Nematocarcinus exilis (Spence Bate, 1888)

Gan, Zhibin & Li, Xinzheng, 2022, First records of three Nematocarcinus species (Crustacea, Decapoda, Nematocarcinidae) in the deep-waters of the north-western Pacific, Biodiversity Data Journal 10, pp. 95101-95101 : 95101

Nematocarcinus exilis (Spence Bate, 1888)

Stochasmus exilis : Spence-Bate (1888), p. 822-824, pl. 82, fig. 14.

Nematocarcinus exilis : Crosnier and Forest (1973), p. 116-123, fig. 32d, e; 33d, e, f; Abello and Valladares (1988), p. 100, fig. 4; Turkay (1998), p. 1787-1794, fig. 2; Burukovsky (2012), p. 108-112, fig. 35.

Materials

Type status: Other material. Occurrence: individualCount: 2; sex: 1 female (DY59-I-ROV08), 1 male (DY59-I-ROV05); lifeStage: adult (female CL 21.0 mm, male CL 12.1 mm); reproductiveCondition: non-reproductive; establishmentMeans: wild; preparations: whole animal (ETOH), DNA extract; disposition: in collection; associatedSequences: OP093560, OP093561, OP089177, OP089178 ; occurrenceID: 6517D2A7-0EA0-5DCF-88CF-EBE8761F09E5; Taxon : scientificNameID: urn:lsid:marinespecies.org:taxname:107574; scientificName: Nematocarcinus exilis (Spence-Bate, 1888); order: Decapoda ; family: Nematocarcinidae ; genus: Nematocarcinus ; specificEpithet: exilis; scientificNameAuthorship: (Spence Bate, 1888); taxonomicStatus: accepted; Location : higherGeography: northwestern Pacific ; waterBody: Pacific Ocean ; locality: the Kyushu-Palau Ridge area ; verbatimDepth: 1956 m (DY59-I-ROV08), 2666 m (DY59-I-ROV05); verbatimCoordinates: 13.330868°N, 134.548018°E (DY59-I-ROV08); 16.931303°N, 134.917863°E (DY59-I-ROV08); Identification: identifiedBy: Zhibin Gan; dateIdentified: 06/08/2021; identificationReferences: Crosnier and Forest, 1973; Abello and Valladares, 1988; Turkay, 1998; Burukovsky, 2012; Event: samplingProtocol: pipet of ROV; eventDate: 20/07/2020, 02/08/2020; fieldNumber: St. DY 59-I-ROV05, St. DY 59-I-ROV08; fieldNotes: Coll. Gan; Record Level: language: en; collectionID: SRSIO20080316; institutionCode: Sample Repository of the Second Institute of Oceanography (SRSIO)

Description

Body moderately slender, integument moderately soft, surface smooth. Rostrum nearly straight, slightly upturned at tip and concave in middle. Rostrum of female specimen over-reaching distal end of antennular peduncle by one-third of its length, reaching to distal one-third of scaphocerite, about half-length of carapace (Fig. 3 A and Fig. 2 C); dorsal margin armed with 32 subequal teeth, including 23 on rostrum proper and nine on carapace posterior to orbital margin, distal four teeth basally sub-articulated, others all articulated; apex somewhat trifurcated (Fig. 3 B); ventral margin unarmed. Rostrum of male specimen slightly over-reaching distal end of antennular peduncle, only reaching to mid-length of scaphocerite, about 0.37 times as long as carapace (Fig. 2 D); dorsal margin armed with 25 subequal teeth, including 18 on rostrum proper and seven on carapace posterior to orbital margin, distal four teeth basally sub-articulated, others all articulated; apex bifid (Fig. 3 C). Antennal and pterygostomian teeth well developed.

Eyes normally developed; cornea wider than eye stalk.

Third maxilliped reaching to distal quarter of scaphocerite; ultimate segment 0.76 times as long as penultimate segment, not markedly broadened at middle, armed with slender apical spinule; antepenultimate segment subequal in length to distal two segments combined, armed with 8-9 spines on lateral margin and two distal spines; exopod reaching to distal two-fifths of antepenultimate segment.

First pereiopod slender, overreaching end of scaphocerite by distal one-sixth of carpus; ischium with four ventrolateral spines, merus with 1-2 ventrolateral spines; ischium of second pereiopod with one distolateral spine, merus with 6-9 ventrolateral spines; ischium of third pereiopod with one distolateral spine, merus with 6-7 ventrolateral spines; ischium of fourth pereiopod with 0-1 distolateral spine, merus with 5-6 ventrolateral spines; ischium of fifth pereiopod unarmed, merus with 1-5 ventrolateral spines.

Posterodorsal margin of third pleomere rounded, continuation of its sides forming an angle slightly larger than 120° (Fig. 3 D). Pleura of fifth pleomere with distinct bump on inner sides, terminating by a prominent tooth (Fig. 3 E-F).

Ventral organ at sixth pleomere formed by two single rows of long plumose setae and two spots; setae rows nearly parallel, extending to end of spots; spots 2.47-2.61 times as long as wide, distance between spots about 2.05 times spots width (Fig. 3 G).

Telson armed with seven pairs of dorsolateral spines, two pairs of distal spines, without accessory spine (Fig. 3 H).

Colour, crimson red in female, faint red in male (Fig. 2 C-D).

Distribution

Previously known in the eastern Atlantic from 62°17'N to Morocco and Canary Is-lands (900-2300 m) and the Mediterranean Sea at depths between 1033-4765 m. ( Crosnier and Forest 1973, Burukovsky 2002b, Komai and Collins 2009, Burukovsky 2012). Presently recorded from the Kyushu-Palau Ridge, north-western Pacific.

Remarks

At present, approximately 74.5% of Nematocarcinus species occur in the Indo-west Pacific origin, but only three species, N. ensifer (SI Smith, 1882), N. faxoni Burukovsky, 2001 and N. tenuipes (also occurring in the Indian Ocean), are distributed both in the Atlantic and Pacific Oceans ( Burukovsky 2012). Under these conditions, we were hesitant to identify the present specimens as N. exilis at first. However, the features of the present specimens, such as a relatively long rostrum extending beyond the distal end of the antennular peduncle, but falling short of the distal margin of the scaphocerite, continuation of the posterodorsal margin of the third pleomere forming an obtuse angle, pleura of the fifth pleomere with a distinct protuberance on inner sides and arrangement of the spots and setae rows of the distoventral organ, coincide with the re-descriptions of N. exilis by Burukovsky (2002b) and Burukovsky (2012). Komai and Collins (2009) reported a closely related species, N. sp. aff. exilis from the Manus Basin of the south-western Pacific, based on a subadult female. By comparison between the present specimens and the Manus specimen, a number of differences could be found, such as the characters of the rostrum (over-reaching distal end of antennular peduncle by one-third of its length in female, all dorsal teeth articulated or sub-articulated, rostrum apex trifurcated or bifid versus only reaching distal end of antennular peduncle in female, only posteriormost three dorsal teeth articulated, rostrum apex simple), the antepenultimate segment of the third maxilliped (8-9 lateral spines versus 12), the pleuron of the fifih pleomere (armed with prominent posteroventral tooth versus tiny posteroventral tooth), the telson (armed with seven pairs of dorsolateral spines versus five) and the most important, the distoventral organs of the sixth pleomere (setae rows extending to the distal end of spots versus only reaching the anterior ends of the spots), based on which Burukovsky (2012) considered the Manus specimen to be a novel species that differed from N. exilis . In view of the differences discussed above, we agree with the inference of Burukovsky (2012) that the Manus specimen may represent a species unknown to science. However, just as Komai and Collins (2009) pointed out that the Manus specimen was a subadult female, more materials are need to clarify its taxonomic status. Partial sequences of COI and 16S rRNA genes of the present specimens were deposited in GenBank for further confirmation (OP093560, OP093561, OP089177, OP089178).

Figures

Figure 2. Photographs: A Nematocarcinus evansi Burukovsky, 2000, MBM 189203, female; B Nematocarcinus undulatipes Spence Bate, 1888, MBM 189205, female; C Nematocarcinus exilis (Spence Bate, 1888), SRSIO 20080316, female; D Nematocarcinus exilis (Spence Bate, 1888), SRSIO 20080316, male.

Figure 3. Nematocarcinus exilis (Spence-Bate, 1888), SRSIO 20080316. A female, anterior part of carapace and cephalic appendages, lateral view; B female, distal part of rostrum, lateral view; C male, distal part of rostrum, lateral view; D female, pleomere 3 - 4, dorsal view; E female, left pleura of fifth pleomere, lateral view; F same, inner view; G female, sixth abdominal somite, ventral view; H female, telson, dorsal view. Scales: 1.0 mm.