Monoliropus concavimanus, Horton, 2008

Horton, Tammy, 2008, Amphipoda from marine caves of Hong Kong Island, Journal of Natural History 42 (9 - 12), pp. 825-854 : 827-832

Monoliropus concavimanus sp. nov.

( Figures 1 , 2 )

Type Material

Holotype, male, 5.5mm, NHM Reg. No. 2004.2928.

Material examined

Long Kei Wan, control site Z, male holotype, female paratype, juvenile paratype, NHM Reg. Nos. 2004.2929–2930.

Description

Mature male holotype, 5.5 mm. Body smooth, pereonites 3 and 4 subequal; pereonite 5 the longest. Gills on pereonites 3–4 elongate, length about five times width. Antenna 1, peduncle scarcely setose; peduncular article 2 longest, almost three times as long as article 3; flagellum composed of eight articles. Antenna 2 slightly shorter than antenna 1; peduncular article 4 longest; flagellum with two articles. Mouthparts: Upper lip lost during preparation. Lower lip apically setose; inner lobes very well demarcated. Mandibles with strong molar process; left mandible, incisor five-toothed (three visible in Figure 2 ), lacinia mobilis five-toothed (four visible in Figure 2 ), three dentate setae; right mandible, incisor six-toothed, lacinia mobilis three-cusped, two dentate setae, molar flake present; palp three-articulate; article 2 with one seta proximally and two distally, article 3 acute apically with a setal formula 1-2-1. Maxilla 1 outer plate with six teeth; distal article of palp with four apical spines and two simple setae medially. Maxilla 2 inner plate with three setae; outer plate, longer than inner plate, with eight setae apically. Maxilliped, inner plate, rectangular, with three robust simple setae and one plumose seta apically; outer plate reaching halfway along palp article 2, margin lobed, with one robust seta distally, one robust simple seta inserted medially in a recess between lobes, and two mediofacial simple setae; palp article 3 with a well developed acute process, five ventral simple robust setae; dactylus slender, elongate, acute. Gnathopod 1 propodus triangular, length 1.7 times proximal width; palm strongly serrate with a single proximal grasping spine; dactylus with six strong teeth ventrally. Gnathopod 2 inserted about a third from the anterior end of pereonite 2; basis a little shorter than pereonite 2; carpus very reduced; propodus strongly curved, length about twice width, palm deeply excavate with a proximal slender projection with a single grasping spine and an acute medial projection; dactylus curved, reaching proximal palmar projection. Pereopods 3 and 4 subequal in length, uni-articulate, approximately one quarter of gill length, about 2.5 times width. Pereopod 3 and 4 with two simple setae and one setule apically, and one simple seta medially. Pereopod 5, of six articles, slender, simple, inserted in posterior third of pereonite 5. Pereopods 6–7 subequal, composed of six articles, more robust than pereopod 5, propodus with proximal projection and grasping spines. Abdomen with a pair of appendages, a pair of lateral lobes, and a single dorsal lobe with two setules. Appendages uniarticulate, setulose with one slender setule sub-apically. Penes short, situated laterally.

Remarks

This species is placed within the genus Monoliropus Mayer, 1903 , which currently contains three species; Monoliropus agilis Mayer, 1903 , M. falcimanus Mayer, 1904 , M. tener Arimoto 1968 , although according to Laubitz (1991) it is probable that M. tener and Orthoprotella hamata Arimoto, 1981 , are synonymous with M. falcimanus . Monoliropus concavimanus sp. nov. resembles M. agilis sensu Laubitz (1991) most closely but can be differentiated from it by the setal formula of article 3 of the mandibular palp (1-2-1 vs 1-3-1), uni-articulate pereopods 3 and 4, (versus 2- articulate for M. agilis ) and the more deeply excavate palm of gnathopod 2.

The genus Monoliropus can also be confused with the genus Triprotella Arimoto, 1970 , which was described from a single specimen collected in the Arabian Sea, and its only species, T. amica Arimoto, 1970 , has since been redescribed from Tanzania by Guerra-Garcia (2002). The Hong Kong species differs from T. amica in the setal formula of article 3 of the mandibular palp (1-2-1 vs 1-1-1), and the morphology of the gnathopods.

Etymology

From the Latin, concavus (f) meaning hollowed or arched inward, and manus (f) meaning hand, reminiscent of the characteristically deeply excavate propodus of gnathopod 2.

Figures

Figure 1. Monoliropus concavimanus sp. nov.

Figure 2. Monoliropus concavimanus sp. nov.