Protella gracilis Dana, 1853

Takeuchi, Ichiro, Lim, Jacqueline Hui Chern & Inoue, Yuki, 2014, Description of two species of Protella Dana, 1852 (Crustacea: Amphipoda): P. gracilis Dana, 1853, from Balabac Strait, the Philippines, and P. amamiensis, new species, from southern Japan, Raffles Bulletin of Zoology 62, pp. 53-65 : 54-57

Protella gracilis Dana, 1853

( Figs. 1 , 2 )

Protella gracilis Dana, 1853: 812–813, 1855: 16 , pl. 54 fig. 2a–f; Bate, 1862: 352, pl. 55 fig. 5; McCain & Steinberg, 1970: 69–70 (in part).

Material examined. Types, 1 male (pereonites 3–7) and 1 immature female, MCZ 1536 , from U.S. Explor. Expedition .

Type locality. Balabac Strait , the Philippines , 56.7 meters and Singapore?

Description. Male, MCZ 1536. Body length,> 11.17 mm. Head, pereonite 1 and pereonite 2 detached/missing. Pereonite 3, 3.27 mm, dorsally smooth. Pereonite 4, 3.27 mm, equal length with pereonite 3 with one rounded anterodistal projection and one rounded dorsodistal projection. Pereonites 5–7 dorsally and laterally smooth. Pereonite 5, 3.17 mm. Pereonite 6 shortest, 0.63 mm. Pereonite 7, 0.83 mm.

Pereon. Gnathopods 1–2 missing. Pereopod 3, 0.15× pereonite 3, uniarticulate with 4 marginal setae and 1 long facial seta near distal margin, apically with 3 setae. Pereopod 4 shorter than pereopod 3 (0.7× shorter), 0.1× pereonite 4, uniarticulate with 3 marginal setae and 1 long facial seta at distal margin, apically with 3 setae. Pereopods 5–7 well developed, becoming more robust progressively. Pereopod 5 basis subequal with ischium and merus combined, with short distal setae on inner and outer corner; ischium with setae on anterodistal corner; merus slightly expanded at posterodistal corner with tuft of setae; carpus longest, 1.7× merus with row of setae on entire inner margin, distally with one small rounded projection, posterodistally with tuft of setae; propodus subequal in length with basis, with a pair of proximal grasping spines, followed by fine marginal setae on palm and outer margin, distally with group of longer setae; dactylus well developed, falcate, length subequal with merus. Pereopod 6 basis with scarce marginal setae, distally with setae on inner and outer corner; ischium with setae on both distal corners; merus expanded at posterodistal corner, with tuft of setae and few fine setae on inner margin; carpus 1.4× longer than merus, inner margin with row of marginal setae, distally with one small projection, posterodistally with tuft of setae; propodus 1.3× carpus, with a pair of grasping spines near proximal end of palm, palm with fine setae, outer margin with fine setae, becoming more dense and long moving towards distal margin of propodus; dactylus falcate. Pereopod 7 basis subequal in length with basis of pereopod 5, with short distal setae on inner and outer corner; ischium with setae on inner and outer distal corner; merus expanded at posterodistal corner with tuft of setae; carpus 1.3× merus, inner margin with row of marginal setae, distally with one small triangular projection, posterodistally with tuft of setae; propodus with a pair of grasping spines at proximal end of palm, inner and outer margin of propodus with marginal setae, distally with longer setae; dactylus well developed, falcate, subequal in length to dactylus of pereopod 5.

Pleon. Penes large, bilobate, positioned medially. Tuft of 4 setae present between penes and uropod 1. Uropod 1 subconical; peduncle with a group of ca. 8 long setae, ramus triangular, subequal in length with peduncle, equipped with 3 long distal setae and 2 short apical setae and a small, knobliked appendage, 0.2× ramus, on distal margin. Uropod 2 ramus very vestigial, confused with abdomen. Telson round.

Female (immature). MCZ 1536. Body length 6.77 mm. Head length 0.50 mm and pereonite 1, 0.25 mm; head and pereonite 1 fused, suture present; head smooth, no dorsal or lateral projections; eye round, distinctive. Pereonite 2, 1.05 mm, dorsally smooth. Pereonite 3, 1.45 mm. Pereonite 4, 1.30 mm. Pereonite 5, 1.38 mm. Pereonite 6, 0.48 mm. Pereonite 7, 0.36 mm. Antenna 1 long, length 0.9× body length; peduncular article 2 longest, 2.1× peduncular article 1; peduncular article 3, 0.73× peduncular article 2; flagellum 0.95× peduncular length with>14 articles, proximal article composed of 3 articles. Antenna 2 slender, 0.39× antenna 1; flagellum 0.25× peduncle, 2-articulate, article 2, 0.33× article 1.

Pereon. Gnathopod 1 basis subequal with ischium, merus and carpus combined. Gnathopod 2 begins 1/4 along anterior margin of pereonite 2, basis subequal in length with pereonite 2, longer than ischium, merus, and carpus combined; propodus 1.2× basis, longer than wide, palm of propodus, proximal projection with 1 grasping spine followed by 2 small projections, distally with 1 small projection and a sinus, followed by one larger triangular projection; dactylus slightly curved, fitting onto palm. Gill 3 length 0.35× pereonite 3, oval. Pereopod 3 subequal with gill 3 length, 0.30× pereonite 3, 1-articulate with 3 distal setae. Gill 4 length 0.38× pereonite 4, oval, subequal with gill 3. Pereopod 4, 0.25× pereonite 4, 0.64× gill 4, smaller than pereopod 3, 1 articulate with 4 distal setae. Pereopods 5–7 well developed, becoming more robust progressively. Pereopod 5 basis with 3 setae at distal margin; carpus subequal in length with merus; propodus subequal in length with basis, proximal projection with a pair of grasping spines, distal margin of propodus with 4 short and long setae; dactylus falcate. Pereopod 6 basis with 3 setae on anterodistal and posterodistal corner; merus with 2 setae on posterodistal corner, carpus with one projection distally; propodus subequal in length with basis, proximal projection with a pair of grasping spines, distal margin of propodus with 8 short and long setae; dactylus falcate. Pereopod 7 basis subrectangular; merus with 2 setae on posterodistal margin; carpus with one projection distally; propodus proximal projection with a pair of grasping spines; distal margin of propodus with 8 short and long setae; dactylus falcate.

Remarks. Protella gracilis [sensu lato] was originally described based on a mature male and female collected from Balabac Strait, south of the Philippine Islands in the tropical Indo-Pacific by Dana (1853). However figures of the types were only provided in Dana (1855), showing a mature male with a short portion of antenna 1 flagellum, pereopod 7 (propodus to dactylus) and a mature female with a short portion of antenna 1 flagellum. Figures of the head and pereonite 1 of another variety as well as a portion of a female gnathopod 2 (carpus to dactylus) were also provided ( Dana, 1855). A few years later, Bate (1862) also cited the descriptions and figures of Dana (1853, 1855), followed by Mayer (1882) who referred to the distribution record of Dana (1853) in his description of Protella gracilis [sensu lato]. This species was then cited in Mayer (1890), whereby the author provided considerably more detailed figures of Protella gracilis [sensu lato] than those of Dana (1853, 1855) that were based on specimens collected from another locality, Misaki, situated near the opening of Tokyo Bay, central Japan. Mayer (1890) also stated that the present species was distributed in two localities: Balabac Strait, Cebu, Lapinig (on the north coast of Bohol), the Philippines, and Misaki, central Japan (about 48 km south of Tokyo).

Arimoto (1929) and Hiro (1937) described P. gracilis [sensu lato] from Tateyama Bay, near the opening of Tokyo Bay, and from Tanabe Bay, Kii Peninsula, central Japan, respectively. McCain & Steinberg (1970) then recorded the type locality for this species as “Balabac Strait, Philippine Islands, 56.7 meters” and other records as “warm water species from Indo-Pacific Islands, Philippine Islands, and southern Japan ”. Following that, Arimoto (1976) cited the descriptions and figures of Arimoto (1929) and reported similar “ type locality” and “other records” as those of McCain & Steinberg (1970). In addition, the authors also provided detailed distribution data along the Japanese coasts.

The identification and records of P. gracilis [sensu lato] by the various authors above have been accepted thus far. Nevertheless, in recent years, Spalding et al. (2007) proposed a new global system for coastal and shelf areas called the “Marine Ecoregions of the World”, a brainchild resulting from the lack of detailed and comprehensive biogeographic system to classify the oceans. This system encompasses 232 ecoregions, in 62 provinces from 12 realms. According to this new system, Balabac Strait is situated in the Central Indo-Pacific (realm), Western Coral Triangle (province), Palawan/ North Borneo (ecoregion), while, Misaki is situated in the Temperate Northern Pacific (realm), Warm Temperate Northwest Pacific (province), Central Kuroshio Current (ecoregion), a totally different realm from the type locality of P. gracilis in the Central Indo-Pacific. According to Spalding et al. (2007), each realm coincides with high levels of endemism, and this prompted the present authors to revise records of P. gracilis [sensu stricto] from the Philippines and P. gracilis [sensu lato] from Japan. Furthermore, Arimoto’s (1929) and Hiro’s (1937) records of P. gracilis [sensu lato] from Tateyama Bay and Tanabe Bay, Japan, are both situated in the same realm and province as Misaki, Japan.

Types that were deposited in the MCZ were loaned for comparisons with specimens from Japan. The types consist of a larger but damaged male and a smaller immature female plus six detached pereopods. In order to determine the origin of these pereopods (whether it belongs to the mature male or immature female), they were separated into 2 groups according to size (2.60–2.86 mm and 3.48–3.52 mm); the 3 larger pereopods were inferred to belong to the larger male while the 3 smaller ones to the immature female .

Dana (1853), provided the “length” of this species as “seven-eighths of an inch” (p. 813), which corresponds to 2.2 cm. But two years later, Dana (1855) also provided a body length on a caption for plate 54 and noted “ Protella gracilis , male, enlarged two and a half diameters; a’, same, natural size, on a coral” (“diameters” should be cm). The body length of “a” on plate 54 is 16 mm (10.5 mm from pereonites 3–7), while “length” in Dana (1853, 1855), was 2.2–2.5 cm (including antennae and body somites). Thus, among the two type specimens, i.e., the larger male of 11.17 mm (from pereonites 3–7) described here is closer to the male described and figured in Dana (1853, 1855). However, the mature female that was described and illustrated in Dana (1853, 1855) is missing; therefore the immature female ( Fig. 2 ) was described and illustrated here instead. In the vial containing the type specimens, the locality of the types were labelled as “ Singapore? / Balabac Str.” although the distribution of this species from Singapore was never recorded clearly in any taxonomical studies ( Dana 1853, 1855, Bate 1862, Mayer 1882, 1890). Furthermore, McCain & Steinberg (1970) recorded the distribution of this species as “Warm water species from the Indo-Pacific Islands, Philippine Islands, and southern Japan ” in their species catalogue of Caprellidae of the world. As a result, it is likely that the smaller immature female type specimen, was collected from Singapore and placed in the vial of the types after Dana (1853, 1855), instead of the original mature female which was described and illustrated in Dana (1853, 1855).

Figures

Fig. 1. Protella gracilis Dana, 1853, type, male,>8.85 mm, MCZ 1536, Balabac Strait, the Philippines.

Fig. 2. Protella gracilis Dana, 1853, type, immature female, 6.77 mm, MCZ 1536, Balabac Strait, the Philippines, 56.7 meters or Singapore?