Aniculus erythraeus Forest, 1984

Osawa, Masayuki, Sakamaki, Takashi & Kawai, Takashi, 2013, First Record of the Diogenid Hermit Crab Aniculus erythraeus (Crustacea: Decapoda: Anomura) from Japan, Species Diversity 18 (1), pp. 33-38 : 33-37

publication ID	https://doi.org/ 10.12782/sd.18.1.033
DOI	https://doi.org/10.5281/zenodo.4730822
persistent identifier	https://treatment.plazi.org/id/03B587CB-FB7E-C35C-4C95-FADE5243D2F1
treatment provided by	Felipe
scientific name	Aniculus erythraeus Forest, 1984
status

Treatment

Aniculus erythraeus Forest, 1984 View in CoL

[New Japanese name: Sarasa-oni-yadokari] ( Figs 1 View Fig , 2 View Fig A–D, 3)

Aniculus erythraeus Forest, 1984: 21 View in CoL (keys), 41, figs 12, 19, 41–45 (type locality: Red Sea); Haig and Ball 1988: 158; Rahayu and Wahyundi 2008: 23, unnumbered fig.; McLaughlin et al. 2010: 18 (list); Poupin 2010: 34 (list); Poupin and Juncker 2010: 218, fig. a.

Material examined. Aka , Kume Island, 26°22.4′N, 126°47.8′E, about 7 m depth, coll GoogleMaps . T. Kawai, 15 June 2012, 1 male (sl 8.7 mm), RUMF-ZC-02041 .

Distinguishing characters. Shield ( Fig. 1A View Fig ) longer than broad; mesogastric region in form of irregular diamond, delimited laterally by furrows. Rostrum ( Fig. 1A View Fig ) triangular, overreaching lateral projections; lateral projections each with submarginal spinule directed laterally. Ocular peduncles ( Fig. 1A View Fig ) slender, 0.7–0.8 as long as shield; corneas not dilated; ocular acicles each with 4 terminal spinules. Antennular peduncles ( Fig. 1A View Fig ) when fully extended, barely reaching corneal bases. Antennal peduncles ( Fig. 1A View Fig ) ending far short of distal margins of corneas; antennal acicle short, reaching slightly beyond proximal margin of fifth peduncular segment. Chelipeds ( Fig. 1 View Fig B–D) equal and similar in armament and ornamentation. Chelae ( Fig. 1 View Fig B–D) circumscribed by transverse striae; each stria marginally with row of short setae in general, but replaced on outer upper surface by small corneous spinules accompanied by long, stiff setae. Dactyli ( Fig. 1 View Fig B–D) with transverse rows of small corneous spinules partially obscured by long stiff setae. Carpi ( Fig. 1B, C View Fig ) each with corneous-tipped dorsodistal spine; outer face with marginally piliferous, generally entire, transverse striae. Meri ( Fig. 1B, C View Fig ) each with ventrolateral proximal margin greatly inflated. Coxae ( Fig. 1E View Fig ) each with 2 long, transverse striae on ventral surface. Ambulatory legs ( Fig. 2 View Fig A–D) with numerous tufts of long setae on dorsal and ventral margins. Dactyli ( Fig. 2 View Fig A–D) each with longitudinal row of 1–3 transversely arranged corneous spinules ventrally on lateral surface and with tufts of long setae, dorsal and mesial surfaces also with several corneous spinules on distal 0.7, ventral margin with row of 6 or 7 corneous spines. Propodi ( Fig. 2 View Fig A–D) each with marginally piliferous, long, transverse striae on lateral surface: proximal-most and penultimate striae interrupted, but median 4 striae uninterrupted; on third pereopod, additional short stria present near ventroproximal end of lateral surface; dorsal surface with several corneous spinules on distal half (second pereopod) or only 1 subdistal mesial spinule (third pereopod); ventral surface also with several corneous spinules on distal half. Carpi ( Fig. 2 View Fig A–D) each with small, corneoustipped dorsodistal spine; lateral surface with marginally piliferous, generally entire, transverse striae. Meri ( Fig. 2 View Fig A–D) with medially interrupted transverse striae (pronounced and much longer in third pereopod) on lateral surface, ventrolateral margin with small subdistal spine (second pereopod) or unarmed (third pereopod), ventromesial margin denticulate (second pereopod) or slightly crenulated (third pereopod). Sixth thoracic sternite ( Fig. 1F View Fig ) with oblong anterior lobe. Telson ( Fig. 1G View Fig ) with somewhat asymmetrical posterior lobes, left larger than right; terminal margins oblique.

Coloration ( Fig. 3 View Fig ). Shield and posterior carapace ( Fig. 3 View Fig A–C) reddish purple, with irregular white streaks. Ocular peduncles ( Fig. 3A, C View Fig ) brownish purple, with white spots at bases of setae; distal margin pale yellow. Ocular acicles and antennular and antennal peduncles ( Fig. 3A, C View Fig ) reddish purple, with irregular white markings. Chelipeds ( Fig. 3B, D, E View Fig ) reddish purple, with white streak along each transverse stria; dactyli, carpi, and meri with additional small white markings; corneous claws and spinules on chela black. Ambulatory legs (second and third pereopods; Fig. 3A, B, F View Fig ) also reddish purple, with white streak along each transverse stria; dactyli each with black corneous claw; propodi each with broad white part proximally and narrow white part distally; carpi white on proximoventral part; meri with irregular white markings. Fourth and fifth pereopods ( Fig. 3B, F View Fig ) with mottled pattern of reddish purple and white, propodal rasps brown. Pleon ( Fig. 3A, B View Fig ) pale red; tergites of first to fifth somites reddish purple, with irregular white transverse lines; tergite of sixth somite and telson also reddish purple, with irregular white markings. Setae purple, with broad, white distal part.

Habitat. Under a large block of dead coral at about 3 m depth ( Haig and Ball 1988) or on outer reef slopes at depths of 5–30 m ( Poupin and Juncker 2010). The present specimen was collected from a hard bottom on a steep coral reef slope at about 7 m depth.

Distribution. Red Sea, Sri Lanka, Banda and Ambon Islands in Indonesia, and Tuamotu Islands in French Polynesia ( Rahayu and Wahyundi 2008; Poupin 2010; Poupin and Juncker 2010). In addition to these records, A. erythraeus has also been collected from Guam and Papua New Guinea (see Legall and Poupin 2012). The specimen examined from the Ryukyu Islands greatly extends the distributional range of this species to the north.

Remarks. The specimen examined is an immature male: the body size is small (sl 8.7 mm) and the gonopore is not well developed and present only on the coxa of the right fifth pereopod. Forest (1984: fig. 12) described the sixth pleonal tergite of A. erythraeus as having posteriorly directed short spinules on the anterolateral part; however, in the present specimen there are no distinct spinules, only a few indistinct small protuberances. The dactylus of the left third pereopod is subequal in length to or longer than the propodus in the type material, but it is shorter in the present specimen. Nevertheless, the present specimen can be identified to A. erythraeus inasmuch as it has other diagnostic morphological and color characters of the species.

Aniculus erythraeus is morphologically allied to A. ursus . The characters shared by the two species are: mesogastric region of shield delimited laterally by furrows; ocular acicle with more than two terminal spinules; chelipeds with small corneous spinules only on outer upper surface of each palm and with two long, transverse striae on ventral surface of each coxa; and propodi of second and third pereopods with uninterrupted striae on median part of lateral surface. Preliminary comparison of the figures provided by Forest (1984: figs 33, 43, and 45) shows that the structure of the proximal-most and penultimate long, transverse striae on the lateral surface of the left third pereopod is different between the two species; however, those striae vary in the two examined specimens of A. ursus ( Fig. 2E, F View Fig ), and thus A. erythraeus and A. ursus cannot be separated by this character. In contrast, the armature of the dactyli and propodi of the second and third pereopods does serve to distinguish the two species: the corneous spinules on the lateral surface (especially in the dorsal half) of the dactyli and dorsal surface of the propodi are much fewer in A. erythraeus than in A. ursus . Coloration of the two species is also clearly different. The shield is reddish purple and has irregular white streaks in A. erythraeus , whereas it is mostly green and bears reddish-brown patches anteriorly in A. ursus . The ocular peduncles of A. erythraeus are mostly reddish purple, while those of A. ursus are deep green. The chelae and the propodi of the ambulatory legs are generally reddish purple in A. erythraeus , not of olive-green as in A. ursus (for A. ursus , see McLaughlin et al. 2007; Poupin and Juncker 2010).

Besides A. erythraeus , four other species of Aniculus have been recorded from Kume Island where the present specimen was found: A. maximus , A. retipes , A. sibogae , and A. ursus ( Rahayu and Osawa 2012) . There are no clear differences in habitat among these five species, all of which occur on coral and rocky reef slopes or in crevices on the reefs ( Kawamoto and Okuno 2003; present study). Aniculus sibogae is a very large hermit crab with the shield length attaining 52 mm ( Forest 1984); it always uses a shell of the turbinid gastropod Turbo marmoratus Linnaeus, 1758 as its domicile ( Nomura et al. 1996; Kawamoto and Okuno 2006). This gastropod is widely distributed in the Indo-West Pacific, but there are no records of A. sibogae from the Indian Ocean despite recent faunal surveys there (e.g., Poupin 2009; Poupin et al. in press). Aniculus sibogae is known only from the western Pacific, ranging from the Ryukyu Islands to Malaysia, New Guinea, and Vanuatu, whereas A. erythraeus , A. maximus , A. retipes , and A. ursus are widely distributed in the Indo-West Pacific but rather sparse in occurrence.