Journal of the Marine Biological Association of the United Kingdom, 2011, 91(5), 1031–1039. # Marine Biological Association of the United Kingdom, 2011 doi:10.1017/S0025315410002225 The larval development of the hermit crab Areopaguristes nigroapiculus (Decapoda: Anomura: Diogenidae) reared under laboratory conditions elena s. kornienko and olga m. korn A.V. Zhirmunsky Institute of Marine Biology, Far East Branch, Russian Academy of Sciences, 17 Pal’chevskogo Street, 6900041, Vladivostok, Russia The larval development of the hermit crab Areopaguristes nigroapiculus (Komai, 2009) (Decapoda: Anomura: Diogenidae) is described and illustrated from the material reared in the laboratory. The development included three zoeal and a single mega- lopal stages. At 22–258C, megalop of A. nigroapiculus was attained 6–9 days after hatching. The present paper is the first description of the complete larval development in the genus Areopaguristes. Morphological characters of zoeas and megalop of A. nigroapiculus are compared with those described for the closely related Paguristes species. The comparison on the zoeal characters revealed that A. nigroapiculus is distinguished from Paguristes species by the absence of anterolateral carapace spines and by the fused fourth telson process in zoea III. These two features are possible generic characters of Areopaguristes. In the rest of larval characters, A. nigroapiculus agree well with Paguristes species having three zoeal stages. In the plankton of Peter the Great Bay, the larvae of A. nigroapiculus sporadically occurred only in July and August, at depths of 3–45 m and surface water temperatures of 18–228C. Keywords: Decapoda, Anomura, Diogenidae, Areopaguristes nigroapiculus, larva, Sea of Japan Submitted 2 June 2010; accepted 29 November 2010; first published online 1 February 2011 INTRODUCTION At present, the genus Areopaguristes is represented by 22 species (Komai, 2009). Among these species the larvae of The species of the genus Paguristes Dana, 1851 was primarily only A. abbreviatus (Dechance´, 1963) were previously described as having 13 pairs of gills. Later it was found that in described (see Dechance´, 1963). However, this species has a several Paguristes species the gill number was reduced to direct larval development; they hatch as megalopal stage. 12 (Rahayu, 2005). Rahayu (2005) reinstated the genus The aim of this study is to give a description of the com- Stratiotes, originally established by Thomson (1899), because plete larval development of A. nigroapiculus based on the lab- the type species had only 12 pairs of gills. In recent studies, oratory reared material. It is the first illustration of non-direct species having this character and previously assigned to larval development in species of the genus Areopaguristes.As Paguristes were transferred to Stratiotes and several new the genera Areopaguristes and Paguristes are closely related to Stratiotes species were also described (Rahayu, 2005, 2007; each other, we have tried to compare the larval characters of Parente & Hendrickx, 2006; Komai, 2009). Areopaguristes nigroapiculus and Paguristes species. In August 2004, a new representative of warm-water hermit crabs was found in Peter the Great Bay (Russian waters of the Sea of Japan) and it was identified as MATERIALS AND METHODS Paguristes ortmanni Miyake, 1978 (see Petryashov & Kornienko, 2006). Subsequent to this publication we sent An ovigerous female of Areopaguristes nigroapiculus was col- some specimens of this hermit crab to Dr Tomoyuki Komai lected from Vostok Bay (inner bay of Peter the Great Bay, Sea (Natural History Museum and Institute, Chiba, Japan) for of Japan) in July 2004, at a depth of about 3 m. The female was confirmation of the identification. As a result, it was found maintained in an aquarium with aerated seawater until hatch- to be actually a new species—Stratiotes nigroapiculus Komai, ing of the larvae. Hatching larvae were concentrated at the 2009 occurring also from Hokkaido to Sagami Bay and to edge of aquarium using a point-light source and transferred Akita Prefecture in Japan, subtidal to 140 m (Komai, 2009). to 1-l glass vessels with filtered and UV-sterilized seawater The name of the genus Stratiotes is now replaced by and reared to the megalopal stage at temperatures of 22– Areopaguristes by Rahayu & McLaughlin (2010). 258C and a salinity of 32‰. The density of the larvae was about 100 specimens per litre. The larvae were fed newly Corresponding author: hatched nauplii of Artemia sp. The water in the vessels was E.S. Kornienko changed daily. The larval development was evaluated twice a Email: [email protected] day. 1031 Downloaded from https://www.cambridge.org/core. University of Athens, on 06 Oct 2021 at 16:39:50, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0025315410002225 1032 elena s. kornienko and olga m. korn The larvae were fixed in 4% formaldehyde for light micro- and with 2 submarginal simple setae; endopod 3-segmented, scopic studies. The fixed larvae were dissected under a proximal segment with 1 short simple seta, median segment MBS-10 stereomicroscope using fine entomological needles. with 1 long plumodenticulate seta, distal segment with 3 The outlines of the larvae and their appendages of different long terminal plumodenticulate setae. developmental stages were drawn using a camera lucida Maxilla (Figure 1G): coxal and basial endites each bilobed; attached to a binocular Ergaval microscope (Carl Zeiss coxal endite with 5 or 6 marginal and 1 submarginal setae on Jena). Respective measurements were made with an ocular proximal lobe and with 3 marginal and 1 submarginal setae on micrometer. Methods of measurements, descriptions of setal distal lobe; basial endite with 4 marginal and 1 submarginal arrangements and terminology followed that of Clark et al. setae on proximal lobe and 3 marginal and 1 submarginal (1998) and Konishi & Shikatani (1998). The setal arrange- setae on distal lobe; all setae on coxal and basial endites plu- ments are listed from protopod or coxal endite to exopod, modenticulate; endopod unsegmented, with 8 plumodenticu- from proximal to distal segments, and from anterior to pos- late setae in 3 tiers (3 + 2 + 3); scaphognathite fused with terior pleonal somites. The carapace length (CL) was protopod in proximal part, distal lobe with 5 marginal measured from the tip of the rostrum to the posterior mid- plumose setae. point of the carapace. Maxilliped I (Figure 1H): coxa with 1 plumodenticulate Specimens of larval stages and the spent female are depos- seta; basis with setal formula 2, 3, 3, 3; endopod 5-segmented, ited in the Museum of the Institute of Marine Biology, Russian setal formula progressing distally 3, 2, 1, 2, 4 + I plus numer- Academy of Sciences, Vladivostok (accession number 22933). ous thin setae on first to third segments; exopod 2-segmented, The seasonal occurrence of larvae of A. nigroapiculus in with 4 terminal plumose natatory setae. Peter the Great Bay was studied using the material of plankton Maxilliped II (Figure 1I): coxa without setae; basis with surveys, twice a month from April to October 2007 and 2008. setal formula 1, 2; endopod 4-segmented, setal formula pro- A Juday net with a ring diameter of 38 cm and a filtering cone gressing distally 2, 2, 2, 4 + I, numerous thin setae on made of a 168 mm mesh was used. Samples were taken at 66 second and third segments; exopod as in first maxilliped. stations across the entire water column from the bottom to the Maxilliped III (Figure 1J): biramous, without setae. surface at depths ranging from 2 to 75 m. Simultaneously the Pereiopods: visible as small buds, first pereiopod bilobed. temperature was measured at the water surface. Pleon (Figure 1A, K): consisting of 5 somites and telson. Somite 2 with 1 prominent mediodorsal spine; somites 3 and 4 each with 1 short mediodorsal spine; somite 5 with 1 RESULTS prominent mediodorsal and 1 pair of lateral spines, 1 fine seta present at base of each lateral spine. Description Telson (Figure 1A, K): fan-shaped, nearly as long as wide; posterior margin with median cleft and with 7 + 7 processes: Areopaguristes nigroapiculus hatched at a prezoea, which first (outermost) process showing a short smooth articulated lasted about half an hour before moulting to the zoea I. It spine, second process a short plumose anomuran hair, third then passed three zoeal stages. The time required to reach to seventh processes plumodenticulate articulated setae, the megalopal stage was 6–9 days at temperatures of 22–258C. fourth process longest; posterior margin also covered with short setules, few long setules in median cleft; small anal Areopaguristes nigroapiculus (Komai, 2009) (Figures 1–5) spine present. Coloration in life: body generally translucent; dorsal surface zoea i of carapace and pleon with red-black chromatophores (as Duration: 2–3 days. shown in Figure 1A); dorsal surface of telson with violet chro- Size:CL¼ 0.90 + 0.04 mm (0.84–0.94 mm, N ¼ 13). matophores (as shown in Figure 1K), ventral surface with Carapace (Figure 1A, B): no setae on surface, low keel ante- yellow-brown chromatophores; basis of maxilliped I with red- riorly in dorsal midline; rostrum short, tapering, not exceed- brown chromatophore, endopod and exopod each with red- ing 1/3 length of carapace, nearly equal in length to brown chromatophores; endopod and exopod of maxilliped antennular exopod but shorter than antennal scaphocerite; II with red-brown chromatophores (as shown in Figure 1H, posterolateral margins rounded; eyes sessile. I); ventral surface of body with red chromatophores at base Antennule (Figure 1C): uniramous, with 3 terminal aesthe- of mandibles. tascs of different lengths, 3 short terminal sparsely plumose setae, and 1 long subterminal densely plumose seta. zoea ii Antenna (Figure 1D): biramous; endopod fused with proto- Duration: 2–3 days. pod, bearing 3 (2 long and 1 short) terminal plumose setae; Size:CL¼ 0.99 + 0.04 mm (0.90–1.05 mm, N ¼ 10).