Munidopsis albatrossae Pequegnat & Pequegnat, 1973

Osawa, Masayuki, Chan, Tin-Yam & Yang, Chien-Hui, 2023, New records of the squat lobster genus Munidopsis Whiteaves, 1874 (Crustacea, Decapoda, Munidopsidae) from the deep sea off Taiwan, ZooKeys 1166, pp. 271-286 : 271

Munidopsis albatrossae Pequegnat & Pequegnat, 1973

Figs 1 , 2

Munidopsis sp.-Wolff, 1961: 148, fig. 16.

Munidopsis albatrossae Pequegnat & Pequegnat, 1973: 163, figs 1, 2 (type locality: south of Madalena Bay, Baja California, 23°23.5'N, 112°30'W, 3219 m)- Hendrickx and Harvey 1999: 376 (list). Stevens 2002: 6 (list). Baba 2005: 280 (key), 284 (key, synonymies). Jones and Macpherson 2007: 480, fig. 2A. Baba et al. 2008: 131 (compilation). García Raso et al. 2008: 1282, fig. 2. Dong et al. 2019: 5, figs 1-3A.

Munidopsis aries -Ambler, 1980: 17. Wicksten 1989: 315 (list) [not M. aries (A. Milne-Edwards, 1880)].

Munidopsis albatrossae ? Munidopsis albatrossae - Arnés-Urgellés et al. 2020: 18, fig. 12. Rodríguez-Flores and Schnabel 2023: 6, table S1.

Material examined.

Taiwan: 1♀ parasitized by rhizocephalan (pcl 77.8 mm), east off Taiwan, station CP4216, 24°15.02'- 24°09.46'N, 122°11.55'- 122°10.37'E, 2360-2928 m, French beam trawl, 16 Jan. 2021 (NTOU A01452 ) .

Diagnosis.

Carapace (excluding rostrum) approximately as long as wide; dorsal surface with numerous transverse ridges and pair of small epigastric processes; front margin oblique; outer orbital angle with short spine (antennal spine); lateral margin decreasing in width posteriorly; anterior branchial margin convex, crested, with row of stout spines generally decreasing in size posteriorly. Rostrum 0.3 length of remaining carapace, slightly shorter than basal width, triangular, strongly narrowed on anterior half; dorsal surface with median carina. Sternite 3 subquadrate in general outline; sternite 4 narrowed and elongated anteriorly, anterior margin narrower than posterior margin of sternite 3. Pleon entirely unarmed; tergites 2 and 3 each with 2 elevated, blunt transverse ridges and many small ridges; posteromedian lobe of tergite 6 almost transverse, straight; telson composed of 8 plates. Ocular peduncle short, somewhat movable dorsoventrally, with strong mesiodorsal eye-spine directed anterolaterally. Article 1 of antennular peduncle with distolateral and distodorsal spines, distolateral spine larger. Antennal peduncle nearly reaching tip of mesiodorsal eye-spine by full length of article 4; article 1 with distomesial spine reaching midlength of article 2; article 2 with distolateral spine reaching midlength of article 3. Mxp3 merus with 2 or 3 small teeth on ventral margin, dorsal margin with small distal spine. P2-4 comparatively short; meri each with row of irregular sized spines on dorsal margin, ventrolateral margins slightly crenulated by short ridges; propodi gently narrowing from proximal to distal, each with dorsolateral and dorsomesial rows of small spines; dactyli approximately two-thirds length of propodi, ventral margins nearly straight, each with 8 or 9 teeth. Epipods absent from P1-4.

Description.

Ridges on carapace and P2-4 each bearing row of minute granules and very short plumose setae. P2-4 with row of dense, short, plumose setae on dorsomesial margin of each propodus; coarse, short stiff setae on surfaces of each dactylus.

Carapace (Fig. 1A-C ) excluding rostrum approximately as long as wide. Dorsal surface moderately arched from side to side; anterior half with numerous, short arcuate ridges; posterior half with longer transverse ridges, posteriormost ridge uninterrupted, somewhat elevated, preceded by shallow groove; pair of epigastric processes small, weakly raised; anterior cervical groove shallow, posterior cervical groove deep. Front margin oblique. Orbit slightly excavated, outer orbital angle with short but prominent spine (antennal spine). Lateral margin decreasing in width posteriorly; anterior branchial margin convex, crested, with row of stout spines generally decreasing in size posteriorly, anterior second spine strongest; anterolateral spine smaller than outer orbital spine, located below level of anterior branchial margin; posterior branchial margin nearly straight, dorsally with shallow, broad sulcus. Rostrum (Fig. 1A-C ) approximately 0.3 length of remaining carapace, slightly shorter than basal width, triangular, slightly directed ventrally; anterior half strongly narrowed, with acute tip; dorsal surface with median carina not extending to epigastric region; lateral margin ridged, with short stout spine medially; ventral surface flattish, with blunt median carina.

Sternal plastron (Fig. 2A ) slightly wider than long. Sternite 3 subquadrate; anterior margin with small denticles, subdivided into 2 lobes by shallow median notch, each lobe with shallow longitudinal groove; small protuberance present below median notch. Sternite 4 narrowed and elongated anteriorly; anterior margin narrower than posterior margin of sternite 3; lateral margins each with row of small tubercles on posterior half; ventral surface slightly concave, with median groove anteriorly and scattered short ridges posteriorly.

Pleon (Fig. 1A, C-E ) entirely unarmed, with numerous flattened tubercles on lateral parts of pleomeres 2-4. Tergite 1 with sparse, short transverse ridges. Tergites 2 and 3 each with 2 elevated, blunt transverse ridges; entire regions bearing many small ridges. Tergite 4 with elevated, blunt transverse ridge anteriorly. Tergites 5 and 6 each with obsolete ridge anteriorly on each side; surfaces covered with short ridges; posteromedian lobe of tergite 6 almost transverse, straight, lateral lobes weakly produced. Telson (Fig. 1E ) distinctly wider than long, composed of 8 plates being numerous, short ridges.

Ocular peduncles (Figs 1A-C , 2B ) short, somewhat movable dorsoventrally, with strong mesiodorsal eye-spine directed anterolaterally. Cornea small, approximately equal to basal width of mesiodorsal eye-spine, not pigmented.

Article 1 of antennular peduncle (Fig. 2B ) with distolateral and distodorsal spines, distolateral spine larger; ventrodistal margin with row of small denticles; dorsomesial distal angle with minute spine; ventral surface with small, flattened tubercles on convex lateral part.

Antennal peduncle (Figs 1B , 2B ) nearly reaching tip of mesiodorsal eye-spine by full length of article 4. Article 1 with distomesial spine reaching midlength of article 2; distolateral spine small, blunt. Article 2 with small distomesial spine ventrally, distolateral spine reaching midlength of article 3; surfaces with sparse, small denticles and tubercles. Article 3 with small distomesial spine dorsally, distal margin with row of small denticles. Article 4 with minute denticles on distal margin.

Mxp3 merus (Fig. 2C ) with 2 or 3 small teeth on proximal half of ventral margin; dorsal margin with small distal spine; carpus unarmed.

P1 missing.

P2-4 (Figs 1A, C , 2D, E ) comparatively short, somewhat compressed laterally. Meri decreasing in size posteriorly, P3 0.9 length of P2, P4 0.8 length of P3; dorsal margins bluntly crested, each with row of irregularly sized spines, terminal spine strongest; lateral surfaces covered with short, transverse or arcuate ridges; ventrolateral margins rounded, terminal angle with small spine (P2) and small tubercle (P3 and P4). Carpi each with 3-5 distinct spines and some much smaller proximal spines on dorsal crest, terminal spine strongest; lateral surfaces with sparse, small, arcuate or transverse ridges entirely and each with somewhat elevated, longitudinal ridge of small spines (P2) and small protuberances (P4) on midline. Propodi approximately 5.0 times length of proximal height, gently narrowing from proximal to distal; dorsal surface flattish, dorsolateral and dorsomesial margins each with irregular row of small spines, dorsomesial spines stronger; lateral surfaces each with row of short, somewhat elevated ridges and blunt spines near ventrolateral margin; ventrolateral margins also crenulated by short, somewhat elevated ridges and blunt spines; ventral surfaces with numerous, small, arcuate ridges; distoventral margins each with 2 rounded, tuberculate lobes bearing 0 or 1 minute corneous spine. Dactyli approximately two-thirds length of propodi, moderately slender; surfaces with small, somewhat elevated ridges, dorsal surface flattish, lateral and mesial surfaces convex on each proximal midline; ventral margins nearly straight, each with 8 or 9 proximally diminishing teeth, each tooth terminating in acute corneous spine; terminal claws short, curved.

Epipods absent from P1-4.

Coloration.

Body and appendages entirely white (Fig. 1A ).

Distribution.

Eastern Pacific: Alaska Bay, off Oregon, Monterey Bay, Baja California, East Pacific Rise and west of Costa Rica; 2550-3680 m depths ( Stevens 2002; Baba et al. 2008). Western Pacific: Weijia Guyot (12°43.01'N, 156°27.20' E) and Hawaii, 3225 m depth ( Dong et al. 2019). Antarctic waters: Bellingshausen Sea, 1920 m depth ( García Raso et al. 2008). In addition, material identified as M. albatrossae based solely on ROV images have been reported from the Galapagos Islands, 3392 m depth, and Hawaii Archipelago, between 3250 m and 3255 m ( Arnés-Urgellés et al. 2020; Rodríguez-Flores and Schnabel 2023). The present specimen collected from off Taiwan at the depths of 2360-2928 m represents the second confirmed record of M. albatrossae from the western Pacific (Fig. 5 ).

Remarks.

The present large specimen lacks both chelipeds and was parasitized by an unidentified rhizocephalan on the internal surface of the pleon.

As discussed by previous authors ( Pequegnat and Pequegnat 1973; Gore 1983; Jones and Macpherson 2007; García Raso et al. 2008), M. albatrossae and M. aries (A. Milne-Edwards, 1880) are morphologically very similar. Recorded distributions show that M. albatrossae occurs only in the Pacific including the eastern Pacific side of the Antarctic (Fig. 5 ), whereas M. aries ranges from the North Atlantic to the South Atlantic and also occurs off Reunion Island in the southwestern Indian Ocean ( Macpherson and Segonzac 2005; Macpherson 2007).

Pequegnat and Pequegnat (1973) argued that M. albatrossae differed from M. aries (as M. sundi Sivertsen & Holthuis, 1956) by the following characters: (1) setose ridges on carapace more pronounced than in M. aries ; (2) anterior branch of cervical groove not as distinct; (3) frontal margin of carapace noticeably less broad; (4) first spine behind anterior branch of cervical groove not appreciably larger than other lateral spines, considerably larger in M. aries ; (5) posterior margin of carapace relatively broader than in M. aries ; (6) pleomere 1 not completely smooth, but with four rows of weak, interrupted ridges and setose grooves on posterior portion; (7) anterior halves of pleomeres 2-4 not all smooth as in M. aries , but bearing interrupted setose ridges; (8) eyes more freely movable than in M. aries . However, these distinguishing characters except for the surface structures on the pleomeres 2-4 vary and are not so evident in the published specimens referred to M. albatrossae and M. aries (or as M. sundi ). The present specimen from off Taiwan agrees more closely with M. albatrossae in the dorsal surfaces of the pleomeres 2-4 with many interrupted, short ridges (Fig. 1D ), unlike being apparently smooth and no such ridges in M. aries (cf. Sivertsen and Holthuis 1956: pl. 4 fig. 2, as M. sundi ; Macpherson and Segonzac 2005: fig. 3). The development of the carapace epigastric process varies in previous accounts of M. albatrossae ; the processes are illustrated as rather distinct ( Pequegnat and Pequegnat 1973; García Raso et al. 2008; Dong et al. 2019) or indistinct ( Jones and Macpherson 2007) as in the present specimen (Fig. 1A-C ).

A comparison of the barcoding segments of the COI gene (657 bp) of the Taiwanese specimen (GenBank accession number OQ996536) and M. albatrossae materials from the eastern Pacific (GenBank accession number DQ677692; Monterey Bay) and western Pacific (GenBank accession number MN397920; Weijia Guyot) reported by Jones and Macpherson (2007) and Dong et al. (2019) revealed only 0.19% and 0.35% sequence divergence, respectively. Meanwhile, there is 1.75% COI sequence divergence between the Taiwanese specimen and the northeastern Atlantic material reported as M. aries (GenBank accession number DQ677691; off Guinea) by Jones and Macpherson (2007; more details on this specimen, see Macpherson and Segonzac 2005).

The mitochondrial COI gene is considered as rather conservative in the genus Munidopsis between populations and among sibling species (cf. Jones and Macpherson 2007; Thaler et al. 2014; Coykendall et al. 2017; Dong et al. 2019; Rodríguez-Flores et al. 2023). Thus, the phylogenetic hypothesis based on COI data by Rodríguez-Flores et al. (2023) concluded that M. albatrossae and M. aries , as well as many other abyssal species of this genus, are not distinguished as different species. Nevertheless, such low genetic divergences may be more apparent than real because increasing depth could reduce the rate of substitution ( Rodríguez-Flores et al. 2022b). While the number of specimens and genetic data required to determine the exact taxonomic status of these abyssal Munidopsis species are still very limited, for the time being we regard M. albatrossae and M. aries as separate species. The present Taiwanese specimen is hence assigned to M. albatrossae for having a higher genetic similarity and closer morphological matches (i.e., surface structure of pleomeres) to this species.

Figures

Figure 1. Munidopsis albatrossae Pequegnat & Pequegnat, 1973, female parasitized by rhizocephalan (pcl 77.8 mm), east off Taiwan, station CP 4216, NTOU A 01452 A entire animal, dorsal view (lacking both P 1) B carapace, dorsal view C carapace and pleon, right lateral view D pleomeres 1 - 4, dorsal view E pleomere 6 and telson, external view. Fresh coloration (A), preserved coloration (B-E).

Figure 2. Munidopsis albatrossae Pequegnat & Pequegnat, 1973, female parasitized by rhizocephalan (pcl 77.8 mm), east off Taiwan, station CP 4216, NTOU A 01452 A sternal plastron, ventral view B left eye, article 1 of antennular peduncle, and antennal peduncle, ventral view C left Mxp 3, merus and carpus, lateral view D left P 2 - 4, meri, lateral view (a P 2, b P 3, c P 4) E left P 3 (a propodus and dactylus, lateral view; b dactylus, lateral view; c propodus, dorsal view; d propodus and dactylus, mesial view).

Figure 5. Global geographic distributions of Munidopsis albatrossae Pequegnat & Pequegnat, 1973 (red) and M. pycnopoda Baba, 2005 (blue). Dotted line symbols are records based only on ROV images. Shaded symbols refer to new records in this work.