Nebalia mortoni, Lee, Christine N. W. & Bamber, Roger N., 2011

Lee, Christine N. W. & Bamber, Roger N., 2011, A new species of Nebalia (Crustacea: Phyllocarida: Leptostraca) from the Cape d’Aguilar Marine Reserve, Hong Kong, Zootaxa 3091, pp. 51-59 : 52-58

publication ID	https://doi.org/ 10.5281/zenodo.203909
DOI	https://doi.org/10.5281/zenodo.6190948
persistent identifier	https://treatment.plazi.org/id/2F0F0A5D-FD55-FF99-20EB-DF5EFDB2CEDE
treatment provided by	Plazi
scientific name	Nebalia mortoni
status	sp. nov.

Treatment

Nebalia mortoni sp. nov.

Figs. 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4

Description of female: Total length (anterior of carapace to posterior margin of telson) of holotype ( Fig. 1 View FIGURE 1 A) 5.16 mm (larger paratype specimens up to 6 mm total length), carapace length 2.75 mm, not reaching posterior margin of second pereonite. Rostrum ( Figs. 1 View FIGURE 1 B, C) downcurved, overreaching eye, 2.4 times as long as wide, without terminal spine; ventral keel narrow, extending just past mid-length. Eye ( Fig.1 View FIGURE 1 D) subovate, longest ventrally, ventral margin almost straight, 1.7 times as long as greatest width, pigmented ommatidia covering anterior twothirds of eye; supraocular scale present, covering most of unpigmented part of eye.

Posterior dorsal margins of pleonites with squared denticles ( Fig. 1 View FIGURE 1 G), mostly about 1.5 times as long as wide. Telson about as long as seventh pleonite.

Antennule ( Fig. 1 View FIGURE 1 E) peduncle of four articles, second article twice as long as wide, with one mid-dorsal, row of ten ventrodistal, and 13 dorsodistal plumose setae, and two shorter and one longer dorsodistal spines; third article just over half as long as second, with dorsodistal tuft of 13 simple setae and stout, slender ventrodistal spine; fourth article one quarter as long as third, with three shorter and one longer stout dorsodistal spines, four subdistal stiff setae, five small distal spinules at base of scale, one long, slender ventrodistal spine exceeding distal margin of fifth flagellar segment; scale 2.7 times as long as wide, nearly four times as long as fourth peduncle article, dorsal and distal margins densely setose, mesial row of fine setules; flagellum of 13 segments, segments 1 to 12 bearing dorsodistal aesthetascs.

Antenna ( Fig. 1 View FIGURE 1 F) peduncle of three distinct articles (owing to fusion of third and fourth articles), second article 1.45 times as long as wide and 1.3 times as long as first article, with dorsodistal spine-like apophysis. Third article 1.12 times as long as second, 2.4 times as long as wide, with midventral plumose seta, dorsally with rows of ten spines (mostly in pairs) and simple setae, distally with crown of 17 plumose setae and seven straight spines. Flagellum of 17 segments, proximal 16 segments with two dorsal and one mesial spines; distal four segments attenuate.

Mandible molar distally rugose with sparse marginal spinules but no accessory tooth; palp ( Fig. 2 View FIGURE 2 A) of three articles, proximal article twice as long as wide, half as long as distal article, naked; second article 1.6 times as long as first, with large rounded proximal apophysis, and with two dorsal submarginal setae, neither reaching distal margin of article; third article slightly expanded distally, with ventral spinules beginning at about one-fifth of margin, proximal 16 spinules shorter, subsequent 34 spinules along entire edge and distal margin; distal margin with outer row of ten shorter, recurved, bilaterally denticulate spinules.

Maxillule ( Fig. 2 View FIGURE 2 C) outer endite with nine plumose setae; inner endite distally with five outer simple spines and two rows of nine distally-bi- or tri-furcate spines on outer lobe, five simple spines and two longer plumose setae on inner lobe; palp with 17 lateral and three distal simple setae.

Maxilla ( Fig. 2 View FIGURE 2 B) four endite lobes bearing plumose setae, in two rows on proximal three lobes, distal seta on fourth lobe longer than proximal article of endopod. Endopod of two articles, proximal article with six inner marginal, eleven mesial and two stouter distal plumose setae; distal article slightly shorter than proximal article, with four proximal mesial, three outer marginal and two unequal distal sparsely-plumose setae. Exopod distinctly longer than proximal endopod article, with 19 outer marginal plumose setae and two stouter distal plumose setae.

Thoracopods ( Fig. 2 View FIGURE 2 D) similar, epipod longer than exopod, naked; exopod rounded, with sparse marginal and distal setae, without proximal lobe; endopod longer than exopod.

Pleopod 1 ( Fig. 3 View FIGURE 3 A) peduncle inner margin with proximal seta and distal spine, outer margin with subdistal slender spine and distal stout spine; exopod 0.63 times long as peduncle, comb-row of complex spines ( Fig. 3 View FIGURE 3 A’) along distal 90% of inner margin, mesial row of six plumose setae extending to outer margin with nine plumose setae, and with one subdistal and three distal spines; endopod with distal spine-like apophysis, proximal mesial row of setules, plumose setae along entire inner margin, one shorter and one longer distal spines; retinaculum not slen- der. Pleopods 2 and 3 similar to each other ( Fig. 3 View FIGURE 3 B), peduncle with tufts of plumose setae and mid-distal triangular apophysis, exopod with paired outer marginal spines, three distal spines and entire inner margin with plumose setae, endopod similar to that of pleopod 1 but with plumose setae along outer and inner margins. Pleopod 4 ( Fig. 3 View FIGURE 3 C) similar to pleopod 3 but outer corner of peduncle with spine-like apophysis. Pleopod 5 ( Fig. 3 View FIGURE 3 D) biarticulate, with six slender spines on outer and distal margin, simple setules along inner margin. Pleopod 6 ( Fig. 3 View FIGURE 3 E) uniarticulate, shorter than pleopod 5.

Caudal furca ( Fig. 3 View FIGURE 3 F) tapering distally, 1.65 times as long as telson, 4.3 times as long as wide, distal spine 1.7 times as long as furca, with 19 spines along outer margin (distal-most half as long as terminal spine), inner margin with 10 spines amongst numerous plumose setae. Anal scale ( Figs 3 View FIGURE 3 F, G) with slender, tapering point towards medial edge which diverges only slightly from mid-line, outer margin sloping gradually, with minimal “shoulder”.

Description of male: Allotype 4.64 mm long, carapace 2.6 mm long. Similar to female, but carapace extending to posterior margin of third pleonite, and antennules and antennae showing sexual dimorphism. Antennule ( Fig. 4 View FIGURE 4 A) peduncle and scale as those of female, flagellum of 13 segments, proximal four segments (e.g. Fig. 4 View FIGURE 4 B) poorly articulated, bearing dense distal tufts of fine setules and aesthetascs, each aesthetasc tapering suddenly at about mid-length; fifth and sixth segments also with dense distal tufts of aesthetascs; segments 7 to 13 with 7, 3, 3, 2, 2, 1 and 1 aesthetascs respectively; segments 10 to 13 very attenuate. Antenna longer than that of female, 0.75 times as long as body.

Etymology. Named in honour of Professor Brian Morton, Chairman of the Hong Kong Government’s Marine Parks Committee that established the Cape d’Aguilar Marine Reserve.

Remarks. Dahl (1985; 1990), in his critical revisions of the Nebalia species of the north-east Atlantic and the southern hemisphere (respectively), pointed out, inter alia, the importance of the shape of the posterior denticles on pleonites 5 to 7, all described species up to now showing either pointed or rounded denticles (where known). Nebalia mortoni sp. nov. is the first species shown to have squared denticles on these pleonites. It is further distinguished from previously described species by the very long distal spine on each caudal furca (unfortunately this spine is often not described for other species, notably those of Dahl, locc. cit.).

The slender medially positioned tapering points on the comparatively “shoulderless” anal scale in the present species are similar only to those of N. antarctica Dahl, 1990 , but that species has pointed pleonite denticles. The distal spines on the second peduncle article of the antennule have not been recorded in any other species of Nebalia , while the short fourth peduncle article with its complex distal spination (i.e. more than one spine) also appears to be a characteristic feature of the present species: the Iberian species N. troncosoi Moreira et al., 2003 , a species with a very short antennular flagellum, and the Red Sea species N. marerubri Wägele, 1983 both have a short fourth article on their antennules, but without a complexity of (or any?) distal spines, and again those species have pointed pleonite denticles, as do all other described species with a particularly short fourth antennular-peduncle article.

The only species of Nebalia described previously from the Asian coasts of the western Pacific is N. japanensis Claus, 1888 , a species described only poorly ( Mees (2011) cites it as nomen dubium, without explanation), but Claus (1888: p. 127) does point out the long carapace which extends over the fifth pleonite, unlike that of the present species. While there are numerous subsequent records of N. japanensis from the coastal waters of Japan, it is likely that the material has not been examined critically, rather it has been assumed to be the only described species from the region. Dahl (1990) bemoans the “excessively wide species concept previously applied to Nebalia species”.