Caprella pitu Sánchez-Moyano & García-Asencio & Guerra-García 2014, sp. nov.

Caprella pitu sp. nov.

(Figures 9–14)

Holotype male (MNCN 20.04 /9211), Allotype female (MNCN 20.04 /9212), Paratypes: 7 males (MNCN 20.04 /9213-19), 4 females (MNCN 20.04 /9220-23).

Five males (MNCN 20.04 /9224), 5 females (MNCN 20.04 /9225), collected from Cerro Pelón (Isla Isabel), México, 25 m, on gorgonians (Pacifigorgia cf. agassizii); St1: 108 males, 110 females, 96 juveniles; St 2: 4 males, 1 juveniles; St 7: 212 males, 245 females, 326 juveniles; St 8: 272 males, 356 females, 446 juveniles; St 9: 17 males, 18 females; St 10: 7 males, 19 females.

Isla de Los Pájaros (Mazatlán), México, 3–6 m, on gorgonians (Leptogorgia rigida and Leptogorgia peruviana).

The species is dedicated to Emilio Sánchez ‘Pitu’, son of the first and second authors; used as a noun in apposition.

Head with rostrum short and triangular. Body stout and wide with tiny tubercles. Peduncle of antenna 1 scarcely setose. Gnathopod 2 basis short with an anterior carina; palm of propodus with a acute projection medially and a rounded distal one. Pereopod 5–7 with carpus elongated and palm of propodus without grasping spines.

Male holotype. Body length: 8.7 mm.

Lateral and dorsal view (Figure 9): Head rostrum short and triangular. Body stout and slightly flattened, with numerous tiny tubercles. Pereonites 2–7 decreasing in length respectively. In dorsal view, body wide, with lateral and flat expansions especially in pereonites 3 and 4 (about as wide as long). Strong pleural development.

Gills (Figure 9): Present on pereonites 3–4, rounded.

Mouthparts (Figure 10): Upper lip symmetrically bilobed with small setulae apically. Mandibles without palp, mandibular molar process strong, incisor and lacinia mobilis five-toothed, left and right mandible with three and two pectinated setae, respectively. Lower lip with inner lobes well-demarcated, inner and outer lobes setose apically. Maxilla 1 outer lobe with seven robust setae, distal article of the palp with six apical robust setae and 12 lateral setae. Maxilla 2 inner lobe oval and outer lobe rectangular, about 1.5 times as long as the inner lobe. Maxilliped inner plate oval with two robust and short setae and eight plumose setae; outer plate with four robust setae and eight long setae; palp four-articulate, with numerous long setae, article 4 with row of setulae on its grasping margin.

Antennae (Figure 9 and 11): Antenna 1 about half of body length; peduncle scarcely setose; article 1 and 2 enlarged; flagellum nine-articulate. Antenna 2 flagellum two-articulate and setose, carrying robust setae in the distal article; swimming setae present.

Gnathopods (Figure 11): Gnathopod 1 basis as long as ischium, merus and carpus combined, with a anterior denticulate carina and tiny tubercles; propodus palm with two proximal grasping spines and setae along the palm; dactylus elongate with rows of setulae. Gnathopod 2 inserted in the middle of pereonite 2 and with numerous tiny tubercles along all surface; basis short, about one-sixth as long as total length of gnathopod, with an anterior carina; propodus oval, length about 1.5 times width, palm of propodus without grasping spines, with an acute projection medially and a rounded distal one; dactylus short and wide with tiny tubercles.

Pereopods (Figure 12): Pereopods 3 and 4 absent. Pereopod 5–7 robust and increasing in length; basis, merus and carpus with a posterior carina with rows of setae; carpus elongated; palm of propodus without grasping spines; dactylus short and robust.

Penes (Figure 12): Situated medially, rounded.

Abdomen (Figure 12): With a pair of two-articulated appendages, a pair of lateral lobes and a single dorsal lobe.

Allotype female. Body length: 5.2 mm. Similar to male (Figures 9 and 11). Body wide, especially in pereonites 3 and 4 (width about twice length). Oostegites present, being slightly setose on pereonite 3. Antenna 1 peduncle not enlarged. Gnathopod 2 similar to male but propodus palm with a minor excavation between medial and distal projections. Abdomen with a pair of lateral lobes and a single dorsal lobe (Figure 12).

Most of the morphological characters from C. pitu were rather constant. However, there are slightly differences between populations from the type locality and other sites based especially on body length and the morphology of the pereopods 5–7 (Figures 9 and 13). In the type locality (Mazatlán), the individuals were more robust and longer than in other localities further south such as Isla Isabel and Bahía Banderas (length varied from 8.7 to 7.8 mm in males, and 5.2 to 4.3 mm in females). The length of the pereopods was apparently larger in specimens from Isla Isabel and these specimens were referred to as a ‘long-leg’ form. These differences are based mainly on the ratio between width and length of the merus and propodus (independently for males or females), which gives a relative appearance of greater length. For example, the propodus of pereopod 7 was one-third as wide as long in Mazatlán versus one-quarter in Isla Isabel; and the carpus was one-half and one-third, respectively (Figures 12 and 14).

The new species is close to Caprella penantis Leach, 1814 in the general shape of the body. Caprella penantis is considered a cosmopolitan species with remarkable intraspecific morphological variation (Mayer 1903; McCain 1968; Laubitz 1972; Cabezas et al. 2010) and the taxonomic status of the different forms has been controversial for years (Cabezas et al. 2013).

Although C. penantis has been cited through the Pacific Ocean, the nearest record to the Mexican Pacific coast was cited by Laubitz (1972) from Monterey Bay but without location, date of collection or drawings. According to Watling and Carlton (2007), C. penantis could be an introduction to the California coast. Laubitz (1972) wrote that specimens of C. penantis from California were less setose and smaller than specimens from the Atlantic, but they showed the typical stout body and strong pleural development. In fact, our specimens are clearly smaller than C. penantis (8.7 mm as opposed to 14 mm). Recently, a genetic and morphological study on the C. penantis group has refuted the cosmopolitan distribution of this species and has highlighted the existence of at least four species (Cabezas et al. 2013). Our specimens were included in this study as ‘ C. penantis from Mexico’ and the results demonstrated that it represents a different species from the C. penantis group. Additionally, Cabezas et al. (2013) pointed out the reciprocal monophyly of the two forms of C. pitu and suggested that the absence of gene flow between populations from Mazatlán and Isla Isabel could be an indication of the existence of two distinct species. However, we have considered these as a single species due to the scarcity of morphological differences between both forms and until more detailed studies can be carried out.

Caprella pitu and C. penantis can be distinguished mainly on the basis of the following characteristics: male gnathopod 2 propodus less setose and with medial projection in C. pitu and with proximal projection in C. penantis (or without projection in some varieties); female gnathopod 2 propodus similar to male in C. pitu, with medial projection, small excavation and distal rounded projection, while in C. penantis female gnathopod 2 propodus is different to male with palm slightly convex with a pair of proximal grasping spines; propodus periopod 5–7 without proximal grasping spines in C. pitu, versus with grasping spines in C. penantis; carpus of periopod 5–7 elongate in C. pitu (half as wide as long in pereopod 7) and subquadrate in C. penantis.

McCain (1968) reported the absence or reduction of grasping spines on the propodus of pereopods 5–7 in specimens of C. penantis taken on the gorgonian Leptogorgia from Florida. Caprella pitu has been found exclusively on gorgonians and, in agreement with Aoki and Kikuchi (1995) for Caprella andreae, the adaptation to an ecologically isolated habitat such as gorgonians could have led to its speciation. Potentially, the material of McCain (1968) lacking grasping spines could also belong to a different species.

Another morphologically similar species from the California coast is Caprella natalensis Mayer, 1903 (= C. angusta in Dougherty and Steinberg 1953, and Laubitz 1970). It is considered to be the Pacific coast equivalent of C. penantis (Laubitz 1972) and it is very abundant along the California coast (Dougherty and Steinberg 1953; Martin 1977; Watling and Carlton 2007). The main differences between C. pitu and C. natalensis are basically similar to the differences with C. penantis. Additonally, the three species can be differentiated because pereonite 5 is usually longer than pereonites 6 and 7 in C. natalensis whereas in C. pitu and C. penantis it is shorter (three pereonites are subequal). Pleural development is not present in adults of C. natalensis.

Caprella pitu has been found exclusively clinging to several species of gorgonians (Leptogorgia sp., Leptogorgia rigida, Leptogorgia peruviana, Pacifigorgia sp and Pacifigorgia cf. agassizii) from 2 to 25 m deep. It was more abundant on L. rigida and P. cf. agassizii (some samples with more than 500 individuals). In some samples from Mazatlán, it shared the substrates with other species such as Aciconula acanthosoma and Caprella mendax; however it was the only species in the samples from Isla Isabel and Bahía Banderas.

The typical form has been collected from Mazatlán (St1, Isla de los Pájaros; St2, Isla Venado), whereas the ‘long-leg’ form is known from Isla Isabel (St7, Las Monas; St8- Cerro Pelón) and Bahía Banderas (St9- Islas Marietas; St10, Los Arcos).