Diogenes armatus, Almón & Cuesta & Schubart & Armenia & García-Raso, 2022

Almón, Bruno, Cuesta, Jose A., Schubart, Christoph D., Armenia, Lisa & García-Raso, J. Enrique, 2022, Redescription of the hermit crab Diogenes pugilator (Decapoda: Anomura) reveals the existence of a species complex in the Atlanto-Mediterranean transition zone, resulting in the resurrection of D. curvimanus and the description of a new species, Zoological Journal of the Linnean Society 195, pp. 1116-1146 : 1127-1132

DIOGENES ARMATUS ALMÓN ET AL. SP. NOV.

( FIGS 3A–G , 4A–G , 7B, E, H, K )

The description of the new species in this paper has been carried out by four of the authors, B. Almón, J. Cuesta, C. Schubart and J.E. García Raso.

Z o o b a n k r e g i s t r a t i o n: l s i d: z o o b a n k. o r g: a c t: 10CBBC54-4576-463A-AFE5-E7BE0D3A179A

Type material: Holotype: ♂ 3.4 mm, Spain: Torregorda , Cádiz, (MNHN-IU- 2019- 3213), 36°26 ′ 51.7 ′′ N 6°14 ′ 49.4 ′′ W, sandy beach, intertidal shallow pools, 16/03/2015 ; Allotype: ♀ 3.8 mm, Isla Canela, Huelva, (MNHN-IU-2014-5736), 37°10 ′ 51.8 ′′ N 7°20 ′ 15.3 ′′ W, sand intertidal, 25 July 2014.

Paratypes: Spain: Torregorda , Cádiz, 1 ♀ ( IEOCD-BR/2645 ), 36°26 ′ 51.7 ′′ N 6°14 ′ 49.4 ′′ W , intertidal sandy beach, 27 July 2014; 1 ♂ ( ZSMA2019 0402), 30 May 2018; 1 ♀ ( IEOCD-BR/2643 ), 23 October 2014; 1 ♂ ( IEOCD-BR/2644 ), 27 July 2014; 1 ♂

(IEOCD-BR/2642), 30/05/2018; 1 ♂ ( IEOCD-BR/2646 ) , 16/03/2015.

Other material: Spain: Bajo la Cabezuela , Cádiz, 5 ♂ and 1 ♀ ( IEOCD-BR/2623-2626 ), 36°31 ′ 43.6 ′′ N 6°15 ′ 01.0 ′′ W, intertidal, 30 August 2019 ; Es Torrent, Ibiza, 8♀ and 4 ♂ ( IEOCD-BR/2629-2638 ), 38°58 ′ 02.2 ′′ N, 1°16 ′ 07.2 ′′ E, shallow subtidal, 26 May 2018 ; Port D’Es Torrent , 1 ♂ ( IEOCD-BR/2639 ), 38º58.036 ′ N, 1º16.12 ′ E, shallow subtidal, 22 May 2018 ; Portugal: Lagoa da Albufeira , 2 ♂ ( IEOCD-BR/2647-2648 ), 38°30 ′ 34.9 ′′ N, 9°10 ′ 28.6 ′′ W, sand, intertidal, 12 June 2018 ; French Mediterranean: Corsica, 1 ♂ ( IEOCD-BR/2628 ), 42°42 ′ 49.8 ′′ N, 9°18 ′ 0.06 ′′ E, sand, shallow subtidal, 12 June 2003 ; French Atlantic: Arcachon, 1 ♂ ( IEOCD-BR/2627 ), 44°40 ′ 0.04 ′′ N, 1°10 ′ 34.5 ′′ E, sand, intertidal, 02 October 2018 ; Tunisia: La Goulette, Tunis, 7 ♂ ( IEOCD-BR/2640-2641 ), 36°49 ′ 10.80 ′′ N, 10°18 ′ 45.11 ′′ E, sand, 3–4 m, 24 November 2009 .

Etymology: The specific name armatus , masculine Latin adjective for armed, is given to highlight the spiny appearance of the chelipeds of this species compared to other Atlantic congeners, with more developed ornamentation composed mainly of spines and spiny tubercles instead of more rounded ones.

Description: Shield ( Figs 3A , 7E ) slightly longer than broad; rostral lobe acutely rounded, exceeded by lateral projections that are triangular, acutely pointed, with single spine at apex; anterior margins between rostral lobe and lateral projections markedly concave and thickened; anterolateral margins sloping, slightly concave, mostly smooth, sometimes with some isolated minute spine; anterolateral angles rounded, with one spine on each side and another smaller submarginal spine sometimes inconspicuous; lateral margins slightly convex; posterior margin roundly truncate; dorsal surface slightly vaulted, with lateral margins usually cut by few transverse tuberculate ridges, extending on to lateral surface of shield; dorsal surface with additional short, transverse rows of small tubercles and tufts of short, stiff setae. Branchiostegites with dorsal margin bearing row of 10–11 strong spines, proximal two to three smaller. Posterolateral plates not well calcified, unarmed.

Ocular peduncles (including corneas) about 0.6 times as long as shield, moderately stout, slightly inflated in upper half; corneas not dilated, corneal diameter about 0.25 peduncular length; row of short, plumose setae over inner surface of peduncles. Ocular acicles ( Fig. 3A, C ) subtriangular, with slightly concave mesial margin; anterior margin slightly convex, bearing 11–12 acute spines, decreasing in size towards outer margin, covering entire length of anterior margin; innermost spine distinctly larger and often slightly curved laterally. Intercalary rostriform process simple, shorter than ocular acicles, tapering acutely.

Antennular peduncles ( Fig.3A,B ) overreaching distal corneal margin by about 0.4 length of ultimate segment, extending slightly beyond distal margin of antennal peduncle; third segment unarmed, not broadened distally, slightly less than five times longer than distal width, subequal in length to penultimate segment, with some isolated setae on dorsal surface and distal tuft; second segment unarmed, with tuft of plumose, short setae on dorsodistal margin; basal segment unarmed, except for the spinose, rounded, ventrodistal border.

Antennal peduncles ( Fig. 3A ) overreaching distal corneal margin by 0.5 length of fifth segment; fifth segment unarmed, with row of moderately long, stiff setae on ventrolateral surfaces, and tuft of short setae on distodorsal margin; fourth segment unarmed, with tufts of plumose setae on disto-inner and some scarce simple setae on disto-outer margins; additional tuft of plumose setae on ventrolateral inner margin; third segment unarmed; second segment distolateral outer process stout and acute, with subdistal smaller spine; smaller but strong spine on distomesial angle; plumose setae near both spines and ventral surfaces; first segment with distal margin crenulated; plumose, short setae present in lateral and ventral surfaces. Antennal acicle short, subtriangular, reaching slightly below distal margin of fourth peduncular segment, bearing a simple strong terminal spine plus three to four strong spines on mesial margin and tufts of plumose setae on both mesial and lateral margins. Antennal flagellum short and robust, noticeably setose; articles with paired, long, ventrolateral and shorter ventral paired setae; short paired ones also on dorsal and outer articles surface.

Third maxilliped ( Fig. 3D ) basis unarmed; ischium with crista dentata bearing three prominent (distal) and two smaller (proximal) spines; ischium and merus with rows of scarce setae on lateral margins; carpus, propodus and dactylus with dense tufts of thick, long setae in dorsodistal and dorsomedian margin, concealing part of the segments; exopod peduncle reaching one-third of endopod carpal length.

Male left cheliped ( Figs 4A–D, G , 7B, H ) much larger than right ( Fig. 3E ). Dactylus about 1.2 times as long as upper margin of palm, gently arched, ending in large calcareous claw, crossing tip of fixed finger; upper, outer margin defined by rows of well-developed spines, inner margin by row of acute tubercles; two additional rows of subacute tubercles below upper, outer margin, first one incomplete; conspicuous strong spine at beginning of first row, near joint of dactyl with palm; dorsal surface between rows concave; rest of outer surface flattened, covered of small subacute tubercles; cutting edge sinuous, with row of calcareous teeth of various size, largest at distal half of dactyl; lower margin with irregular row of blunt sunken tubercles and tufts of setae associated with most of tubercles; inner surface with an additional complete row of rounded tubercles, separated by a depression from tubercles of upper, inner margin; inner, lower surface with two irregular rows of smaller sunken tubercles parallel to cutting edge, with tufts of dense setae associated with each tubercle.

Fixed finger delimited proximoventrally by a shallow concavity separating the slightly convex outer surface of fixed finger and beginning of inflated palm surface; lower margin with two to three rows of small, rounded tubercles extending on to palm; a row of larger blunt sunken tubercles above this, another row parallel to cutting edge and a third medially, each with tufts of short, stout setae; rest of outer surface with small, blunt or subacute tubercles; cutting edge sinuous, with single row of various sized teeth, largest on proximal one-third; inner surface almost smooth except for three to four irregular rows of sunken tubercles, each with tufts of short dense setae.

Palm robust, about 1.2 as long as high (max. medial length – maximum height); upper margin shorter than carpus; dorsal surface with four to six irregular rows of spines, space between rows widening distally with less produced spines; spines on upper, outer margin stronger and more produced, decreasing in size towards upper, inner margin; outer surface strongly inflated in proximal half, with proximal border defined by a crest of subacute tubercles; distal, lower surface depressed, near fixed finger; upper, outer part (below upper, outer row of spines), markedly concave; distinct bispinose protuberance present at distal angle just below upper margin; lower margin sinuous, convex proximally and slightly concave at distal half, defined by closely spaced rows of obtuse, spinose tubercles; rest of palm outer surface covered with spines of different sizes, biggest forming four longitudinal rows, usually evident especially when some colour remains; marginal series of subacute tubercles on upper, proximal half, as extension of proximal crest; transverse row of small spines at distal part of palm; inner surface covered with scattered rounded tubercles, with several rows of bigger tubercles below upper, inner margin; two additional well-defined rows, first on upper half, running from proximal medial margin to upper, distal margin, ending in a blunt protuberance, and second on midline zone, extending to half length of palm; sometimes a third faint row on lower half, composed by scattered tubercles; lower, inner surface, with irregular rows of low tubercles; most of largest tubercles with tufts of short thick setae.

Carpus longer than high ( Fig. 4A, B ); dorsal margin with two to three irregular rows of spines; outermost row strongest; outer surface convex, covered with small spines becoming rounded tubercles near lower proximal area; row of stronger spines present on middle outer surface, largest near distal margin; broad almost smooth, concave area just below upper, outer and inner margins, becoming deeper and widening proximally; lower margin denticulate, gently protruded, forming a sinus proximally; disto-outer border dentate; pilosity abundant, with simple setae, except in lower, outer margin, where they are less abundant and plumose; inner surface covered with closely spaced, thick tubercles, and dense tufts of stiff, plumose setae; distal inner margin crenulated.

Merus longer than high ( Fig. 4A, G ), subtriangular in dorsal view; distal margin with spines of different sizes, largest on dorsal area, with row of short setae; dorsal surface with rows of acute tubercles decreasing in size proximally and associated tufts of long, plumose setae; lateral surface with acute tubercles adjacent to dorsolateral margin and small spines near ventrolateral margin, with sparse setae associated with tubercles and spines; spinose transversal furrow subdistally, with short setae; rest of lateral surface smooth; ventrolateral margin denticulate, slightly concave in proximal half, with a row of strong acute tubercles increasing in size distally, accompanied by rows of plumose, long setae; mesial face with weakly calcified u-shaped patch, distally divided by shallow, transverse, unarmed furrow, with tufts of long setae; distal mesial part divided into dorsal and ventral lobes by median cleft; dorsal lobe with distal margin bearing spines of different sizes and tufts of medium-sized setae; ventral lobe with distoventral margin defined by large, acute tubercles, and dense tufts of long, plumose setae. Ischium with transversal row of small spines on distolateral margin and row of minute tubercles on proximal margin; mesial surface with longitudinal row of strong spines on ventral margin ( Fig. 4G ).

Female left cheliped ( Fig. 4E ) differs from male in the following features. Palm oval, globose, almost as long as high, with lower margin convex throughout, without sinuous, concave area of males. Carpus lower margin with pronounced smooth sinus at proximal half; distal half protruding in a rounded projection defined by large spines of similar sizes. Merus dorsal and ventrolateral margins defined by well-developed spines.

Right cheliped ( Fig. 3E ) appreciably shorter than left, robust, usually reaching proximal one-third of palm of left cheliped; dactylus and fixed finger with prominent hiatus, both terminating in small but strong calcareous claws. Dactylus (measured along mesial margin) slightly more than 2.0 times longer than palm, noticeably arched; upper, inner and outer margins defined by rows of small spines decreasing in size distally, with tufts of long setae arising from tubercles; outer surface with additional row of spines parallel to upper, outer margin with tufts of long setae; inner surface with two rows of tufts of long, stout setae, first on upper half and second near lower margin. Palm with outer surface not broadened, slightly flattened, with irregular rows of strong spines obscured by tufts of long setae, especially evident at midline and distal margin of propodus and fixed finger; upper, outer margin defined by row of strong spinose tubercles, inner margin not well defined; lower margin defined by row of small low acute tubercles; fixed finger not broadened proximally, cutting edge with row of small subacute calcareous teeth decreasing in size distally, and two rows of tufts of setae parallel to cutting edge.

Carpus with row of large spines on upper, outer margin, increasing in size distally, and an additional row of small acute tubercles below it defining a concave area between them; rest of outer surface with low tubercles arranged regularly and numerous long, simple and plumose setae; lower surface unarmed; disto-outer margin spinose; inner surface smooth and glabrous.

Merus distal margin with spines of different size, largest on dorsal area, with long, simple setae; dorsal margin with row of small, obtuse spines of similar size and tufts of long, plumose setae; lateral surface covered with low, rounded tubercles, with long setae; shallow furrow subdistally, with sparse setae; ventrolateral margin delimited by row of subacute tubercles, with subdistal spine and tufts of long, plumose setae; mesial face with small, weakly calcified, u-shaped patch proximally, smooth, with ventromesial margin defined by row of acute tubercles increasing in size proximally. Ischium with row of spinules on distolateral and ventromesial margins.

Second and third pereiopods stout ( Figs 3F , 7K ) subequal in length. Dactylus 1.4 times as long as propodus, weakly curved; terminating in small corneous claws; upper, outer surfaces unarmed, with sparse simple setae of different length; lower with row of more numerous, long setae; outer surface with shallow, longitudinal sulcus medially, with row of setae below sulcus in proximal one-fifth, then continuing along upper border of sulcus; inner surface with two rows of long, stout setae running along upper and lower margins, and a short row occupying proximal one-fifth of inner sulcus.

Propodus about same length as merus (second) or shorter (third), each with upper margin defined by rows of small spines (second), or faintly dentate (third), and with row of short to long stiff, simple setae combined with some plumose; lateral surfaces each with longitudinal row of setae arising from tiny, low, spinose tubercles near upper margin; lower margins smooth, with two rows of short setae; inner surface smooth and almost glabrous, with few sparse, plumose setae.

Carpus upper margin defined by rows of strong spines (second) or smaller spines (third) increasing in size distally, with rows of simple and plumose setae; lateral surfaces with two rows of low tubercles in the upper half, with moderately long setae; lower surface smooth except for three to four tufts of stout, plumose setae on distal half; inner surface smooth and almost glabrous.

Merus upper margin of second and third pereiopods defined by row of low, small, spinose tubercles decreasing in size distally, with tufts of long, plumose setae; lower margin of both pereiopods with row of low, spinose, small tubercles and long, simple and plumose setae; lower distal margin with a single spine (second) or without spines (third); rest of outer and inner surfaces smooth and glabrous. Ischium with upper and lower distal margin serrated, with long, plumose setae.

Fourth pereiopods ( Fig. 4F ). Dactyl with row of 11 outer subacute submarginal spiniform setae. Propodus suboval, with a conspicuous spine dorsodistally and abundant plumose setae; propodal rasp consisting of seven to eight rows of corneous scales increasing in size distally, covering one-third of propodus distoventral surface. Carpus with a row of small tubercles dorsally, ending in a broad spine; with clumps of long, simple and plumose setae.

Fifth pereiopods. Propodus slightly shorter than merus, carpus 1.5 times shorter than propodus; groups of subacute corneous scales in distodorsal surface of propodus and smaller ones in dactylus and fixed finger; long clumps of strong simple setae.

Male unpaired left pleopods 2–5 uniramous, marginally setose. Female gonopores paired; two to four unpaired pleopods, well-developed, biramous; fifth pleopods without exopod, as in male.

Telson ( Fig. 3G ). Asymmetrical, with small, median cleft; left posterior lobe distinctly larger than right, with strong terminal spine and row of smaller spines on lateral margin, becoming blunt anteriorly; oblique terminal margin with strong spines mixed with some small ones; right posterior lobe with row of strong spines mixed with small ones on less oblique terminal margin, becoming blunt anteriorly and extending on to posterior half of lateral margin.

Coloration ( Fig. 7B, E, H, K ). Ocular peduncles reddish white, with brownish red, triangular stain covering around two-thirds of peduncle; eyeballs velvet black with honey yellow stippling. Ocular acicles orange proximally, turning greenish medially and white apically. Antennular background bluish; third segment and flagellum with diffuse orange patch mingled with background; second segment with dark brown dorsal stripe. Antennas translucent blue, going greenish at basal segments level; characteristic brown spot on antennal scale proximally. Merus and carpus of left cheliped greenish in background, with some diffuse tile red areas; brown transversal stripes on medial zone of merus, and base, medial and disto-inner areas of carpus. Palm greenish white, lighter than merus and carpus, with orange path in upper, proximal surface of dactylus, and some narrow ones following main spinose ridges; base of largest tubercles with orange taints; small, deep reddishbrown taints at mid-dorsal and apical area of palm. Right cheliped overall colour oil green, with white ventral area; brown spots on mid-dorsal area of the merus, mid-dorsal and basal area of carpus and more blurred one at apex of carpus, base of palm and basal area of fingers. Second and third pereiopods with general green colour in dorsal part, yellowish white ventrally; brown dorsolateral stripes in middle and apical areas of merus, basal and middle areas of carpus and propodus, and base of dactylus.

Habitat: Sandy beaches, intertidal, tide pools and shallow subtidal up to 25 m depth.

Distribution: Known, so far, from Mediterranean islands (Ibiza and Corsica), Tunisian coasts (La Goulette), Andalusian Mediterranean and Atlantic coasts (Cádiz, Huelva, Algeciras), South Portugal (Lagoa da Albufeira) and French Atlantic (Arcachon).

Remarks: Within the East Atlantic, only Diogenes pugilator s.s. shares some characters with the new species. However, there are several characters that can be used to separate them. The new species has a slightly longer than broader shield, the rostrum rounded but elevate and thickened, while in D. pugilator the shield is subquadrate and the rostrum is lower and broader, not thickened. Branchiostegites with 10–11 spines in D. armatus , while D. pugilator usually has eight to nine. The ocular acicles carry 11–12 spines in D. armatus , decreasing in size from the inner margin, while D. pugilator has three to four (sometimes five) large spines decreasing in size from inner margin, with the rest of anterior margin with 11–12 small blunt tubercles. The ocular peduncles are proportionally shorter in D. pugilator in relation to the antennae and antennulae, and the antennal acicle has one terminal spine and an additional five in D. pugilator , while only three to four in D. armatus ; the acicle is also shorter in the new species, reaching well below distal margin of the fourth antennal segment. Shape and proportions of the left cheliped are also different, although the spination can be similar in many cases. In D. pugilator , spination is always less developed for the same shield length; palm is as long as high in D. pugilator , while in D. armatus it is longer than high and with a conspicuous concavity at distal half of lower margin; outer surface strongly and regularly inflated throughout in D. pugilator , while in D. armatus only the proximal half is elevated, more abruptly in the middle; inner surfaces of the palm and carpus are also inflated in D. pugilator when observed in dorsal view, while in D. armatus , those surfaces are flat, depressed. The right cheliped also differs between species, with the fixed finger proximally broadened in D. pugilator and small spines in upper margin of the carpus and palm outer surface, while D. armatus has several rows of strong spines, combined with smaller ones on the palm surface.

Figures

Figure 3. Diogenes armatus sp. nov. ♂ 3.4 mm, Torregorda, Cádiz, Spain, holotype, (MNHN-IU-2019-3213): A, anterior part of body; B, right antennule, inner aspect; C, ophtalmic scales; D, left maxiliped 3 (inset: detail of the spines, ventral aspect); E, right cheliped, dorsal aspect; F, left pereiopod 2 (insets: variations in P3 carpus; dactylus inner aspect); G, telson, dorsal view. (Scales: A, E–G = 1 mm, B–D = 0.5 mm).

Figure 4. Diogenes armatus sp. nov. ♂ 3.4 mm, Torregorda, Cádiz, Spain, holotype, (MNHN-IU-2019-3213): A, male left cheliped, outer aspect (arrow indicating bispinose protuberance); B, left cheliped, dorsal aspect; C, left cheliped inner surface; D, left cheliped dactylus, dorsal aspect; F, left pereiopod 4, outer aspect; G, left cheliped merus, mesial view (setae omitted). Diogenes armatus sp. nov. ♀ 3.8 mm, Isla Canela, Huelva, Spain, allotype, (MNHN-IU-2014-5736): E, female left cheliped, outer aspect. (Scales: A, C, G = 2 mm; B, D, E = 1 mm; F = 0.5 mm).

Figure 7. Live coloration of the three species of Diogenes: A–C, left cheliped, outer aspect; D–F, cephalothorax and cephalic appendages; G–I, detailed photographs of the inner face of palms, showing the shape of the row of tubercles; J–L, left pereiopod 2. A, D, G, J, Diogenes pugilator; B, E, H, K, Diogenes armatus sp. nov. C, F, I, L, Diogenes curvimanus.