Medaeus alidae, Mendoza & Clark & Paul F., 2025

Medaeus alidae , new species

( Figs. 1–4 View Fig View Fig View Fig View Fig )

Material examined. Holotype, female, 11.5 × 7.8 mm ( NHM 1953.10 .27.1, re-registered from NHM 1892.8.28.241-263), Macclesfield Bank, South China Sea, coll. P. W. Bassett Smith, Surgeon RN, HMS Penguin , 1892, pres. by the Lords of the Admiralty.

Paratypes: 1 female (with swollen left branchial region), 11.8 × 7.5 mm, 2 females, 9.5 × 6.2 mm, 10.5 × 6.6 mm, 1 ovig. female, 11.1 × 7.3 mm ( NHM 1953.10.27.2-5, re-registered from NHM 1892.8.28.241-263), same data as holotype ; 1 female, 9.2 × 6.3 mm ( ZRC 2023.0299 View Materials ), northern coast of Panglao Island , Bohol Sea, Philippines, tangle net, 50–200 m, coll. J. Arbasto, between July 2004 – May 2005 .

Comparative material. Medaeus aztec Davie, 1997 : holotype, male, 9.1 × 6.1 mm ( MNHN-B 22807; =MNHN- IU-2014-22733), stn DW183, 330– 367 m, 23°18.3′S, 168°04.9′E, Aztec Bank , New Caledonia, coll. SMIB 8, RV Alis, Bouchet & Richer de Forges – IRD, 31 January 1993. Medaeus danielita Mendoza & Ng, 2010 : holotype, male, 12.3 × 8.0 mm ( NMCR 30063), stn R 30, reef slope with black coral, 15–37 m, 9°37.1′N, 123°46.1′E, Napaling, Panglao Island, Bohol, Philippines, coll. PANGLAO 2004, 8 June 2004; paratype, male, 7.7 × 5.4 mm ( ZRC 2010.0101), stn B16, coral rubble on sand & gravel, 20 m, 9°37.6′N, 123°47.3′E, Bingag, Panglao Island, Bohol, Philippines, coll. PANGLAO 2004, 17 June 2004; paratype, female, 7.9 × 5.3 mm ( ZRC 2010.0102), stn B41, floor of cave, 17–19 m, 9°30.9′N, 123°40.8′E, Balicasag Island, Bohol, Philippines, coll. PANGLAO 2004, 4 July 2004.

Description. Carapace ( Figs. 1A View Fig , 4A View Fig ) transversely subhexagonal, about 1.5–1.6 times as broad as long, regions well defined; anterior half of dorsal surface convex transversely and longitudinally, posterior half relatively flatter; 2M partially divided longitudinally, inner branch fused with 1M, which is separated by deep groove from 2F, outer branch wider than inner but faintly and incompletely divided longitudinally; 3M, 4M, 2L, 3L, 5L distinct, entire; 1L indistinct; 4L merging with third anterolateral tooth; 6L into 4 or more distinct areolets; 1P with smooth, transverse crest; 2P with 4 distinct granular transverse ridges laterally, intervening central area with distinct individual granules; 1R, 2R fused, separated from 3R by distinct, oblique groove; grooves bordering regions, particularly 3M, posterior 2M, 6L deep, smooth; dorsal regions of carapace strongly granular, with regions bearing transverse rows of granules fused at their bases or compacted groups of distinct granules; suborbital, subhepatic, pterygostomial regions ( Figs. 1B View Fig , 2A, B View Fig , 4C View Fig ) with distinct granules. Front ( Figs. 1A View Fig , 4A View Fig ) about one-third carapace width, minimally produced beyond internal orbital tooth in dorsal view; frontal lobes separated by V-shaped cleft in dorsal view, which continues posteriorly as median sulcus on frontal region; submarginal row of prominent granules appearing as false anterior margin of frontal lobes in dorsal view, front actually deflexed ventrally ( Figs. 2A View Fig , 4B View Fig ), with true anterior margin of frontal lobes sinuous in anterior view; deep median pit surrounded by callose granular rim separating frontal lobes in anterior view. Orbits relatively small, width about 0.1 times carapace width, orbital margins granular, without fissures. Anterolateral margin ( Figs. 1A View Fig , 4A View Fig ) convex with 4 triangular teeth posterior to exorbital angle, their margins denticulate; first and fourth teeth smaller than second and third, apices of third, fourth teeth at point of maximum carapace width; anterior part not clearly meeting orbital margin, instead seemingly descending towards suborbital region and anterolateral angle of buccal cavern, with 1 small granular tooth in subhepatic region. Posterolateral margin as long as anterolateral margin, straight, convergent posteriorly, lined with sharp granules. Median part of posterior carapace margin straight, lined with single row of round granules.

Eyes ( Figs. 2A, B View Fig , 4B View Fig ) with short stalks, distal edge lined with large, tooth-like granules, abutting cornea; corneas well developed, globose. Antennules ( Figs. 1B View Fig , 2A, B View Fig , 4C View Fig ) folding transversely and slightly obliquely, basal article with two prominent granular crests. Basal article of antenna ( Figs. 2A View Fig , 4C View Fig ) granular, subrectangular, distal part occupying entire orbital hiatus, with small portion of distolateral angle extended further toward orbit; well-developed flagellum entering orbit, almost reaching its outer edge. Urinary article, small, oval-shaped, wedged between basal article and epistome. Epistome ( Fig. 2A View Fig ) well developed, external surface mildly concave, central part of posterior margin having a weakly produced, triangular projection with apical notch, and on either side two convex lateral lobes, separated from central part by distinct V-shaped notches.

Third maxillipeds ( Figs. 2B View Fig , 4C View Fig ) granular. Merus subquadrate, anterior margin with slight mesial concavity, median length about half that of ischium, with 2 shallow depressions on either side of low, oblique, submedian, granular ridge; margins nearly straight, lined with small granules, anterolateral angle slightly projecting. Ischium subrectangular, inner margin with short, stiff setae; with shallow, longitudinal submedian groove; separated from basis by faint suture. Exopod granular, tapering slightly toward distal end, which does not quite reach anterior edge of merus; flagellum long.

Thoracic sternum ( Figs. 1B View Fig , 3A, B View Fig ) moderately broad, granular. Sternites 1, 2 completely fused into triangular plate without trace of suture, separated from sternite 3 by distinct transverse suture. Sternites 3, 4 partially fused, with lateral notch on either side, which is replaced by distinct groove mesially. Sutures 4/5, 5/6 interrupted mesially, where they join to circumscribe sternite 5, giving the latter a triangular outline; sutures 6/7, 7/8 complete; distinct decalcified gap, especially mesially, along suture 6/7. Median line distinct only at level of sternites 7, 8; faint trace on sternite 4. Sternopleonal cavity wide, sternal tubercle of press-button locking mechanism not prominent, positioned midway between sutures 4/5 and 5/6.

Chelipeds ( Figs. 1A, B View Fig , 2C–E View Fig ) slightly unequal; major cheliped more robust, with enlarged tooth proximally on occlusal margin of dactylus. Merus granular on external surface, distal end slightly exceeding anterolateral margin of carapace in dorsal view; posterior margin with several, evenly spaced, large, conical tubercles. Carpus short; external surface with distinct clumps or short rows of granules, inner angle with small but distinct tooth. Palm of both chelae with external surfaces covered with large granules, with distinct groove near upper margin bordered on either side by 2 granular ridges; upper margin with a cluster of round granules, lower margin lined with sharp granules; inner surface granular on upper, proximal portion and smooth on lower distal portion. Fingers pigmented, with pigmentation on fixed finger not extending onto palm (based on traces and pigmentation scars on type specimens); tips pointed, incurved, crossing each other when fingers closed. Fixed finger slightly deflexed ventrally, with submarginal groove on external surface, cutting margin with 6, 7 low teeth. Dactylus longer than upper margin of palm, slightly curved; external surface with 2 grooves; upper margin with sharp granules proximally, extending to half-length on minor chela, less extensive on major chela; occlusal margin with smaller or no teeth, except for large subproximal tooth on major chela.

Ambulatory legs ( Figs. 1A, B View Fig , 2F, G View Fig , 4A View Fig ) relatively long, slender; second and third legs (P3, P4) longest, coxa-todactylus length about 1.0 times carapace width; dorsal surfaces granular. Merus subrectangular (length-to-width ratio of P3, P4 about 3.9, of P5 about 3.3); anterior margins armed with distinct, large, conical tubercles (ca. 9 per merus), posterior margin more finely granular; distal end of anterior margins with prominent tooth. Carpus narrow proximally, widening distally, dorsal surface granular, with submarginal row of granules (except in P5), anterior margin lined with large granules, posterior margin smooth. Propodus subrectangular, with conical granules on margins, dorsal surface. Dactyli straight, anterior, posterior edges covered with short, stiff setae; distal tip ending in short, curved, chitinous claw.

Pleon ( Figs. 1B View Fig , 3C–E View Fig ) longitudinally oval in outline, covering most of thoracic sternum when closed; with six freely articulating pleonal somites and telson. Telson (fig. 2C) subtriangular with round apex, convex lateral margins, external surface smooth, basal width 1.85 times midline length. Pleonal somites 4–6 subrectangular, with convex lateral margins, external surfaces sparsely granular especially laterally, somite 4 widest. Pleonal somites 1–3 trapezoidal, lateral margins of somite 1 straight, converging anteriorly; lateral margins of pleonal somites 2, 3 more-or-less straight, diverging anteriorly; external surfaces much more granular than those of pleonal somites 4–6. Lateral margins of pleonal somites 3–6 and telson bearing long supple setae.

Vulvae ( Fig. 3A, B View Fig ) positioned close together and anteriorly on sternite 6, abutting against suture 5/6; small, subcircular in outline, opening mesially; operculum flat, unadorned.

Male morphology unknown.

Etymology. The new species is named in honor of Dutch carcinologist and former Curator of Crustacea at the Rijkmuseum van Naturalijke Historie (Leiden), Alida Margaretha Buitendijk (1903–1950), who examined the present type material in 1947 and made the initial determination that they were new to science.

Habitat & distribution. Macclesfield Bank, South China Sea and Bohol Sea , Philippines; coral reef-associated, 9–200 m depth .

Remarks. The only locality recorded in the NHM register for the type material of M. alidae is “Macclesfield Bank”; and it was not possible to derive additional data pertaining to this material from the reports on contemporary collections from Macclesfield Bank by Bassett-Smith (1890a, b) [corals], Kirkpatrick (1890) [Hydrozoa and Polyzoa], and Pocock (1890, 1893) [Crustacea and Stomatopoda, respectively].

Medaeus alidae , new species, is most similar to its congeners, M. aztec Davie, 1997 and M. danielae Mendoza & Ng, 2010 , in the general outline of the carapace, the weakly advanced front as seen from dorsal view, the presence of well-defined crests on the 1P and 2P regions of the dorsal carapace, and the general proportions of the ambulatory legs, which are relatively long and slender. It can, however, be distinguished from these two species by the following morphological features:

(1) the dorsal surface of the carapace (especially on regions 1M, 2M, 1L+2L–6L) appears rugose with more pronounced granular ridges, consisting of rows granules fused at their bases, as well as conspicuous clumps of large, round granules on other carapace regions ( Figs. 1A View Fig , 4A, B View Fig ) (vs corresponding areas more finely granular and less rugose in M. aztec and M. danielita ; cf. Davie, 1997: figs. 9e, 15a; Mendoza & Ng, 2010: figs. 1, 2A, B);

(2) the median pit (cleft) on the anterior margin of the front has a callose, quadrilobate rim when observed in the anterior view, and posterior to this, a submarginal, granular ridge consisting of a single row of large granules ( Figs. 1A View Fig , 2A View Fig , 4B View Fig ) (vs no callose rim and, although present, the submarginal granular ridge is not as prominent as it bears much smaller granules in both M. aztec and M. danielita ; cf. Davie, 1997: fig. 9a; Mendoza & Ng, 2010: fig. 2E, F);

(3) the dorsal carapace region 6L is not entire and is instead divided into two or more areolets ( Figs. 1A View Fig , 4A View Fig ) (vs 6L indented on mesial border but not completely divided in M. aztec and M. danielita ; cf. Davie, 1997: fig. 15a; Mendoza & Ng, 2010: fig. 2A, B);

(4) the teeth on the carapace anterolateral margin have distinctively more serrated margins, and the posterolateral margins are lined with large, pointed granules ( Figs. 1A View Fig , 4A View Fig ) (vs anterolateral margin teeth and posterolateral margins finely granular, cf. Davie, 1997: fig. 15a; Mendoza & Ng, 2010: fig. 2A, B);

(5) the dorsoexternal surfaces of the cheliped palm and carpus are much more pronouncedly granular, with the larger granules sometimes arranged in discrete clumps or tuberosities, and the posterior margin of the cheliped merus is lined with prominent, large, conical tubercles ( Figs. 1A, B View Fig , 2C–E View Fig ) (vs dorsoexternal surfaces of cheliped palm and carpus less granular, with smaller granules, not necessarily arranged in discrete clumps in M. aztec and M. danielita ; large conical tubercles of posterior margin of merus present in M. aztec , absent in M. danielita ; cf. Davie, 1997: figs. 9e, 15a; Mendoza & Ng, 2010: figs. 1, 2A); and

(6) the ambulatory meri, carpi and propodi have their anterior margins armed with large conical tubercles and the ambulatory propodi have their posterior margins likewise armed, their dorsal surfaces, particularly in the P5, are also covered with large granules ( Figs. 1A, B View Fig , 2F, G View Fig , 4A View Fig ) (vs anterior margin of meri armed with conical tubercles, except in P5 where they are replaced by sharp granules, anterior margin of carpus and anterior and posterior margins of propodus armed with sharp granules only, and the dorsal surfaces are finely granular in M. aztec ; cf. Davie, 1997: fig. 9c, d; anterior margin of meri armed with sharp granules, except in P5 where it is finely granular, anterior margin of carpi and anterior and posterior margins of propodi likewise with sharp granules, and the dorsal surfaces are finely granular in M. danielita ; cf. Mendoza & Ng, 2010: figs. 1, 2A).

As there are currently no male specimens of M. alidae , the male morphological characters to distinguish among the three closely related species are not available. The current morphological differences, however, are sufficient to distinguish M. alidae from other species of Medaeus , and should also be present in any male specimens that may be found in the future.

A sole female paratype specimen ( ZRC 2023.0299 View Materials ) from the waters off Panglao Island ( Bohol Sea) in the central Philippines was also examined and found to have the same diagnostic features as the other types of M. alidae and has been determined to be conspecific with them .