the major chela palm with a dorsally non-swollen, bluntly ending (vs. dorsally swollen and with a small sharp point) distodorsal tooth and the minor chela without setae grouped in rows (vs. with setae organised in a single dorsal row) (cf. Ríos & Duffy 2007; Anker & Tóth 2008; Hultgren et al. 2011).

The presence of three spiniform setae on the ventral surface of the ultimate article of the third maxilliped appears to be another important and possibly diagnostic character of Synalpheus maxillispinus sp. nov. Anker & Tóth (2008) did not illustrate these setae in S. paraneptunus , S. duffyi , S. riosi and S. belizensis , although some stout setae in the same position can be seen in their figure 4C of S. duffyi . In addition, Hultgren et al. (2011) illustrated slender spiniform setae (clearly thicker than adjacent serrulate setae) on the third maxilliped of S. microneptunus . Therefore, these spiniform setae may also be present, although less developed, in other species of the S. paraneptunus complex.

All species of the Synalpheus paraneptunus complex are associated with sponges (see Table 1 in Anker et al. 2012 for sponge records) and at least three of them ( S. duffyi , S. riosi and S. microneptunus ) live in social colonies ( Anker & Tóth 2008; Hultgren et al. 2011; Anker et al. 2012). The sponge hosts of S. paraneptunus , S. riosi and S. maxillispinus sp. nov. remain unknown; all sponges listed as hosts for S. paraneptunus in Table 1 of Anker et al. (2012) are in fact sponge records for S. paraneptunus sensu lato and not for S. paraneptunus sensu stricto as redefined by Anker & Tóth (2008). Whether S. maxillispinus sp. nov. is a social or pair-living species presently remains unknown.

Figures

FIGURE 2. Synalpheus maxillispinus sp. nov., A – K, holotype, female (cl 3.0 mm) from Abrolhos Bank, Brazil [MZUSP 30093]; L, M, paratype, male (cl 3.5 mm) from Rio Doce, Espírito Santo, Brazil [MZUSP 30095]: A—frontal region, dorsal; B—same, lateral; C—abdomen, lateral; D—telson, dorsal; E—third maxilliped, lateral; F—same, carpus and ultimate article, mesial; G—second pereiopod, lateral; H—third pereiopod, lateral; I—same, distal propodus and dactylus, lateral; J—fifth pereiopod, lateral; K—uropod, dorsal; L—frontal region, dorsal; M—uropod, dorsal.

FIGURE 3. Synalpheus maxillispinus sp. nov., A, B, holotype, female (cl 3.0 mm) from Abrolhos Bank, Brazil [MZUSP 30093]; C – G, paratype, male (cl 3.5 mm) from Rio Doce, Espírito Santo, Brazil [MZUSP 30095]: A—major (right) cheliped, lateral; B—same, chela, mesial; C—major (left) chela, lateral; D—same, mesial; E—same, distal palm and fingers, lateral; F—minor (right) cheliped, lateral; G—same, carpus and chela, mesial.