Pagurus pseudoalbus, Ayón-Parente & Wehrtmann, 2019

Ayón-Parente, Manuel & Wehrtmann, Ingo S., 2019, Description of a new species of Pagurus Fabricius, 1775 (Crustacea: Paguroidea: Paguridae) from the Pacific coast of Costa Rica, Central America, with notes on Pagurus albus (Benedict, 1892), Zootaxa 4712 (1), pp. 101-113 : 107-112

Paguru s pseudoalbus sp. nov.

( Figs 4–6 )

Pagurus albus .— Vargas & Cortés, 2006: 482.— Campillay, 2012: 63, fig. 2A–F.

Material examined. Holotype: male (SL 6.7 mm), Puntarenas , Golfo de Nicoya, 07 March 1967, trawl, 40 m, leg. Kalf, (UCR-MZ-1193) . Paratypes: 3 ovigerous females (SL 5.2–6.6 mm), Puntarenas , Golfo de Nicoya, 07 March 1967, trawl, 40 m, leg. Kalf (UCR-MZ-1193) ; 3 males (SL 5.6–7.8 mm), 1 ovigerous female (SL 6.4 mm), Isla Negritos , Golfo de Nicoya, 23 January 1978, (UCR-MZ-1805) ; 1 male (SL 8.5 mm), 4 females (SL 7.0– 7.4 mm), Isla Chira , Golfo de Nicoya, 15 February 1994, 20 m, (UCR-MZ-1994-05) .

Description. Eleven pairs of biserial gills weakly divided distally ( Fig. 4A ). Shield ( Fig. 4B ) about 1.2 times as broad as long; anterolateral margins sloping; anterior margin between rostrum and lateral projections concave; anterolateral angle with a slit; posterior margin roundly truncate; dorsal surface flattened, with numerous tufts of short setae. Rostrum obtusely triangular, length equal to or slightly exceeding lateral projections; lateral projections obtusely triangular, armed with small spine.

Ocular peduncles ( Fig. 4B ) stout, short, approximately 0.5 length of shield, slightly constricted medially, dorsal surface with few tufts of short setae. Cornea dilated, width about 0.6 length of ocular peduncle. Ocular acicles bluntly subtriangular, weakly concave dorsally, tip subacute, with small, submarginal spine, and moderately long setae, acicles separated basally by about 0.5 basal width of 1 acicle.

Antennular peduncle ( Fig. 4B ), when totally extended, exceeding ocular peduncles by 0.3–0.5 length of ultimate segment; ultimate and penultimate segment both with few short setae on dorsal surface; basal segment with moderately strong spines on laterosubdistal margin.

Antennal peduncle ( Fig. 4B, C ) moderately long, exceeding ocular peduncle by 0.7 length of ultimate segment. Fifth segment unarmed, with scattered setae on dorsal and ventral margins. Fourth segment unarmed, with scattered setae. Third segment with small spine on ventrodistal margin, partially obscured by tufts of setae. Second segment with dorsolateral distal angle (reaching about 0.5 of antennal acicle), terminating in strong spine, lateral margin unarmed; dorsomesial distal angle with strong spine, mesial margin with short setae. First segment with small lateral spine; margin ventral produced, with one small laterodistal spine. Antennal acicles moderately long, not exceeding length of ocular peduncles, reaching distal margin of fourth antennal peduncle segment, terminating in truncated spine; dorsal surface and mesial margin with tufts of short setae. Antennal flagella long, exceeding tip of right cheliped; each article with few short bristles (shorter than 1 article length).

Mandible ( Fig. 5A ) with upper and lower incisor edges calcareous; molar process with longitudinal shallow groove; palp 3-segmented, ultimate segment setose, slightly longer than combined length of penultimate and basal segments. Maxillule ( Fig. 5B ) with proximal endite subquadrate, distal endite subrectangular, enlarged distally; endopod with external lobe moderately developed (subrectangular), not recurved; internal lobe with long terminal bristle. Maxilla ( Fig. 5C ) with endopodite inflated basally, exceeding scaphognathite by 0.3 in distal extension. First maxilliped ( Fig. 5D ) with endopodite approximately 0.5 length of exopodite; basal segment of exopodite inflated. Second maxilliped ( Fig. 5E ) without distinguishing characters. Basis of third maxilliped ( Fig. 5F, G ) with 1 strong spine; ischium with well-developed crista dentata, consisting of 6–9 corneous-tipped teeth and one accessory tooth; merus and carpus with small spine at dorsodistal margin.

Chelipeds unequal ( Fig. 6A, B ), right longer than left. Right cheliped long and stout. Dactyl moderately long, about 0.9 length of propodus; dorsal surface with row of conical spines decreasing in size distally; mesial margin with row of conical spines increasing in size distally; cutting edge with row of calcareous teeth, ending in calcareous claw. Palm 1.3 times longer than broad, very slightly bent upward; dorsal, mesial, lateral, and ventral surfaces thickly covered with rough, flattened granules, those on middle surface larger; dorsolateral margin with conical calcareous teeth, decreasing in size proximal and distally. Fixed finger with cutting edge bearing several calcareous teeth, ending in small claw. Carpus slightly longer than palm; mesial surface flattened, upper and outer faces rounded; ventral surface inflated or convex. All surfaces thickly covered with rough flattened granules or scale-like tubercles, those on middle surface and dorsomesial margin are larger. Merus armed with 5 or 6 stout conical spines on distal margin, and numerous small conical spines on mesial and lateral margins; dorsal, mesial, outer and ventral surfaces with flattened granules or scale-like tubercles. Ischium with row of small denticles or spines on ventromesial margin.

Minor cheliped ( Fig. 6C, D ) enlarged, reaching 0.3 proximal of palm of major cheliped, dactyl and fixed finger curved ventrally. Dactyl about 1.7 times length of palm, dorsal surface weakly convex with one submedian longitudinal row of small spine-like tubercles; dorsomesial margin not well defined, with row of small spine-like tubercles extending on proximal half; mesial surface with few spine-like tubercles flattened proximally; ventral surface with few tufts of long setae; cutting edge with corneous teeth, ending in large corneous claw. Palm convex, about 1.1 times broader than long, and 0.7 times length of carpus; all surfaces covered with small scale-like tubercles, extending on proximal middle of fixed finger, larger medially; cutting edge of fixed finger with calcareous teeth interspaced with corneous teeth. Carpus as long as merus, subtriangular in dorsal view; all surfaces covered with scale-like tubercles, larger medially; dorsodistal margin with few spine-like tubercles. Merus subtriangular, dorsodistal and subdistal margins with numerous calcareous teeth extending on lateral surfaces; mesial, outer and ventral surfaces with numerous short rows of small calcareous teeth; ventrolateral distal margin with few small calcareous teeth. Ischium with row of small calcareous spines on ventromesial margin. In major and minor chelipeds, all spines or spine-like tubercles fringed with very short setae.

Second and third pereiopods similar, long ( Fig. 6E, F ), reaching half of fixed finger of right cheliped; dorsal and ventral surfaces with tufts of moderately long, stiff setae. Dactyls slender, long and curved ventrally, 1.5–1.6 times length of propodus, ending in sharp corneous claw; dorsal margins with a row of small calcareous spines on proximal half, decreasing in size distally and accompanied by long stiff setae; mesial faces with longitudinal groove medially, shallower distally and flanked proximally by few small calcareous spines; dorsomesial margin with row of small corneous spines; lateral faces with longitudinal groove medially, shallower distally, flanked dorsally by row of small spine-like tubercles on half proximal; ventral margins each with row of very slender spines flanked by long setae. Propodus elongated, 1.3–1.5 length of carpus; dorsal surfaces with short transverse rows of low protuberances or scale-like tubercles fringed distally by short setae; mesial, lateral and ventral faces with numerous flatted protuberances or scale-like tubercles fringed with short setae. Carpus with numerous scale-like tubercles fringed with short setae on dorsal and outer surfaces; those on dorsal surface stronger; outer surface somewhat inflated, with toothed distal margin; mesial and ventral surfaces smooth. Merus 1.3–1.5 times length of carpus, with dorsal surfaces with a row of low protuberances becoming scale-like tubercles distally; distal margin fringed with small teeth; mesial surface smooth, ventromesial margin with small, simple or toothed tubercles; outer surface and ventrolateral margin with numerous flatted protuberances or scale-like tubercles. Ischium with row of small spines on ventromesial margin.

Sternite XII (third pereiopods) with subrectangular anterior lobe ( Fig. 4D ), bearing long stiff setae.

Fourth pereiopods ( Fig. 4E ) semichelate. Dactyls without preungual process at base of claw, with ventrolateral row of 17–21 closely set, small, corneous spines. Propodal rasp with 3 or 4 rows of lanceolate scales; scales in posterior row smaller than the others.

Fifth pereiopods chelate. Dactyls with four rows of small ovate scales on proximal half and one row on distal half. Propodal rasp with 11–12 rows of lanceolate scales, extending posteriorly nearly to midpoint of segment. Coxae almost symmetrical.

Males and females with paired gonopores and unpaired pleopods 2–5. Males with biramous pleopods 3–5, exopod well developed and endopod reduced or obsolete. Females with pleopods 2–4 with both rami moderately developed; pleopod 5 weakly developed, uniramous.

Uropods asymmetrical. Telson ( Fig. 4F ) subquadrate, with posterior lobes asymmetrical, left slightly longer than right, separated by very shallow median cleft; terminal margins slightly convex, each with 3 rows of calcareous spines; marginal spines longer than submarginal ones; anterior lobes unarmed, margins with long setae.

Habitat. The specimens were collected in the Golfo de Nicoya by bottom trawling between 20 and 40 m depth. No specific habitat details are available for the collected individuals; however, habitat information about the Golfo de Nicoya has been summarized by Cortés & Wehrtmann (2009).

Colour. Living colour unknown. In alcohol: body and appendages straw-colored.

Distribution. Currently only known from the Pacific coast of Costa Rica.

Etymology. The name of the species refers to the strong resemblance to Pagurus albus ( Benedict, 1892) .

Remarks. Pagurus pseudoalbus sp. nov. can be easily distinguished from other eastern Pacific species of the “ exilis ” group Pagurus . In Pagurus gladiu s ( Benedict, 1892) and P. mertensii Brandt, 1851 , the antennal acicle exceeds the ocular peduncle in length, and the terminal margin of telson is armed with a single row of spines, while in P. pseudoalbus sp. nov. the antennal acicle does not exceed the length of the ocular peduncle, and the terminal margin of telson is armed with three rows of spines. The new species, however, has major resemblances to P. albus and P. perlatus H. Milne Edwards, 1848 ( Benedict, 1892; H. Milne Edwards, 1848) in having the ocular peduncles short, stout, and laterally compressed; cornea dilated; ocular acicles short, triangular, wide at the base and with small submarginal spine. The new species differs from these two species in a number of characters, including the antennal acicles, the chelipeds, and in the shape of the telson. In P. pseudoalbus sp. nov. as in P. albus , the shield is broader than long; however, in P. pseudoalbus sp. nov. the antennal acicles are short, not exceeding the distal margin of the fourth segment antennal, whereas in the second species the antennal acicles exceed the fourth antennal segment. The armature of both chelipeds is very similar, but the proportion of the palm of the major cheliped is different, being 1.3 times longer than broad in P. pseudoalbus sp. nov. and in P. albus it is 1.1 times as long as broad. Moreover, the carpus is subrectangular in P. pseudoalbus sp. nov. but subtriangular in P. albus ; the cutting edge of fixed finger of the minor cheliped in P. pseudoalbus sp. nov. bears sharper and more teeth than in P. albus ; the posterior margin of the telson is convex in P. pseudoalbus sp. nov. and straight in P. albus . Pagurus pseudoalbus sp. nov. is also close to P. perlatus . In both species, the rostrum is obtusely triangular and exceeding in length of lateral projections, but in P. perlatus these projections are unarmed while ending in a small spine in P. pseudoalbus sp. nov. In addition, the shield in P. pseudoalbus sp. nov. is broader than long while it is as long as broad in P. perlatus . In P. pseudoalbus sp. nov. the antennular peduncles exceeds the ocular peduncles by 0.3–0.5 length of the ultimate segment, whereas in P. perlatus the antennular peduncles are shorter than the ocular peduncles. The antennal acicles of P. pseudoalbus sp. nov. do not exceed the fourth antennal segment in length, while they reach 0.7 of the fifth segment in P. perlatus . The palm of the major cheliped is proportionally longer than broad in P. perlatus compared to that in P. pseudoalbus sp. nov. (1.4 vs. 1.3 times, respectively). In P. pseudoalbus sp. nov. the cutting edges of the dactyl and the fixed finger of the minor cheliped meet. In contrast there is a gap on the proximal part of fingers in P. perlatus (see Campillay 2012: fig. 20C). In P. pseudoalbus sp. nov. the sternite XII of the third pereiopod has a subrectangular anterior lobe, which is subcircular in P. perlatus . Moreover, the posterior lobes of telson are asymetrical and convex, and are armed with 2 or 3 rows of calcareous teeth in P. pseudoalbus sp. nov., whereas in P. perlatus these lobes are symmetrical and straight, and armed with one row of calcareous teeth.

Comparing the illustration of P. perlatus presented by Haig (1955: fig. 4a–d) with P. pseudoalbus sp. nov., some resemblances are evident. For example, in both species the shield is broader than long, the rostrum obtusely triangular, and the antennular peduncles exceed the ocular peduncles. Despite of these resemblances conspicuous differences are noticeable: the palm of the major cheliped is covered with large granules, while these are small in P. pseudoalbus sp. nov. The fixed finger of the minor cheliped is 1.5 times broader than the dactyl in P. perlatus , while it is two times broader in P. pseudoalbus sp. nov. Also, in P. perlatus the upper surface of both hand and carpus is covered with spine-like tubercles and those on the palm extend almost totally along the fixed finger. Conversely, the tubercles located on the palm and carpus of P. pseudoalbus sp. nov. are scale-like and the lines of the tubercles on the palm reach only the proximal third of the fixed finger.

Including P. pseudoalbus sp. nov., the number of Pagurus species from the Eastern Tropical Pacific is now 16. According to the morphological characters presented by P. pseudoalbus sp. nov., the new species can be assigned to the Group II (“exilis” group) proposed by Forest & Saint Laurent (1968).

Figures

FIGURE 4. Pagurus pseudoalbus sp. nov. Holotype male (SL 6.7 mm), Puntarenas, Golfo de Nicoya, Pacific Costa Rica, UCR-MZ-1193. A, gill lamellae; B, shield and cephalic appendages, dorsal view; C, right 1st–5th antennal segments and antennal acicle, in ventro-lateral view; D, sternite XII of 3rd pereiopods; E, dactyl, propodus and carpus of 4th right pereiopod, outer view; F, telson, dorsal view. Scale: A, C–F, 1 mm; B = 5 mm.

FIGURE 5. Pagurus pseudoalbus sp. nov. Holotype male (SL 6.7 mm), Puntarenas, Golfo de Nicoya, Pacific Costa Rica, UCR- MZ-1193. A, mandible; B, maxillule, C, scaphognathite; D, 1st maxilliped; E, 2nd maxilliped; F, 3rd maxilliped; G, isquium, merus and carpus of 3rd maxilliped, outer view. Scale: 1 mm.

FIGURE 6. Pagurus pseudoalbus sp. nov. Holotype male (SL 6.7 mm), Puntarenas, Golfo de Nicoya, Pacific Costa Rica, UCR- MZ-1193. A, 1st right pereiopod, dorsal view; B, same, mesial view; C, 1st left pereiopod, dorsal view; D, same, mesial view; E, 3rd right pereiopod, mesial view; F, same, outer view. Scale: 5 mm.