Parapseudaeginella australiensis, Guerra-García, 2020

Parapseudaeginella australiensis View in CoL n. sp.

( Figs. 2–6 View Figure 2 View Figure 3 View Figure 4 View Figure 5 View Figure 6 )

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Material examined. Holotype: mature male, WAM C76110 About WAM (ex AM P.101302) (vial + 2slides) (mouthparts dissected, used for description, figured), Ningaloo Reef , south of Tantabiddy, reef front, Western Australia, Australia, 21°54’37”S 113º55’42”E, 9 m depth, coral heads, preserved 80% ethanol, 12 June 2008, coll. N.L. Bruce and M. Blazewicz-Paszkowycz. GoogleMaps — Paratypes (same data as the holotype): (a) mature female, AM P.101303 (vial + 1 slide) (mouthparts dissected, used for description, figured); (b) mature male, AM P.101304 (vial + 3 slides) (mouthparts dissected, used for description in part) GoogleMaps .

Etymology. The named australiensis is alluding to the country where the species was found.

Diagnosis. Head and pereonite 1 with an acute dorsal projection, bent forward.Pereonite 2 with a pair of small dorsal projections medially, and acute lateral projections near the coxa of gnathopod 2. Gnathopod 1 propodus palm with a pair of proximal grasping spines. Gnathopod 2 basis with a distal projection; propodus palm with one proximal grasping spine. Antennae 1 and 2 setose in males. Pereopods 5–7 propodus palm with strong setae but lacking proximal grasping spines.

Description. Holotype male (2.6 mm) ( Figs. 2–6 View Figure 2 View Figure 3 View Figure 4 View Figure 5 View Figure 6 ):

Lateral view ( Fig. 2 View Figure 2 ). Eyes present and distinctive. Head with an acute dorsal projection, curved forward. Pereonite 1 fused with head, suture present. Pereonite 1 with acute dorsal projection bent forward distally. Pereonite 2 with a pair of small dorsal projections medially, an acute hump distally, and acute lateral projections (one on each side) near the coxa of gnathopod 2. Pereonites 3 and 4 ventrally expanded and rounded near gills. Pereonites 3–7 without projections. Pereonites 6 and 7 fused ( Fig. 6 View Figure 6 ).

Gills ( Fig. 2 View Figure 2 ). Present at middle of pereonites 3–4, elongate, length about two times width.

Mouthparts ( Fig. 3 View Figure 3 ). Upper lip symmetrically bilobed, smooth apically. Mandibles without mandibular molar. Three-articulate palp with a setal formula 1-3-1, medial article provided with one seta; left mandible with incisor five-toothed, lacinia mobilis five-toothed, followed by two or three accessory blades; right mandible with incisor five-toothed, lacinia mobilis blade-like, followed by two accessory blades; molar flake absent. Lower lip without setulae; inner lobes quadrangular. Maxilla 1 outer lobe carrying five serrated spines, palp two-articulate, distal article with three apical spines and 1 medial seta. Maxilla 2 inner lobe small, shorter than outer lobe, both with five setae respectively. Maxilliped inner plate small, about 1/3 of outer plate in length, carrying two apical setae and a small tooth; outer plate elongate, with 3 apical setae; palp four-articulate, distal article (dactylus) curved and with rows of minute setulae.

Antennae ( Figs. 2 View Figure 2 , 4 View Figure 4 ). Antenna 1 peduncle setose, some setae plumose; article 1 robust; article 2 longest; article 3 shortest; f lagellum with nine articles, first article apparently composed of two articles fused as indicated by aesthetascs at midlength. Antenna 2 setose, slightly shorter than peduncle of antenna 1; swimming setae absent; proximal peduncular article with a distal projection (gland cone); flagellum two-articulate.

Gnathopods ( Figs. 2 View Figure 2 , 4 View Figure 4 ). Gnathopod 1 basis of the same length as the combination of ischium, merus and carpus; grasping margin of propodus nonserrated; 2 proximal grasping spines, dactylus bifid distally. Gnathopod 2 broken in holotype ( Fig. 2 View Figure 2 ); description of carpus, propodus and dactylus based on the gnathopod 2 of paratype male “b” ( Fig. 4 View Figure 4 ); gnathopod 2 inserted medially on pereonite 2; coxa well developed, with a proximal projection; basis as long as pereonite 2, with an acute distal projection; ischium small, rectangular; merus rounded; carpus short and triangular; propodus elongate, setose, with one proximal grasping spine and a projection followed by U-shaped notch medially; dactylus with setulae.

Pereopods ( Figs. 2 View Figure 2 , 5 View Figure 5 ). Pereopod 3 and 4 vestigial (approx. 0.05 mm), one-articulate, provided with two distal plumose setae. Pereopods 5–7 similar but slightly increasing in size and robustness respectively; carpus and propodus provided with strong setae ventrally, propodus lacking proximal grasping spines; dactylus smooth.

Penes ( Fig. 6 View Figure 6 ) distinctive, length approx. 1.5 times width.

Abdomen ( Fig. 6 View Figure 6 ) without appendages, with two setose lateral lobes and a single dorsal lobe with 2 plumose setae.

Paratype female “a” (2.1 mm) ( Figs. 2 View Figure 2 , 6 View Figure 6 ):

Flagellum of antenna 1 with eight articles. Pereonite 1 less elongate than male. Pattern of dorsal pereonite projections as in male except for the acute hump medially in pereonite 2 rather than distally. Mouthparts similar to male but setal formula of mandibular palp 1-2-1. Insertion of gnathopod 2 on the anterior half of pereonite instead of medially. Gnathopods 2 were lacking in the female specimen so they could not be described. Oostegites present on pereonites 3 and 4, more setose on pereonite 3. Gills shorter than in male. Lateral lobes of abdomen lacking setae. The female was carrying hatchlings in the brood pouch (see brood pouch in the female of Fig. 2 View Figure 2 ). Pereopods 6 and 7 are also totally fused in the juvenile, flagellum of antennae 1 and 2 is two-articulate, and the head and pereopods are proportionally larger in comparison with those of adult specimens.

Remarks. The new genus is very similar to Pseudaeginella . Presently, thirteen species have been described within Pseudaeginella (cf. Horton et al., 2020). Lacerda et al. (2011) provided a key to species of the genus Pseudaeginella and body illustrations. All the Pseudaeginella species have pereonites 6 and 7 separated (unfused), which is a diagnostic character of this genus. Therefore, the main difference between the two genera is that pereonites 6 and 7 are totally fused in Parapseudaeginella n. gen., whereas they are separated in Pseudaginella. Additional differences occur in the pereopods, in species of Pseudaeginella the propodus of pereopods 5–7 has a pair of proximal grasping spines (usually located on a small projection) whereas these are absent in Parapseudaeginella n. gen.

Apart from Parapseudaeginella n. gen., there are only two other genera in the Caprellidae with fused pereonites 6 and 7: Metaprotella Mayer, 1890 and Luisacaprella Guerra-García,2020 .The main differences among these three genera are: (1) a mandibular molar is present in Metaprotella and Luisacaprella , while it is absent in Parapseudaeginella n. gen.; (2) the setal formula of the mandibular palp is 1-x-y- 1 or 1-x- 1 in Metaprotella , 2-x- 1 in Luisacaprella , and 1-x- 1 in Parapseudaeginella n. gen.; (3) the outer plate of the maxilliped is significantly larger in Metaprotella than in Luisacaprella and Parapseudaeginella n. gen., (4) the palm of the propodus of gnathopod 1 has one grasping spine in Metaprotella and two in Luisacaprella and Parapseudaeginella n. gen.; (5) pereopod 5 is fully developed in Metaprotella and Parapseudaeginella n. gen. while the distal article of pereopod 5 is vestigial in Luisacaprella ; (6) the abdomen of male Metaprotella is provided with two appendages (cf. pleopods) while these are absent in Luisacaprella and Parapseudaeginella n. gen.

The material of the new genus was collected from coral heads in shallow waters of Ningaloo Reef. The study conducted by Guerra-García (2004) of the caprellids from Western Australia and Northern Territory included material collected from Ningaloo Reef (stations from WA-317 to WA-361 — cf. Guerra-García, 2004: 70, 71). However, this tiny caprellid was not present in those collections. Probably, the considerably small size of Parapseudaeginella australiensis n. sp. has prevented its previous collection and/or sorting. This reveals that further efforts are needed focussing on sorting and studying the smallest specimens to fully understand the global diversity and relationships of caprellids.