Heptacarpus sadoi Komai 2023, n. sp.
Creators: name: Komai, Tomoyuki
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Thoridae
Heptacarpus
Heptacarpus sadoi

description: Heptacarpus sadoi n. sp.
[New Japanese name: Boso-toge-tsuno-mo-ebi]
(Figs. 1–7)
Type material. Holotype: CBM-ZC 15148, ovigerous female (cl 4.5 mm), Aoki, Emi, Kamogawa, Chiba Prefecture, 35.0585°N, 140.0697°E, rocky intertidal, dip net, coll. T. Sado, 19 April 2018.
Paratypes: CBM-ZC 17520, 3 males (cl 1.7, 3.0, 3.5 mm), Amatsu, Kamogawa, Chiba Prefecture, 35.1196°N, 140.1398°E, rocky intertidal, under rock, hand, coll. T. Komai, 24 June 2001; CBM-ZC 17521, 1 ovigerous female (cl 4.6 mm), same data as holotype; CBM-ZC 17522, 1 ovigerous female (cl 3.9 mm), 1 male (cl 2.3 mm), Osawa (Osenkorogashi), Katsuura, Chiba Prefecture, 35.1159°N, 140.2235°E, rocky intertidal, dip net, coll. T. Sado, 20 May 2019.
Diagnosis. Females. Body robustly built. Rostrum 0.46–0.57 times as long as carapace, reaching distal margin of article 2 of antennular peduncle; dorsal margin armed with 5 teeth over entire length, including 3 postorbital, posteriormost tooth located at 0.3 of carapace; ventral margin with only 1 subterminal tooth, blade poorly developed. Carapace with acutely pointed pterygostomial angle. Pleonal pleuron 4 and 5 each with small posteroventral tooth. Telson with 4 pairs of dorsolateral spiniform setae. Ocular peduncle subcylindrical with non-dilated cornea shorter than remaining part of peduncle; ocellar spot evident. Antennular peduncle article 1 with only 1 spine at distolateral angle. Antennal scale 0.6 times as long as carapace, 2.2 times as long as wide. Pereopods 1–3 each with strap-like, terminally hooked epipod. Pereopod 1 merus armed with 1 spiniform seta at ventrolateral distal angle. Pereopod 3–5 merus each with 1–2, 1 and 0–1 spiniform setae on lateral surface distoventrally.
Males. Body smaller and less robust than females. Rostrum 0.61–0.65 times as long as carapace; dorsal margin armed with 4 or 5 teeth, including 2 or 3 postrostral, distal half occasionally unarmed. Carapace pterygostomial angle rounded, unarmed. Maxilliped 3 not elongate, similar to that of female. Pereopod 1 not particularly thickened.
Description. Females. Body (Figs. 1, 7A) robustly built. Rostrum (Figs. 1, 2A, B) short, 0.5–0.6 times as long as carapace, almost straight, directed forward or slightly downward, reaching distal margin of article 2 of antennular peduncle; dorsal margin armed with 5 teeth, including 2 on rostrum and 3 postrostral, posteriormost tooth located at 0.3 length of carapace; ventral margin not forming limb or blade, armed with 1 subterminal tooth; no conspicuous lateral carina. Carapace (Figs. 1, 2A) with dorsal margin gently convex in lateral view, postrostral ridge reaching beyond midlength; dorsum with sparse long setae; antennal spine moderately small; inferior orbital angle triangular with blunt tip, reaching as far as antennal spine; pterygostomial tooth tiny; anterolateral margin between antennal and pterygostomial angle slightly sinuous; no supraorbital spine.
Pleon (Fig. 1) rounded dorsally. Posterodorsal margin of third tergite fairly produced, unarmed. Pleura 4 and 5 each with small posteroventral tooth. Pleomere 6 1.8 times as long as pleomere 5, 1.5–1.6 times as long as high; posterolateral tooth terminating in acute tooth; small posteroventral tooth present. Telson (Fig. 2C, D) 1.4 times as long as pleomere 6, about 3 times as long as anterior width, gradually tapering convex posterior margin; dorsal surface with 4 pairs of dorsolateral spiniform setae (not including 1 pair at posterolateral corner); posterior margin with tiny median spine flanked by 2 pairs of unequal spiniform setae (mesial pair more than 2 times longer than lateral pair) and 1 mesial pair of stiff plumose setae.
Ocular peduncle (Fig. 2B) subcylindrical; cornea not dilated, as wide as peduncle, its width approximately 0.1 of carapace length; ocellar spot evident on dorsal surface.
Antennular peduncle (Figs. 1, 2A) overreaching midlength of antennal scale. Article 1 distinctly longer than distal 2 articles combined, armed with 1 moderately strong distolateral spine; ventromesial margin with small spine subdistally; stylocerite reaching midlength of article 2, terminating in acute, slender spine, without proximolateral process. Article 2 wider than long, with 1 distolateral spine. Article 3 with strong dorsodistal spine. Outer flagellum with aesthetasc-bearing portion thick.
Antennal peduncle (Figs. 1, 2A, E) basicerite bearing small ventrolateral distal spine, dorsolateral distal margin roundly truncate. Carpocerite nearly reaching midlength of antennal scale. Antennal scale 0.6 times as long as carapace, about 2.2 times longer than wide; lateral margin nearly straight; distolateral tooth just reaching rounded distal margin of lamella.
Mouthparts not dissected. Maxilliped 3 (Figs. 1, 3A) moderately long and stout, overreaching antennal scale by half length of ultimate article; ultimate article 2.5 times as long as penultimate article (= carpus), tapering distally, distal part bearing 5 small, darkly pigmented spiniform setae (Fig. 4A); dorsal and lateral faces with scattered tufts of stiff setae. Penultimate article subcylindrical. Antepenultimate article shorter than distal two articles combined, slightly compressed proximally, distal margin with 2 minute spiniform setae; lateral surface with row of stiff setae along dorsal margin. Coxa with strap-like, terminally hooked epipod. Exopod absent.
Strap-like, terminally hooked epipods on pereopods 1–3 (Fig. 2F); setobranchs, consisting of few long setae, on pereopods 1–4.
Pereopod 1 (Figs. 3B, 4B) relatively stout, falling slightly short of distal margin of antennal scale. Chela about 1.9 times as long as carpus, about 2.5 times longer than wide; dactylus 0.7 times as long as palm, terminating into 2 terminal claws; palm subcylindrical, fixed finger terminating in single claw. Carpus with grooming apparatus subdistally on mesial face, consisting of moderately deep excavation and surrounding stiff setae. Merus slightly widened distally, armed with 1 spiniform seta at ventrolateral distal angle and short row of minute spiniform setae on ventral surface proximally. Ischium short, articulation to merus oblique.
Pereopod 2 (Fig. 3C) moderately slender, overreaching antennal scale by length of chela and distalmost carpal segment. Carpus divided into 7 segments, length ratio of segments: 1.0: 0.5: 1.1: 0.9: 0.8: 0.6: 1.0. Merus 0.8 times as long as ischium.
Pereopods 3–5 relatively short and stout. Pereopod 3 (Figs. 3D) overreaching antennal scale by length of dactylus; dactylus 0.4 times as long as propodus, about 3.0 times longer than high, armed with 5 accessory spines over entire length of flexor margin, increasing noticeably in size and making dactylus as biunguiculate (Fig 4C); propodus with 2 rows of minute spiniform setae on flexor margin; carpus about half length of propodus; merus with 2 closely spaced, distoventral spiniform setae on lateral face; ischium not particularly widened distally, unarmed. Pereopod 4 (Figs. 3E, 4D) similar to pereopod 3, reaching midlength of antennal scale by tip of dactylus; merus with 1 distoventral spiniform seta. Pereopod 5 (Figs. 3F, 4E) similar to but shorter than pereopods 3 and 4, reaching level of distal margin of antennal basicerite; dactylus 0.3–0.4 times as long as propodus; propodus with cluster of grooming setae distally on flexor margin; merus armed with 1 ventrodistal spiniform seta.
Pleopods without distinctive features. Uropodal protopod (Fig. 2C) with strong posterolateral spine. Both rami (Fig. 2C) overreaching posterior margin of telson; exopod lateral margin sinuous, terminating in minute spine, small posterodistal spiniform seta present.
Males. Body (Fig. 5) smaller and slenderer than females. Rostrum (Fig. 6A) 0.61–0.65 times as long as carapace; dorsal margin armed with 4 or 5 teeth, including 2 on rostrum proper and 2 or 3 postrostral; distal half sometimes unarmed. Carapace pterygostomial angle rounded, unarmed (Fig. 6A); dorsal outline in lateral view almost straight (Fig. 5). Outer flagellum of antennule relatively longer and thicker than in female. Maxilliped 3 not particularly elongate, similar to that of females (Fig. 5), just reaching distal margin of antennal scale by tip of ultimate article or overreaching it by half-length of ultimate article. Pereopod 1 chela (Fig. 6B, C) relatively larger than in females; dactylus subequal in length to palm; fixed finger with row of long setae on proximal half of extensor side of occlusal margin; occlusal surface excavate, margin of flexor side also with row of setae proximally. Pereopods 3–5 similar to those of females, not showing sexual dimorphism in shape; pereopod 5 merus rarely unarmed. Pleopod 1 endopod (Fig. 6D, E) about 0.6 length of exopod, with appendix interna located at terminal position; mesial margin slightly sinuous, with row of stiff setae; lateral margin constricted at base of appendix interna, otherwise gently convex. Pleopod 2 endopod (Fig 6F.) with short, stout appendix masculina (about half length of appendix interna, truncate terminus bearing 6 or 7 stiff setae distinctly overreaching appendix interna.
Size. Ovigerous females cl 3.9–4.6 mm; males cl 1.7–3.5 mm.
Colouration in life. Female paratype specimen from Katsuura (CBM-ZC 17522) entirely pinkish, with greenish area on posterior part of carapace; cornea grayish brown; antennal flagellum generally yellowish translucent; distal half of pereopod 2 translucent.
Male paratype specimen from same lot fairly translucent with red tinge on dorsal surface of pleomeres 4– 6, anterior and posterior parts of pleomere 6, sternites of pleomeres 1–6, antennal carpocerite and basal parts of pereopods 3–5; outer flagellum translucent with few brown spots; antennal carpocerite, maxilliped 3 and pereopod 1 light reddish brown; pereopods 2–5 generally translucent, with dark brown spots on meri and propodi; pleopods 1–5 reddish; tail fan with broad dark brown transverse band.
Distribution and habitat. Presently known only from southeastern part of Boso Peninsula; intertidal to shallow subtidal. Occurring in tide pools of rocky shore.
Remarks. As is apparent from the above description, the new species exhibits sexual dimorphism in the body shape, armature of the carapace pterygostomial angle, and the structure of the pereopod 1. Similar sexual variation is also known in other congeners (e.g., Hayashi 1979; Hayashi & Chiba 1987). Although only two examples are presently available, it is suggested that the living colouration is substantially variable in Heptaccarpus sadoi n. sp., as well as other congeners inhabiting shallow sea grass or algal beds (e.g., Miyake & Hayashi 1968; Hayashi & Miyake 1968; Butler 1980; Hayashi & Chiba 1987).
Species in Heptacarpus are classified into five informal species groups based on the number and position of epipods on the maxilliped 3 and pereopods 1–3 (e.g., Rathbun 1904; Hayashi 1979, 1993; Butler 1980; Jensen 1983; Komai & Ivanov 2008). Heptacarpus sadoi n. sp. is referred to the species group characterized by the possession of epipods on the pereopods 1–3, represented by 12 known species (Hayashi 1979, 1992; Hayashi & Chiba 1989). Morphologically, the new species appears closest to H. jordani, known from Japan and Korea (Hayashi & Chiba 1987; Yang & Kim 2005), in the poorly developed ventral blade of the rostrum bearing only one or two subterminal ventral teeth, the presence of one ventrolateral distal spiniform seta on the pereopod 1 merus and the possession of no more than three spiniform setae on the pereopods 3 and 4 meri (cf. Hayashi & Chiba 1987). The new species is readily distinguished from H. jordani by the following particulars: (1) the rostrum does not reach the distal end of the antennular peduncle in H. sadoi n. sp., whereas it reaches it in H. jordani (Figs. 1, 2B versus Hayashi & Chiba 1987: fig. 2a); (2) the dorsal rostral teeth are 4–6 in H. sadoi n. sp., rather than 6–9 in H. jordani; (3) the posteriormost tooth of the dorsal rostral series is located at the anterior 0.3 of the carapace length in H. sadoi n. sp., while 0.2 or less in H. jordani (Fig. 1 versus Hayashi & Chiba 1987: fig. 1); (4) the basal article of the antennular peduncle bears only one spine at the distolateral angle in H. sadoi n. sp., whereas there are one or more additional spines on the dorsodistal margin of the basal article of the antennular peduncle in H. jordani (Fig. 2B versus Hayashi & Chiba 1987: fig. 2a).
The possession of a ventrolateral distal spiniform seta on the pereopod 1 merus, seen in the new species, is shared also with H. grebnitzkii and H. rectirostris. Those two species, however, are readily distinguished from H. sadoi n. sp. by the proportionally long rostrum (subequal to longer than the carapace), overreaching the distal end of the antennular peduncle, and with a much better developed ventral blade (cf. Miyake & Hayashi 1968; Hayashi 1979). The rostral armature is also substantially different among the three species. In the new species, the dorsal rostral teeth are at most 5 in the number, while they are 5 or 6 in H. rectirostris (cf. Miyake & Hayashi 1968; Hayashi 1979), 6–9 in H. grebnitzkii (cf. Hayashi 1979); the ventral margin is armed only with 1 subterminal tooth in H. sadoi n. sp., while there are more than 2 ventral teeth in the latter two species. Furthermore, in H. grebnitzkii, the distal portions of both dorsal and ventral margin of the rostrum are unarmed (Hayashi 1979). Heptacarpus rectirostris further differs from the present new species in having more numerous meral spiniform setae of the pereopods 3–5 (4–6 versus 1 or 2 in the third, 3–5 versus 1 in the fourth, 3–5 versus 0 or 1 in the fifth).
In the sites where the specimens of the new species were collected, Heptacarpus futilirostris (Bate, 1888), which also look similar to the new species, occurs sympatrically. Nevertheless, H. futilirostris is readily distinguished from H. sadoi n. sp. by the relatively long rostrum (overreaching the distal end of the antennular peduncle) with more numerous dorsal and ventral teeth and a better developed ventral blade and the lack of a ventrolateral distal spiniform seta on the pereopod 1 merus (Miyake & Hayashi 1968). Furthermore, the male H. futilirostris attains larger size than the female and has a greatly elongate maxilliped 3 (Miyake & Hayashi 1968).
Sequences of the COI gene are available only for 10 species of Heptacarpus, including the present new species (Table 1). The K2P genetic divergence of the COI gene among species of Heptacarpus available for analysis ranges from 18.5 to 32.9% (Table 2), well supporting that the taxa involved in the analysis are all distinct (cf. Lefébure et al. 2006). Sequence divergence between the new species and other congeners is 18.5–29.5%, with H. jordani being closest.
Sequences of the 16S rRNA gene are available for 10 nominal species of Heptacarpus, including Heptacarpus sadoi n. sp. (Table 1). The K2P genetic divergence of the 16S rRNA gene among the 10 taxa (11 sequences) ranges from 6.5 to 19.4% except for that between H. palpator and H. sitchensis (0.4%). The genetic divergence between the new species and the other species involved in the analysis ranges from 9.4–18.4%, also well supporting that the new taxon is distinct from the analysed taxa. It is highly likely that the two sequences referred to the two separate species (H. palpator and H. sitchensis) actually represent the same species. Conversely, it could be noted that the two sequences currently referred to Heptacarpus futilirostris are substantially different (K2P divergence 8.5%), suggesting that the voucher specimens are not conspecific.
In spite of our efforts of collection, specimens of Heptacarpus sadoi n. sp. have been collected only from the southeastern coast of the Boso Peninsula, central Japan, although the habitat lies in shallow intertidal rocky shores, which are easily accessible. The true distribution of the new species remains unknown.
Etymology. The new species is dedicated to my friend and colleague, Dr. Tetsuya Sado, for collecting a part of material examined in this study and for his kind assistance in DNA experiments.
description: Published as part of Komai, Tomoyuki, 2023, A new intertidal species of the thorid shrimp genus Heptacarpus Holmes, 1900 (Decapoda: Caridea) from Japan, pp. 263-274 in Zootaxa 5361 (2) on pages 265-273, DOI: 10.11646/zootaxa.5361.2.7, http://zenodo.org/record/10150853