A new species of Aciconula (Amphipoda, Senticauda, Caprellidae) from Sultan Iskandar Marine Park, Malaysia

Abstract A new species of caprellid, Aciconulatinggiensis (Amphipoda, Senticaudata, Caprellidae) was discovered from Pulau Tinggi, Sultan Iskandar Marine Park (SIMP), South China Sea, Malaysia. The new Malaysian species can be distinguished from the other Aciconula species by the combination of the following characters: 1. the presence of a very small suture between head and pereonite 1; 2. antenna 1 flagellum with 4 articles; 3. inner lobe of lower lip unilobed; 4. gnathopod 2 palm of propodus with a large proximal projection (stretching from the proximal margin of the palm to nearly mid-way of palm); 5. pereopods 3–4 with 2 articles (article 1 subrectangular, article 2 conical or tapering at the tip with 1 plumose seta and 2 normal setae) and; 6. pereopod 5 covered with relatively dense and long setae. An updated identification key for the five known species in the genus, including information on the respective geographical distribution and habitat, is presented.


Introduction
The amphipod genus Aciconula was established by Mayer (1903) with A. miranda Mayer, 1903 as its type species. However, the exact diagnostic characteristics of this genus were unclear because the types described by Mayer (1903) for this genus were both females (that were collected from three different localities: Singapore, Malaysia and Koh Krau, Thailand) and only figures of the whole body, pereopod 3, pereopod 4, pereopod 5, mandibular palp article 3 and maxilliped were drawn. Mayer (1912) then described a male but the abdomen and mouthparts were also not included. Nevertheless, general morphology of the male specimen agrees well with the type and the rest of the appendages such as pereopods 3 to 7 are also similar to the female. The abdomen was also left out. Following that, Arimoto (1976) referred to Utinomi's (1969) description based on specimens collected from Kii Peninsula, Japan and revised its generic diagnosis. Subsequently, three more species of Aciconula were reported; Aciconula acanthosoma Chess, 1989 from southern California; A. australiensis Guerra-García, 2004 from Western Australia and most recently A. tridentata Guedes-Silva & Souza-Filho, 2013 described from Pernambuco, Brazil.
The Sultan Iskandar Marine Park (SIMP) is one of Malaysia's marine protected areas located 15-65 km from Mersing, off the north-east coast of the Johor State, Malaysia in the South China Sea. This body of water covering an area of about 8000 hectares holds one of the most diverse marine ecosystems on the east coast of Peninsular Malaysia, ranging from sandy shores, coral reefs, mangroves, estuaries, mudflats to seagrass and open water habitats (see Harborne et al. 2000;Japar Sidik and Muta Harah 2003;Maritime Institute of Malaysia 2006;Japar Sidik et al. 2006;Azman et al. 2008;Japar Sidik and Muta Harah 2011;Lim et al. 2015). The SIMP (Fig. 1) consists of 13 main islands namely Pulau Harimau, Pulau Mensirip, Pulau Goal, Pulau Besar, Pulau Tengah, Pulau Hujung, Pulau Rawa, Pulau Tinggi, Pulau Mentinggi, Pulau Sibu, Pulau Sibu Hujung, Pulau Pemanggil and Pulau Aur. This paper continues the previous significant contributions on the biodiversity of SIMP and its vicinity including Othman and Azman (2007), Lim et al. (2010), Gan et al. (2010), Melvin (2011), Lim et al. (2012), Azman and Othman (2013), Chew et al. (2014), Tan et al. (2014, 2015, Lim et al. (2015), Chew et al. (2016) Lim et al. (2017) and Tan and Azman (2017, 2018) on marine crustaceans. The present paper also deals with the detailed description of this new species; an updated identification key to all the known Aciconula species is also given.

Sampling
The caprellids examined in this study were collected from an artificial reef of Kampung Pasir Panjang, Pulau Tinggi, Sultan Iskandar Marine Park (SIMP) at 9-11 m water depth ( Fig. 1). Collections were made by SCUBA; hosts (stinging hydroids) together with attached caprellids were put into fine mesh bags. Specimens used for morphological descriptions were preserved in 4% formaldehyde before examination.

Laboratory procedures
Appendages were dissected from the right side of the specimens and stored in several semi-permanent slides mounted in glycerol and then drawn under an optical microscope (Olympus BX43) and a stereomicroscope with a camera lucida. The drawings were digitized on Adobe Illustrator CS3 using the methods described in Coleman ( Aciconula tinggiensis sp. nov. http://zoobank.org/DEE62918-DA9C-4090-9245-872B7D982DBD Figs 2-5 0.7 × pereonite 2; ischium and merus subquadrate; carpus triangular; propodus 1.6 × as long as wide, 1.3× length of basis, palm with large proximal projection (stretching from proximal margin of palm to nearly mid-way of palm), provided with one robust grasping spine proximally, a small triangular projection medially and ending with a triangular projection provided with 1 seta, distal margin of palm with 1 triangular projection; dactylus falcate, fitting on palm.

Remarks.
Considering the four reported species from the genus Aciconula, A. tinggiensis sp. nov. is most similar to A. australiensis in terms of antenna 1 and 2, gnathopod 1, mouthparts (maxilliped and maxillas) and abdomen. Pereopods 3 and 4 of the male are also similar except for the presence of a seta on article 1 of A. australiensis. The Malaysian specimen differs from the Australian counterpart in terms of the absence of 1) a head projection (present in A. australiensis); 2) inner lobe of lower lip unilobed (A. australiensis bilobed); 3) gnathopod 2 propodus proximal projection shallow and wide, about 1/2 of palm (A. australiensis more pronounced, about 1/3 of palm); 4) pereopod 3 of female similar to the male with only 2 articles while A. australiensis shows sexual dimorphism with 3 articles; 5) longer (articles 4 and 5 about 2 × longer) pereopod 5, 0.43 × body length, terminal article with one plumose seta and generally more setose (A. australiensis only 0.23 × body length; terminal articles with one normal seta); 6) mandibles with setal formula of 1-3-1 (setal formula 1-4-1 in A. australiensis).
Aciconula acanthosoma Chess, 1989 clearly differs from the Malaysian specimen firstly by its numerous dorsal projections throughout its body, maxilliped inner lobes more robust and wide, terminally with one tooth and three setae (slender with two normal setae in A. tinggiensis sp. nov.), maxilla 2 with very short terminal setae and mandibles with large, well-developed molar and palp with setal formula of 1-6-1. Apart from its body armature and mouthparts, it also varies in terms of appendages such as gnathopod 2 (basis with a distolateral projection, palmar margin of propodus with a proximal projection followed by a strong spine and a deep sinus), pereopod 5 with short and fine dense setae (setae longer and less extensive in A. tinggiensis sp. nov. ), and abdomen with one pair of well-developed, 1-articulate abdominal appendage. The species from southern California is also much larger than the present specimen (3.3 × longer) and the other two existing species from the Indo-Pacific. In spite of this, A. acanthosoma does have a few similarities in pereopods 3 and 4 with 2 articles and article 2 conical (except for the 3 terminal plumose setae) and pereopods 6 and 7 with 7 articles and grasping structure on article 6. There is more dissimilarity in these two species than similarities. According to Guerra-García (2004), A. acanthosoma could be placed in a new genus based on the abdominal appendages and several mouthparts but presently there is only one genus, which exhibits the soft and flexible character of pereopod 5, therefore it is retained in the genus Aciconula.
The female specimen of A. tinggiensis sp. nov. was primarily used to compare with Mayer's (1903) type and Mayer's (1912) account of A. miranda because he only provided more detailed description and figures of females compared to males. Females of A. tinggiensis sp. nov. are similar to A. miranda Mayer, 1903 based on a single dorsal projection on pereonite 2, antenna 1 flagellum with 4 articles, pereopod 4 with 2 articles (similar in shape and terminally with one plumose seta), and its gill shape. However, the present species (female) differs from A. miranda Mayer, 1903 in its pereopod 5 which has longer but less dense setae (more densely setose in A. miranda); pereopod 3 with 2 articles (3 articles in A. miranda); and pereopod 3 article 2 is conical and short (article 2 is subcylindrical with several seta marginally). Mouthparts of A. tinggiensis sp. nov. for males and females are similar therefore only the male mouthparts are used for comparison with Mayer's (1903) description and figures. Aciconula tinggiensis sp. nov. differs from A. miranda in terms of the setal formula of the mandibular palp 1-3-1 (setal formula 1-7-1 in A. miranda) and maxilliped outer plate with only 3 distal setae (maxilliped entire inner margin lined with setae in A. miranda).  Aciconula tridentata Guedes-Silva & Souza-Filho, 2013 reported from Brazil, is similar to the present species in the: 1) presence of a small sharp median forward projection of the head; 2) pereopods 3 and 4 of male with two-articles, and absence of abdominal appendages but differs in the length of the outer plate of maxilliped (longer in Aciconula tinggiensis sp. nov. reaching the mid-length of palp article 2), the sculpturing on the palm of male gnathopod 2, (with a 3-dentate projection, followed by a large excavation leading to a projection with two sharp processes in A. tridentata) and number or articles in female pereopods 3 and 4 (pereopod 3 4-articulate and pereopod 4 3-articulate in A. tridentata ) In conclusion, Aciconula tinggiensis sp. nov. described here is recognized as distinct from the four existing species of this genus based on these combination of characters; 1) a very small suture between head and pereonite 1; 2) antenna 1 flagellum with 4 articles, its setal formula of 1-3-1; 3) unilobed inner lobe of lower lip with pair of ducts on outer lobe; 4) gnathopod 2 palm of propodus with a large proximal projection, (stretching from the proximal margin of the palm to nearly mid-way of palm) provided with one robust grasping spine proximally, a small triangular projection medially and ending with a triangular projection provided with 1 seta; 5) pereopods 3 and 4 with 2 articles (article 1 subrectangular, article 2 conical or tapering at the tip with 1 plumose seta and 2 normal setae); 6) pereopod 5 covered with relatively dense and long setae; and 7) abdomen region with penes situated medially, uropod 2 degenerated into 4 setae, uropod 2 degenerated into 1 seta medially and 2 setae distally.
Habitat. The specimens have been found from 10-12 meters deep, living on stinging hyroids.
Distribution. Currently only known from Pulau Tinggi, Johor, Malaysia.
and Marine Park Section, Department of Fisheries, Malaysia. This study was supported by the Universiti Kebangsaan Malaysia research grant (LIV-2015-02) and the Japan Society for the Promotion of Science (JSPS) Core-to-Core Program (B.Asia-Africa Science Platforms).