Luisacaprella eliae, Guerra-García, 2020

Guerra-García, J. M., 2020, A new genus and species of Caprellidae (Crustacea: Amphipoda) from Kiribati, Journal of Natural History 53 (45 - 46), pp. 2817-2832 : 2819-2829

publication ID	https://doi.org/ 10.1080/00222933.2020.1752405
publication LSID	lsid:zoobank.org:pub:1F5A24BE-A7AC-4D3C-A087-F7284F84A2DC
persistent identifier	https://treatment.plazi.org/id/03E5FD25-0473-F854-2A9C-1CB2FC4AFA10
treatment provided by	Carolina
scientific name	Luisacaprella eliae
status	sp. nov.

Treatment

Luisacaprella eliae View in CoL sp. nov. ( Figures 1 – 8 View Figure 1 View Figure 2 View Figure 3 View Figure 4 View Figure 5 View Figure 6 View Figure 7 View Figure 8 )

Material examined

Type material. Holotype mature male AM P.101305 (vial + 3 slides) (mouthparts dissected, used for description, figured), Teirio Island , outer reef slope, Abaing Atoll, Kiribati, 1°47 ʹ 41 ” N, 172º54 ′ 57 ” E, 3 – 32 m depth, associated with calcareous dead branching coral, fixative not recorded, subsequently preserved 80% ethanol, November 1973, coll. P.A. Hutchings and B. Goldman. GoogleMaps

Paratypes (collected from the type locality together with the holotype):

Paratype ‘a’ mature female AM P .103546 (vial + 1 slide) (mouthparts dissected, used for description, figured).

Paratype ‘b’ mature female AM P .103547 (vial + 1 slide) (mouthparts dissected)

Paratype ‘c’ mature female AM P .103548 (vial + 1 slide) (mouthparts dissected)

Paratype ‘d’ inmature male AM P .103549 (vial + 2 slides) (mouthparts dissected)

Other paratypes AM P.103550: 2 mature males, 1 mature female, 1 inmature male, 1 juvenile .

Etymology

The species is dedicated to Elia Ariza Guerra, niece of the author.

Diagnosis

Eyes present. Head with an anteriorly curved dorsal acute projection. Pereonites 2 – 4 with dorsal projections. Pereonites 3 and 4 with lateral acute projections. Male with small acute anterolateral projection near coxa in pereonites 2. Pereonites 6 and 7 fused. Mandibular palp 3-articulate, with the setal formula 2-x-1, being x = 2; molar present, of medium size; molar flake absent. Outer lobe of maxilla 1 with six distal spines. Third article of the maxilliped palp without distal projection. Basis of gnathopod 2 shorter than pereonite 2. Pereopods 3 and 4 two-articulate; proximal article larger than distal one; distal article conical. Pereopods 5 – 7 six-articulate. Pereopod 5 weak, very thin and provided with long setae, distal article vestigial. Pereopods 6 and 7 without grasping spines. Abdomen without appendages.

Description

Holotype, male (2.9 mm) AM P.101305

Lateral view ( Figure 1 View Figure 1 ). Eyes present, with distinct ommatidia. Head fused with pereonite 1, suture present. Head with an anteriorly curved dorsal acute projection. Pereonite 2 provided with three projections dorsally (the proximal one straight, the medial larger and the distal smaller, both anteriorly curved) and an acute anterolateral projection near coxa of gnathopod 2. Pereonite 3 with four dorsal projections and three lateral acute projections. Pereonite 5 with a proximal rounded projection and three lateral acute projections. Body surface of pereonites 2, 3 and 4 with tiny tubercles dorsally among the projections. Pereonites 4 and 5 with a ventral acute projection. Pereonites 6 and 7 completely fused.

Antennae ( Figures 1 View Figure 1 and 4 View Figure 4 ). Antenna 1 about 1/2 of body length; peduncular article 1 with a bunch of plumose setae distally; article 2 the longest, provided with plumose and simple setae; article 3 shortest with a short blunt on distal end provided with smooth setae; flagellum five-articulate, surface of articles with minute tubercules. Antenna 2 about 2/3 of antenna 1 length; flagellum two-articulate. Distal article of the peduncle and the two articles of the flagellum with tiny sparse tubercles.

Mouthparts ( Figures 2–3 View Figure 2 View Figure 3 ). Remarkably small (ca. 0.05 mm). (Mandibles described from the holotype and paratypes ‘ a ’, ‘ b ’ and ‘ c ’; maxilliped, maxillae, upper and lower lips described from the paratype ‘ a ’). Upper lip symmetrically bilobed, smooth. Mandibles with three-articulate palp; mandibular molar present, of medium size, not very strong; setal formula for distal article 2-2-1, with a row of small and rounded tubercles on the bases of the setae; left mandible with incisor six-dentate, lacinia mobilis seven-dentate, followed by a row of two-three plate-like setae; incisor of right mandible six-dentate, lacinia mobilis plate-like, followed by two plate-like setae; molar flake absent. Lower lip without setae; inner lobes separated, small, smooth; outer lobes triangular, large, smooth. Maxilla 1 outer lobe with six robust spines, palp two-articulate, distal article with three apical and one medial setae. Maxilla 2 inner and outer lobe with three and four setae, respectively. Maxilliped inner plate rectangular, carrying three setae and one small tubercle; outer plate oval, with row of setae on inner margin; palp four-articulate, distal article with five (four+one) setae.

Gnathopods ( Figures 1 View Figure 1 , 4 View Figure 4 and 5 View Figure 5 ). Gnathopod 1 basis as long as the combination of ischium, merus and carpus; propodus elongate, length about two times width, palm

with two proximal grasping spines, dactylus with very fine setulae, bifid distally with two distal setae. Gnathopod 2 inserted on the anterior half of pereonite 2; basis longer than half of pereonite 2, provided with an acute projection distally, ischium short and rectangular; merus rounded; carpus triangular and very short; propodus elongate, as long as basis, with a grasping spine proximally, medial projection followed by small U-shaped notch; dactylus elongate with two setulae medially and one seta distally.

Gills ( Figure 1 View Figure 1 ). Present on pereonites 3 – 4, oval, length about two times width.

Pereopods ( Figures 5–6 View Figure 5 View Figure 6 ). (Pereopods 5 – 7 detached in holotype, figured from male paratype ‘ d ’). Pereopods 3 and 4 subequal, very reduced, two-articulate; basal article with one seta, distal article conical provided with three setae. Pereopods 5 – 7 with weak coxae, six-articulate. Pereopod 5 with different morphologies to pereopods 6 and 7, weak, elongate and provided with long setae, distal article vestigial, reduced to a tiny button. Pereopod 6 and 7 subequal, six-articulate; propodus without grasping spines, dactylus with a seta distally.

Penes ( Figure 7 View Figure 7 ). Situated laterally, elongate, length about three times width. Abdomen ( Figure 7 View Figure 7 ). With a pair of setose lateral lobes and a single dorsal lobe (telson), with a pair of plumose setae.

Paratype ‘ a ’, female (2.1 mm) AM P.103546. Pereonite 2 ( Figure 1 View Figure 1 ) provided with a pair of proximal dorsal projections, followed by a large acute one anteriorly curved and two distal ones. Pereonite 3 with three dorsal projections and two lateral ones. Pereonite 4 with three dorsal projections, lacking ventral projection. Pereonite 5 with a tiny dorsal projection proximally and lacking ventral projection. Antenna 1 flagellum four-articulate. Oostegites present on pereonites 3 and 4, scarcely setose on pereonite 4. Gnathopod 2 ( Figures 1 View Figure 1 and 5 View Figure 5 ) inserted on the anterior end of pereonite 2; basis without distal projection and propodus palm without medial projection. Abdominal lateral lobes without setae ( Figure 7 View Figure 7 ).

Intraspecific variation and ontogenetic development

Most of the morphological characters of the species are relatively constant in all the specimens examined. The setal formula of the mandibular palp is always 2-2-1 and the dentation of the incisor and lacinia mobilis is also constant (incisor six-toothed, and lacinia

mobilis seven-toothed in the left mandible and transformed into a plate on the right mandible). The maxilla 1 outer lobe has six spines in all specimens except for one specimen which apparently has only five spines; the distal article of the palp is normally provided with three apical setae and one medial seta, although some specimens have an additional seta medially. Maxilla 2 is similar in all the dissected specimens, but the number of setae on the inner and outer lobes varies between three to four (inner lobe) and four to five (outer lobe). The inner plate of the maxilliped always has three strong setae, and in some specimens these setae are slightly plumose; the outer plate is provided with a number of setae which varies from one to three apically and three to four laterally; the palp is provided with five apical (four+one) setae in all specimens examined. The gnathopod 1 has always two proximal grasping spines, and gnathopod 2 has only one in all the specimens examined.

Small juveniles lack most of the dorsal projections; the one on the head is the first to appear ( Figure 8 View Figure 8 ). The number of articles of the flagellum of antennae 1 increases with development. Pereonites 6 and 7 are fused in all stages of development.

Remarks

The new genus is very close to Aciconula Mayer, 1903 on the basis of similar antennae, lateral view, maxilliped, and mandible molar reduced, distal article of pereopod 5 reduced and male abdomen lacking appendages. Aciconula is presently including five species: Aciconula miranda Mayer, 1903 , Aciconula acanthosoma Chess, 1989 , Aciconula australiensis Guerra-García, 2004 , Aciconula tridentata Guedes-Silva & Souza-Filho, 2013 and Aciconula tinggiensis Lim, Azman & Othman, 2019 .

The new species Luisacaprella eliae can be distinguished from all the Aciconula species on the basis of differences in mouthparts, pereopods and pereonites (see Mayer 1903; Chess 1989; Guerra-García 2004; Guedes-Silva and Souza-Filho 2013).

Regarding the mouthparts, size and shape of mandible molar is similar in both genera. Moreover, the small tubercles on the insertion of setae of the terminal article of the mandibular palp are shared by both genera (see e.g. Guerra-García 2004: fig. 20 D,E, p. 24; Guedes-Silva and Souza-Filho 2013: Figure 2 View Figure 2 , p. 1837). However, the setal formula of the mandibular palp clearly differs between them, with two long setae proximally in Luisacaprella (formula 2-x-1) and only one seta in Aciconula (formula 1-x-1). In caprellids, the usual mandibular setal formula is 1-x-1 (one long seta near proximal end followed by a number of shorter setae and one long seta near the apical end) ( Laubitz 1993), but two variants have also been described: formula 1-x-y-1, which indicates the presence of 1 long seta at either end of row of variable number of short setae (x) and intermediate one (y) ( McCain 1968), and formula 2-x-1 indicating 2 long setae near the proximal end followed by a number of short setae and one long seta near the apical end ( Takeuchi and Guerra García 2002). Some authors describe a formula 0-x-y-1 (a variant of 1-x-y-1 lacking the long setae of the proximal end) (see e.g. species of Liropus Mayer, 1890 in Guerra-García et al. 2018). In some cases, the distal article of the mandibular palp is provided with only one or few apical setae, without following a specific setal formula (see e.g. Benedict 1977). The formula 1-x-y-1 is present in the genera Abyssicaprella McCain, 1966 , Abyssododecas Takeuchi et al., 2016 , Orthoprotella Mayer, 1903 , Paraprotella Mayer, 1903 , Protella Dana, 1853 and Metaprotella Mayer, 1890 , such as the type species M. haswelliana ( Mayer, 1882) (see Takeuchi and Lowry 2007). The formula 2-x-1 is very unusual in caprellids and has been described, so far, only in three genera. It is considered a diagnostic character of the genus Pseudoprotella Mayer, 1890 ( Guerra-García, 2002b), occurring in all species of the genus. A formula 2-x-1 is also present in some species of Deutella Mayer, 1890 , such as Deutella indica Guerra-García, 2002 (see Guerra-García 2002c), and Paraprotella Mayer, 1903 , such as P. saltatrix Takeuchi & Guerra-García, 2002 (see Takeuchi and Guerra García 2002) and P. teluksuang Lim, Othman & Takeuchi, 2015 (see Lim et al. 2015). However, these three genera differ from Luisacaprella in other diagnostic features such as the separation of pereonites 6 and 7 (fused in Luisacaprella ), molar well developed (reduced in Luisacaprella ), grasping spines present in pereopods 6 and 7 (absent in Luisacaprella ), and presence of abdominal appendages (absent in Luisacaprella ).

Regarding pereopods, pereopods 3 and 4 are two-articulate in males and females of Luisacaprella , whereas there is sexual dimorphism in Aciconula . Males of Aciconula have pereopods 3 and 4 two-articulate while females have pereopod 3 two- or three-articulate (three articles in Aciconula tridentata Guedes-Silva & Souza-Filho, 2013 and two articles in the remaining species), and pereopod 4, four-articulate. The atypical shape of pereopod 5 is shared by the two genera, although the distal article is much more reduced (almost vestigial) in Luisacaprella . However, a reduction in the number of articles of pereopod 5 is very common in caprellids ( Takeuchi 1993). A similar feature of a weak and setose sixarticulate pereopod 5 has also been described for other caprellid genera such as Cubadeutella Ortiz, Guerra-García & Lalana, 2009 ( Ortiz et al., 2009) and some species of the genera Deutella (e.g. Deutella aspiducha Guerra-García, 2002 , see Guerra-García 2002b) and Noculacia Mayer, 1903 (e.g. Noculacia australiensis Guerra-García, 2002 , see Guerra-García 2002b). Possibly these pereopod 5 characteristics (very slender, with long setae, and dactylus very reduced) are the result of adaptations (see e.g. Corbari et al. 2005) involved in clinging or mating behaviours but this remains to be tested. The morphology of pereopods 6 and 7 also differs between Luisacaprella and Aciconula . In species of Aciconula , the propodus has two proximal grasping spines placed in a small protuberance (see e.g. Guerra-García 2004: Figure 22 E,F, p. 26; Guedes-Silva and Souza-Filho 2013: Figure 5 View Figure 5 , p. 1840). Grasping spines and the protuberance are lacking in Luisacaprella .

Overall, the main difference between the two genera is that pereonites 6 and 7 are totally fused in Luisacaprella (see Figures 1 View Figure 1 and 7 View Figure 7 ) while they are separated in Aciconula (see e.g. Guerra-García 2004: Figure 19, p.22; Guedes-Silva and Souza-Filho 2013: Figure 1 View Figure 1 , p. 1836). The only other known caprellid genus with peronites 6 and 7 fused is Metaprotella (see Takeuchi and Lowry 2007). These pereonites are partially fused (not totally) in some species of Orthoprotella ( Lim et al. 2015) . Therefore, this study describes the second genus in the Caprellidae which have pereonites 6 and 7 totally fused. Both genera, Metaprotella and Luisacaprella can be easily distinguished by the following characters: (1) the molar is larger and more robust in Metacaprella ; (2) the setal formula of the mandibular palp is 1-x-y-1 or 1-x- 1 in Metaprotella and 2-x- 1 in Luisacaprella ; (3) the outer plate of maxilliped is significantly larger in Metaprotella ; (4) the palm of propodus of gnathopod 1 has one grasping spine in Metaprotella and two in Luisacaprella ; (5) pereopod 5 is fully developed in Metaprotella while the distal article of pereopod 5 is vestigial in Luisacaprella ; (6) the abdomen of males of Metaprotella has two appendages (cf. pleopods) while these are absent in Luisacaprella .

Specimens belonging to L. eliae were collected from dead branching coral of shallow waters (3 – 32 m). The new species is characterised by tiny size (<3 mm). These small specimens are usually overlooked when sorting samples or in general sampling programmes using large mesh sizes. Therefore, it is expected that further studies targeting tiny caprellids from sediments and dead corals will reveal many new genera and species, which will provide important insights into understanding caprellid diversity and relationships.