New species of Pycnogonum (Pycnogonida: Pycnogonidae) from Green Island Taiwan, with an additional note on the holotype of P. spatium
Author
Lee, Damin
Author
Kim, Won
text
Zootaxa
2020
2020-03-10
4750
1
122
130
journal article
10.11646/zootaxa.4750.1.6
7c160556-e0e1-4fd6-85e1-1f6fa0ab87d7
1175-5326
3702903
575B1970-C7B5-4688-9B41-99F046AFD3F1
Pycnogonum
(
Nulloviger
)
granulatum
sp. nov.
Figures 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
.
Description.
Male
holotype
. Trunk granulated (
Fig. 2A
,
3A
); 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
,
2B
); segment
4 in
trapezoidal shape, expanding posteriorly (
Fig. 1A
,
2A
).
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
,
2A
,
3A
) 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
,
2C
,
4C
) 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
). 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
). 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
). 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
). 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
).
FIGURE 1.
Pycnogonum
(
Nulloviger
)
granulatum
sp. nov.
, holotype, male. A, trunk, dorsal view; B, trunk, lateral view; C, trunk, anterodorsal view; D, third leg. Scale bars: 1 mm (A–C); 0.5 mm (D).
FIGURE 2.
Pycnogonum
(
Nulloviger
)
granulatum
sp. nov.
, holotype, male. A, trunk, dorsal view; B, trunk, anterodorsal view; C, third leg, long spine on femur and tibia 1 broken, lateral view; D, femur of fourth leg, dorsal view; E, spine on tarsus; F, fourth leg, arrow indicating gonopore. Scale bars: 1 mm (A); 0.5 mm (B–C); 0.01 mm (E); 0.1 mm (F).
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
) (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).
FIGURE 3.
Integument.
Pycnogonum (Nulloviger) granulatum
s
p. nov.; A–B. A, granulated integument of abdomen, dorsal view; B, granulated integument of femur, distal surface.
P. spatium
;
C–D. C, pitted integument of abdomen, dorsal view; D, granulated and fitted integument of femur, distal surface. All images are observed under the light microscope (Olympus BX51, Japan). Scale bars: 0.1 mm (A, C).
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.
FIGURE 4.
Legs of
Pycnogonum
(
Nulloviger
)
granulatum
sp. nov.
A, first leg; B, second leg; C, third leg; D, fourth leg. Scale bars: 0.5 mm (A–D).
TABLE 1.
Measurements of length and ratio of femur and tibiae and number of sole spines on propodi of
Pycnogonum
(
Nulloviger
)
granulatum
sp. nov.
| Femur (mm) |
Ratio |
Tibia 1 (mm) |
Ratio |
Tibia 2 (mm) |
Number of sole spines on propodus |
| Leg 1 |
0.88 |
57% |
0.5 |
53% |
0.26 |
12 |
| Leg 2 |
0.81 |
55% |
0.45 |
54% |
0.24 |
16 |
| Leg 3 |
0.77 |
59% |
0.45 |
53% |
0.24 |
8 |
| Leg 4 |
0.79 |
58% |
0.46 |
50% |
0.23 |
8 |
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.