Pagurus holmi, Ng, Ngan Kee & Mclaughli, Patsy A., 2009

Ng, Ngan Kee & Mclaughli, Patsy A., 2009, A new hermit crab (Decapoda: Anomura: Paguroidea: Paguridae) from the eastern North Pacific, Zootaxa 2227, pp. 63-68 : 64-68

Genus Pagurus Fabricius, 1775 Pagurus holmi n. sp.

( Figs. 1–2 )

Paratypes: 1 male (sl = 1.0 mm), 2 females (sl = 1.3, 1.5 mm, latter dry and lacking pleon), 1 ovigerous female (1.1 mm), same data as holotype, USNM 1122508.

Description. Shield ( Fig. 1 A) somewhat broader than long, dorsal surface with few tufts of short setae; anterior margin between rostrum and lateral projections straight or slightly sloping; anterolateral margins sloping; posterior margin truncate. Rostrum prominent, acutely triangular, reaching nearly to midlength of ocular acicles. Lateral projections obsolete. Lateral carapace lobes moderately broad but only faintly delineated.

Ocular peduncles stout and moderately short, 0.4–0.7 length of shield; corneal diameter 0.3–0.5 of peduncular length. Ocular acicles moderately large, subovate, terminally acute, with or without terminal spinule; separated basally by approximately basal width of one acicle.

Antennular peduncles when fully extended overreaching distal margins of corneas by 0.3–0.5 lengths of ultimate segments. Ultimate and penultimate segments unarmed; basal segment with spine laterally on statocyst lobe.

Antennal peduncles not quite reaching to slightly overreaching distal corneal margins; with supernumerary segmentation; fifth and fourth segments unarmed; third segment with ventrodistal spine; second segment with dorsodistal angle produced, terminally acute or with small spine, dorsomesial distal angle with small spine or spinule; first segment with small spine at laterodistal margin. Antennal acicle, slender, arcuate, not reaching to base of cornea, terminating acutely or with tiny spinule. Antennal flagellum longer than cephalothorax; articles each with 1 or 2 very short bristles.

Maxillule ( Fig. 1 B) with 1 stiff seta terminally on internal lobe of endopod, external lobe somewhat produced, not recurved. Maxilla ( Fig. 1 C) with endopod overreaching distal margin of scaphognathite. First maxilliped ( Fig. 1 D) with endopod approximately half length of exopod. Second maxilliped ( Fig. 1 E) without distinguishing characters. Third maxilliped ( Fig. 1 F) with well developed crista dentata and1 accessory tooth on ischium; merus with dorsodistal spine.

Right cheliped ( Fig. 1 G) considerably larger than left but slightly shorter than ambulatory legs. Dactyl approximately equal to length of palm; dorsomesial margin with row of small tubercles, dorsal surface with scattered smaller tubercles and sparse setae; mesial face with few low protuberances and sparse setae; ventral surface unarmed; cutting edge with 2 calcareous teeth proximally and row of corneous teeth distally, terminating in small corneous claw. Palm slightly shorter than carpus; dorsomesial margin not delimited, dorsal and mesial surfaces with sparse short setae and scattered small tubercles, forming irregular rows on dorsal surface of holotype, dorsolateral margin with row of slightly larger tubercles extending full length of fixed finger; lateral and ventral surfaces with only very sparse short setae. Carpus slightly shorter than merus; dorsomesial margin not distinctly delimited, but with irregular row or rows of low tubercles, extending onto dorsal portion of mesial face in holotype, armature of dorsal surface varying from very few small tubercles and sparse setae to numerous scattered quite small tubercles or tuberculate spines, dorsodistal margin unarmed or with few quite small tubercles or tuberculate spines, dorsolateral margin not delimited; lateral and ventral surfaces with few short setae. Merus ( Fig. 1 H) triangular; dorsal margin with sparse row of short setae; mesial and lateral faces unarmed; ventral surface with prominent spine on ventromesial surface proximally. Ischium unarmed.

Left cheliped ( Fig. 1 I) reaching propodal-carpal articulation of right cheliped or beyond; dactyl slightly shorter to approximately equaling length of palm; dorsomesial margin not delimited; surfaces with sparsely scattered short setae; cutting edge with row of corneous teeth, terminating in small corneous claw. Palm slight shorter than carpus; dorsomesial margin with row of few tubercles, dorsal surface elevated in midline and armed with row of small tubercles or tuberculate spines, dorsolateral surface spinulose or tuberculate, extending at least distally onto fixed finger and with scattered sparse, short setae, dorsolateral margin not delimited; ventral surface with scattered setae, longest on fixed finger; cutting edge with row of small corneous teeth, terminating in corneous claw. Carpus approximately 0.7 length of merus; dorsomesial and dorsolateral margins each with row of spines or spinulose tubercles and sparse setae; mesial, lateral and ventral surfaces each with few setae. Merus triangular; dorsal margin with few widely-spaced setae; mesial and lateral faces unarmed; ventral surface with few setae and low protuberances. Ischium unarmed.

Second ( Fig. 2 A) and third pereopods ( Fig. 2 B) generally similar, third slightly longer. Dactyls shorter than propodi; dorsal, mesial and lateral faces unarmed, ventral margins each with 5–9 prominent corneous spines; terminating in moderately long corneous claws. Propodi with sparse tufts of setae dorsally and ventrally, ventrodistal margins each usually with 1 or 2 corneous spines and frequently 1 additional spine subdistally. Carpi lacking dorsodistal spines. Meri and ischia each with sparse setae dorsally and ventrally. Fourth pereopods ( Fig. 2 C) weakly semichelate; each with propodal rasp consisting of several rows of corneous scales. Fifth pereopods chelate. Sternite of third pereopods ( Fig. 2 D) with subovate anterior lobe.

Males without sexual tubes; unpaired left pleopods 3–5 with exopods well developed, endopods vestigial. Females without paired first pleopods; unpaired left pleopods 2–4 with exopods well developed, endopods appreciably shorter; pleopod 5 with exopod reduced, endopod rudimentary. Non-eyed eggs 0.4–0.5 mm diameter.

Tergite of sixth pleomere ( Fig. 2 E) large, ovate. Uropods markedly asymmetrical, left appreciably larger. Telson ( Fig. 2 F) with lateral indentations suggesting division into anterior and posterior portions; posterior margin entire or with broad, shallow rectangular concavity.

Etymology. This species is dedicated to George P. Holm, the principal collector.

Coloration. In life, cephalothorax and chelipeds overall reddish-orange to brownish orange; dactyls of ambulatory legs reddish-orange or brownish-orange, each with white band proximally; propodi white, each with broad reddish-orange or brownish-orange median band; carpi white; meri white, each with moderately narrow reddish-orange or brownish-orange band in distal half.

Habitat. Found occupying gastropod shells of Lacuna variegata Carpenter, 1864 , Littorina scutulata Gould, 1849 , and Margarites helicinus Phipps, 1874 , in eel grass and on rocky substrates.

Distribution. Presently known only from the type locality, Marrowstone Point, Washington; intertidal.

Remarks. Among the shallow-water hermit crabs of the eastern North Pacific, Pagurus holmi n. sp. is most similar to P. hartae ( McLaughlin & Jensen, 1996) in overall size, with females ovigerous at shield lengths of slightly more than one millimeter. However, morphologically, P. h o l m i n. sp. shares the synapomorphic character of one prominent spine on the proximal ventromesial surface of the right cheliped with three other species, P. caurinus Hart, 1971 , P. hemphilli ( Benedict, 1892) and P. hirsutiusculus . Of the three, P. holmi n. sp. is readily distinguished from P. h e m p h i l l i by the broader shield and unarmed ambulatory carpi of the new species. Additionally, the very prominent ventral inflation of the carpus of the right cheliped of P. hemphilli differentiates this taxon from all other regional species. Although the shield is broader than long in P. caurinus , P. hirsutiusculus and P. holmi n. sp., the rostrum in the former species is poorly developed in comparison with the rostra of the latter two. However, the spinose armature of the chelipeds and telson will readily distinguish P. caurinus from both other species.

Pagurus holmi n. sp. is most closely allied to P. hirsutiusculus , sharing with that species not only the distinctly broader shield but also the weakly developed or obsolete lateral projections. However, in specimens of comparable size, the ratio of shield width to shield length is slightly greater in juveniles of P. hirsutiusculus and increases with increased animal size. Although the tuberculate armature of the chelae are similar in both species, the spines on the dorsodistal margins of the carpi of the left chelae of P. hirsutiusculus are much more prominent even in the smallest of juvenile males (sl = 1.1, 1.3 mm) than are seen in the solitary male of P. holmi n. sp. or any of the four females. Similarly, the dorsodistal margins of the carpi of at least the second pereopods each is provided with a small spine in juveniles of P. hirsutiusculus , whereas these carpi in P. h o l m i n. sp. are unarmed. The propodal rasps of the fourth pereopods of P. holmi n. sp. with their several rows of corneous scales ( Fig. 2 C) are indicative of maturity, whereas the one or two rows seen in the small specimens of P. hirsutiusculus examined clearly represent juvenile level development. Differences are also seen in the anterior lobes of the sternites of the third pereopods of the two species, as well as in the telsons; however, variations in these characters are reported for both taxa. Of the five females of P. hirsutiusculus examined (sl = 1.3–1.8 mm) none were ovigerous and all still exhibited color patterns pinpointing juveniles. In contrast, two of the three females of P. holmi with intact pleons (1.1, 1.2 mm) were carrying eggs.

Living color may also be used to distinguish between P. holmi n. sp. and P. hirsutiusculus . As reported above, the overall colors of P. h o l m i n. sp. are reddish to brownish orange and white. Stevens (1925) reported that coloration differed markedly between juveniles and adults of P. hirsutiusculus , with the chelipeds and walking legs of the young varying from mahogany to blue-black or sometimes light olive with white or light blue at the articulations. Recent collection of juveniles of this species have shown that the propodi of the ambulatory legs of P. hirsutiusculus are white or bluish-white distally with the proximal halves to two thirds of these segments deeply colored. The propodi of P. holmi n. sp. each have a median reddish or brownishorange band. The stripe found on the lateral face of the dactyl of each ambulatory leg of P. hirsutiusculus is not present in the smallest of specimens (sl = 1.1 mm) but has developed in somewhat larger specimens (sl = 1.4 mm). No stripes were observed on the dactyls of P. h o l m i, n. sp. Despite the small size of the new species, its coloration will differentiate this taxon from juveniles of P. hirsutiusculus .

Figures

FIGURE 1. Pagurus holmi n. sp., holotype, female (1.2 mm, USNM 1122507). A, shield and cephalic appendages. B, right maxillule. C, right maxilla. D. right first maxilliped. E, outer view of right second maxilliped. F, outer view of right third maxilliped. G, right cheliped. H, mesial view of merus of right cheliped. I, left cheliped. (Scale: A, G – I = 1.0 mm; B – F = 0.25 mm).

FIGURE 2. Pagurus holmi n. sp., holotype, female (1.2 mm, USNM 1122507). A, right second pereopod. B, left third pereopod. C, right fourth pereopod. D, sternite of third pereopods. E, tergite of sixth pleomere. F, telson. (Scale: A – C = 1.0 mm; D – E = 0.5 mm).