Metharpinia protuberanti

Pina, M. Alonso De, 2001, new phoxocephalids (Crustacea: Amphipoda: Phoxocephalidae) from the south-west Atlantic, Journal of Natural History 35 (4), pp. 515-537 : 527-536

Metharpinia protuberanti s n. sp.

(®gures 7±11)

Material examined

ALLOTYPE, ovig. m approx. 5.5 mm, Chubut: Golfo Nuevo, PenõÂnsula ValdeÂs, Punta Pardelas (42ss37¾S, 64ss16¾W), 2±5 m depth, 31 October 1995, MACN No. 34181 . HOLOTYPE, l 5 mm, same data, MACN No. 34182 . PARATYPES, same data, one m (with setose oostegites) approx. 6.5 mm, MACN No. 34183; one m (with setose oostegites) ca 6.7 mm, MACN No. 34184; three mm 5.6±6.7 mm, MACN No. 34185; two ll 4.8 and 5.5 mm, MACN No. 34186. 2± 4 m depth, three mm 3.2(subadult)± 6.7 mm, MACN No. 34187; one l 4.8 mm, MACN No. 34188. Colombo beach (near Punta Pardelas), 2 m depth, 2 November 1995, ®ve mm 2.8(subadult)± 5.35 mm, MACN No. 34189; two ll4.8 and 5 mm, MACN No. 34190. Collectors: Meijide and Ianovski, donor: D. Roccatagliata. BahõÂa Nueva, Gol ®to (approx. 42ss46¾S, 65ss02¾W), 8±10 m depth, 6 August 1992, three mm 5±5.25 mm, MACN No. 34191. Collector and donor: G. Pagnoni. Golfo San Jose (42ss20¾S, 64ss20¾W), 4 m depth, 12 September 1986, two lland two mm (damaged), MACN No. 34192. Collectors: Z. Lizarralde and H. Zaixso, donors: E. GoÂmez Simes and C. Pastor .

Description

Allotype, ovigerous female (body length aproximatel y 5.5 mm). Head about 20% of total body length, greatest width 61% of length, rostrum constricted, narrow, spatulate, elongate, reaching middle of article 2 on antenna 1. Eyes medium, subovate, with dark pigment, near lateral margins. Antenna 1, peduncle article 1 about 1.5 times as long as wide, about 1.8 times as wide as article 2, ventral margin with about three plumose setules, produced dorsal apex with one long seta; article 2 about 0.7 times as long as article 1, with ventral crescent of four setae placed proximally, one apicolateral plumose setule and two apical medium setae; primary ¯agellum with 11 articles, about 0.7 times as long as peduncle, bearing one short aesthetasc each on articles 5±10; accessory ¯agellum with nine articles. Antenna 2, article 1 simple, without any process; article 3 with short and much longer setules; article 4, dorsal margin with proximal notch bearing one short spine and one long seta, ventral margin with four groups of two to three long to medium setae, three ventrodistal long setae, facial spine formula5 1-3-4-3; article 5 about 0.8 times as long as article 4, facial spine formula5 3, dorsal margin bearing one set of small setae, ventral margin with four medial small setae, one of these plumose, one long subdistal seta, three ventrodistal long setae and one short facial spine; ¯agellum slightly longer than peduncle articles 4 and 5 combined, with 14 articles.

Upper lip, epistome rounded. Mandibles, right incisor with three teeth rather poorly developed, left incisor with three small apical teeth and irregular toothing distally; right lacinia mobilis bi®d, distal branch shorter than proximal, left lacinia mobilis with ®ve teeth, one of these small, ¯at; right rakers 13 plus one rudimentary, left rakers 12 plus one rudimentary; molar composed of bulbous plaques with ®ve long stout spines plus one shorter and thinner disjunct spine; palp, article 1 short, article 2 with one short inner apical seta, one long inner seta medially and two other short inner setae, article 3 about 1.4 times as long as article 2, oblique apex with 10 spine-setae, basofacial formula 5 0-2. Lower lip, each outer lobe with one cone. Maxilla 1, inner plate large, broad, bearing one medium apical seta, one similar apicomedial seta and two apicolateral much shorter setae, all plumose; outer plate with 11 apical spines, outer spine enlarged; palp, article 2 with one apical spine, two apicolateral spines, about three apicomedial setae and about three submarginal setae. Maxilla 2, inner plate slightly shorter than outer; outer plate broader than inner, with two apicolateral setae; inner plate with three medial setae. Maxilliped, inner plate bearing two large thick apical spines, four apicofacial setae and four medial setae, all plumose; outer plate with seven masticatory spines; palp, article 1 with one apicolateral seta, article 2 with two lateral setae, medial margin strongly setose, article 3 bearing one lateral seta and about ®ve facial setae, article 4 narrow, bearing medium nail almost fully fused.

Coxae 1 and 2 not expanded anteriorly, anterior margin almost straight. Coxa 3 rectangular. Coxa 4 elongate, anterior and posterior margins divergent, posterior margin oblique, convex, width±length ratio 5 60:85. Coxae 1±4, main ventral setae5 17-9-7-6. Coxae 1±3, setae long except posteriormost seta. Coxa 1, setae ornamenting the whole ventral margin. Coxae 2 and 3, setae con®ned to posteroventral margin. Gnathopods similar, small, article 6 stout; gnathopod 2 slightly larger than gnathopod 1; width ratios of articles 5 and 6 of both pairs of gnathopods5 19:24 and 19:24, length ratios5 48:42 and 45:44. Gnathopod 1, article 5 elongate, ovate, posterior margin rounded-āt, long. Gnathopod 2, article 5 elongate, ovate, posterior margin rounded, shorter than in ®rst pair. Gnathopods 1 and 2, palmar humps large, ornamented, palms oblique, almost transverse.

Peraeopods 3 and 4 similar (except in coxae), the latter appendage a little stouter especially on article 5. Peraeopods 3 and 4, facial setal formula on article 4 5 5 and 6 almost parallel to apex, on article 5 5 6 and 6; main spine of article 5 extending 75% on article 6; article 5 of peraeopod 3 without proximoposterior spines and no proximal setae, of peraeopod 4 without proximoposterior setae and with one spineseta separated from regular posterior setae; spine formula of article 6 5 41 7 plus large mid-distal spine, some spines long; dactylus with sharp acclivity, produced as tooth, mid-facial plumose setule placed proximal and posteriorly. Coxae 5±7, posteroventral seta formula5 4-8-3, mostly short. Peraeopod 5, articles 4 and 5 broad. Peraeopod 6, article 4 broad and article 5 medium width. Peraeopods 5 and 6, facial spine rows dense to sparse. Peraeopods 5±7, facial ridge formula of article 2 5 0-1-1; width ratios of articles 2, 4, 5, 6 of peraeopod 5 5 62:66:48:21, of peraeopod 6 5 91:63:33:14, of peraeopod 7 5 101:21:16:10; length ratios of peraeopod 5 5 111:65:59:56, of peraeopod 6 5 125:87:54:76, of peraeopod 7 5 120:25:25:33. Peraeopod 7, article 2 reaching apex of article 4, posterior margin with about 11 small serrations, medial apex of article 6 ®nely combed, bearing four to ®ve digital processes (di cult to individualize the exact number).

Gills on coxae 2±7, those of coxae 6 and 7 smaller. Oostegites on coxae 2±5.

Pleopods ordinary. Epimera 1±3 somewhat damaged, especially posterior margins.

Urosomite 1 with ventral brush of setae emerging on to lateral surface proximally, articulation line incomplete. Urosomite 3 produced upwards, into a triangular process with vertex pointing up. Uropod 1, peduncle without basofacial setae, medially with one small proximal marginal spine and two longer spines, apical larger, displaced spine weak; inner and outer rami with two and four dorsal spines, respectively. Uropod 2, peduncle with four long dorsal spines, distal-most thick, medially with two marginal spines; inner and outer rami with one and three dorsal spines, respectively. Uropods 1 and 2, peduncle apical corners coarsely combed; outer rami bearing two subapical nails and inner rami one, both rami without apical nails. Uropod 3, peduncle with six ventral spines, dorsally with one lateral spine, medially with one spine; rami unequal in length, inner extending 82% on article 1 of outer ramus, apex carrying one seta, medial and lateral margins naked; article 2 of outer ramus elongate, 0.40, bearing two setae of diOEerent length, the longest one shorter than article 2, medial margin of article 1 naked, lateral margin with two acclivities, spine formula 5 2-2-2, without setae. Telson medium length, length±width ratio 5 100:79, almost fully cleft, each apex of medium width, produced medially but protrusion rounded, apex subtruncate, bearing short lateral and long medial spines separated by short plumose setule, each side with cluster of three long setae and proximally two small mid-lateral plumose setules of diOEerent length.

Additional observations

Paratype, female with setose oostegites (body length ca 6.5 mm). Antenna 2, article 4 with dorsal notch bearing two short spines (one of these hidden by the other) and long seta. Left mandible, lacinia mobilis with ®ve de®ned teeth. Right mandible as in allotype.

Peraeopods 3 and 4, article 5 with proximoposterior edge naked and bearing spine-setae disjunct from rest of setae.

Epimeron 1, posteroventral corner produced, posterior margin convex, weakly undulate, with one proximal setule, three long setae increasing in length towards posteroventral corner and then one shorter seta, anterior face bearing six medium setae with short plumosity, ventral margin with nine plumose setae increasing in length posteriorly. Epimeron 2, posteroventral corner acutely produced, posterior margin serrate, bearing three sets of long and very short setae and a broken seta above posteroventral corner, anterior face with two medium setae, facially with 10 plumose setae, two posteriormost setae set vertically. Epimeron 3, posteroventral corner strongly produced into a large tooth, posterior margin almost straight, serrate, bearing one setule proximally and ®ve spread long setae increasing in length towards posteroventral corner, anterior margin and face with four setae, ventral face with oblique row of seven spine-setae, posteriormost longest.

Paratype, female with setose oostegites (body length approximately 6.7 mm). Antenna 2, article 4 with dorsal notch bearing two short spines and one long seta, ventral margin more setose than in allotype; article 5 facial spine formula5 4, ventral margin with many groups of long to short setae.

Uropod 1, peduncle with one proximal slender spine and three longer spines medially; inner and outer rami with three and six dorsal spines, respectively. Uropod 2, peduncle with six dorsal spines and medially one spine; inner ramus bearing two dorsomedial spines. Uropod 3, peduncle with seven ventral spines, one lateral spine and dorsal setule; inner ramus, lateral margin with three plumose setae; outer ramus article 1, medial margin bearing three plumose setae. Telson, each lobe with cluster of six spine-setae.

Holotype, male (body length approximately 5 mm). Pigmented eyes very large, extending from lower margin almost to mid-dorsal line. Antenna 1, article 1 with medial patch of ®ne setae distally and about 13 plumose setules; article 2 with ®ve ventral setae proximally; primary ¯agellum with 11 articles, bearing one calceolus each on articles 2±6 and one aesthetasc each on articles 2± 9; accessory ¯agellum with eight articles. Antenna 2, articles 3 and 4 with dorsomedial margins bearing brushes of sensory ®ne setae; article 4, facial spine formula5 2-4-3, apparently dorsodistal spine forming ®rst group, missing (socket not clearly evident), article 4 of left antenna 2 with spine formula5 1-2-4-3, ventral margin bearing three plumose setules proximally and three sets of three long and short setae, one ventrodistal medium spine, three medium facial setae apically and one marginal plumose setule; article 5 about as long as article 4, bearing fewer and shorter setae than in female, dorsal margin with four sets of male setae and one distal calceolus, ventral margin with three medium setae on distal half and three plumose setules, apex with two thin submarginal spines, facial spine formula 5 3; ¯agellum elongate, with 32 articles, bearing one calceolus each on every other article: 1, 3, ..., 31. Left mandible, incisor with three humps in two branches; lacinia mobilis with ®ve teeth; palp article 3 about 1.1 times as long as article 2, basofacial formula 5 0-3. Maxilla 1, inner plate elongate, almost as long as outer plate, narrow. Maxilla 2, inner plate shorter than outer plate.

Peraeopods 3 and 4, article 5 posteroproximal edge naked for shorter distance than in female, bearing two disjunct spine-setae from regular posterior setae. Peraeopod 4, article 6 spine formula5 41 8 plus mid-distal spine shorter than in female. Peraeopod 7, article 5 with two elongate copulating spines.

Epimera 1 and 2 less setose, posterior margin with more attenuated serrations, and posteroventral corner weakly produced. Epimeron 3, posterior margin with shorter setae, anterior margin and face with three setae, two of these plumose, ventral face with more oblique row of six spine-setae, ventral margin bearing four short spines placed almost posteriorly but spread.

Uropod 2, peduncle with seven dorsal spines, medially with one apical spine. Uropod 3, peduncle with more ventral spines; inner ramus as long as outer ramus article 1; outer ramus article 1 spine formula 5 2-2-2, setal formula5 0-0-1; medial and lateral margins of both rami profusely plumose setose; article 2 of outer ramus shorter than in female, 0.20, apex with longer plumose setae. Telson much longer than in the allotype, length±width ratio 5 110:84, apical spines shorter and apical plumose setule longer, lateral plumose setules situated more proximally.

Etymology The speci®c name refers to the protuberance on urosomite 3.

Relationships

Metharpinia Schellenberg, 1931 is composed of ®ve species distributed in North and South America, with only one species described for the southern hemisphere, in the magellanic region and coast of Buenos Aires province ( Schellenberg, 1931; Barnard, 1980). Metharpinia protuberantis n. sp. is closely related to Microphoxus Barnard, 1960 , with two species, one known for Costa Rica ( Barnard, 1960) and the other for South America, in the magellanic region ( Schellenberg, 1931; Barnard, 1980).

The assignment of the new species to one genus or the other is problematic because it exhibits generic features, or a combination of characters, found in both genera. Barnard (1979) anticipated the probability of discovering in South America species intermediate between Metharpinia and Microphoxus , since the large dorsal hook on urosomite 3 and the dactylar articulate apical nail on the maxilliped proper of Microphoxus did not seem to be strong characters to separate it from Metharpinia . That is con®rmed with the new taxon. Although it does not have an articulate nail on the maxilliped palp, it displays a special process on urosomite 3.

Metharpinia protuberantis is assigned to Metharpinia according to the diagnoses of both genera by Barnard and Karaman (1991) and the revised literature mentioned in this paper. The general aspect of the individuals, with their long rostrum, bring them close to Metharpinia longirostris Schellenberg, 1931 , the type species, and the other species of the genus. The rostrum presents a length gradation in Microphoxus , being short in M. cornutus ( Schellenberg, 1931) and very short in the type species, M. minimus Barnard, 1960 . Other resemblances with Metharpinia are the ventral setae proximally placed on article 2 of antenna 1, which in Microphoxus are widely spread and situated more distally. The molars look alike with regard to the primary spines and the smaller disjunct spine, whereas in Microphoxus there is no disjunct spine or this spine is vestigial and weakly disjunct. The inner plate of the maxilliped has two apical spines as in some species of Metharpinia instead of one as in Microphoxus . The maxillipedal nail on the dactylus is fused in the new species as well as in other genus members, versus articulate as mentioned above. The propodus of gnathopods 1 and 2 is poorly setose anteriorly instead of heavily setose. Peraeopods 3 and 4, article 6 has spines all the same width whereas in Microphoxus these are thin and thick; article 5 posteroproximal spines on these latter appendages could be a variable feature, less useful due to the interpretation given to the character. This kind of spine is absent in Microphoxus and can be seen in Metharpinia , with the exception of M. oripaci W ca Barnard, 1980, while in the new species, according to the author’s interpretation, they have been observed on peraeopod 4 in the allotype, on both peraeopods 3 and 4 in the paratype female (6.5 mm) and on both pairs of appendages in the male. The displaced spine on peduncle uropod 1 is lacking in Microphoxus but is present and remarkably enlarged in all species of Metharpinia . In M. protuberanti s this spine is weak if the apicomedial spine is correctly interpreted as a displaced spine. The peduncular apical corners of uropods 1 and 2 have been described as not combed in both genera, except in Metharpinia X oridana ( Shoemaker, 1933) where the combed condition is weak or absent; the new species has the peduncular apicolateral corners coarsely combed. The uropod 3 inner ramus is naked laterally with its apex bearing a seta in the allotype. In the paratype female (6.7 mm) the inner ramus, besides its apical seta, has lateral plumose setae. The condition displayed by the allotype is found in Microphoxus species , although Barnard (1980) remarked that the holotype of M. minimus has two setae on the apex and the rest of the ramus naked. All known species of Metharpinia show the apex with two setae and the ramus setose. Urosomite 3 is produced into a special process, a character typical of Microphoxus used provisionally by Barnard (1979) to separate it from Metharpinia . Although the urosomite 3 process is like a hook in the ®rst genus, in the new species it is a wide and triangular process.

Metharpini a protuberanti s n. sp. exhibits, in addition to the characteristic urosomite 3 not found in any species of Metharpinia , and the conspicuous combed peduncular apicolateral corners of uropods 1 and 2, a particular epimeron 3 with posteroventral corner strongly produced. Only Metharpinia jonesi ( Barnard, 1963) has a similar epimeron 3 although the spination scheme is completely diOEerent since in the new species the ventral surface is armed with an oblique row of spines and in the other species the face is naked.