Mesanthura pacoi, Castelló, 2017

Castelló, José, 2017, New and little-known species of isopods (Crustacea, Isopoda) from the eastern Mediterranean, Zootaxa 4311 (2), pp. 151-182 : 153-159

Mesanthura pacoi sp. nov.

( Figs 2–5 )

Material examined. Holotype: female, 7.0 mm, sample 1M4, station 1, Famagusta, Cyprus, 35°07’57”N, 33°56’14”E, unknown depth, no ecological data, G. Bitar coll., 23 Nov. 1998 ( MZB2016-3567, 15 slides).

Paratypes: manca, 2.4 mm (sample 2M5, stn. 2: Ramkine Island , Lebanon) dissected, 3 slides ( MZB2016- 3570 ) ; female (sample 2M13, stn. 8: Beirut inside harbor) dissected, 3 slides ( MZB2017-0600 ) ; female, damaged (sample 2M16, stn. 13: Khaldeh Marina Villamar , Lebanon) dissected, 5 slides ( MZB2017-0601 ) ; female (sample 3M13, stn. 4: El Heri Marina Beaulieu , Lebanon) dissected, 3 slides ( MZB2017-0602 ) ; male, damaged (sample 5M8, stn. 10: Beirut Harbor outer side of breakwater, Lebanon) dissected, 2 slides ( MZB2017-0603 ), and female (sample 5M8, stn. 10: Beirut Harbor outer side of breakwater, Lebanon) ( MZB2017-0604 ) ; 3 females (sample 5M12, stn. 9: Beirut inside harbor quay 60, Lebanon) ( MZB2017-0605 to MZB2017-0607 ): ovigerous female dissected, 2 slides ( MZB2017-0605 ), and 1 manca (sample 5M12, stn. 9: Beirut inside harbor quay 60, Lebanon) ( MZB2017-0608 ) ; 2 females (sample 5M17, stn. 11: Raoucheh, Lebanon) (MZB2017-0609 to MZB2017-0610): non-ovigerous female dissected, 2 slides (MZB2017-0610); 2 males (sample 5M19, stn. 3: Tripoli inside harbor, Lebanon) ( MZB2017-0611 to MZB2017-0612 ), 11 females (sample 5M19, stn. 3: Tripoli inside harbor, Lebanon) ( MZB2017-0613 to MZB2017-0623 ): ovigerous female dissected, 2 slides ( MZB2017-0613 ), 1 postmanca (sample 5M19, stn. 3: Tripoli inside harbor, Lebanon) ( MZB2017-0624 ), and 5 mancas (sample 5M19, stn. 3: Tripoli inside harbor, Lebanon) ( MZB2017-0625 to MZB2017-0629 ) ; 4 males (sample 5M23, stn. 12: Beirut Airport pier, Lebanon) ( MZB2017-0630 to MZB2017-0633 ), and 9 females (3 damaged) (sample 5M23, stn. 12: Beirut Airport pier, Lebanon) ( MZB2017-0634 to MZB2017-0642 ): damaged female dissected, 2 slides ( MZB2017-0634 ), another damaged female dissected, 2 slides ( MZB2017-0635 ) ; 1 manca (sample 5M28, stn. 5: Chak El Hatab , Lebanon) dissected, 23 slides ( MZB2017-0643 ) ; 1 manca (sample 5M31, stn. 6: Selaata , Lebanon) dissected, 2 slides ( MZB2017-0644 ) ; ovigerous female, 10.8 mm (sample 5M36, stn. 3: Tripoli inside harbor, Lebanon) dissected, 2 slides ( MZB2016-3568 ) ; male, 6.5 mm (sample 5M36) dissected, 5 slides (MZB2016- 3569); 1 manca (sample 5M45, stn. 5: Chak El Hatab , Lebanon) dissected, 2 slides ( MZB2017-0645 ) ; 2 females (sample 5M51, stn. 12: Beirut Airport pier, Lebanon) ( MZB2017-0646 to MZB2017-0647 ): female dissected, 3 slides ( MZB2017-0646 ). Depth: between 1 and 35 m. G. Bitar & H. Zibrowius coll., between 22 Oct. 1999 and 16 July 2003.

Diagnosis. Color yellowish, without chromatophores. Mandibular palp article 3 with 7 setae. Maxillipedal endite absent; palp 3-segmented, segment 1 with outer margin slightly excavated, apical segment with plumose seta and 3 simple setae mediodistally and robust plumose seta basally. Pereopod 1 palm with shallow crenulated basal step, with 7 setae; propodus expanded with 2 long simple setae near lower angle of articulation with dactylus; dactylus with toothed boss at base of unguis. Uropodal exopod oval, with low concavity on distal outer margin. Telson with apex slightly excavated, with pair of short plumose setae, and 3 pairs of long setae, outer one less than half length of others.

Description of holotype [MZB2016-3567]. Cephalon slightly longer than wide, with small eyes (18–19 ommatidia) of one fourth of length of cephalon, disposed obliquely. Relative lengths of C: Pn1: Pn2: Pn3: Pn4: Pn5: Pn6: Pn7: Pln1–6: Pt are 1.0: 1.3: 1.7: 3.0: 3.1: 2.8: 2.2: 2.1: 2.3: 3.0. Proportions Cephalon-Pleotelson: C<Pn1<Pn2<Pn3=Pn4>Pn5>Pn6=Pn7<Pl<Pt. Greatest width 0.6 mm at level of articulation of pereonites 4–5. Pereonites 2–3 each with anterodorsal hollowed area. Pleonites 1–5 fused; pleonite 6 bilobed. Telson with pair of statocysts at base.

Antenna 1 with 3 peduncular articles; article 1 largest, almost as long as articles 2 and 3 together; articles 1 and 2 with plumose sensory setae and article 3 with 4 long setae distally; first flagellar article extremely short, bearing plumose sensory seta; article 2 twice as long as article 3, without setae; article 3 with 4 long setae and 3 aesthetascs distally. Antenna 2 with 4 peduncular articles bearing simple setae; article 4 with some plumose sensory setae apically; flagellum with 4 articles, first one stouter and as long as the remaining ones, with simple long setae.

Mandible with incisor blunted, with 4 notches; lamina dentata with 5 serrations; pars molaris acute; palp with 3 articles, relative lengths of articles 1.5: 2.2: 1.0; first and second articles with simple long seta mediodistally each; last article with 7 setae. Maxilla with apex of lateral endite slightly curved medially showing strong distal tooth and 6–7 smaller teeth. Maxilliped without endite; small oval epipod; palp of 3 articles; article 1 with 2 simple setae on inner margin, outer margin slightly concave; article 2 widest with simple seta on inner margin, 2 simple setae ventrally near inner margin, 2 simple setae near inner angle of articulation with third article, and simple seta near outer angle of articulation with third article; and apical article with plumose seta and 3 simple setae mediodistally and stouter plumose seta basally. Apical article triangular, clearly surpassing the preceding article; articulation between last two articles almost parallel to preceding one. Two apical articles showing inner margin with numerous thin and long hairs.

Pereopod 1 broadest, subchelate; palm without medial projection, only with shallow crenulated basal step with 5 setae, and 2 setae distally; propodus expanded with 2 long simple setae near lower angle of articulation with dactylus; dactylus with 9 long simple setae distally, 4 of them near lower angle of articulation with unguis; dactylus with toothed boss at base of unguis. Pereopods 2–3 similar, stouter than following ones; propodus not oval, with palm slightly concave. Pereopod 4 shortest, similar to pereopod 5. Pereopods 6–7 more stylized than pereopods 4– 5 and similar in length to pereopods 2–3.

Pleopod 1 with 6 retinaculae on sympod; exopod operculiform, with 30 plumose setae; endopod shorter with 8 plumose setae. Sympod of pleopod 2 with 2 retinaculae; exopod with 10 and endopod with 8 plumose setae.

Uropods as long as telson ; exopod oval, with concavity on distal outer margin; endopod shorter than sympod (1.0: 1.2), 1.5 times longer than wide.

Telson linguiform, 2.2 times longer than greatest width; apex slightly excavate, with pair of short plumose setae, and 3 pairs of long setae, outer one less than half of length than others.

Color in alcohol yellowish, without chromatophores.

Etymology. This species is dedicated to the memory of my father, Francisco (Paco) Castelló-Guasch (Ibiza, 1909–1984), who taught me to appreciate the beauty of marine life.

Remarks. Differences with respect to the female 7.0 mm [MZB2016-3567]: The ovigerous female 10.8 mm [MZB2016-3568] has pereopod 1 with palm bearing 5 simple setae; its color is darker, brownish, with reddish pigment pattern as in Fig. 2 . The male 6.5 mm [MZB2016-3569] has a thinner body, larger eyes (22–24 ommatidia) reaching a length of one third of the cephalon, and longer pleon; the antenna 1 shows a flagellum of 13 articles, the last one the smallest, and the articles 2–12 with numerous long aesthetascs; it extends slightly beyond the cephalon; the pereopod 1 has a narrower propodus than the female, and the palm with serrated medial projection bearing 5 simple setae on external side; the distal half of the palm has 3 simple setae, and the mesial side of the palm shows a strip of numerous simple setae, increasing in length distally; pleopod 1 presents 5 retinaculae on the sympod, and the endopod and the exopod have 13 and 25 plumose setae respectively; pleopod 2 has the appendix masculina inserted at a third of the length of the endopod, reaching beyond its end; the sympod presents 2 retinaculae, and the endopod and the exopod 7 and 14 plumose setae respectively. The manca 2.4 mm [MZB2016-3570] has the mandibular palp with 4 setae on the last article; and the palm of pereopod 1 bears 2 simple setae, without medial projection.

The genus Mesanthura currently includes 47 species, usually very shallow, distributed widely throughout the world except the polar regions, which are characterized by a specific dark dorsal coloring; mandibular palp article 3 with a row of up to15 distal setae; maxilliped with obsolete or absent endite, palp three-segmented with mesial margin of the distal article free between its suture and a distal group of setae; propodus palm of pereopod 1 with step or prominent tooth, and dactylus often with a complex toothed surface at base of unguis ( Poore, 2001). Mesanthura pacoi sp. nov. is unique because of its usual pale yellowish color, without spots (only the ovigerous females present a darker color and dorsal pigment pattern), and the characteristic setation of the mesial margin of the apical maxillipedal article, with 5 setae leaving almost no free margin, and one robust plumose basal seta (this can also be observed in many species, although it is stouter in M. pacoi sp. nov.); moreover, the fine hairs observed along the margin of the penultimate article, together with two plumose setae of the apical article, form a true filtering mechanism that is not observed in any other species. Other features shared with other species are: 7 setae on mandibular palp article 3, the absence of maxillipedal endite, and the propodus palm of pereopod 1 with shallow, granulate step.

The genus Mesanthura was first mentioned in the Mediterranean Sea by Lorenti et al. (2009), in two harbors of the west (Salerno, Tyrrhenian Sea) and south (Taranto, Ionian Sea) of Italy. These authors find similarities between the specimens studied and M. romulea Poore & Lew Ton, 1986 based on dorsal pigment spots. Unfortunately the description of M. romulea is incomplete because the authors only described pereopod 1, and the drawings of the mandible and maxilliped of specimens from Italy cannot be compared. In any case, M. romulea has dactylus of pereopod 1 as a diagnostic character because it presents distinctive granulations, especially at base of unguis. The drawings by Lorenti et al. (2009) do not appear to show this character; these authors did not determine their specimens as M. romulea and considered them as Mesanthura sp. It is evident that the characteristics of M. pacoi sp. nov. are different from Mesanthura sp. from Italy, firstly due to the color but also due to the maxilliped, with rectilinear margins of basal article of palp in Mesanthura sp. and with concave outer margin in M. pacoi sp. nov., and setation of inner margin of the distal article, 3 simple setae and one plumose seta mediodistally in Mesanthura sp., versus one plumose seta and 3 simple setae mediodistally and one robust plumose seta basally in M. pacoi sp. nov.

In this study, M. pacoi sp. nov. was collected in Cyprus and along almost the entire Lebanese coast, on rocky bottoms, calcareous concretions and corals of cliffs and caves, at depths of between 1 and 35 m.

Figures

FIGURE 2. Mesanthura pacoi sp. nov. Holotype female 7.0 mm [MZB 2016 - 3567]: A, body, dorsal View; B, body, lateral View; C, antenna 1; D, antenna 2; E, mandible; F, maxilla; G, schematic dorsal pattern of the oVigerous female 10.8 mm [MZB 2016 - 3568]. Scale bars: A – B, G = 1 mm; C – F = 0.25 mm.

FIGURE 3. Mesanthura pacoi sp. nov. Holotype female 7.0 mm [MZB 2016 - 3567]: A, maxilliped; B – H, pereopods 1 – 7. Scale bars: A = 0.25 mm; B – H = 0.5 mm.

FIGURE 4. Mesanthura pacoi sp. nov. Holotype female 7.0 mm [MZB 2016 - 3567]: A, pleopod 1; B, pleopod 2; C, uropod; D, telson. OVigerous female 10.8 mm [MZB 2016 - 3568]: E, pereopod 1. Manca 2.4 mm [MZB 2016 - 3570]: F, pereopod 1. Scale bars: A – E = 0.5 mm; F = 0.1 mm.

FIGURE 5. Mesanthura pacoi sp. nov. Male 6.5 mm [MZB 2016 - 3569]: A, cephalon, lateral View; B, antenna 1; C, antenna 2; D, pereopod 1; E, pleopod 2. Scale bars: A – C = 1 mm; D – E = 0.5 mm.