Decaphyllus deliquus, Komai & Rahayu, 2013

Komai, Tomoyuki & Rahayu, Dwi Listyo, 2013, Six New Species Of The Hermit Crab Genus Decaphyllus De Saint Laurent, 1968 (Crustacea: Decapoda: Anomura: Paguridae) From The Boholo Sea, The Philippines, And The Ryukyu Islands, Japan, Raffles Bulletin of Zoology 61 (2), pp. 589-620 : 595-600

publication ID	https://doi.org/ 10.5281/zenodo.5352524
publication LSID	lsid:zoobank.org:pub:3EC76281-1ABA-4E72-BBE1-0BF811387484
persistent identifier	https://treatment.plazi.org/id/850B9A25-FFD2-FF92-7326-F9B0FF3F98E0
treatment provided by	Tatiana
scientific name	Decaphyllus deliquus
status	sp. nov.

Treatment

Decaphyllus deliquus , new species

( Figs. 4–7 View Fig View Fig View Fig View Fig )

Material examined. — Holotype: ovigerous female (sl 1.6 mm), PANGLAO 2004, stn P1, Maribohoc Bay , Panglao Islands, 09°36.1'N, 123°45.0'E, 90–200 m, 30 May 2004, tangle nets from local fishermen, NMCR 39087. GoogleMaps

Description. — Eight pairs of biserial phyllobranchiae (no pleurobranchs). Arthrobranch gills above base of third maxilliped absent.

Shield ( Fig. 4A View Fig ) approximately as long as wide; anterior margin between rostral region and lateral projection slightly concave; anterolateral margins sloping; posterior margin roundly truncate; dorsal surface with anteromedian and posteromedian parts poorly calcified, with few short setae laterally. Rostrum very broadly rounded. Lateral projections weakly developed, producing as far as rostrum, each with terminal spinule.

Ocular peduncle ( Fig. 4A View Fig ) subequal in length to shield; dorsal surface with mesial row of tufts of moderately short to long setae directed mesially, few lateral setae, and prominent tuft of long setae at base of cornea; cornea not dilated, its width slightly more than 0.2 of length of ocular peduncle; basal part slightly inflated, basal width slightly greater than corneal width. Ocular acicle drawn out distally into acute spine, mesial margin with several long setae; separated basally slightly less than width of 1 acicle. Interocular lobe visible in dorsal view, anteriorly slightly concave.

Antennular peduncle ( Fig. 4A View Fig ) overreaching distal corneal margin by about 0.3 length of ultimate segment. Basal segment with prominent spine on lateral margin of statocyst lobe, but without ventromesial subdistal spine. Penultimate and ultimate segments unarmed, almost glabrous except for 1 short thin seta at dorsomesial distal angle of ultimate segment.

Antennal peduncle ( Fig. 4A View Fig ) only reaching distal 0.4 of ocular peduncle. Fifth and fourth segments with few setae. Third segment with small spine on ventromesial distal margin. Second segment with dorsolateral distal angle strongly produced, terminating in bifid spine; dorsomesial distal angle with small spine. First segment with 1 strong spine on ventrodistal margin; lateral surface unarmed. Antennal acicle slightly overreaching distal margin of fifth peduncular segment, and reaching to corneal base, terminating in small spine; mesial surface with several long setae; lateral margin unarmed. Antennal flagellum with 2–4 short setae on distal margin of each article.

Third maxilliped ( Fig. 4B View Fig ) with merus armed with strong dorsodistal spine (right) or unarmed (left); crista dentata on ischium consisting of row of 4 triangular teeth; basis with 1 acute distal denticle on mesial face. Exopod long, reaching to distal margin of carpus.

Chelipeds ( Figs. 5 View Fig , 6 View Fig ) subequal in length; right only slightly longer, but appreciably stronger. Right cheliped ( Fig. 5 View Fig ) with chela about 2.5 times longer than wide. Dactylus ( Fig. 5C View Fig ) set at slightly oblique angle to palm, slightly shorter than palm; dorsal surface with 1 small acute proximal spine mesially; all surfaces with scattered moderately short to long setae, particularly numerous on mesial surface; cutting edge with row of small, blunt calcareous teeth, terminating in tiny corneous claw. Palm ( Fig. 5A, C View Fig ) subequal in length to carpus; dorsomesial margin with row of moderately small spines, dorsal midline with row of moderately small spines or tubercles not extending onto fixed finger, dorsolateral margin with irregular row of small spines or tubercles, dorsal surface lateral to midline with only few small tubercles; lateral and mesial surfaces with scattered moderately short setae; ventral surface convex, smooth, with scattered setae. Fixed finger with row of blunt calcareous teeth on cutting edge, terminating in tiny calcareous claw. Carpus ( Fig. 5A–C View Fig ) slightly widened distally, subequal in length to merus, about 2.1 times longer than wide; dorsomesial margin with row of 5 spines of various sizes (distal second spine largest), dorsolateral margin with row of 5 smaller spines (proximalmost spine minute, tubercle-like); all surfaces with scattered short to long setae, subdistal transverse row of setae particularly prominent; ventrolateral distal angle with 1 minute spine; distomesial angle unarmed. Merus ( Fig. 5A, B, D View Fig ) with 1 small spine on dorsodistal margin mesially; dorsal surface with sparse setae; ventrolateral margin with 1 moderately large spine subdistally; mesial surface with 1 small protuberance proximoventrally, ventromesial margin with 2 widely spaced small spines; ventral surface with small spine medially. Ischium ( Fig. 5D View Fig ) with only proximal spinule on ventromesial margin, directed mesially; lateral surface with 1 spinule ventrally.

Left cheliped ( Fig. 6 View Fig ) with narrow hiatus between dactylus and fixed finger. Dactylus ( Fig. 6A, C View Fig ) about 1.3 times longer than palm, unarmed, but with short to long setae particularly numerous mesially; cutting edge with row of minute corneous teeth in distal half. Palm ( Fig. 6A, C View Fig ) about 0.7 length of carpus; dorsomesial margin with row of 4 small spines, dorsal midline with 2 small spines proximally and 2 tiny spinulose tubercles distally, dorsolateral margin with irregular row of tiny spines or spinulose tubercles extending onto fixed finger; all surfaces with scattered short to long setae. Fixed finger with faintly denticulate cutting edge, terminating in tiny corneous claw. Carpus ( Fig. 6A–C View Fig ) slightly widened distally, about 3.2 times longer than wide; dorsolateral margin with 4 small tubercles or spines, dorsomesial margin with 3 moderately small spines; ventrolateral distal angle with 1 minute spine; all surfaces with scattered setae. Merus ( Fig. 6A, B, D View Fig ) with sparse setae on dorsal surface; dorsodistal margin with 1 small spine; ventrolateral margin with 2 small, widely spaced spines; mesial surface with 1 prominent, proximally curved spine proximoventrally, ventromesial margin with 2 small spines; ventral surface unarmed, with scattered long setae. Ischium ( Fig. 6D View Fig ) with 1 anteriorly directed and 1 posteriorly directed spines on ventromesial margin; lateral surface with 1 minute spine.

Ambulatory legs ( Fig. 7 View Fig ) overreaching tip of right cheliped. Dactyli ( Fig. 7A, B, D View Fig ) 1.5–1.8 times longer than propodi, 12.5–12.8 times longer than broad, slightly curved ventrally; all surfaces unarmed, but with numerous setae, particularly longer and stronger on dorsal margins. Propodi ( Fig. 7A, D View Fig ) unarmed, but with scattered short to long setae on surfaces and margins. Carpi each with dorsodistal spine (second) or minute tubercle (third, Fig. 7E View Fig ), and 1 additional small spine located on proximal one-third of dorsal margin (second and third, Fig. 7C, E View Fig ). Meri ( Fig. 7A, C–E View Fig ) each with 1 small spine slightly distal to midlength of dorsal margin, also with 1 additional spine at about proximal 0.2 on second pereopods; dorsal and ventral margins with numerous long setae, latter spineless. Ischium ( Fig. 7C, E View Fig ) unarmed.

Fourth pereopods ( Fig. 4C View Fig ) with claw of dactylus entirely masked by tufts of short, dense setae; propodus with 1 minute scale subterminally ( Fig. 4C View Fig ). Fifth pereopods semichelate.

Female with unpaired left gonopore.

Anterior lobe of sixth thoracic sternite (third pereopods, Fig. 4D View Fig ) subsemicircular, slightly skewed to left, bearing moderately long submarginal setae. Sternite of eighth thoracic sternite (fifth pereopods) in female ( Fig. 4E View Fig ) subovate, with row of moderately long setae anteriorly.

Telson ( Fig. 4F View Fig ) with median cleft not apparent; left terminal margin with 1 minute denticle, left exterior angle prominently produced; right terminal margin narrow, with 4 minute denticles, right exterior angle spinose, weakly developed; left lateral margin with narrow chitinous plate.

Males unknown. Colouration. — In preservative. Shield with slight iridescence posteriorly. Cornea light yellowish brown. Chelipeds and ambulatory legs with slight iridescence; merus of right cheliped with reddish brown patch on dorsal surface subdistally.

Distribution. — Known only from the type locality, Maribohoc Bay, Panglao Island. The real bathymetrical range is unknown, because the unique holotype came from steep slope at depths of 90– 200 m.

Remarks. — Although only a single ovigerous female is available, this new species is safely assigned to Decaphyllus by unarmed but setose dactyli of the ambulatory legs, the non-chelate fourth pereopod, and the entire eighth thoracic sternite.

The complete loss of the arthrobranch gills on the third maxilliped links Decaphyllus deliquus , new species, to D. barunajaya . The general proportion of the ocular peduncles and antennular peduncles and the shape and general armature of the chelipeds are also similar between the two species. Additionally, as in D. barunajaya , the first segment of the antennal peduncle is armed with a strong ventrodistal spine in this new species. Nevertheless, the new species can be distinguished morphologically from D. barunajaya by the following characters (cf. McLaughlin, 1997). The lateral projections of the shield are less produced in D. deliquus than in D. barunajaya ; in the new species, they exceed as far as the rostral lobe, whereas distinctly overreaching it in D. barunajaya . The antennal peduncle is relatively shorter in D. deliquus than in D. barunajaya ; in the new species, it only reaches to the distal 0.4 of the ocular peduncle, but it reaches nearly to the corneal base in D. barunajaya . The dactylus of the right cheliped is armed with one small but distinct proximal spine on the dorsal surface in D. deliquus , but it is unarmed in D. barunajaya . The right palm bears numerous additional spines lateral to the midline in D. barunajaya , but such numerous spines are not seen in D. deliquus . The cutting edge of the fixed finger of the left chela is entire and armed only with a distal row of minute corneous teeth in D. deliquus , rather than having a row of small calcareous teeth in D. barunajaya .

Decaphyllus deliquus also resembles D. brevis , new species, and D. litoralis , new species. As noted above, there are no arthrobranchs on the third maxilliped in D. deliquus , but in the latter two species, a single bud ( D. litoralis ) or paired tiny lamellae ( D. brevis ) are present. Other characters differentiating D. deliquus and the latter two taxa are: the ocular peduncle is proportionally longer in D. deliquus than in the latter two species (subequal in the length to the shield versus 0.8–0.9 times as long); and spines on the right chela are stronger and more conspicuous in D. deliquus than in the latter two species. Furthermore, the lateral projections of the shield are less produced in D. deliquus than in D. litoralis (cf. Fig. 4A View Fig versus Fig. 8A View Fig ). The antennal acicle slightly overreaches the distal margin of the fifth peduncular segment in D. deliquus , rather than slightly falling short of or just reaching to it in D. brevis .