Planotergum kowalevski, Marin & Spiridonov & Ng, 2019

Marin, Ivan N., Spiridonov, Vassily A. & Ng, Peter K. L., 2019, Ophiacantha scissionis Lee & Stöhr & Bae & Shin 2019, sp. nov., Zoological Studies 58 (26), pp. 1-11 : 3-9

Planotergum mirabile Balss, 1935 ( Fig. 2 )

Planotergum mirabile Balss, 1935: 36 , figs. 1–3 [type locality: Western Australia]; Balss 1957: 1628 (list); Serène 1965: 457, 121, figs. 1–4, pls. 1, 2; Serène 1968: 53 (list); Griffin and Tranter 1986: 92; Števčić 1991: 121, fig. 1; Davie 2002: 332, unnumbered figure (list); Poore et al. 2008: 62; Ng et al. 2008: 121 (list).

Anomalopisa incongruens Johnson, 1965: 174 , fig. 1 [type locality: Singapore].

Material examined: Female syntype (6.4 × 8.0 mm) ( ZMH K-11583), Western Australia, Shark Bay, NW of Denham, Hartmeyer Expedition to southwest Australia, depth 3 m, coll. W. Michaelsen, 12.06.1905; 1 female (7.7 × 10.1 mm) ( ZRC 1985.130), east of St John’s Island, 5.5–18.3 m, on Sargassum bed, sandy bottom with some rocks, coll. D.S. Johnson, 26.08.1953; 1 female (10.2 × 13.4 mm) ( ZRC 1969.11.19.12), Java Sea, Indonesia, 4°02'S 106°09'E, 20 m, among coral sand, in dredge, coll. K. Romimohtarto, on R. V. Djalandhi, 26.04.1963.

Description: Carapace pyriform, smooth or covered with epibionts (usually bryozoans), with uneven edges, curved outward, with 2 pyramidal protrusions or tubercles ( Fig. 2a, b ): one at center of gastric region, other on cardiac region; 2 parallel lines of fine granules between gastric and cardiac tubercles ( Fig. 2a ); with 3 broad lateral lobes on each side of carapace (anterior, median, posterior): anterior lobe with broad concave lateral margin and sharp corners; median (second) lobe directed obliquely, consisting of 2 quasi-triangular parts separated by deeper concavity and fissure; posterior lobe broadly triangular with truncated tip. Posterior margin of carapace rounded ( Fig. 2b ).

Rostrum ( Fig. 2a, b ) very broad, horizontally lamelliform, quasi-rectangular in dorsal view, distal anterior margin jagged. Orbit relatively shallow, with small angular pre-orbital and cupped quasi-triangular postorbital lobes, and dorsal incision. Eyes mobile, with stout eyestalk bearing 2 marked distinct blunt processes; when positioned along postorbital lobe, eye not reaching to postorbital angle ( Fig. 2e, f )

Epistome absent. Sternal part of cephalothorax nearly completely covered by broad pleon. Thoracic sternum with fused sternites 1–4; sutures absent except for ridge-like structure between sternites 2 and 3. Sutures between sternites 4 and 5 nearly complete, others interrupted in proximal one-third. Episternites narrow, attached to postero-lateral margins of sternites, with sutures nearly fused to sternites.

Antenna ( Fig. 2d, e ) with flattened broad articles; basal article short, broad, expanded anteriorly, immovably fixed to ventral rostral surface; second article large, broadly lamellate, bearing greatly extended outer margin; third article significantly smaller with gently produced anterolateral portion; fourth article deeply inserted in anterior margin of third article. Flagellum about as long as third and fourth articles combined.

Third maxilliped ( Fig. 2c ) with ischium and merus markedly convex, mesial margin covered with moderately dense setae, anterior margin of merus oblique, laminated, carpus enlarged distally, with short stick-shaped process on anterior margin; broad gap between ischia of third maxilliped.

P1 (chelipeds) asymmetrical, heterochelous, short, slender, not reaching distal rostral margin, mostly concealed by carapace in dorsal view. Carpus of cheliped with lamelliform anterior face. Right chela larger than left chela, with dorsal ridge. Cutting margins of fingers entire, without teeth.

P2–5 ( Fig. 2g –o ) with short, flattened articles; anterodistal corner of merus spiniform, posterior face of merus with denticulated ridges. Anterior and posterior faces of carpus serrated. Anterior margin of propodi expanded with blunt dorsodistal point, ventral (flexor) margin with distal spines. Dactylus shorter than propodus, curved, slender, subchelate with small protrusions on posterodistal corner of propodus. Small spinule at ventrodistal margin of propodus near articulation with dactylus. P3 with 4 well marked teeth along distoventral and lateral margins of ischium ( Fig. 2k ).

Pleon very broad, rounded, emarginated by long soft setae. Telson small, ovoid, deeply inserted in distal margin of somite 6, with terminal notch.

Female genital opening, large, about half of sternite length, located at anterior margin of sternite 6, deflexed anteriorly, with rounded posterior margin.

Taxonomic notes on the type material: The original description of P. mirabile by Balss (1935) was based on two specimens, one male (6.5 × 7.5 mm) and one female without measurements. Balss did not indicate on which specimen the figures of the overall habitus and third maxilliped was based, but that of the thoracic sternum and pleon was stated to be the male. This male specimen, however, has a very wide pleon ( Balss 1935: fig. 3) and may just be an immature female. It is also relatively small in size (6.5 × 7.5 mm) ( Balss 1935: 38). Since the holotype was not selected in the original description, both specimens are syntypes. The lot with the type material of P. mirabile ( ZMH K-11583, 6.4 × 8.0 mm) contains only one specimen —a female that is severely damaged. In this specimen, all pereopods except the right cheliped are absent. The carapace is flattened and the dorsal protuberances are absent, but this may be due to its badly damaged condition. The other features of the specimen: bilobed second lateral lobe on the carapace, distinctly truncated posterior lateral lobe, relatively more shallow orbit, condition of the second antennal article (with a serrated anterior margin and small spiny lateral process), relatively more narrow merus of the third maxilliped and structure of the carpus of the cheliped, nevertheless agree well with the material of P. mirabile we have on hand from Singapore and Indonesia.

The carapace, as figured by Serène (1965) and Davie (2002), is not very accurate as it does not show the orbital and postorbital armature correctly. In addition, the third antennal article figure in Johnson (1965: fig 1c) is somewhat schematic, as it appears to show a lateral projection, but this is not accurate—the “projection” is actually the articulation point for the flagellum. This condition is not the same as the Red Sea specimen, whose projection is much larger and is more proximal in position.

Ecology: The species is known from a relatively wide depth range, from a depth of 3 m ( Balss 1935) to 85 m ( Poore et al. 2008). The present record and the record from the Java Sea ( Serène 1965) are from intermediate depths (20–25 m). Johnson (1965) indicated that the species lives in “shallow water,” and the seas around Singapore are only 15–20 m in depth. The recorded substrates include gravel and coral sand. The carapace of these crabs is often covered with various fouling, for example, bryozoans ( Fig. 2a ). The morphology of the ambulatory appendages (see Schäfer 1954) and the flattened body suggests that the crab most likely leads a relatively sedentary lifestyle, living on the sea floor or on rocks.

Distribution: Western Australia (type locality, Shark Bay) ( Balss 1935), south-western Australia ( Poore et al. 2008); Queensland, Australia ( Griffin and Tranter 1986), Java Sea ( Serène 1965), Singapore ( Johnson 1965).

Remarks: At present, we do not know why there is only a single female syntype P. mirabile in the ZMH collection. It is possible that H. Balss retained the male syntype in the Zoological Collection of the Bavarian State in Munich (Zoologische Staatssammlung München, ZSM), where he worked. The ZSM collection, however, suffered great damage during World War II (Dr. M. Türkay, pers. Comm.) and the status of the material is not known. A lectotype selection would be useful for nomenclatural stability, but the condition of the syntype female in ZMH is so poor that it is not very useful to designate it as such.

Planotergum kowalevski sp. nov. ( Figs. 3–5 ) urn:lsid:zoobank.org:act:F50472DF-9D23-462F-87DF-9ACE5A1E4E3D

Material Examined: Holotype female (8.6 × 11.7 mm) ( ZMMU Ma 3506), Indian Ocean , southern Red Sea , Straits of Bab al Mandab, r/v “Akademik Alexander Kowalevski”, station 602/52, 13°14.8'N 43°10.6'E, depth 25 m, reef-gravel bottom, beam trawl dredging, coll. V. V. Murina, 06.11.1963.

Description: Carapace smooth, pyriform, with uneven edges, curved outward, with 2 pyramidal protrusions or tubercles ( Fig. 3a, b ): 1 medially on gastric region, other in cardiac region ( Fig. 3a–d ). Three broad lateral lobes on each side of carapace: anterior lobe with broad concave lateral margins and sharp corners; median (second) lobe broadly truncate, directed laterally, divided into 2 parts by shallow concavity ( Fig. 2a ); posterior lobe triangle-shaped with truncated tip. Posterior margin of carapace rounded ( Fig. 3a, b ).

Rostrum ( Figs. 3a, b , 4d ) very broad, horizontally laminiform, quasi-rectangular in dorsal view; anterior margin jagged distal. Orbit moderately deep, with small angular pre-orbital and cupped quasi-triangular postorbital lobes and dorsal incision. Eye ( Figs. 4b– d , 5d ) mobile, with stout eyestalk bearing 2 marked distinct blunt processes; when positioned along postorbital lobe, eye reaching to postorbital angle ( Figs. 4c–d , 5a, d ).

Epistome absent ( Fig. 4e ). Sternal part of cephalothorax nearly completely covered by broad pleon. Thoracic sternum with fused thoracic sternites 1–4, sutures absent except for ridge-like structure between sternites 2 and 3. Sutures between sternites 4 and 5 nearly complete, others interrupted in proximal third. Episternites narrow, attached to postero-lateral margins of sternites, with indistinct sutures between sternites ( Fig. 4e ).

Antenna ( Figs. 4d , 5a–c ) with flattened, broad articles; basal article short, broad, expanded anteriorly, immovably fixed to ventral rostral surface; second article large, broadly lamellate bearing greatly extended outer margin; third article significantly smaller, with prominently produced anterolateral portion; fourth article deeply inserted in anterior margin of third article. Flagellum about as long third and fourth articles combined.

Mouthparts, first and third maxillipeds not dissected. Ischium and merus of third maxilliped ( Fig. 5e ) with markedly convex mesial margin with moderately dense setae. Anterior margin of merus oblique, laminated. Carpus enlarged distally, with short stick-shaped process on anterior margin. Broad gap between ischia of third maxillipeds ( Fig. 4e ).

P1 (chelipeds) asymmetrical and heterochelous ( Figs. 3c , 4h ), short, slender, not reaching distal rostral margin, mostly concealed by carapace in dorsal view ( Fig. 3a, b ). Carpus of cheliped with anterior face lamelliform. Right chela larger than left chela, with dorsal ridge. Cutting margins of fingers entire, without teeth.

P2–5 ( Fig. 4f ) with short, flattened articles; anterodistal corners of meri spiniform, posterior faces of merus with denticulated ridges. Anterior and posterior faces of carpus serrated. Anterior margin of propodi expanded with blunt dorsodistal point, ventral (flexor) margin with distal spines. Dactylus shorter than propodus, curved, slender, subchelate with small protrusions on posterodistal corners of propodus. Small spinule present at ventrodistal margin of propodus near articulation with dactylus. P3 without teeth on distoventral margin of ischium ( Figs. 4g , 5f ).

Pleon very broad, rounded, margin with long soft setae. Telson small, ovoid, deeply inserted in distal margin of somite 6, with terminal notch ( Fig. 4e ).

Female genital opening, large, about half length of sternite 6, located at anterior margin of sternite, deflexed anteriorly, posterior margin rounded ( Fig. 4e ).

Affinity: Planotergum kowalevski sp. nov. is morphologically similar to P. mirabile but can clearly be distinguished by the following characters: the second anterolateral lobe (excluding postorbital tooth) is directed laterally, being broadly truncate, with a shallow concavity at the lateral margin ( Fig. 3a ) (vs. tooth directed more obliquely, triangular in shape and divided into two by a deep concavity and fissure in P. mirabile ; Fig. 2a, b ); the posterior lateral lobe of the carapace is markedly angular ( Fig. 3a, b ) (vs. more rounded; Fig. 2b ; see Balss 1935: fig. 1); the third antennal article has a pronounced lateral projection ( Fig. 3c ) (vs. article quadrate, without any projection in P. mirabile ; Fig. 2e, f ); the merus of the third maxilliped is distinctly more quadrate ( Fig. 4a ) (vs. more elongate with distal projection in P. mirabile ; Fig. 2c ); and the armatures of ambulatory pereopods (P2–P5) is different, especially along the inner part of merus of P2, which is unarmed in the new species ( Figs. 3f, g , 4f ) (vs. armed with 4 large sharp teeth in P. mirabile ; Fig. 2k, h ). These differences are significant and argue for recognizing the Red Sea specimen as a new species.

Ecology: Not known.

Etymology: The species is named after the r/v “Akademik Alexander Kowalevski,” which worked for a long time in the tropical seas and brought many new and interesting marine species. The name is used as a noun in apposition.

Distribution: The species is known only from the southern Red Sea.

Figures

Fig. 2. Planotergum mirabile Balss, 1935. a, c, d, g–n, female (7.7 × 10.1 mm) (ZRC 1985.130), Singapore; b, e, f, female (10.2 × 13.4 mm) (ZRC 1969.11.19.12), Java Sea: a and b, general dorsal view; c, left third maxilliped; d, right antenna (ventral view, dorsal covered by bryozoan); e, right antenna (dorsal view); f, left eye; g, i, l, n, P2–5 (dorsal views, setae intact); h, j, k, m, o, P2–5 (ventral views, setae denuded); k, P2, ventral view.

Fig. 3. Planotergum kowalevski sp. nov., holotype female (8.6 × 11.7 mm) (ZMMU Ma 3506), Red Sea: a and b, general dorsal view; c, ventral view; d, lateral view. Scale bars = 5.0 mm.

Fig. 4. Planotergum kowalevski sp. nov., holotype female (8.6 × 11.7 mm) (ZMMU Ma 3506), Red Sea: a, ventral view of chelipeds and third maxillipeds; b and c, eyes; d, front of carapace, dorsal view; e, thoracic sternites; f, ventral view of ambulatory appendages (P2–5); g, P2; h, chelipeds. Scale bars = 3.0 mm

Fig. 5. Planotergum kowalevski sp. nov., holotype female (8.6 × 11.7 mm) (ZMMU Ma 3506), Red Sea: a, front of carapace, eye and antenna, dorsal view; b, antenna, dorsal view; c, antenna, ventral view; d, ventral view of P2; e, left third maxilliped; f, ventral view of P2. Scale bars = 1.0 mm.