Aciconula acanthosoma Chess, 1989

Sánchez-Moyano, J. E., García-Asencio, I. & Guerra-García, J. M., 2014, Littoral caprellids (Crustacea: Amphipoda) from the Mexican Central Pacific coast, with the description of four new species, Journal of Natural History 49 (1), pp. 77-127 : 78-84

Aciconula acanthosoma Chess, 1989 ,

( Figure 2 )

St 8 Cerro Pelón Isla Isabel 21º51 ′ 15.58 ″ N 25 Hydroids (Thecata and Aciconula acanthosoma , 7

105º53 ′ 34.65 ″ W athecata), gorgonians Paracaprella carballoi sp.

( Leptogorgia peruviana , L. nov., Caprella pitu sp. nov.,

rigida , Leptogorgia sp., Caprella equilibra , Liropus

Muricea cf. californica , isabelensis sp. nov.

Pacifigorgia cf agassizii,

Pacifigorgia sp.), bryozoan

( Bugula sp.)

St 9 Islas Bahía 20º42 ′ 01.75 ″ N 10 Gorgonians Caprella pitu sp. nov. 1 Marietas Banderas 105º33 ′ 50.03 ″ W

St 10 Los Arcos Bahía 20º33 ′ 02.35 ″ N 12 Gorgonians Caprella pitu sp. nov. 1 Banderas 105º17 ′ 35.82 ″ W

Material examined

St1: 41 males, 23 females, 5 juveniles; St2: 2 males; St6: 3 males, 6 females, 5 juveniles; St7: 11 males, 7 females; St8: 30 males, 22 females, 21 juveniles.

Remarks

The specimens are in agreement with the original description by Chess (1989) with material from Santa Catalina island (California). Typical features of the species are present such as all pereonites dorsally spinose or basis of gnathopod 2 with acute distolateral projection. However, the studied specimens have some intraspecific variation in the head projection pattern compared with the four prominent curved projections from the material type: two anterior prominent and two posterior reduced ones (about one-third of the length of anterior ones). In some specimens from Mazatlán (St1 and St2), one or two posterior projections can be absent or very reduced. The length is slightly smaller in Mexican A. acanthosoma (male to 5.5 mm, female to 4.5 mm) than in the type material (male and female to 7.3 mm and 6.3 mm, respectively). Additionally, pereonites 3 and 4 have fewer lateral spinose projections. Other generic characters are present such as the six-articulate pereopod 5, elongate, with long setae (although slightly less setose than in the original description) and the distal article reduced to a small cone, instead of the typical dactylus.

Habitat

Aciconula acanthosoma was found attached to different species of Thecata and Athecata hydroids, gorgonians ( Leptogorgia rigida , Leptogorgia peruviana , Pacifigorgia sp., Pacifigorgia cf. agassizii, Muricea sp., Muricea cf. californica ), a bryozoan Bugula sp., and the seaweed Zonaria cf. farlowii with epiphytic hydroids. Chess (1989) collected specimens from different substrata but they were more abundant on seaweeds (e.g. Cystoseira neglecta , Sargassum palmeri or Zonaria farlowii ). In the present study, however, they were more abundant on sessile animals, being absent in most of the sampled seaweeds. Although in temperate ecosystems the highest densities of caprellids can be found in seaweeds (Guerra- García 2001), in the tropical region caprellids are mainly associated with hydroids and secondarily with gorgonians and other corals (Guerra-García 2006; Scinto et al. 2008). The unique available seaweed as substrate, Zonaria cf. farlowii , had a high coverage of hydroids which could indicate a strong relationship between A. acanthosoma and cnidarians.

According to Chess (1989), A. acanthosoma feeds on sponges and ascidians. Recently in a study on feeding habits of Pacific Mexican caprellids, Alarcón-Ortega et al. (2012) reported that this species feeds mainly on detritus (75% of the gut content), crustaceans (17.5%) and hydroids (6.7%). In agreement with Guerra- García and Tierno de Figueroa (2009), the caprellid species with molars in mandibles (such as genus Aciconula ) are characterized by a diet mainly based on detritus, although in general caprellids are rather opportunistic because they can change their feeding habits depending on the substrates to which they cling.

Distribution

Type locality. Santa Catalina island, California ( USA) ( Chess 1989). Other records: Mazatlán and Isla Isabel, Pacific coast of México ( Alarcón-Ortega et al. 2012).

Figures

Figure 2. Aciconula acanthosoma Chess 1989. Lateral view. Scale bar: 1 mm.