Barathricola rimensis Humes, 1999

Ivanenko, Viatcheslav N., Lee, Jimin, Chang, Cheon Young & Kim, Il-Hoi, 2019, Description of Barathricola thermophilus, a new species from a deep-sea hydrothermal vent field in the Indian Ocean with redescription of the Barathricola type species (Crustacea, Copepoda, Cyclopoida), ZooKeys 865, pp. 103-121 : 106-111

Barathricola rimensis Humes, 1999 Figs 4 , 5 , 6 , 7

Material.

Females and males from the type locality dissected by A.G. Humes and marked as Barathricola rimensis in the Zoological Museum of Lomonosov Moscow State University (collection numbers: w.cyc.sch.1.1-1.5). The hydrothermal vent field is at Juan de Fuca Ridge (44°08.6'N, 129°42'W) in the northeastern Pacific, 26 August 1996 at 2254 m depth.

Redescription of female.

Body as in original description. Differs from Barathricola thermophilus sp. nov. in following features.

Caudal ramus ( Fig. 4D ) elongate, 99 × 9 mm, ratio of length to width 11:1. Outer lateral seta located approximately at junction of first and second thirds of ramus. Dor sal seta short. Outermost terminal seta also short, placed dorsally. Innermost terminal seta short. All these setae smooth. Two long median terminal setae 117 mm (outer) and 234 mm (inner), both with lateral setules. Few minute spinules at distal outer corner of ramus.

Antennule ( Fig. 4A ) 14-segmented with numerous subdivisions. Armature formula: 3-8-8-5-3-0-1-0-1-(2 + aesthetasc)-(2 + aesthetasc)-(2 + aesthetasc)-(6 + aesthetasc).

Antenna ( Fig. 5A ) four-segmented, with coxa, basis, and two-segmented endopod, armed with 0, 1, 5, and 7 setae. Exopod absent. Length 122 mm without setae.

Mandible ( Fig. 5B, C ) with coxa having medially directed gnathobase armed distally with row of seven or eight slender teeth. Palp biramous. Basis elongate, with minute exopodal process carrying two long setae, and two prominent setae distally on margin of basis; endopod two-segmented, first segment small, trapezoidal, bearing two setae and row of minute spinules, second segment small with four distal setae and row of minute spinules along anterior edge.

Maxillule ( Fig. 6A ) with large praecoxa bearing arthrite with eight setae; coxa-basis with 3+1 setae; exopod with two short stout setae and two long slender setae; endopod with five setae.

Maxilla ( Fig. 6B ) with praecoxa having two endites, proximal endite bearing four setae, distal endite represented by single seta. Coxa with two endites, both with three setae. Basis with endite bearing three setae, one short, one long and slender, and one stout and claw-like, and having few minute subterminal spinules. Endopod three-segmented, with first segment having two endites with two setae each, small second segment bearing two setae, and minute third segment with four setae.

Maxilliped ( Fig. 6C ) with both coxa and basis swollen medially and bearing three and two setae, respectively; endopod slender, consisting of five segments armed with 1, 1, 1, 1, and 3 setae. Coxae of maxillipeds joined ventrally by one sclerotized line.

Legs 1-4 ( Fig. 7A, C, E ) biramous with three-segmented rami; armature formula for legs 1-4 as in Table 1. Leg 1 ( Fig. 7A ), inner side of basis with barbed spine and row of eight slender curved setules. Leg 3 ( Fig. 7C ) with 2 distal spines on third endopodal segment.

Leg 5 ( Fig. 7F ). Both legs connected by small quadrangular intercoxal sclerite and consisting of coxa, basis, and one-segmented exopod. Coxa and basis with setules along both sides. Basis with outer seta 44 mm long. Exopod 21 mm in greatest dimensions (15.5 mm wide distally) bearing three spines and one seta. Outer marginal barbed spine 57 mm, two terminal spines 58 mm (outer) and 41 mm (inner), both with minute outer spinules and longer inner fringelike setules. Seta between these two spines smooth, 55 mm. Outer margin of segment proximal to spine with setules; distal to spine and along inner side of segment with shorter setules, inner margin with minute spinules.

Redescription of male.

Differs from Barathricola thermophilus sp. nov. in following features:

Caudal ramus ( Fig. 4E ) resembling that of female but shorter, ratio 8.5:1. Antennule ( Fig. 4B, C ) 17-segmented; armature formula (2 + aesthetasc)-(5 + aesthetasc)-4-2-(2 + aesthetasc)-2-2-2-2(2 + aesthetasc)-(1 + spine)-(2 + aesthetasc)-2-[3 + aesthetasc (or 2+aesthetasc)]-[0 (or 1)]-(1 + aesthetasc)-(9 + 2 aesthetascs); eleventh segment with short posterior margin and much longer anterior margin, spine on this segment slender. Legs 1 ( Fig. 7B ) inner side of basis with barbed spine and row of eight slender curved setules. Leg 3 sexually dimorphic; third endopodal segment ( Fig. 7D ) bearing two spines, three setae, and distally two small specialized elements, one curved, non-articulating, spine-like element and one straight element. Leg 5 ( Fig. 7G ) different from that of female in having additional seta on inner margin of exopod (armature formula 0-0; 1-0; I, I+1+I, 1).

Remarks.

Martínez Arbizu (2006) established the family Schminkepinellidae into which he incorporated five genera, Cyclopinella , Muceddina , Barathricola , and his two new genera Einslepinella and Schminkepinella . The family is a monophyletic group of genera distinguished from other cyclopoid families by the reduction of a maxillulary coxal endite and the transformation of the distal inner seta on the middle endopodal segment of leg 3 into a spine ( Martínez Arbizu 2006). None of the synapomorphies for the order Cyclopoida (a brush-like seta on the exopod of mandible, a brush-like seta on the exopod of maxillule, one or more flange-like setae on the endopod of swimming leg 4, pores with sensory dendrites laterally on the male cephalosome) proposed by Abiahy et al. (2006) are found in Schminkepinellidae . Karanovic (2008) described Cyclopinella tincanbayensis as a new species and synonymized two monotypic genera Muceddina and Barathricola with Cyclopinella and included these genera within Cyclopinidae based on the two major characters as synapomorphic shared by these nominal genera and Cyclopinella : the third endopodal segment of leg 4 with all armature elements transformed into spines and the three-segmented female leg 5 with an uniform armature and the elongate exopod. Karanovic (2008) recognized the mandibular palp as the most important morphological character differentiating species of Cyclopinella and its reduced segmentation and setation is consistent with reductions in other cephalic appendages and in the maxilliped. Our re-examination of the type species of the genus Muceddina , confirmed the original description and did not reveal the presence of a sexually dimorphic leg 3. This as well as our re-examination of the type specimens of Barathricola rimensis does not provide sufficient support for inclusion of Muceddina multispinosa and Barathricola rimensis in Cyclopinella . Additional data are needed to provide for the proposed taxonomic changes; here Barathricola and Muceddina are considered valid genera with clear distinctive characters separating them from other genera (see Key and Table 2). Cyclopinella tincanbayensis should remain in Cyclopinella although its distinctive characters may be significant enough to consider moving it to a new genus after revision. Barathricola , Cyclopinella , and Muceddina should remain in the Schminkepinellidae as was proposed by Martínez Arbizu (2006) until more data are available.

Data here show that the sexual dimorphism in leg 3 occurs in B. thermophilus and B. rimensis . Thus, the sexually dimorphic leg 3 known from the two species living in the hydrothermal vent environment is clearly the derived character of the genus Barathricola as mentioned by Martínez Arbizu (2006). Barathricola thermophilus sp. nov. shares with B. rimensis the shape of the mandibular palp and a number of other characters, e.g., Humes (1999) described the mandibular exopod of B. rimensis as "a minute process carrying two long setae", but his illustrations and those here for this appendage show that the exopod is indistinctly 3-segmented, with two setae on the third segment, as in B. thermophilus sp. nov. In addition, the two species share the identical armature formula for the antenna (0-1-5-7), the loss of an inner seta on the basis of the mandible, a two-segmented mandibular endopod bearing two and four setae on the first and second segments, respectively, and elongate caudal rami.

Although the two species of Barathricola are very similar to each other, they cannot be treated as conspecific due to a significant difference in leg 5 of the male. The exopod (terminal segment) of leg 5 is armed with three spines and two setae (formula I, I+1+I, 1) in B. rimensis , in contrast to three spines and one seta (formula I, I+1+I) in B. thermophilus sp. nov. lacking a seta on the inner margin of the exopod. Within the Schminkepinellidae males of six species are known, including B. rimensis and B. thermophilus sp. nov. In these species a sexual dimorphic leg 5, as in B. rimensis , is known in Muceddina multispinosa , Schminkepinella plumifera , and Einslepinella ulrichi . However, Sars (1913) recorded that leg 5 of male Cyclopinella tumidula is of exactly the same appearance as in the female. Thus, the sexual dimorphism in leg 5 appears to be a character differentiating species, but not genera, in the Schminkepinellidae . An additional morphological difference between the two species of Barathricola is the ratio of the length to the width of the caudal ramus is 11.0:1 in the female and 8.5:1 in the male of B. rimensis , which is 8.9:1 in the female and 6.1:1 in the male of B. thermophilus sp. nov.

Figures

Figure 4. Barathricola rimensis Humes, 1999: A antennule of female B antennule of male, distal segments 8 - 17 C antennule of male, proximal segments 1 - 12 D caudal ramus of female E caudal ramus of male. Scale bars: 0.05 mm.

Figure 5. Barathricola rimensis Humes, 1999, female: A antenna B mandible C distal part of the mandibular gnathobase. Scale bars: 0.05 mm.

Figure 6. Barathricola rimensis Humes, 1999, female: A maxillule B maxilla C maxilliped. Scale bars: 0.05 mm.

Figure 7. Barathricola rimensis Humes, 1999: A leg 1 of female, inner part of protopod B leg 1 of male, inner part of protopod C leg 3 of female, distal endopodal segment, posterior D leg 3 of male, distal endopodal segment, anterior E leg 4 of female, endopod, anterior F leg 5 of female, exopod, anterior G leg 5 of male, distal segment. Scale bars: 0.05 mm.