Trianguloscalpellum regium ( Wyville-Thomson, 1873 )

Zhibin, Gan & Xinzheng, Li, 2019, Report on four deep-water barnacles (Cirripedia, Thoracica) from the north west Pacific, with remarks on Trianguloscalpellum regium (Wyville-Thomson, 1873), Zootaxa 4565 (2), pp. 201-212 : 202-205

Trianguloscalpellum regium ( Wyville-Thomson, 1873)

Figures 1–3

Scalpellum regium Wyville-Thomson, 1873: 347 –348.— Hoek 1883: 106, pl. IV figs 3–5.— Pilsbry 1907: 28, pl. III fig. 5.

Trianguloscalpellum regium .— Young 1998a: 28 –30, figs 20a–h, 22.—1998b: 111, fig. 2c.—1999: 617, fig. 5B.—2001a: 464, fig. 7.—2001b: 741.— Chan et al. 2010: 13 , figs 1G, 10.— Poltarukha 2012: 37 –38, fig. 11.— Shalaeva & Boxshall 2014: 45 –49, figs 33A, 33B.

Material examined. JL-Dive114-S01-01, 1 specimen (CL 39.9 mm, CW 21.8 mm, PL 20.3 mm), Station JL- Dive114 (10°51.691’N, 141°57.110’E), Mariana Trench, depth 5,462 m, collected by manned submersible Jiaolong from onboard R/V Xiangyanghong 9, 0 1 June 2016.

Diagnosis. Capitulum leaf-like, with 14 closely packed plates, all plates with umbo apical; tergum triangular; carina arched, with narrow laterals, tectum flat or slightly raised medially with longitudinal bordering ribs and medial V-shaped ribs; inframedian latus triangular; carinolatus as high as wide or wider than high, with two apicobasal ridges, both plates basally contacting below carina; carinolatus significantly longer than inframedian latus; peduncle slightly longer than half length of capitulum, with compactly concentric scales.

Description. Capitulum (Fig. 1A–D) entirely white, coated by very thin cuticle with short setae; 14 plates closely packed, growth lines conspicuous. Peduncle slightly longer than half length of capitulum, covered by compactly concentric scales.

Tergum large, occludent and scutal margins straight, carinal margin arched; apex somewhat curved towards carinal side; surface with distinct medial apico-basal ridge, very low ridge from apex to basilateral margin; umbo apical. Scutum smaller than tergum, quadrangular, with prominent apico-basal ridge; occludent margin very straight, basal margin slightly concave; apex bluntly pointed; umbo apical. Carina arciform, exceeding apex of scutum in height; lateral margin narrow; tectum flat, with longitudinal bordering ribs and medial V-shaped ribs. Upper latus quadrangular; tergal margin nearly straight, scutal margin concave; umbo apical, apex pointed. Rostrum (Fig. 1E) very small, strip-like in exposed part. Rostro-latus trapeziform, scutal margin longer than basal margin; surface with apico-basal ridge; basal margin slightly longer than that of inframedian latus. Inframedian latus triangular, height slightly longer than width; umbo apical, apex pointed. Carino-latus as high as wide; upper latus margin with distinct upper flange; surface with two prominent apico-basal ridges; basal margin obviously longer than that of inframedian latus; umbo apical, apex curved; both plates basally contacting below carina, junction length ~0.27 length of carino-latus (Fig. 1F).

FIGURE. 1 Trianguloscalpellum regium ( Wyville-Thomson, 1873) . A, B, lateral views of specimen; C, carinal view of specimen; D, rostral view of specimen; E, Rostrum; F, carinal view of carino-latera.

Soft body without filamentary processes and penis (Fig. 2A). Cirrus I (Fig. 2B) separated from, and shorter than, remaining cirri; inner ramus broad, 11 segmented, medial segments broader than others; outer ramus long, 16 segmented. Cirrus II (Fig. 2C) much longer than cirrus I, rami of nearly equal length, inner ramus 28 segmented, outer ramus 30 segmented. Cirrus VI (Fig. 2D) longest, both rami nearly equal length, inner ramus 37 segmented, outer ramus 41 segmented, intermediate segments of rami with 3–4 (mostly 4) pairs of long setae on ventral margin (2–6 short seta among each pair of long setae) and 1 pair of long setae on dorsal margin (sometimes with 1–2 short seta). Caudal appendage (Fig. 2E) long, 5 segmented, reaching to end of protopodite.

Labrum swollen (Fig. 3A), cutting edge with flat ridge; mandibular palp narrow (Fig. 3B), with long setae along apical margin. Mandible with 3 large teeth excluding inferior angle (Fig. 3C), apex of inferior angle rough, without setae, inferior margin with long spinules (Fig. 3D). Maxillule slightly curved (Fig. 3E), cutting edge nearly straight, with many long, spinous setae. Maxilla with dense long setae along margins (Fig. 3F), anterior margin with notch.

Distribution. Trianguloscalpellum regium ( Wyville-Thomson, 1873) is a cosmopolitan species distributed in the Atlantic, Indian and Pacific Oceans ( Zevina, 1981; Foster & Buckeridge, 1994; Chan et al., 2010; Poltarukha, 2012; Jones & Hosie, 2016). However, Young (1998b; 2001b) considered it to be distributed only in the Atlantic Ocean. As noted by Young (1998b), it is difficult to determine the geographic distribution patterns of T. regium due to taxonomic confusion, and the present specimen does exhibit some features that differ to those reported by Chan et al. (2010) and Poltarukha (2012) (see Remarks).

FIGURE. 2 Trianguloscalpellum regium ( Wyville-Thomson, 1873) . A, lateral view of soft body; B, cirrus I; C, cirrus II; D, cirrus VI; E, caudal appendage.

Remarks. Based on cladistic analysis, Gale (2016) proposed a new classification system for the family Scalpellidae Pilsbry, 1907 and established a new genus, Regioscalpellum, to embrace Scalpellum regium Thomson, 1873 , S. darwini Hoek, 1883 , S. gigas Hoek, 1883 , S. moluccanum Hoek, 1883 , Pollicipes maximus J. de C Sowerby, 1829, and Arcoscalpellum sanchezae Withers, 1953 ; however, the taxonomic status of some remaining species assigned to Trianguloscalpellum by Zevina (1978; 1981) is unclear. The present study only focuses on the morphological characters of Trianguloscalpellum regium ( Wyville-Thomson, 1873) and we use the classification system of Zevina (1978), which is convenient for comparison between T. regium and its closely related species. The plates of the present specimen agree well with the detailed re-description of Young (1998b) based on the type specimen of Trianguloscalpellum regium , and with the photographs in Shalaeva & Boxshall (2014) also taken from the type specimen. The present specimen exhibits all the morphological differences between T. darwinii , T. gigas , T. mollucanum and T.ovale proposed by Young (1998b). For example, it differs from T. gigas and T. ovale by the carinolatus (only as high as wide vs. significantly higher than wide), from T. darwinii by the shape of the carina (tectum flatter and lateral margin narrower vs. tectum pronounced and lateral margin broad), and is immediately distinguishable from T. mollucanum by features of the carinolatus and inframedian latus (carinolatus significantly wider than inframedian latus vs. carinolatus as wide as inframedian latus). Chan et al. (2010) and Poltarukha (2012) reported T. regium from Taiwan and the Indian Ocean, respectively; however, their specimens show the carinolatus higher than wide, a morphological character presented by T. gigas and T. ovale . The present specimen also differs from their specimens in the appendages of the soft body. For example, Cirrus I has more segments than that of Chan et al. (2010); the caudal appendage of the present specimen is longer (5-segmented) and reaches to the end of the second segment of the protopodite, which is short (4-segmented) and falls short of the end of the first segment of the protopodite in that of Chan et al. (2010) and Poltarukha (2012); and the inferior angle of the mandible of the present specimen has five small spines that are absent in that of Chan et al. (2010). Furthermore, the similarities of the nucleotide sequences of the genes COI from the present specimen is less than 90% in comparison to that provided by Lin et al. (2015) (genbank number: KF484203 ). The taxonomic status of T. regium , T. mollucanum , T. gigas and T. ovale has always been disputed in the previous literature ( Zevina, 1981; Jones, 1992; Young, 1998b) and some authors consider that T. regium represents a complex of cryptic species ( Shalaeva & Boxshall, 2014). Therefore, more detailed morphological characteristics, such as the features of the soft body of the type specimens, are imperative, as well as molecular data. The nucleotide sequences of 16S rRNA and mt COI gene from the present specimen were submitted to tGenbank (genbank number: MH938354 and MH973609 , respectively), and we hope they are useful for future taxonomic studies.

FIGURE. 3 Trianguloscalpellum regium ( Wyville-Thomson, 1873) . A, mouthparts; B, mandibular palp; C, mandible; D, inferior angle of mandible; E, maxillule; F, maxilla.