Asterocheres eugenioi, Bandera, Eugenia & Conradi, Mercedes, 2014

Bandera, Eugenia & Conradi, Mercedes, 2014, A new species of Asterocheres (Copepoda, Siphonostomatoida) with a redescription of A. complexus Stock, 1960 and A. sarsi Bandera & Conradi, 2009, Zootaxa 3827 (4), pp. 542-558 : 546-551

Asterocheres eugenioi sp. nov.

( Figs 2–5 )

Asterocheres suberitis Giesbrecht, 1897 in Norman and Scott 1906

Material examined.— holotype female (preserved in ethanol, NHM 1911.11.8.47277-281) and 8 female paratypes plus one allotype male and 2 male paratypes (preserved in ethanol, NHM 1191.11.8.47277-281) associated with Suberitis domuncula (Olivi) , collected in Salcombe, Devon ( Great Britain), on September of 1903 by Norman.

Description of adult female. Body cyclopiform, slender with cephalothorax oval and cylindrical urosome ( Fig. 2 A). Total length measured from rostral margin to posterior margin of caudal rami (excluding caudal setae) 585 µm; maximum width 384 µm. Ratio of length to width of prosome 1.1:1. Ratio of length of prosome to that of urosome 2.6:1. Prosome comprising cephalothorax fully incorporating first pedigerous somite and 3 free pedigerous somites. Epimeral areas of somites bearing legs 2 and 3 with pointed posterolateral angles ( Fig. 2 A). Somite bearing leg 4 much smaller and narrower than preceding ones.

Urosome 4-segmented comprising leg 5-bearing somite, genital double-somite and 2 free abdominal somites. Posterior margin of urosomites ornamented with hyaline frills with serrated free margins. Somite bearing leg 5 wider than long. Genital double-somite about 1.25 times wider than long, bearing genital apertures, paired gonopores located dorsolaterally; lateral margins with setular rows along distal third, posterior to genital apertures ( Fig. 2 B). Each genital area armed with one plumose seta and one spiniform element. Integumental pores and sensilla present on urosomal somites ( Fig. 2 B).

Caudal rami 1.5 times longer than wide ( Fig. 2 C); armed with 6 setae; seta I absent, setae II-VII all arranged around posterior margin with setae II and VII slightly offset onto dorsal surface.

Antennule 21-segmented ( Fig. 2 D), about 270 µm long; segmental fusion pattern 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)-7, 10(XIII)-2, 11(XIV)-1+1 spine, 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)-3, 20(XXIV-XXV)-3 and 21(XXVI-XXVIII)-6. Segment 10 (XIII) reduced, partly overlapped by distal expansion of compound segment 9 (IX-XII).

Antenna biramous ( Fig. 2 E), about 195 µm long; coxa unarmed, with few spinules; basis unarmed, with fine spinule rows. Exopod 1-segmented, with one small lateral seta and two terminal setae. Endopod 3-segmented; first segment elongate, ornamented with lateral rows of fine spinules; second segment produced distally on medial side but articulating with distal segment proximally on lateral side and armed with one smooth terminal seta. Third segment with distal claw and two subterminal plumose setae; claw provided with fine spinules on lateral margin. Siphon slender, about 195 µm long, reaching to posterior margin of intercoxal plate of leg 1.

Mandible ( Fig. 3 A) comprising stylet-like gnathobase and slender 2-segmented palp. First segment of palp ornamented with rows of spinules; second segment with 2 plumose, unequal apical setae. Stylet with an expansion at the middle of its length.

Maxillule bilobed ( Fig. 3 B); praecoxal endite (inner lobe) more than three times longer than palp (outer lobe). Praecoxal endite armed with 5 distal setae, one of them smooth and short, ornamented with a row of long setules medially and a row of spinules on proximal outer margin. Palp armed with 3 terminal and one subterminal setae, all of them barbed.

Maxilla ( Fig. 3 C) 2-segmented but with partial suture on syncoxa (proximal segment) possibly marking plane of praecoxa-coxa fusion; praecoxal portion bearing flaccid aesthetasc-like element medially, representing tubular extension of external opening of maxillary gland; coxal part unarmed but ornamented with few spinules proximally. Claw-like basis with recurved end and ornamented with spinules distally.

Maxilliped 5-segmented ( Fig. 3 D) comprising short syncoxa, long basis and distal subchela consisting of 3 free endopodal segments armed with distal claw-like element. Syncoxa with one short seta distally; basis elongate and slender, with a row of spinules on lateral margin. First endopodal segment bearing two short setae and one longer distal seta; second endopodal segment armed with one medial seta. Third endopodal segment bearing recurved terminal claw plus additional subapical plumose seta. Distal margin of claw smooth.

Legs 1-4 biramous ( Figs. 4 A-D) with 3-segmented rami. Intercoxal sclerite present in legs 1-4, ornamented with patches of spinules in leg 1. Spine and seta formula as Table 2 .

Coxae of legs ornamented with spinule rows laterally; coxal seta not present in leg 1. Outer spines of exopodal segments in legs 1-4 bilaterally serrate. Lateral margins of exopodal segments with minute serrations; lateral margins of endopodal segments with rows of setules.

Fifth leg ( Fig. 2 B) with protopodal segment incorporated into somite, with outer seta located dorsolaterally; elongate free segment, armed with two larger terminal setae and one shorter terminal seta, all of them smooth.

Sixth leg ( Fig. 2 B) represented by paired opercular plates closing off gonopores on genital double somite; leg armed with one plumose seta and one spiniform element.

Adult male: Body cyclopiform ( Fig. 5 A), slightly slender and shorter than female, with cephalothorax oval and cylindrical urosome. Body length 485 µm and greatest width 290 µm. Prosome comprising cephalothorax fully incorporating first pedigerous somite and 3 free pedigerous somites. Epimeral areas of somites bearing legs 2 and 3 with pointed posterolateral angles ( Fig. 5 A). Somite bearing leg 4 much smaller and narrower than preceding ones. Urosome 5-segmented comprising 5th pedigerous somite, genital somite and 3 free abdominal somites. Genital somite about 1.2 times wider than long, bearing genital apertures posterolaterally on ventral surface ( Fig. 5 B). Appendages as for female except for antennules, maxillipeds, and sixth leg.

Antennule 18-segmented ( Fig. 5 C), about 260 µm long, geniculate; segmental fusion pattern as follow: 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)-7, 10(XIII)-2, 11(XIV)-1+ 1 spine, 12(XV)-2, 13(XVI)-2, 14(XVII)-2, 15(XVIII)-2, 16(XIX-XX)-3, 17(XXI-XXII)-3 and 18(XXIII-XXVIII)-9. Geniculation located between segments 16 (XIX-XX) and 17(XXI-XXII). Segment 10 (XIII) reduced, partly overlapped by distal expansion of compound segment 9 (IX-XII).

Maxilliped 5-segmented ( Fig. 5 D), similar to that of female but basis with a small expansion provided with spinules in proximal half of medial region.

Sixth leg ( Fig. 5 B) forming large opercular plates closing off genital apertures, armed with 2 smooth setae, ornamented with rows of fine spinules.

Etymology. This species is named after Eugenio Bandera, father of the first author.

Distribution. United Kingdom ( Norman and Scott 1906).

Remarks. This species was reported by Norman and Scott in 1906 as Asterocheres suberitis Giesbrecht and was collected in a gathering from Salcombe in 1903. They pointed out that the usual habitat of these specimens was the water-passages of Suberites domuncula , and probably also of other sponges. However, a detailed comparison with the original description revealed that these specimens do not belong to Asterocheres suberitis but represent a new species, Asterocheres eugenioi sp. nov.

The most striking features to distinguish these two species are: (1) The epimeral areas of somites bearing legs 2 and 3 have pointed posterolateral angles in A. eugenioi , thus contrasting with the rounded posterolateral corners of these somites in A. suberitis ; (2) the inner maxillular lobe bears 4 distal setae in A. suberitis vs. 5 distal setae in A. eugenioi ; (3) the maxillary proximal segment of the new species has a flexible setal element resembling an aesthetasc; this element is absent in A. suberitis ; (4) the siphon reaches the posterior margin of the intercoxal plate of leg 1 in the new species but in A. suberitis it barely reaches the insertion of maxillipeds; (5) the leg 1coxal seta is absent in A. eugenioi and it is present, short and plumose in A. suberitis (Taf. 2, I Asterocheres suberitis , Fig. 4 ; Giesbrecht 1899).

This species belongs to a group of congeners possessing a 21-segmented antennule in the female, 2-segmented mandibular palp, and oral cone reaching the intercoxal plate of leg 1. This group is composed by six more species: A. urabensis Kim, 2004 , A. hirsutus Bandera, Conradi & López-González, 2005 , A. peniculatus Kim, 2010 , A. ellisi Hamond, 1968 , A. latus ( Brady, 1872) , and A. hoi Bandera & Conradi, 2013 . There is no information about the length of the siphon in A. tenuicornis . However, this species can be easily separated from the new species due to the length of the caudal rami, six times longer than wide, the longest within the genus ( Eiselt 1965). In contrast, caudal rami are only 1.5 times longer than wide in the new species. Among these six species, A. ellisi , A. urabensis and A. hoi have the caudal rami slightly longer than wide, shorter than A. eugenioi ; and A. hirsutus and A. latus possess a caudal rami equal or longer than 2.5 times longer than wide, longer than in the new species and in A. peniculatus they are about as long as wide ( Bandera & Conradi 2009b; Kim 2004a; Bandera & Conradi 2013; Bandera et al. 2005; Bandera & Conradi 2009a; Kim 2010).

Kim (2010) expressed the requirement of being strict with the definition of the genus Asterocheres , especially in reference to the setation on the rami of legs 1-4, which is quite conservative in this genus. There are only three species, together with the new species here described, with the coxal seta of leg 1 absent: A. pilosus Kim, 2004 , A. trisetatus Kim, 2010 , and A. fastigatus Kim, 2010 . These species do not share any additional significant similarity which justify placing them in a separate genus, it is likely that this common characteristic is a homoplasy (Dr. I.-H. Kim pers. comm.).

In addition, this group of seven species, including A. tenuicornis , can be distinguished from A. eugenioi sp. nov. by the shape of the body because the new species is the only one in the group with the epimeral areas of somites bearing legs 2 and 3 with pointed posterolateral angles, slightly produced into backwardly directed processes.

Figures

FIGURE 2. Asterocheres eugenioi new species (female). A, habitus dorsal; B, leg 5 - bearing somite and genital double-somite; C, anal somite and caudal rami; D, antennule; E, antenna.

FIGURE 3. Asterocheres eugenioi new species (female). A, mandible; B, maxillule; C, maxilla; D, maxilliped.

FIGURE 4. Asterocheres eugenioi new species (female). A, leg 1; B, leg 2; C, leg 3; D, leg 4.

FIGURE 5. Asterocheres eugenioi new species (male). A, habitus dorsal; B, urosome ventral; C, antennule; D, maxilliped.

Tables

TABLE 2. Spine and seta formula of swiming legs for Asterocheres eugenioi n. sp.

	Coxa	Basis	Exopod	Endopod
Leg 1	0-0	1-1	I-1;I-1;III,2,2	0-1;0-2;1,2,3
Leg 2	0-1	1-0	I-1;I-1;III,I+1,3	0-1;0-2;1,2,3
Leg 3	0-1	1-0	I-1;I-1;III,I+1,3	0-1;0-2;1,1+I,3
Leg 4	0-1	1-0	I-1;I-1;III,I+1,3	0-1;0-2;1,1+I,2