Parapontophilus stenorhinus, Komai, 2008

Komai, Tomoyuki, 2008, A world-wide review of species of the deepwater crangonid genus Parapontophilus Christoffersen, 1988 (Crustacea, Decapoda, Caridea), with descriptions of ten new species, Zoosystema 30 (2), pp. 261-332 : 324-328

Parapontophilus stenorhinus n. sp. ( Figs 32 ; 33 )

TYPE MATERIAL. — Holotype: Tonga. BORDAU 2, stn DW 1508, 21°02’S, 175°19’W, 555-581 m, 31.V.2000, 1 ♀ 5.0 mm (MNHN-Na 16078).

Paratypes: Indonesia. KARUBAR, stn DW 08, Banda Sea, 05°20’S, 132°31’E, 358-360 m, 23.X.1991, 1 ♀ 3.7 mm (MNHN-Na). — Stn CP 09, Kai Islands, 05°23’S, 132°29’E, 368-389 m, 23.X.1991, 1 ♀ 5.6 mm (MNHN- Na 16076). — Stn CC 21, Kai Islands, 05°14’S, 133°00’E, 688-694 m, 25.X.1991, 1 ♂ 4.5 mm (MNHN-Na).

ETYMOLOGY. — The specific name is formed by a combination of the Greek stenus, narrow, and rhinos, nose, in reference to the narrow rostrum of this new species.

DISTRIBUTION. — Tonga and Banda Sea, Indonesia ( Fig. 36 ), 368- 694 m.

DESCRIPTION

Rostrum ( Fig. 32 A-C) slender, 0.20 of carapace length, directed slightly upward, straight, falling short of distal margins of corneas; lateral margins armed with 2 pairs of very small, subacute teeth, anterior pair arising distal to midlength of rostrum. Carapace ( Fig. 32A, B, D ) 1.30 times longer than wide; anterior epigastric tooth tiny, posterior epigastric tooth relatively small, supported by weak middorsal ridge reaching beyond midlength of carapace; cardiac tooth absent; postorbital tooth very small, blunt; epibranchial tooth absent; epibranchial ridge absent; branchiostegal tooth relatively small, falling short of dorsodistal margin of antennal basicerite.

Third pleonal somite ( Fig. 32E ) with moderately convex tergum and with moderately produced posterodorsal margin. Fifth somite rounded dorsally. Sixth somite ( Fig. 32F, G ) about 3.00 times longer than wide, about 2.20 times longer than deep; dorsal surface rounded.

Eye ( Fig. 32A ) nearly subpyriform; cornea pigmented with gray in preservative, distinctly faceted with moderately small lenses; maximal diameter of cornea 0.21 of carapace length; eye-stalk slightly constricted; mesial face without papilla-like projection. Antennular peduncle ( Fig. 32A ) reaching midlength of antennal scale. Antennal scale ( Fig. 32A, H ) 0.65 of carapace length and 2.80 times longer than wide; lateral margin slightly concave, lamella strongly produced, distinctly overreaching distolateral tooth.

Palm of first pereopod ( Fig. 33A, B ) 2.39 times longer than wide; pollex moderately small, width of palm including tip of pollex 1.25-1.30 of width proximal to base of pollex; cutting edge moderately oblique; merus with relatively strong dorsodistal tooth. Second pereopod ( Fig. 33C ) slightly overreaching midlength of merus of first pereopod. Fourth pereopod ( Fig. 33D ) overreaching distal margin of antennal scale by half to full length of dactylus; dactylus elongate, subspatulate, 0.95 of propodal length; carpus about 0.60 of propodal length. Fifth pereopod similar to fourth, slightly falling short of distal margin of antennal scale.

Appendix masculina apparently not fully developed, about 0.85 length of appendix interna, with several short stiff setae distally ( Fig. 33E ).

Coloration in life

Unknown.

Size

Male CL 4.5 mm; females CL 3.7-5.6 mm.

REMARKS

The present new species appears closest to P. juxta n. sp. in the development of the armament of the carapace and the shape of the antennal scale and of the dactylus of the fourth pereopod. Nevertheless, P.stenorhinus n. sp. is characteristic within the species group in the relatively large cornea ( Table 2) and the relatively narrow rostrum armed with two pairs of tiny blunt teeth ( Fig. 32C ). Furthermore, the presence of lateral teeth distal to the midlength of the rostrum distinguishes P. stenorhinus n. sp. from P. juxta n. sp. From P. demani and P. sibogae n. sp., the present new species differs in the less developed branchiostegal tooth of the carapace. The epigastric teeth are distinctly smaller in P. stenorhinus n. sp. than in P. demani (cf. Fig. 32D and Fig. 22E ). The antennal scale is proportionally longer and narrower in P. stenorhinus than in P. sibogae n. sp. ( Table 2).

BATHYMETRIC AND GEOGRAPHIC DISTRIBUTION OF PARAPONTOPHILUS SPECIES

Compared with other crangonids, species of Parapontophilus generally occur at greater depths. All but P. sibogae n. sp. are found at bathyal depths greater than 200 m ( Table 3). Five species of the P. modumanuensis group ( P. juxta n. sp., P. caledonicus n. sp., P. demani , P. psyllus n. sp. and P. stenorhinus n. sp.) and P. junceus are found in upper to middle bathyal zone between 200 and 1000 m, and appear most abundant between 300 and 700 m; P. gracilis ranges from 405 to 1435 m, but appears most abundant between 600 and 1000 m; P. difficilis n. sp. ranges from 435 to 2340 m, but is most abundant between 800 and 1200 m; other six species, P. abyssi , P. cyrton n. sp., P. geminus n. sp., P. occidentalis , P. longirostris n. sp. and P. talismani occcur below 1000 m, particularly P. abyssi , P. occidentalis and P. talismani chiefly inhabit in abyssal zone deeper than 3000 m. Real bathymetric ranges of P. modumanuensis and P. cornutus n. sp. are unclear, because the specimens of the two species were collected from very steep slopes (536-1463 m for the holotype of P. modumanuensis ; and 500-1200 m for the type specimens of P. cornutus n. sp.). As mentioned before, the depth record of the only known specimen of P. profundus is questionable. The known shallowest depth where Parapontophilus has been found is 11 m ( P. sibogae n. sp.); and the deepest is 5852 m ( P. abyssi ). It is remarkable that species of the P. gracilis group extend to abyssal zone, whereas species of the P. modumanuensis group are restricted to the upper bathyal zone except for the shallow water inhabitant P. sibogae n. sp. It is noteworthy that the structure of the cornea seems to correlate to the depth range in the genus. Species occurring in bathyal zone ( P. gracilis , P. junceus , P. cornutus , P. longirostris n. sp. and members of the P. modumanuensis group) all possess normally developed cornea, whereas species inhabiting low- er bathyal to abyssal zone, i.e. P. abyssi , P. cyrton n. sp., P. occidentalis , and P. talismani have lightly pigmented, non-faceted cornea, although notable reduction of its size is not found. Species occurring in intermediate zone (about 1000-2000 m), i.e. P. difficilis n. sp. and P. geminus n. sp., have lightly pigmented corneas with distinctly delineated facets. Comparison with other crangonid genera suggests that the reduction of the faceted structure and loss of pigment are apomorphic. Nevertheless, it is still unclear that the evolutional trend toward the reduction of the corneal structure is phylogenetic or adaptive, since the phylogenetic relationship of species of Parapontophilus is still unclear.

The geographic distribution of the 18 species treated in this study is summarized in Figures 34-36 . It is remarkable that the P. gracilis group ranges world wide, whereas the P. modumanuensis group is confined to the Indo-West Pacific. This may suggest that the evolutionary history is considerably different between the two groups. Parapontophilus gracilis and P. talismani are restricted to the Atlantic Ocean, although they show wide distributions in that ocean. Parapontophilus abyssi is also widely distributed in the Atlantic Ocean, and further extends to the Indian Ocean. Parapontophilus occidentalis is confined to the eastern Pacific, ranging from California to northern Chile. Other species are found in the Indo-Pacific region, although the distributional patterns are different according to species. Parapontophilus longirostris n. sp. has a wide distribution across the western Indian Ocean to the central Pacific and French Polynesia. Two species, P. difficilis n. sp. and P. junceus , occur in the western Pacific, including Taiwan, the Philippines, Indonesia, and South Pacific islands, and the latter extends to Japan and to French Polynesia. Parapontophilus geminus n. sp. also occurs in the western Pacific, although so far it is known only from Japan, Taiwan and Makassar Strait in Indonesia. Parapontophilus demani and P. psyllus n. sp. are found in the northwestern Pacific, but the former ranges from Japan to French Polynesia, and the latter is found in the Ryukyu Islands, Taiwan and the Philippines. So far, P. juxta n. sp. is known only from off Réunion Island in the western Indian Ocean. Two species, P. sibogae n. sp. and P. stenorhinus n. sp. are known only from the type locality in the Celebes Sea, and the Banda Sea and Tonga, respectively. Similarly, P. cornutus is represented only by the three specimens from the Austral Islands in French Polynesia. Parapontophilus cyrton n. sp. appears to be restricted to waters around New Caledonia.Two species, P. modumanuensis and P. profundus , are represented respectively only by the holotype, the former from Hawaii and the latter from southeastern Australia. Real distributional ranges of many species still remain unclear.

Figures

FIG. 32.— Parapontophilus stenorhinus n.sp.: A, carapace and cephalic appendages,dorsal view;B, carapace,lateral view;C, rostrum dorsal view; D, anterior part of carapace,eye and basal part of antennae, lateral view; E, third and fourth pleonal somites, lateral view; F, sixth pleonal somite, dorsal view; G, same, dorsal view; H, left antennal scale, dorsal view; A-E, H, ♀ 5.0 mm, holotype, Tonga (BORDAU 2, stn DW 1508) (MNHN-Na 16078); F, G, ♀ 5.6 mm, Banda Sea, Indonesia (KARUBAR, stn CP 09) (MNHN-Na 16076). Scale bars: 1 mm.

FIG. 33. — Parapontophilus stenorhinus n. sp., left appendages. A, first pereopod, lateral view; B, same, subchela, ventral view; C, second pereopod,lateral view; D, fourth pereopod,lateral view;E, appendix masculina and appendix interna of left second pleopod, mesial view; A-D, ♀ 5.0 mm,holotype,from Tonga (BORDAU 2, stn DW 1508) (MNHN-Na 16078);E, ♂ 4.5 mm, paratype,Banda Sea, Indonesia (KARUBAR, stn CC 21) (MNHN-Na). Scale bars: A-D, 1 mm; E, 0.5 mm.

FIG. 36.— Geographic distribution of Parapontophilus demani (Chace,1984) (●), P. caledonicus n. sp. (▼), P. juxta n. sp. (▲), P. modumanuensis (Rathbun, 1906) (◆), P. psyllus n. sp. (✖), P. sibogae n. sp. (■), and P. stenorhinus n. sp. (✚).

FIG. 22. — Parapontophilus demani (Chace, 1984), ovig. ♀ 5.1 mm, holotype,Selat Roti, Lesser Sunda Islands,Indonesia (Siboga, stn 297) (ZMA): A, carapace and cephalic appendages, dorsal view (right antennal scale missing); B, carapace, lateral view; C, anterior part of carapace and eyes, dorsal view; D, rostrum, dorsal view; E, anterior part of carapace, cornea and basal part of antennae, lateral view;F, third to sixth pleonal somites,lateral view;G, fourth to sixth pleonal somites,dorsal view;H, left ophthalmic appendage, ventromesial view; I, left antennal scale, dorsal view. Scale bars: A-C, E-H, 1 mm; D, 0.5 mm.

FIG. 34. — Geographic distribution of Parapontophilus abyssi (Smith, 1884) (■), P. gracilis (Smith, 1882) (●), P. occidentalis (Faxon, 1893) (◆) and P. talismani (Crosnier & Forest, 1973) (▲).

FIG. 35.— Geographic distribution of Parapontophilus abyssi (Smith,1884) (■), P.cornutus n. sp.(❖), P.cyrton n. sp.(✽), P.difficilis n. sp. (▼), P. geminus n. sp. (✖), P. junceus (Bate, 1888) (●), P. longirostris n. sp. (▲), P. occidentalis (◆) and P. profundus (Bate, 1888) (✚).