Bythiopagurus macrocolus, McLaughlin, 2003

McLaughlin, P. A., 2003, A new genus and species of hermit crab (Decapoda: Anomura: Paguridae) from seamounts off south-eastern Tasmania, Australia, Memoirs of Museum Victoria 60 (2), pp. 229-236 : 231-234

publication ID	https://doi.org/ 10.24199/j.mmv.2003.60.23
persistent identifier	https://treatment.plazi.org/id/AB5B7D25-FFC1-FFD9-FF66-F9CAFD59EB39
treatment provided by	Felipe
scientific name	Bythiopagurus macrocolus
status	sp. nov.

Treatment

Bythiopagurus macrocolus View in CoL sp. nov.

Figures 1–3 View Figure 1

Paguridae View in CoL n. gen. n. sp.— Koslow and Gowlett-Holmes, 1998: 30 (in part, see remarks).

Pagurid sp.—Poore, et al., 1998: 71 (in part, see remarks).

Material examined. Holotype. (6.0 mm), NMV J44765 About NMV , CSIRO SS01 View Materials /97 stn 41, 44˚19.2´S, 147˚07.2´E, 1083 m; 82.8 km SSE of SE Cape “U” seamount, Tasmania, Australia.

Paratypes. All from Tasmanian seamounts, collected on cruise CSIRO SS01 View Materials / 97. Stn 15, 82.9 km SSE of SE Cape “Sister 1”, 44˚16.2´S, 147˚17.4´E, 1100 m, 23 Jan 1997, 6 (2.6–5.9 mm), 9 + O (3.2–6.4 mm), 5 ovigerous + O (4.2–6.2 mm), NMV J44760 About NMV . Stn 28, 89.5 km SSE of SE Cape “K1”, 44˚17.4´S, 147˚24.6´E, 1225 m, 25 Jan 1997, 4 (4.3–6.8 mm), 1 ovigerous O + (3.6 mm), NMV J44762 About NMV . Stn 34, 85.4 km SSE of SE Cape “U”, 44˚19.8´S, 147˚10.2´E, 1083 m, 27 Jan 1997, 3 + O (4.2–5.3 mm), NMV J44759 About NMV . Stn 37, 84.0 km SSE of SE Cape “J1”, 44˚16.2´S, 1477˚19.8´E, 1300 m, 27 Jan 1997, 1 (4.9 mm), 1 + O (4.2 mm), 1 ovigerous + O (6.2 mm), NMV J44803 About NMV . Stn 40, 82.6 km SSE of SE Cape “J1”, 44˚14.4´S, 147˚21.8´E, 1200 m, 27 Jan 1997, 2 (4.4, 5.1 mm), 5 + O (5.1–6.4 mm), 5 ovigerous + O (sl = 5.1–6.3 mm), NMV J44758 About NMV . Stn 41, 82.8 km SSE of SE Cape “U”, 44˚19.2´S, 147˚07.2´E, 1083 m, 27 Jan 1997, 1 (4.2 mm), 1 + O (4.3 mm), 3 ovigerous + O (5.0– 5.5 mm), NMV J44765 About NMV ; 2 (3.8, 6.4 mm), 1 ovigerous + O (5.3 mm), USNM 1007810 About USNM . Stn 58, 81.2 km SSE of SE Cape “38”, 44˚13.2´S, 147˚22.8´E, 1140 m, 30 Jan 1997, 1 (5.6 mm), NMV J44768 About NMV . Stn 59, 81.6 km SSE of SE Cape “38”, 44˚13.8´S, 147˚22.8´E, 1200 m, 30 Jan 1997, 1 (4.5 mm), NMV J44763 About NMV . Stn 62, 87.8 km SSE of SE Cape “A1”, 44˚19.8´E, 147˚16.2´E, 1200 m, 30 Jan 1997, 1 ovigerous + O (5.4 mm), NMV J44761 About NMV .

Other material examined. CSIRO SS91/97, no other data, 1 (5.6 mm), NMV J44801.

Description. Shield ( Figs. 1a View Figure 1 , 2a) broader than long; anterior margin between rostrum and lateral projections concave; anterolateral margins sloping; posterior margin truncate; dorsal surface with numerous sparse tufts of simple setae. Rostrum triangular, reaching to or slightly beyond bases of ocular acicles; with or without terminal spinule. Lateral projections reaching level of rostrum or slightly beyond, each with prominent marginal or submarginal spine.

Ocular peduncles very short and stout, 0.40–0.50 length of shield; dorsal, mesial and lateral surfaces calcified, median longitudinal region of ventral surface membranous; dorsal surfaces of peduncles each with 3 or 4 short transverse rows of simple setae; corneas reduced dorsally by projection of peduncular integument, corneal diameter 0.40–0.50 of peduncular length. Ocular acicles each with slender triangular projection, terminating acutely and with small submarginal spine or spinule not usually visible dorsally; separated basally by approximately 0.50 basal width of 1 acicle.

Antennular peduncles overreaching distal margins of corneas by length of ultimate segments to nearly entire lengths of penultimate segments. Ultimate segments nearly twice length of penultimate segments, dorsal surfaces each with 3–5 short transverse rows of simple setae. Penultimate segments with few sparse tufts of setae. Basal segments each with slender spine on dorsolateral margin of statocyst lobe.

Antennal peduncles overreaching distal margins of corneas by entire lengths of fifth and fourth segments, but reaching only to approximately midlength of ultimate segments of antennular peduncles. Fifth and fourth segments with few sparse tufts of short setae. Third segment with spine at ventrodistal margin. Second segment with dorsolateral distal angle prominently produced, terminating in small spine and with 1 or 2 small spines on mesial margin; dorsomesial distal margin with well developed spine. First segment sometimes with spine on dorsolateral distal margin, ventrolateral margin with 1 spine. Antennal acicles reaching to or nearly to distal margin of fifth peduncular segment, terminating in small spine; mesial margin with row of sparse tufts of stiff setae.

Mandibles with upper incisor edge of left ( Fig. 1c View Figure 1 ) with 2 to several calcareous denticles, cutting edge with corneous-tipped tooth at lower angle, sometimes also at upper angle, stout internal ridge presumably representing molar process with usually corneous-tipped tooth at lower angle; right mandible with upper edge of incisor process ( Fig. 1d View Figure 1 ) unarmed or with 1 or 2 calcareous denticles, upper and lower angles of cutting edge each usually with corneous-tipped tooth, presumed molar process with usually corneous-tipped tooth at lower angle; palp three-segmented, distal segment with row of short marginal setae. Maxillule ( Fig. 1e View Figure 1 ) with internal lobe of endopod not produced, but provided with 1 stiff bristle, external lobe somewhat produced, not recurved, with 3 terminal setae. First maxilliped ( Fig. 1g View Figure 1 ) with setae of external margin of exopod only on proximal half. Third maxilliped ( Fig. 1h View Figure 1 ) with prominent tooth at ventrodistal angle of coxa; basis with 2 or 3 spine-like teeth on ventral margin; ischium with well developed crista dentata, usually 1 or occasionally 2 widely separated accessory teeth; merus and carpus each with dorsodistal spine.

Right cheliped ( Figs 3a, b View Figure 3 ) long and slender. Dactyl 0.50 to nearly equal to length of palm; dorsomesial margin not delimited, rounded mesial face unarmed or with numerous minute spinules in proximal half; dorsal surface often with scattered small pits and individual or sparse tufts of short to moderately long setae; ventral surface with scattered tufts of longer setae; cutting edge usually with 2 or 3 large calcareous teeth, terminating in small corneous claw and slightly overlapped by fixed finger, occasionally crossed with fixed finger in larger specimens. Palm 0.70–0.95 length of carpus; armature of dorsomesial margin varying from ill-defined and irregular single or double row of small spinules or tubercles over entire length in small specimens to row of prominent spines in proximal 0.80–90 of margin and small spines or spinules in distal 0.10–0.20 in large individuals; dorsal surface with scattered very small tubercles or spinules, particularly in mesiodistal 0.35, dorsal midline with longitudinal row of 6–13 tiny to prominent spines, not extending to junction of dactyl and fixed finger; dorsolateral margin not delimited except faintly in some small specimens, but armed with numerous very small and tiny spinules, tubercles or granules, extending to distal 0–25–0.50 of fixed finger; mesial, lateral and ventral surfaces with tiny tubercles or spinules, sometimes forming short, transverse rows; surfaces all with scattered sparse tufts of short to moderately long setae, most numerous ventrally; cutting edge of fixed finger with 2 or 3 prominent calcareous teeth, calcareous ridge or sometimes few to several small calcareous teeth distally. Carpus slightly shorter to slightly longer than merus; dorsomesial margin with row of small to moderately prominent spines, dorsodistal margin usually with 1 small to large spine mesially and several very small spines laterally, occasionally only single small spine in small specimens; dorsal midline with row of small spines or spinules becoming row of prominent spines in large individuals, dorsolateral surface sloping, dorsolateral margin armed with weakly defined row of tiny spinules or tubercles in small specimens, increasing in size and number with increased body size; mesial and lateral faces each with scattered to moderately dense covering of very small tubercles or spinules, most numerous in small individuals, distal margins each sometimes with several spines or spinulose tubercles; ventromesial margin often tuberculate, ventral surface with scattered tubercles; ventrolateral margin usually not delimited, but with 1 or 2 spines at ventrolateral distal angle. Merus subtriangular; dorsal surface with row of short transverse ridges and sparse tufts of setae; mesial face with few sparse tufts of setae, ventromesial margin with row of conical, subacute spines, ventral surface often with scattered spines; ventrolateral margin not distinctly delimited but with short transverse rows of small tuberculate spines extending onto ventral surface. Ischium with row of small spines or spinules on ventromesial margin, ventral surface with few low protuberances or small spines and sparse setae. Coxa with spine on distal margin ventromesially and additional spine ventrolaterally.

Left cheliped ( Figs 3c–e View Figure 3 ) often as long as or slightly longer than right; dactyl approximately 0.50 longer than palm; dorsal surface slightly elevated proximally, dorsomesial margin not delimited, but with transverse tuberculate or minutely spinulose ridges and sparse setae, few spinules on dorsal surface in proximal half, dorsal surface also with scattered stiff setae; cutting edge with row of small corneous spines, rounded tip of dactyl slightly overlapped by corneous claw of fixed finger ( Fig. 2c) in small specimens (e.g. 2.6 mm), just beginning to show overlap by fixed finger (e.g. ovigerous + O 3.6 mm), or completely overlapped by hooked end of fixed finger ( Figs 2d, e) in large specimens (e.g. 3.5 mm, + O 5.0 mm); inner surface of dactyl concave, small corneous claw laterally positioned at tip of dactyl. Palm 0.65–0.80 length of carpus; dorsomesial margin variable: not delimited in small specimens, but rounded surface frequently armed with numerous tiny spinulose tubercles or small spines often increasing in size proximally and tufts of setae; large specimens with well delimited margin armed with row of small spines not quite extending to distal margin, 1 or 2 prominent spines at proximal angle; dorsal surface elevated in midline and armed with row of 3–11 minute to moderately prominent tuberculate spines, not reaching to articulation of dactyl, but often continued as irregularly-set very small spinules in large individuals; dorsomesial surface unarmed in small specimens, but with increasing number of small or very small spinules with increased size, primarily in distal half; dorsolateral surface sloping and armed with numerous minute to small spinules and/or tubercles, continued onto proximal half of fixed finger, dorsolateral margin varying from well delimited by row of small spines to not delimited, but rounded surface with numerous tiny to small spinules or spinulose tubercles also continued onto fixed finger but not extending to tip, dorsolateral proximal angle with blunt tubercle or spine; ventral surface with small spinules or spinulose tubercles laterally, remainder of ventral surface with tufts of sparse setae; distal portion of fixed finger curved and slightly overlapping dactyl in small specimens, but becoming drawn out into hook-like tip with increased size, terminating in small corneous claw; inner surface of fixed finger oblique in small individuals to prominently concave, particularly distally in larger specimens. Carpus slightly shorter to approximately equal to length of merus; dorsodistal margin with 1 to several small spines; dorsomesial margin with irregular row of small to moderately large spines, dorsal surface often with few small spines, at least distally and tufts of sparse setae, irregular row of small to moderately large spines beginning proximally at dorsolateral angle but becoming almost median distally in larger specimens because of sloping dorsolateral surface; in smaller specimens lateral face tending to be more perpendicular, surface armed with numerous tiny to small spinules or tubercles, ventrolateral margin delimited by row of small spines or simply rounded with surface armature continued onto ventral surface laterally; mesial face with scattered tufts of sparse setae, distomesial margin and mesial surface ventrally spinulose or tuberculate; remainder of ventral surface with few low protuberances and tufts of sparse setae. Merus subtriangular; dorsal surface with short transverse rows of sparse setae; ventromesial margin with row of irregularlysized spines; ventrolateral margin with row of somewhat small- er spines, lateral face ventrally with short transverse rows of very small tubercles or granules accompanied by tufts of setae; ventral surface with few small spines, particularly laterally, and scattered tufts of sparse setae. Ischium with row of small spines on ventromesial margin, 1 small spinule on ventrolateral margin distally, ventral surface occasionally with few scattered small spines. Coxa with spine on ventromesial distal margin and additional spine on distal margin ventrolaterally.

Ambulatory legs ( Fig. 3f View Figure 3 ) similar from left to right, usually only slightly overreaching tips of chelipeds, if at all. Dactyls 0.10–0.30 longer than propodi; dorsal surfaces each with row of tufts of moderately short sparse setae, interspersed with corneous spinules in distal 0.25–0.45; lateral faces generally flattened, each with faint longitudinal sulcus flanked dorsally and ventrally by row of sparse setae; mesial faces each with weak longitudinal sulcus and row of corneous spinules dorsally; ventral margins each with row of 15–23 corneous spines; terminating in sharp corneous claw. Propodi 0.50–0.70 longer than carpi; dorsal surfaces each with low protuberances and numerous tufts of sparse setae; lateral faces each usually with row of tufts of sparse setae dorsally; ventral surfaces each with few tufts of sparse setae, 1 or 2 corneous spines on each ventrodistal margin, at least on second. Carpi each with small dorsodistal spine; dorsal surfaces with few low, occasionally weakly spinulose, protuberances and tufts of sparse setae; lateral faces each with row of sparse setae dorsally; ventral surfaces each with 2 or 3 tufts of setae. Meri each with transverse ridges and sparse setae dorsally; ventral margins of second pereopods each with irregular row of small spines and tufts of sparse setae, lateral faces often with few to numerous spinules or granules in lower half; third with ventral margins usually unarmed, rarely with few minute spinules or granules, but with scattered tufts of setae. Ischia each with dorsal and ventral tufts of setae. Anterior lobe of sternite of third pereopods ( Fig. 2b) subrectangular, anterior margin with 1 or 2 pairs of small subacute or acute spines.

Telson ( Fig. 2e) with posterior lobes symmetrical or only weakly asymmetrical; terminal margins somewhat oblique, each armed with 1 or 2 to several spines.

Colour (in preservative). Cephalothorax and appendages all generally orange to reddish-orange.

Reproduction. Slightly more than half of the females collected were ovigerous, but few if any of the eggs were near to hatching (eyed). The eggs were relatively small (diameter 0.75–0.98 mm) and quite numerous, although precise counts were not possible because of obvious loss during preservation and transport.

Variation. Variation in shape and armature of the chelipeds is appreciable in B. macrocolus as is indicated in the description, and this appears to be a function of size rather than sexual dimorphism. Small specimens of both sexes do not have the prominent spines on the dorsomesial margin of the right chelae ( Fig. 3a View Figure 3 ) or on the dorsomesial margins of the right and left carpi seen in large specimens. Similarly, the median row of spines on the right chela becomes increasingly more pronounced with increasing animal size. In contrast, the row of spines often delimiting the dorsolateral margin of the chela of the right in small individuals becomes indistinguishable in larger specimens. The very unusual development of the dactyl and fixed finger of the left cheliped may be an adaptation to its distinctive environment; however, it is unquestionably correlat- ed with animal growth. In the smallest specimen (2.6 mm) the corneous claw of the fixed finger overlaps the rounded tip of the dactyl ( Fig. 3c View Figure 3 ) but the terminal portion of the fixed finger has not yet developed into a hook. The ventral surfaces of the dactyl and fixed finger, while sloping inward in this small male, do not exhibit the prominent concavities seen in larger individuals ( Fig. 3e View Figure 3 ). Although these morphological variations are seen in both sexes, there appears to be a developmental “lag” in females. In males and females of similar size, spination on the dorsomesial margins of chela and carpi tends to be more prominent in males, whereas the loss of marginal distinction dorsolaterally on the chela occurs more rapidly.

Distribution and habitat. Seamounts U, J1, K1, A1, 38 and Sister 1 off south-eastern coast of Tasmania; 1083–1300 m; typically occupying small gastropod shells; found in association with primarily dead colonies ( Gowlett-Holmes, 1998: 47) of stony coral, Solenosmilia variabilis .

Etymology. From Greek makros, meaning long, and kolon meaning leg, and indicative of the long-leggedness of this hermit crab.

Remarks. Because size-related diagnostic characters are not apparent in small specimens, individuals of shield lengths <2.8 mm, particularly females, Goreopagurus poorei Lemaitre and McLaughlin, 2003 look superficially like small B. macrocolus . Consequently, specimens reported by Koslow and Gowlett-Holmes (1998: 21) from “Andys” and “Main Pedra” seamounts and Poore et al. (1998: 77) from stations 03, 06, and 56 were incorrectly referred to B. macrocolus . Two lots, one from “Andys” (stn 56) and one from “Main Pedra” (stn 03), are G. poorei . The single female (4.2 mm) from “Main Pedra” seamount (stn 06) belongs to Pagurodes inarmatus Henderson, 1888 , which shares with the aforementioned species distinctly shortened ocular peduncles.

The majority of specimens of B. macrocolus had been removed from their shells shortly after capture but a few examined still occupied shells. These shells were worn and frequently damaged but the most notable observation was that the shells rarely even completely covered the abdomens of the crabs. Correspondingly, there appeared to be reduction in overall abdomen length with increased animal size. The need for only minimal abdominal protection is undoubtedly correlated with the appreciable calcification of the cephalothorax of B. macrocolus as it is in species of Labidochirus Benedict, 1892 , Porcellanopagurus , and Solitariopagurus . Whether a similar correlation exists between abdomen length and shell size cannot be adequately determined from the limited material.