Pycnogonum (Nulloviger) granulatum, Lee & Kim, 2020

Lee, Damin & Kim, Won, 2020, New species of Pycnogonum (Pycnogonida: Pycnogonidae) from Green Island Taiwan, with an additional note on the holotype of P. spatium, Zootaxa 4750 (1), pp. 122-130 : 123-128

publication ID	https://doi.org/ 10.11646/zootaxa.4750.1.6
publication LSID	lsid:zoobank.org:pub:575B1970-C7B5-4688-9B41-99F046AFD3F1
DOI	https://doi.org/10.5281/zenodo.3706313
persistent identifier	https://treatment.plazi.org/id/03D687D4-7C0A-4132-FF51-F450FAF4D6CE
treatment provided by	Plazi
scientific name	Pycnogonum (Nulloviger) granulatum
status	sp. nov.

Treatment

Pycnogonum (Nulloviger) granulatum View in CoL sp. nov.

Figures 1 View FIGURE 1 A–D, 2A–F, 3A–B, 4A–D

Material examined. Holotype, male, ASIZCH000073, Gong Guan Bi diving point, Green Island, Taiwan, 22°40’55.0”N, 121°29’17.9”E, 18 m, SCUBA, Damin Lee, 24 May 2016. GoogleMaps

Description. Male holotype. Trunk granulated ( Fig. 2A View FIGURE 2 , 3A View FIGURE 3 ); segment 1, 2, and 3 articulated; segment 3 and 4 fused. Anterior three segments with transverse ridge, each 1/4 times as high as trunk height ( Fig. 1B, 1C View FIGURE 1 , 2B View FIGURE 2 ); segment 4 in trapezoidal shape, expanding posteriorly ( Fig. 1A View FIGURE 1 , 2A View FIGURE 2 ).

Lateral processes half as long as broad, separated by 1/4 to 1/3 of base width; dorsodistal tubercle about 1/4 times as high as transverse ridges on trunk.

Ocular tubercle on anterior margin of cephalon, truncated cone shape with round tip, height half of base width, slightly taller than transverse ridges on trunk. Four eyes pigmented.

Proboscis cylindrical, 1.7 times as long as base width, with slight constriction at half length; ventral surface slightly longer than dorsal surface; dorsal tubercle present at 2/3 length from base, rising steeply on anterior surface, sloping down gently on posterior surface. Oral glands not found.

Abdomen ( Fig. 1A View FIGURE 1 , 2A View FIGURE 2 , 3A View FIGURE 3 ) articulated at base, spindle shaped directing horizontally, reaching to distal end of coxa 2 of fourth legs, slightly bifid at tip.

Palps, chelifores and ovigers absent.

Third leg ( Fig. 1D View FIGURE 1 , 2C View FIGURE 2 , 4C View FIGURE 4 ) stout, granulated, having intermittent small spines. Coxa 1 with two dorsodistal tubercles, without ventral spines. Coxa 2 slightly longer than coxa 1 and coxa 3, with two minute dorsodistal tubercles, several spines on ventral surface. Coxa 3 slightly longer than coxa 1, with two minute dorsodistal tubercles, several spines ventrally. Femur about 3 times as long as base width, bearing two heavy dorsodistal lobes, two dorsolateral digitiform processes, and ventroproximal swelling; mid-dorsal projection large, with two tubercles of which anterior tubercle larger, nodulous, leaning slightly forward with short spine and posterior tubercle smaller, bearing spine. Tibia 1 3.6 times as long as base width, with pair of dorsodistal tubercles, several irregular dorsal tubercles, bearing ventrodistal swelling with two small spines on ventrodistal surface. Tibia 2 1.7 times as long as base width, half as long as tibia 1, with pair of dorsodistal tubercles, having nodulous tubercles on dorsal surface, bearing several spines on ventrodistal surface. Each femur and tibia with long, dorsodistal spine. Tarsus 0.25 times as long as propodus; dorsal surface concave; ventral surface convex, with several spines. Propodus moderately curved, with eight spines dorsally and eight sole spines ventrally, heel spines absent. Spines on ventral surface of tibia, tarsus, and propodus with cleft tips ( Fig. 2E View FIGURE 2 ). Main claw curved, 0.6 times as long as propodus. Auxiliary claws absent.

Male gonopores present on ventral surface of coxa 2 of fourth legs ( Fig. 2F View FIGURE 2 ). Coxal pellicula (vide Staples 2007) absent on dorsal surface of coxa 2 of all legs.

Measurements (mm). Holotype. Trunk length, 2.03; width, 0.94; proboscis, 0.66; abdomen, 0.48. Third leg; coxa 1, 0.20; coxa 2, 0.26; coxa 3, 0.22; femur, 0.77; tibia 1, 0.45; tibia 2, 0.24; tarsus, 0.10; propodus, 0.40; main claw, 0.21.

Distribution. At present only recorded from Green Island, Taiwan.

Etymology. The specific name is from the Latin granulatum (granulated), referring to the granulated integument of the trunk and legs.

Remarks. The legs of the present species were examined in detail. The femur and tibia of the first leg were longer than those of the other legs, but the ratio did not differ significantly ( Table 1 View TABLE 1 ). Comparing only the absolute length seems insufficient, taking the ratio of length of leg segments seems more appropriate. Since the number of sole spines in the propodus vary depending on the order of the legs, species diagnosis based on the exact number seems inappropriate ( Table 1 View TABLE 1 ). The mid-dorsal projection of all legs has two tubercles, the posterior tubercle of the first leg being the largest and most distinct ( Fig. 4 View FIGURE 4 ).

In the absence of ovigers and the presence of gonopores on the ventral surface of coxa 2 of the fourth pair of legs, this species belongs to the subgenus Nulloviger ( Stock 1968b) .

The present species is morphologically similar to P. (N.) moolenbeeki Stock, 1992 , P. (N.) lobipes Stock, 1991 , P. (N.) tuberculatum Clark, 1963 , P. nodulosum Döhrn, 1881 , and P. spatium Takahashi et al., 2007 by the presence of a cylindrical proboscis and distinct features of femora.

Compared with the descriptions of P. (N.) moolenbeeki ( Stock 1992; Staples 2002), the following different characteristics are found in the new species. (1) Distinct transverse ridges on the dorsal surface of trunk (incon- spicuous in P. (N.) moolenbeeki ). (2) 33% in length ratio of the proboscis to the trunk (compared to 42 to 45%). (3) Two tubercles on mid-dorsal projection of femur arranged in proximodistal axis ( Fig. 2D View FIGURE 2 ) (anteroposterior axis). (4) Long spine on dorsal surface of femur without dorsal tubercle (spine on dorsal tubercle). (5) Moderately curved propodus (compared to less curved and swollen). (6) Cleft tips of the spines on the ventral surface of tibia, tarsus, and propodus (molariform tips).

Compared with the description figures ( Stock 1991; Staples 2002), the following features are the main differences between the present species and P. (N.) lobipes . (1) Trunk segment 3 and 4 fused (articulated in P. (N.) lobipes ). (2) Tip of ocular tubercle round (acuminate). (3) Dorsal tubercle present on the proboscis (absent). (4) Abdomen distally round in dorsal view (truncated). (5) Abdomen articulated at base (non articulated). (6) 8 to 16 sole spines on the propodus (four spines).

Pycnogonum (Nulloviger) tuberculatum was well described by Clark (1963) and Staples (2002). The present species is distinguished from the P. (N.) tuberculatum by following characteristics. (1) Trunk length 2.03 mm (4.58 to 5.65 mm in P. (N.) tuberculatum ). (2) Lateral processes separated by 1/4 to 1/3 of base width (slightly separated). (3) 33% in length ratio of the proboscis to the trunk (compared to 25 to 27%). (4) Dorsal tubercle on the proboscis prominent (small). (5) Abdomen reaching to the distal end of coxa 2 (half of coxa 3). (6) Cleft tips of the spines on the ventral surface of tibia, tarsus, and propodus (blunt tips).

Through the descriptions and figures ( Döhrn 1881; Kocak & Katagan 2007; Lehmann et al. 2014; Munilla & Soler-Membrives 2014; Stock 1968a; Stock 1994), the present species is different from P. nodulosum in some characters. (1) Trunk segment 3 and 4 fused (articulated in P. nodulosum ). (2) Posterior surface of lateral processes smooth instead of enlarged or swollen. (3) Two tubercles on the dorsal surface of femur instead of three. (4) Cleft tips of the spines on the ventral surface of tibia, tarsus, and propodus instead of club shaped.

Among the congeners, P. spatium is geographically closest to the present species, but can be distinguished by the following: (1) Trunk integument granulated (pitted in P. spatium ). (2) Trunk segment 4 expanding posteriorly without parallel part (expanding posteriorly after the parallel part in P. spatium ). (3) Lateral processes separated by 1/4 to 1/3 of base width, wider in P. spatium . (4) Femur with larger ventroproximal swelling. (5) Scarce spines on the ventral surface of the femur compared to several spines in P. spatium . (6) Tibia 2 1.7 times as long as base width, not 2.4 times. (7) Cleft tips of the spines on the ventral surface of tibia, tarsus, and propodus instead of round tips.

Experiments were carried out to attempt to add DNA data to the species determination but non-degraded DNA could not be obtained. With only one specimen collected it was difficult to conduct further experiments.