Setacheres eudistomus, Johnsson, Rodrigo, Bahia, Cristiano & Neves, Elizabeth, 2016

Johnsson, Rodrigo, Bahia, Cristiano & Neves, Elizabeth, 2016, A new genus of Asterocheridae (Copepoda: Siphonostomatoida) ectoassociate of the ascidian Eudistoma vannamei Millar, 1977 (Polycitoridae) from Brazil, Zootaxa 4114 (2), pp. 162-170 : 165-168

Setacheres eudistomus sp. nov.

( Figs. 2–4 )

Material examined. Holotype female ( UFBA 1722) and two paratype females ( UFBA 1723); ( UFBA 1724), Porto da Barra Beach (13°0'14.01"S, 38°32'3.14"W), Salvador city, Bahia State, Brazil, collected by C. Bahia and V. Queiroz on 10 December 2012. All specimens were found attached externally on the tunic of Eudistoma vannamei . Paratype ( UFBA 1723) dissected and mounted on slide. Remaining types preserved in alcohol.

Description of female. Mean body length (excluding caudal setae) 740 µm (736–744 µm) and mean body width 431 µm (428–434 µm) (n = 3). Body ( Fig. 2 A) cyclopiform, dorsoventrally flattened, prosome longer than wide, and urosome cylindrical. Pedigerous somite 1 completely fused to cephalosome to form cephalothorax. Pedigerous somites 2–4 with lateral posterior margins rounded. Pedigerous somite 3 more curved, longer than pedigerous somite 2 and partly covering pedigerous somite 4. Pedigerous somite 4 smaller than third somite and slightly larger than fifth somite.

Prosome 511 µm long and 431 µm width. Length: width ratio = 1.2:1. Urosome ( Fig. 2 B) 4-segmented. Fifth pedigerous somite 43 µm long and 113 µm width. Genital double-somite 86 µm long, maximum width 102 µm, length: width ratio = 0.8:1. Vestigial leg 6 mid-laterally located, close to spinule; row of setules along posterolateral margins and two tooth-like projections close to genital openings. Two postgenital somites, both wider than long (36 × 59, 36 × 54 µm, respectively), lateral margins naked; epimera postero-laterally pointed. Ventral surface of anal somite covered by spinules. Prosome: urosome ratio = 2.5:1. Caudal rami ( Fig. 2 B) slightly longer than wide, 27 × 25 µm with spinules along inner margin, with six setae (seta I absent); setae VI and VII naked and setae IV and V plumose. Posterior margin with rounded projection between setae III and IV. Length of setae II–VII 45, 125, 186, 245, 80 and 42 µm, respectively.

Rostrum ( Fig. 2 C) large, wider than long (234 × 145 µm), triangular with rounded apex. Antennule ( Fig. 2 D) 300 µm long (not including setae), 21-segmented. Length of segments: 34, 17, 8, 8, 11, 5, 11, 7, 11, 4, 13, 13, 19, 20, 17, 20, 24, 27, 12, 13 and 6 µm, respectively. Segmental homologies and armature as follows: 1(I)-2; 2(II)-2; 3(III)-2; 4(IV)-2; 5(V)-2; 6(VI)-2; 7(VII)-2; 8(VIII)-2; 9(IX–XII)-6; 10(XIII)-2; 11(XIV)-2; 12(XV)-2; 13(XVI)-2; 14(XVII)-2; 15(XVIII)-2; 16(XIX)-2; 17(XX)-2; 18(XXI)-2 + aesthetasc; 19(XXII–XXIII)-2; 20(XXIV–XXV)-2; 21(XXVI–XXVIII)-6. Aesthetasc 64 Μm long. First segment with both setae plumose at distal half. Segments 9-11 with distal tooth-like projection.

Antenna ( Fig. 3 A) 211 µm long (including distal claw); coxa 25 µm long, with small seta along outer margin; basis 54 µm long, with sparse spinules along inner margin and setules along outer margin. Exopod 1-segmented, 11 µm long, with two apical setae and small lateral seta; all setae naked. Endopod 3-segmented; first segment 59 µm long, unarmed; second segment 9 µm long, armed with naked seta; third segment 12 µm long, armed with two distal setae, small seta proximally and distal claw (52 µm long).

Oral cone ( Fig. 3 B) 162 × 61 µm (long × width), reaching to point between bases of maxillipeds and leg 1. Mandible ( Fig. 3 C) with 2-segmented palp; both segments slender and naked, measuring 18 and 13 µm long, respectively; second segment with two distal setae, smallest seta spinulated and half the length of longer one which is unilaterally spinulated. Mandibular stylet 122 µm long, proximally stout, tapering distally with ten subterminal teeth. Maxillule ( Fig. 3 D) bilobed; inner lobe 36 µm long, with five distal setae, one of them smaller and more slender than the others; three of the remaining setae unilaterally plumose; inner margin of inner lobe with setules proximally and bunch of setules distally; outer margin with set of spinules. Outer lobe 13 µm long, armed with four distal setae, two being plumose; outer margin with few spinules. Maxilla ( Fig. 3 E) 250 µm long, consisting of syncoxa (100 µm long, with tubular extension of maxillary gland opening) and strongly distally curved claw with naked seta near inner subdistal margin.

Maxilliped ( Fig. 2 F) 5-segmented, 267 µm long; syncoxa 82 µm long, with setules along outer margin; basis 84 µm long, with row of setules and few setules along inner and outer margins, respectively. Endopod 3- segmented, segments measuring 8, 11 and 21 µm, respectively; first segment naked; second one with distal toothlike projection and two naked setae; third segment with serrated spine and distal curved claw-like element, 61 µm long.

Legs 1–4 ( Fig. 4 A −D) biramous, with 3-segmented rami. Armature formula as follows: Leg 1 with setules along outer margin of exopod and endopod; proximal exopod segment with large outer spine and without inner seta; middle exopod segment with small outer spine. Legs 2–4 with spinules and setules along outer margins of exopods and endopods, respectively. Leg 5 ( Fig. 4 E) with three distal setae, with spinules and setules along outer and inner margins, respectively. Intercoxal plate of leg 1 covered with setules, intercoxal plates of remaining legs totally naked.

Male. Unknown.

Type locality. Porto da Barra Beach (13°0'14.01"S, 38°32'3.14"W), Salvador city, Bahia State, Brazil.

Etymology. The specific name “ eudistomus ” refers to the ascidian host of the new species.

Remarks. Among the species belonging to the new genus Setacheres it is recognizable the presence of one to three segments posteriorly to the ancestral antennulary segment XXI indicating their degree of fusion ( Johnsson 1998, Brian 1927, Johnsson et al. 2001, Johnsson 2002). Setacheres eudistomus sp. nov. shows, as observed in S. lunatus and S. paraboecki , 3 segments posterior to the ancestral XXI ( Johnsson 1998). However, in S. paraboecki the ancestral segments IX-XIII are fused and therefore show a total of 20 segments while S. lunatus and the new species share the fusion of articles IX-XII resulting in a 21-segmented antennule. Setacheres eudistomus sp. nov. differs from S. lunatus in its having of 5 setae on the inner maxillulary lobe, instead of 4 in the latter species and a 5-segmented maxilliped vs. a 6-segmented one in S. lunatus ( Johnsson 1998) . The new species shows the first exopodal segment of leg 1 without an inner seta (I-0) while all other species of the new genus shows the regular setation pattern with an inner seta (I-1).

Distribution. The nine species of Setacheres gen. nov. are recorded exclusively from the Atlantic Ocean. Setacheres ventricosus is known from the Aegean Sea, an embayment of the Mediterranean Sea. The remaining eight species have been recorded exclusively from the western Atlantic; most of them are so far restricted to the Brazilian coast. Setacheres picinguabensis is known to occur in São Paulo State, Warm Temperate Southwestern Atlantic province (WTSA) and S. abrolhensis in Bahia State (Johnsson & Neves 2012), Tropical Southwestern Atlantic province (TSA) ( Spalding et al. 2007). Three species, S. lunatus , S. aplysinus and S. spinopaulus are restricted to the northeastern coast, occurring in Bahia, Pernambuco and Alagoas States (Johnsson & Neves 2012), all in TSA ( Spalding et al. 2007). Setacheres paraboecki and S. unicus are the only species recorded in Rio de Janeiro and Bahia States and São Paulo and Alagoas, respectively and therefore occur in both WTSA and TSA provinces. As S. paraboecki is also recorded from Cuba ( Varela 2012), this species ranges in two distinct biogeographic realms, the Tropical Atlantic and the Temperate South America, thus suggesting a wide distributional range than that known in other species as S. unicus . So far, the remaining six species appear to be restricted to the TSA province. These data corroborate the distributional similarity found in other organisms as stony corals, decapods, mollusks and polycladids ( Neves et al. 2006, Neves et al. 2008, Neves et al. 2010, Queiroz et al. 2011, Queiroz et al. 2013, Sales et al. 2011).

Figures

FIGURE 2. Setacheres eudistomus gen. et sp. nov. female (paratype: UFBA 1723). A, body, dorsal view; B, urosome; C, antennule; D, rostrum. Scale bars: A = 300 µm; B = 250 µm; C = 100 µm; D = 50 µm.

FIGURE 3. Setacheres eudistomus gen. et sp. nov. female (paratype: UFBA 1723). A, antenna; B, oral cone; C, mandible; D, maxillule; E, maxilla; F, maxilliped. Scale bars: A – F = 50 µm.

FIGURE 4. Setacheres eudistomus gen. et sp. nov. female (paratype: UFBA 1723). A, leg 1; B, leg 2; C, leg 3; D, leg 4; E, leg 5. Scale bars: A – D = 50 µm; E = 10 µm.