Caprella equilibra Say, 1818

Peart, Rachael A. & Woods, Chris, 2025, Caprellidae (Crustacea: Amphipoda) of Aotearoa New Zealand waters: a constantly changing landscape, Zootaxa 5568 (1), pp. 1-65 : 10-11

Caprella equilibra Say, 1818

( Fig. 2 , Appendix 1)

Caprella equilibra Say, 1818: 391–392 . — Schellenberg, 1926: 470.— McCain, 1968: 26–30, figs. 12–13, 55.— McCain & Steinberg, 1970: 19–21.— McCain & Gray, 1971: 113–114, fig. 3.— McCain, 1979: 471.— De Broyer & Jażdżewski, 1993: 103.— Krapp-Schickel, 1993: 782–783, fig. 533.— De Broyer & Rauschert, 1999: 287.—Guerra-García & Thiel, 2001: 878–879.— Guerra-García, 2003: 181–182, fig. 4.—Lowry & Stoddart, 2003: 22–23.— De Broyer et al., 2004: 66.— De Broyer et al. 2007: 244–245.—Webber et al., 2010: 155 (unnumbered fig.), 156, 219.— Schnabel et al., 2023: 436.

Caprella aequilibra . — Mayer, 1882: 45, pl. 1: fig. 7, pl. 2: figs. 1–11, pl. 4: figs. 20–25, pl. 5: figs. 16–18.— Chevreux & Fage, 1925: 455, fig. 433.

Caprella monacantha Heller, 1866: 54 , figs. 17–19.

Type locality. South Carolina, United States of America .

Distribution.?Cosmopolitan; 0–3000 m.

New Zealand biosecurity status. Presumed adventive in New Zealand.

Remarks. Specimens identified as Caprella equilibra are the most common species reported in the New Zealand shallow water environment. However, detailed study into the morphological and molecular variations that can be aligned to distributional ranges of the species were beyond the scope of this paper. Therefore, due to this and the early synonymisation of a variety of nominated species with Caprella equilibra (Thomson & Chilton, 1886) , it is uncertain if Caprella equilibra sensu stricto occurs in New Zealand. Despite the very similar morphology between records, this study reveals there are potentially multiple species in New Zealand waters under Caprella equilibra . Molecular studies across many groups of marine invertebrates have shown that despite presumed cosmopolitan distributions, many such species actually comprise species complexes (e.g., Fehlauer-Ale et al. 2014; Cabezas et al. 2013a, Cabezas et al. 2013b). Darling & Carlton (2018) presented the concept of ‘pseudocosmopolitan’ species. These are taxa that are considered cosmopolitan until they have detailed molecular assessment that proves they are in fact genetically and geographically distinct species. There are numerous records of C. equilibra recorded in New Zealand, from systematics checklists ( Kirk, 1878) to ecological and biosecurity evaluations, such as Ahyong & Wilkins (2011). Until a detailed study can be carried out to re-examine previous records, and, ideally with resampling of fresh material, C. equilibra is provisionally treated as part of the New Zealand fauna. It has been observed that C. equilibra has potentially a higher dispersal ability and thus have a naturally wide distribution as it has been observed for long periods in the water column and has a huge potential to occupy artificial substrates (Guerra-García, pers comm.) and therefore cannot yet be excluded from New Zealand’s fauna without further data.

Due to the uncertain distribution patterns in New Zealand, this species has been omitted from the map despite forms being known from New Zealand. McCain (1979) started moving different forms out of synonymy with C. equilibra showing very similar morphological forms previously documented as that species.

Molecular sequences presented here ( Fig. 2 ) are from elsewhere in the world, and, as mentioned above, it was beyond the scope of this paper to fully evaluate the status of New Zealand records of C. equilibra . The sequences noted here in the analysis demonstrate the distance from Caprella equilibra sensu lato of Caprella novaezealandiae (resurrected here), which Thomson & Chilton (1886) had synonymised under C. equilibra .

Figures

FIGURE 2. Maximum likelihoodphylogram basedon COIsequence data.Support values areshown on each branch:approximate Likelihood Ratio Test (aLRT, %) and ML bootstrap (%) values above, and Bayesian PP values below. Only values greater than 80% (aLRT), 80% (bootstrap) and 0.9 (PP) are shown; all support values are shown if two support methods for a clade reach the cutoff value. Sequences from New Zealand taxa in bold.