Diogenes albimanus, Landschoff & Rahayu, 2018

Landschoff, Jannes & Rahayu, Dwi Listyo, 2018, A new species of the hermit crab genus Diogenes (Crustacea: Decapoda: Diogenidae) from the coast of KwaZulu-Natal, South Africa, Zootaxa 4379 (2), pp. 268-278 : 269-276

Diogenes albimanus n. sp.

( Figs 1–3 , Suppl. mat. 1)

Type material. Holotype: ovigerous female 2.0 mm ( SAMC MB-A066353 ), from rocky reef off Pumula , KwaZulu-Natal, South Africa, 30°38.34'S, 30°32.94'E, SCUBA, 20 m, 14 October 2015, coll. J. Landschoff.

Description of holotype. Shield ( Fig. 1A ) as long as broad, dorsal surface somewhat smooth medially, with minutely rugose tubercles and short to moderately long fine setae on lateral and anterolateral regions, with 1 or 2 small anterolateral spines; rostral lobe broadly rounded, weakly produced. Lateral projections triangular, slightly exceeding tip of rostral lobe, each with small, prominent anterior spine. Branchiostegites membraneous, except for dorsal margin being well calcified, bearing 5 or 6 small spines; anterior angle rounded to weakly truncate, unarmed (left) or with 2 small spines (right); surface with long and finely plumose setae increasing in density towards dorsal and anterior margins.

Ocular peduncles ( Fig. 1A ) inflated, somewhat bulbous in proximal portion, distal half cylindrical, about 0.7 length of shield, with few short setae dorsally and mesially. Corneas at most very weakly dilated, their diameter about 0.2 of peduncular length. Ocular acicles longer than broad, subtriangular, their mesioproximal angles almost touching at base, with two large mesial spines in addition to row of 2–5 spinules and few fine setae on mesial 0.6 of terminal margin. Intercalary rostriform process simple at tip, not reaching tips of mesial spines of ocular acicles.

Antennular peduncles ( Fig. 1A ), when fully extended, overreaching corneas by 0.5 length of ultimate segment. Ultimate and penultimate segments unarmed, dorsally with few short to moderately long and fine setae. Ultimate segments distally dilated. Basal segment unarmed.

Antennal peduncles ( Fig. 1A ) overreaching distal margins of corneas by 0.2–0.3 length of fifth segments; fifth segments unarmed, ventrally with row of long setae; fourth segments with triangular dorsodistal margin and mesiodistal tuft of short setae, and with single long seta on ventrodistal margin; third segments short, with few medium-long setae mesially, and single long seta ventrally; second segments each with dorsolateral distal angle produced into prominent spine accompanied by tuft of finely plumose medium-long setae, dorsomesial distal angle with tiny spinule, mesial margins with very short setae, laterodistal margin subtriangular, bearing few short to medium–long finely plumose setae, distally with small spine or spinule, ventrodistal angle with prominent spine laterally and spinule ventrally; first segments unarmed, or at most with few tubercles on dorsolateral distal angle, with scattered short setae, mesially with very short plumose setae. Antennal acicles reaching to half-length of third segment of antennal peduncles, with row of 5 or 6 irregular spines and medium–long setae on mesial margin, lateral most spine strongest. Antennal flagella, when fully extended, reaching tip of left cheliped, each article proximally with lateral and mesial long and minutely plumose seta, sometimes with additional short seta dorsally.

Chelipeds unequal and dissimilar, left significantly larger than right. Left cheliped ( Fig. 1B ) with very narrow hiatus between dactyl and fixed finger. Dactyl about 0.7 length of palm measured along dorsal margin; cutting edge with row of irregularly sized and spaced, blunt, calcareous teeth, and 2 or 3 single or tufts of short setae, distally terminating in calcareous claw; outer surface convex to straight, regularly to irregularly covered by small, distally acute to minutely crenulate, rounded tubercles, with row of larger tubercles or spines near outer margin interspersed by scattered short setae, subdistally with tuft of very short setae, tubercles less developed near cutting edge; upper margin with 1 or 2 irregular rows of distally subacute or minutely crenulate tubercles or spines, with 1 or 2 short setae; inner surface somewhat smooth, with broad longitudinal sulcus on upper half, and with weakly elevated median ridge bearing 1 or 2 rows of very low, rounded tubercles, with 3 tufts of short setae near cutting edge. Fixed finger with outer surface covered by tubercles as on dactyl, distally with scattered very short setae; cutting edge forming nearly straight line, with 3 major regular calcareous teeth larger than of movable finger, and 2 or 3 single or tufts of short setae, terminating in calcareous small claw; lower margin convex; inner surface nearly smooth with 1 or 2 single or tufts of short setae near cutting edge, and with tuft of longer setae at mid-length near lower margin. Palm with outer surface covered by distally minutely crenulate tubercles, distally convex to straight, proximally with larger tubercles or spines on slightly elevated median ridge, spaces either side of median ridge shallowly concave, near upper margin with 1–4 irregular rows of stronger tubercles or spines; upper margin with row of distally-curved, prominent spines; lower margin delimited by 1 or 2 irregular rows of subacute tubercles extending onto fixed finger; inner surface distally with round, proximally with subquadrate very low, flattened tubercles of irregular size arranged in somewhat transversal bands, near upper margin with 2–4 rows of larger tubercles or spines, uppermost row with sparse short setae. Carpus approximately 0.5 length of palm; outer surface with longitudinal, irregular row of spines near midline increasing in size towards distal, upper outer surface flattened, with 1 or 2 irregular rows of larger tubercles or spines, lower surface tuberculate; upper margin with row of strong distally-curved spines, increasing in size distally, and at distal base giving rise to tufts of short to mediumlong setae; lower margin distally with protuberances, bearing small acute tubercles; inner surface strongly convex, sparsely covered by fine, medium-long plumose setae, low and rounded tubercles arranged in somewhat transverse bands, forming row on distal margin, slightly larger and acute tubercles or small spines forming 1 or 2 rows near upper margin accompanied by short to medium-long setae. Merus subtriangular in dorsal view; dorsodistal margin with several spines of different sizes and medium-long to long setae or bristle-like setae, subdistally delimitated by shallow transversal furrow proceeding onto lateral and mesial faces; dorsal surface in distal half with small, elongated, round or acute tubercles or spines and tufts of short setae, in proximal half with low tubercles and medium-long fine, plumose setae; lateral face with very low tubercles and somewhat appearing smooth, ventrally with some blunt low tubercles; ventrolateral margin with irregularly spaced, distally-curved spines accompanied by sparse short setae; mesial face ( Fig.1C ) with weakly-calcified V to U-shaped patch, distally divided by transversal furrow dorsally bearing denticulate protuberances and row of short setae, distal section further separated into dorsal and ventral lobes by median cleft; dorsal lobe with distal margin bearing small spines and short to medium-long setae, medially rounded; ventral lobe with distal margin also medially rounded, ventrally with large spines, and with medium-long, fine, plumose setae. Ischium with row of minute denticulation on ventral margin; ventrolateral face with sparse setae.

Right cheliped ( Fig. 2A ) slightly overreaching upper dorsodistal angle of carpus of left cheliped; slight hiatus between dactyl and fixed finger. Dactyl 1.3 times length of palm, moderately arched; upper margin with row of small acute spines; outer surface with several small acute tubercles or spines arranged in 2 irregular rows, and also covered by moderately dense, long setae, individual setae minutely plumose; cutting edge with row of small calcareous teeth, distally terminating in strong and sharp claw overlapped by fixed finger; inner surface with 2 rows of tufts of short setae near cutting edge. Fixed finger with outer surface covered by minute blunt or acute tubercles, and also by long fine setae, distally becoming more bristle-like; lower margin with small acute tubercles or spines, distally with tufts of long setae; cutting edge straight to convex distally, with row of calcareous teeth terminating in sharp claw; inner surface with 2 rows of tufts of short setae near cutting edge, subdistally with small corneous spine. Palm with small acute spines on upper margin, increasing in size towards distal and interspersed by long setae; outer surface with irregularly to regularly spaced blunt or acute tubercles or spines, and also with moderately dense long, fine setae; lower margin with acute tubercles or small spines and long setae; inner surface with single or tufts of long setae. Carpus triangular from dorsal view, with row of equally large spines on upper margin interspersed by long setae, upper outer surface flattened to concave and smooth, distal margin with blunt tubercle; outer surface with longitudinal row of small spines, increasing in size distally; lower outer surface somewhat smooth with few blunt or acute tubercles and few medium-long setae; lower margin not delimited, with at most few short setae. Merus with low tubercles or protuberances on dorsal margin accompanied by sparse short setae, dorsodistally with row of long straight setae; ventrolateral margin with short and medium-long, fine setae, in distal half with acute tubercles or spines; ventromesial margin with short simple setae arising from few tubercles; ventral surface flattened, distally with medium-long plumose setae. Ischium with row of setae and row of minute spinules or tubercles on ventromesial margin; ventrally with row of small spines and short setae along articulation with merus.

Second and third pereopods slender ( Fig. 2B, C ). Second pereopods with dactyls 1.1 times longer than propodi, slightly curved ventrally but not twisted in dorsal view, terminating in long corneous claw, 0.1–0.2 length of dactyl; dorsal and ventral surfaces each with lateral and mesial rows of fine, medium-long setae or tufts of few setae; lateral surface with longitudinal shallow sulcus; mesial surface sparsely covered by fine, medium-long setae. Propodi 1.5 times longer than carpi; dorsal margin with minute, low tubercles, and with single or tufts of fine, medium-long setae; ventral margin with sparse tufts of 2 or 3 shorter setae; lateral and mesial surfaces smooth, with sparse fine setae. Carpi 0.7 length of meri; dorsal margin each with row of very small spines (distalmost strongest) and long and medium-long setae or tufts of setae; ventral margin unarmed, but on left with row of short setae on ventrodistal margin; surface of lateral face on left with very shallow dorsal sulcus resulting in slightly elevated, broad longitudinal ridge near midline, less developed on right; mesial face smooth. Meri each with row of short to long setae on dorsal margin; ventral margin with low tubercles or protuberances and sparse long, fine setae; lateral face somewhat smooth. Ischia with low tubercles or protuberances and row of medium-long fine setae on dorsal and ventral margins. Third pereopods with dactyls similar as in second pereopods, but 1.2–1.3 times longer than propodi. Propodi each with dorsal row of low tubercles, left with fine short to medium-long setae, right with less and shorter setae on dorsal margin; ventral margin of left with tufts of 2 or 3 setae or medium-long single setae, right almost non-setose; lateral faces smooth or at most with very low tubercles. Carpi 0.8–0.9 length of meri; dorsal margin with row of very small acute tubercles or minute spines and sparse short to medium-long setae; ventral margin unarmed, ventrodistal margin with row of short setae; lateral surface as in second pereopods. Meri and ischia unarmed, or at most with small tubercles and sparse setae on dorsal and ventral margins.

Fourth pereopods semichelate ( Fig. 2D ). Dactyls dorsodistally with long, dense plumose setae on left, and with long, predominantly simple setae on right. Propodi and carpi each with small dorsodistal projection covered by tufts of long setae and terminating in single spine; propodal rasp with 5–7 rows of oval corneous scales. Anterior lobe of sternite of third pereopods ( Fig. 2E ) with 1 or 2 small spines on each side of anterior margin. Female with paired gonopores.

Telson ( Fig. 1D ) with indistinct shallow median cleft; left lobe moderately longer and round, terminal margin with two large spines and long setae, continued on lateral margin, spines decreasing in size towards anterior; right lobe subquadrate, terminal margin with 2 minute spines and long setae, not continued onto lateral margin.

Colour. General background white, with orange-red and dark brown or black dots, patches and stripes ( Fig. 3 ). Shield white, with two major longitudinal orange lines. Anterior carapace transparent to deeply orange towards branchiostegites. Ocular peduncles sprinkled white, with small red to brown dots of different sizes, orange at base; corneas black; ocular acicles white, orange at base. Antennular peduncles white-transparent, with small orange and red to brown dots. Antennal peduncles white to transparent; first segments with two major red-brown patches; second segments orange at base and with small red to brown dots; antennal acicles and fourth segments with few small red to brown dots and each with one large dorsolateral dot subdistally, third and fourths segments also with large ventrodistal red to brown dots; fifth segments transparent and with laterodistal red to brown dots; flagella with red to brown band about every fourth article. Mouthparts with second and third maxillipeds bearing red to brown dots on endopods, exopods with narrow black and yellow to white bands. Left cheliped with entire surface of dactyl and propodus brightly white, at most minute red dots and with orange patch on base of dactyl and propodus on inner surface; integument between propodus and carpus with orange vertical bands; carpus with upper outer surface orange, tubercles, spines and lower surface white; inner surface with median white patch surrounded by orange areas, tubercles white; integument between carpus and merus orange; merus similar to carpus. Right cheliped similar to left, with dactyl and palm white with orange base; carpus with upper surface orange, more pronounced distally, orange at base, spines and tubercles white. Second and third pereopods white, with orange and black bands and orange longitudinal stripes; dactyls each with white tip, broad orange band subdistally and broad orange to dark-orange band in proximal half, dorsoproximally each with weak black spots; propodi each with orange longitudinal stripes on dorsal margin and on median line of lateral faces, dark orange bands at base, and dorsoproximally each with pronounced dark spots; carpi laterally each with two longitudinal stripes; meri laterally each with longitudinal stripe on median line, dorsally each with proximal black spot, and also with larger black spot on proximal side of proximal half. Fourths and fifths pereopods mostly white. Pleopods transparent to white. Eggs deeply orange, with yellow yolk. Pleon deeply orange. Telson, uropods and pleonal tergites white.

Etymology. From latin albus, (=white), and manus (=hand), referring to the bright-white coloration of the chelipeds.

Distribution. Known only from the type locality off Pumula, KwaZulu-Natal, South Africa.

Habitat. Rocky reef, in worn gastropod shell of subadult Favartia maculata Reeve.

Genetic data. Pumula, South Africa, 20 m reef, holotype, ovigerous female 2.0 mm SL, BOLD: SEAKY1091- 16 (SAMC MB-A066353).

3D µCT data. The species description is complemented by a rotation movie clip of the holotype in the Supplemental material (Video 1). While the scan was performed at a high resolution of 6 µm voxel size, image artefacts of the wrapping material that prevented the specimen from drying out during the scan had a similar density to the soft tissue of the sample (setation, pleon, etc.) and hence were not easily separated from the latter. In the movie clip visualization, and in order to remove the majority of the unwanted artefacts, the focus was placed on the presentation of the main surfaces of the calcified body parts (majorly chelipeds and the pereopods). This was achieved by lowering the density/brightness threshold, which had the side effect of also eliminating weakly calcified body parts of the sample. Also, using this approach as a compromise for the visualization, one area of scanning artefacts (beam hardening plus wrapping material) remained present on the upper outer surface of the palm of the left cheliped that can still be seen in Video 1. Further lowering of the brightness threshold would have cleared it, but would also have removed more other material of the sample. Should more information (e.g. on the soft tissue) be needed the raw data of the µCT scans can be consulted, which are publicly available for download from the GigaDB data repository (Landschoff et al. 2017). Data acquisition and quality of the data are also separately discussed in more detail in an accompanying datanote (Landschoff et al., in prep. B). The µCT derived 3D data alone do not show all, but do illustrate many characters needed to describe and identify the new species and provide extremely useful ‘3D virtual type data’ enabling visualisation of the specimen that is not possible by traditional methods ( Faulwetter et al. 2013).

Remarks. Within the diverse genus Diogenes , D. albimanus n. sp. belongs to the ‘ edwardsi ’ group as defined by Asakura & Tachikawa (2010). This group is characterized by a simple intercalary rostral process, and by antennal peduncles that exceed the ocular peduncle and have long flagella. Among the species of this group, five, D. dorotheae Morgan & Forest, 1991 , D. guttatus Henderson, 1888 , D. tirmiziae Siddiqui & McLaughlin, 2003 , D. holthuisi Asakura & Tachikawa, 2010 , and D. takedai Rahayu, 2012 , have short antennal acicles that reach only to the mid-length of the fourth segment of the antennal peduncles. Diogenes albimanus n. sp. has short antennal acicles, the longest spine of each acicle does not reach the mid-length of the fourth peduncular segment. Moreover, with the basally inflated ocular peduncles and slightly dilated corneas, it most closely resembles D. holthuisi and D. dorotheae . The most obvious character to distinguish these three species is the shape of the telson. The telson of D. dorotheae has unequal subtriangular lobes (left much larger) separated by a distinct median cleft, and the posterior and posterolateral margins of the lobes are armed by several strong spines. The telson of D. holthuisi is subtriangular, armed with two small spines on each posterior lobe, which are separated by a broad median cleft. In the new species the telson is subquadrate, the median cleft is indistinct, and the posterior margin of the left lobe armed with two strong spines. The posterolateral and posterior margin of the right lobe has only microscopic spines. Furthermore, the left cheliped of D. holthuisi bears small tubercles or rows of spines on the palm, the palm of D. dorotheae bears numerous acute tubercles and four large spines along a short longitudinal row from the proximoventral angle, while the palm of the new species is covered by small, rounded, acute or multi-dentate tubercles with a short proximal row of stronger tubercles at the midline. The surface of the palm of D. tirmiziae is also different, in that it does not have drop-like tubercles. As stated by Siddiqui & McLaughlin (2003), D. guttatus is distinguished from all other Diogenes species by the mushroom-shaped tubercles on the chelipeds. The white colouration of the chelipeds of D. albimanus n. sp. resembles in general that of D. takedai , however, the remaining colouration differs markedly between the two species. Diogenes takedai has dark brown or black bands on the ocular peduncle and the second and third pereopods, while D. albimanus n. sp. has light and dark orange bands and longitudinal stripes on the second and third pereopods.

Compared to the known local species in South Africa, D. albimanus n. sp. is readily identifiable by the short antennal acicles. Even if it shares some similarities with D. extricatus in the shape and armature of the chelipeds (rows of spines on the dorsal surface of the carpus), apart from length ratios of the cephalic appendages it is also easily distinguished from D. extricatus by the armature of the pereopods (propodi and meri without spines vs. with spines in the latter), as well as by its small adult size (2 mm SL vs.> 8 mm Sl), and by colour in life (white with orange vs. pale-yellow colour; Barnard 1950, Landschoff, pers. observ.).

So far, only a single individual of D. albimanus n. sp. was found in the coastal area of southern KwaZulu- Natal. Reefs at diving depths of this area are poorly sampled. Further sampling may well lead to the discovery of other undescribed species, as well as more specimens of D. albimanus n. sp. that will reveal the distribution along the coast of KwaZulu-Natal and provide characters for males.

Figures

FIGURE 1. Diogenes albimanus n. sp., Pumula, South Africa, holotype, ovig. female 2.0 mm SL (SAMC MB-A066353): A, shield and cephalic appendages, dorsal view (setae omitted); B, dactylus, propodus, carpus and merus of left cheliped, lateral view; C, merus of same, mesial view; D, telson, dorsal view.

FIGURE 2. Diogenes albimanus n. sp., Pumula, South Africa, holotype, ovig. female 2.0 mm SL (SAMC MB-A066353): A, dactylus, propodus, carpus and merus of right cheliped, lateral view; B, second left pereopod, lateral view; C, third left pereopod, lateral view; D, dactylus, propodus, carpus and merus (in part) of fourth left pereopod, lateral view; E, sternite XII and basal portion of coxae of third pereopods, ventral view.

FIGURE 3. Diogenes albimanus n. sp., Pumula, South Africa, holotype, ovig. female 2.0 mm SL (SAMC MB-A066353), colouration (in life or fresh): A, B, in situ in worn shell of Favartia maculata, C extracted from shell, right lateral aspect; D, same, left lateral aspect;E, same, dorsal aspect.