Caridina spongicola Zitzler & Cai, 2006

Rintelen, Kristina von & Cai, Yixiong, 2009, Radiation Of Endemic Species Flocks In Ancient Lakes: Systematic Revision Of The Freshwater Shrimp Caridina H. Milne Edwards, 1837 (Crustacea: Decapoda: Atyidae) From The Ancient Lakes Of Sulawesi, Indonesia, With The Description Of Eight New Species, Raffles Bulletin of Zoology 57 (2), pp. 343-452 : 405-410

Caridina spongicola Zitzler & Cai, 2006

( Figs. 36–38 ; Table 14)

Caridina spongicola Zitzler & Cai, 2006: 271 , Figs. 1-3 . (type locality: outlet bay of Lake Towuti)

Caridina spongicola – von Rintelen et al., 2007b: 262, Figs. 1 , 2008: 2244, Table 1.

Material examined. – Holotype: ovigerous female (eggs without eyes), cl 2.4 mm ( MZB Cru 1559), Lake Towuti , west shore, outlet bay, west of Cape Tokaluku, 02°47.261'S, 121°23.17'E, loc. 119-04, on sponge, coll. K. & T. von Rintelen, 29 Jul.2004.

Paratypes ( Lake Towuti ) – 3 females (cl 2.0- 2.4 mm) ( MZB Cru 1560); 2 ovigerous females (cl 2.4-2.8 mm) ( MZB Cru 1560) , same data as holotpye; 5 males (cl 1.8-2.3 mm)( MZB Cru 1560) , same data as holotype; 11 females (cl 1.9-2.6 mm)( ZMB 29027, some SEM material), 2 ovigerous females (cl 2.4 mm)( ZMB 29027, some SEM material), Lake Towuti , west shore, outlet bay, west of Cape Tokaluku, 02°47.32'S 121°23.38'E, loc. 52-03, on sponge, coll. K. & T. von Rintelen, 21 Sep.2003 ; 4 males (cl 1.9-2.1 mm)( ZMB 29027, some SEM material) , same data as previous sample; 9 males (cl 2.1-2.4 mm), 12 females (cl 2.2-2.6 mm), 6 ovigerous females (cl 2.4-2.6 mm)( ZRC 2006.0114 ), Lake Towuti , west shore, outlet bay, west of Cape Tokaluku, 02°46.277'S 121°21.83'E, loc. 02-05, on sponge, coll. Y. Cai, K. & T. von Rintelen, 3 Jan.2005 .

Others (Lake Towuti)) – 170 ex. ( MZB Cru 1845, n=75; ZMB 29125, n=95 and several juveniles), same data as paratypes of ZRC 2006.0114 , loc. 02-05, on sponge ; 23 ex. ( ZMB 29313, n=23 and several juveniles), west shore, outlet bay, 02°47.345'S, 121°23.356'E, loc. 14-05, on sponge, coll. K . & T. von Rintelen, 9 Jan.2005 ; 12 ex. ( ZMB 29129, n=12 and several juveniles), west shore, outlet bay, 02°47.623'S, 121°22.724'E, loc. 13-05, on sponge, coll. K . & T. von Rintelen, 9 Jan.2005; ( ZMB 29294, several juveniles) , same data as holotype, loc. 119-04, on sponge .

Description. – Carapace length 1.8-2.8 mm (n=48). Rostrum ( Figs. 36B , 37.A , 38.A ; Table 14) short, straight and slender, anterior third slightly upturned, reaching to or slightly beyond third segment of antennular peduncle, 0.7-3.0 times as long as carapace (n=48), armed dorsally with 14-25 teeth (including 3-5 teeth posterior to orbital margin), anterior less densely spaced, armed ventrally with 3-15 teeth. Antennal spine situated below inferior orbital angle. Pterygostomial angle broadly rounded. Eyes well developed, anterior end reaching to or beyond half length of basal segment of antennular peduncle. Antennular peduncle 0.8-1.2 times as long as carapace (n=10), second segment 2.0-2.3 times length of third segment, third segment 0.2-0.3 times length of basal segment (n=5). Stylocerite reaching 0.8-0.9 length of basal segment of antennular peduncle (n=5). Scaphocerite ( Fig. 37C ) slender, 3.5-5.0 times as long as wide (n=8).

Sixth abdominal somite 0.5-0.7 times length of carapace (n=48), 1.2-2.3 times as long as fifth somite (n=21), 0.7- cl (mm) 1.8-2.8 2.3 ± 0.3 2.4 48 rl / cl 0.7-3.0 1.6 ± 0.8 1.2 48 n dorsal rostral teeth 14-25 20 ± 2 20 48 n ventral rostral teeth 3-15 6 ± 2 6 48 abds6 / cl 0.5-0.7 0.6 ± 0.1 0.6 48 abds6 / abds5 1.2-2.3 1.9 ± 0.3 1.9 21 abds6 / h tel 0.7-1.0 0.9 ± 0.1 0.9 28 h tel / w tel 2.8-4.1 3.4 ± 0.3 3.4 13 n spines uropodal diaeresis 10-12 11 ± 1 11 12 h ch1 / w ch1 2.3-2.9 2.6 ± 0.2 2.7 20 h ch1 / h ca1 0.8-1.4 1.2 ± 0.1 1.2 48 h ca1 / w ca1 2.5-3.5 2.9 ± 0.3 3.0 20 h ch2 / w ch2 3.0-4.0 3.4 ± 0.3 3.3 20 h ch2 / h ca2 0.7-0.8 0.8 ± 0.0 0.8 46 h ca2 / w ca2 5.9-7.9 6.6 ± 0.5 6.6 20 n spines p3 1-3 2 ± 1 2 7 n spines p5 21-31 26 ±4 27 7

1.0 times length of telson (n=28). Telson ( Fig. 37D,F ) 2.8- 4.1 times as long as wide (n=13), distal margin rounded, without projection, with 3-4 pairs of spinules and 1 pair of dorsolateral spinules; distal end with 4 pairs of spines, lateral pair distinctly longer than intermediate pairs, median pair shortest. Preanal carina ( Fig. 37B ) rounded, without spine. Uropodal diaeresis ( Fig. 37E ) with 10-12 movable spinules (n=12).

Incisor process of mandible ( Fig. 38B ) ending in irregular teeth, molar process truncated. Lower lacinia of maxillule ( Fig. 38C ) broadly rounded, upper lacinia elongated, with a number of distinct teeth on inner margin, palp slender. Upper endites of maxilla ( Fig. 38G ) subdivided, palp elongate, scaphognathite tapering posteriorly. Palp of first maxilliped ( Fig. 38D ) truncate, ending in triangular shape. Podobranchs of second maxilliped ( Fig. 38F ) reduced to small lamina. Third maxilliped ( Fig. 38E ) with ultimate segment slightly shorter than penultimate segment.

Chela and carpus of first pereiopod distinctly stouter and broader than chela and carpus of second pereiopod ( Fig. 37 K-M); chela of first pereiopod 2.3-2.9 times as long as wide (n=20), 0.8-1.4 times length of carpus (n=48); tips of fingers rounded, without hooks; dactylus 1.2-1.5 times as long as palm (n=5); carpus 2.5-3.5 times as long as wide (n=20), 1.2-1.5 times length of merus (n=5). Chela of second pereiopod 3.0-4.0 times as long as wide (n=20), 0.7-0.8 times length of carpus (n=46); tips of fingers rounded, without hooks, dactylus 1.3-1.7 times as long as palm (n=5); carpus 5.9-7.9 times as long as wide (n=20), 1.4-1.6 times as long as merus (n=5).

Third pereiopod ( Fig. 37 G-H) slender, dactylus 3.0-5.8 times as long as wide (terminal spine included, without spines of flexor margin; n=5), terminating in one large claw with 1-3 accessory spines on flexor margin (n=7); propodus 11.1-15.0 times as long as wide, 3.3-5.3 times as long as dactylus; carpus 5.0-6.1 times as long as wide, 0.5-0.7 times as long as propodus, 0.5 times as long as merus; merus 8.1-10.0 times as long as wide, bearing 2-4 strong, movable spines on posterior margin of outer surface.

Fifth pereiopod slender ( Fig. 37 I-J), dactylus 3.5-4.4 times as long as wide (terminal spine included, without spines of flexor margin; n=5), terminating in one large claw with 21-31 accessory spines on flexor margin (n=7); propodus 13.1-15.0 times as long as wide, 3.6-4.5 times as long as dactylus; carpus 4.6-5.9 times as long as wide, 0.4-0.5 times as long as propodus, 0.6 times as long as merus; merus 7.1- 9.0 times as long as wide, bearing 2 strong, movable spines on posterior margin of outer surface.

Endopod of male first pleopod ( Fig.38H ) elongated triangular, 2.0-2.8 times as long as proximally wide (n=5), without appendix interna, appendix interna of male second pleopod ( Fig. 38I ) not reaching end of appendix masculina.

Ovigerous females with 12- 18 eggs (n= 4 females); egg size 0.8-0.9 x 0.4-0.6 mm (n=53, eggs with and without eyes).

Distribution. – Caridina spongicola is endemic to Lake Towuti and so far only known from the outlet bay, where its sponge host occurs ( Fig. 36A ; Zitzler & Cai, 2006).

Biology and ecology. – During an extensive substrate specific sampling in the Malili lake system in 2003, 2004, and 2005, Caridina spongicola was exclusively found on a currently undescribed freshwater sponge of the suborder Spongillina . It grows in the outlet of lake Towuti at depths of 2-5 (-10)m. The shrimps either occur on the sponge or dwell inside its oscula (Zitzler & Cai, 2006; von Rintelen et al., 2007b).

A preliminary gut content analysis was carried out to investigate the shrimp’s diet (Zitzler & Cai, 2006). According to these authors, none of the six dissected guts contained traces of poriferean spicules. The spicules are presumably too big (0.2-0.3 mm) to be consumed by the shrimp. On the other hand, a variety of diatoms, which possibly accumulate on or within the sponge, were found in the guts. These findings suggest that the shrimp does not feed on sponge tissue and thus does not parasitize its host. Instead, it appears to be a commensal using the sponge’s cavities as shelter and the inherent accumulation of diatoms as a food supply (Zitzler & Cai, 2006).

Colour pattern. – Carapace with three transversal dark brown bands ( Fig.36 C-D), first two usually joined at dorsal surface to form a n-shaped band in lateral view. Anterior part of cephalothorax, antennular peduncle, bases of antennae and posterior rostrum similarly pigmented, whereas anterior rostrum, antennae and distal antennules mostly unpigmented. First and second pereiopods white with brown bands, abdomen with a conspicuous white stripe expanding laterally along each side, dorsally densely covered with dark brown bands except for a white patch on third sternum, ventrally uniformly brown. Uropods with a characteristic brown band on distal endopods, endopods and exopods with white-pigmented tips, respectively. Pleopods and telson colourless. Eggs usually dark brown. This colour pattern remains visible even if the shrimp is under stress, the intensity of the colour merely fades (compare Zitzler & Cai, 2006; von Rintelen et al., 2007b). In a few specimens, the colour pattern resembled C. glaubrechti , but the majority was observed to be as mentioned above.

Taxonomic remarks. – The rostrum of C. spongicola displays a high degree of variation within the populations ( Fig. 36B ; compare Zitzler & Cai, 2006), similarly to many other species from the Malili lakes. However, certain qualitative characters, i.e. the general shape or the arrangement of the rostral teeth, are constant not only in C. spongicola , but in all other ancient lake species (e.g. Schenkel, 1902; Woltereck 1937a, b; Cai & Wowor, 2007).

The colour morph of the majority of living specimens closely resembles C. woltereckae , and both species can easily be confused in the field, although C. woltereckae is a typical rock dweller and has a much wider distribution. C. spongicola is generally smaller (carapace length 1.8- 2.8, median 2.4 vs. 2.4-3.8, median 2.8 in C. woltereckae ) and has a shorter rostrum (reaching to or slightly beyond third segment of antennular peduncle vs. reaching beyond end of scaphocerite in C. woltereckae ). Its smaller size (cl 1.8-2.8 mm, median 2.4) also distinguishes C. spongicola from most of the other lake species apart from C. loehae and C. parvula . From these, it differs by a longer rostrum (reaching to or slightly beyond third segment of antennular peduncle vs. shorter in the other species), a different shape of the rostrum (more slender and fragile in C. loehae and distinctly stouter in C. parvula ), and a different number of spines on the dactylus of the fifth pereiopod (21-31, median 27 vs. 12-16, median 16 in C. loehae vs. 34-39, median 37 in C. parvula ).

In the molecular phylogeny ( Figs. 63-64 ), C. spongicola appears within an unresolved clade of the rock dwellers C. striata , C. glaubrechti , and C. woltereckae (compare von Rintelen et al., 2007b), although C. spongicola differs in morphology and choice of habitat (sponge) from the other species (for example its generally smaller size and a shorter rostrum vs. rostrum reaching beyond end of scaphocerite in the rock dwellers).

Figures

Fig. 36. Caridina spongicola from the Malili lake system. A. Distribution. B. Rostrum variability (ZMB 29027). C.-D. Colour pattern of living animals (not to scale). Figure from Zitzler & Cai (2006), i.e. by the same authors.

Fig. 37. Caridina spongicola from the Malili lake system. A. Cephalothorax and cephalic appendages, female (ZMB 29027); B. Preanal carina; C. Scaphocerite,female (ZMB 29125); D. telson, female (ZMB 29027); E. Uropodal diaeresis; F. Distal end of telson; G. Third pereiopod; H. Dactylus of third pereiopod; I. Fifth pereiopod; J. Dactylus of fifth pereiopod; K. First pereiopod; L. Second pereiopod; M. SEM image of chela and carpus of first and second pereiopods. Scale bars: A, C = 1.0 mm; B, D, F-G, I, K-M = 0.5 mm; E, H, J = 0.1 mm. Figure modified from Zitzler & Cai (2006).

Fig. 38. Caridina spongicola from the Malili lake system. A. Cephalothorax and cephalic appendages, female (ZMB 29027); B. Mandible; C. Maxillule; D. First maxilliped; E. Third maxilliped; F. Second maxilliped; G. Maxilla; H. Endopod of male first pleopod (ZMB 29027); I. Appendix masculina of male second pleopod fifth pereiopod. Scale bars: A = 1.0 mm; B-G = 0.5 mm; H-I = 0.2 mm. Figure from Zitzler & Cai (2006), i.e. by the same authors.

Fig. 1. The ancient lakes of Sulawesi. A. The two ancient lake systems on the Indonesian island Sulawesi. B. Overview of Caridina collecting sites from Lake Poso. C. Overview of Caridina collecting sites from the Malili lake system.

Fig. 2. General morphology of Caridina (modified from Holthuis, 1955: 3; shrimp drawing modified from Woltereck, 1937a: 215).

Fig. 3. Standard morphometric characters in Caridina. A. Cephalothorax and abdomen (shrimp drawing modified from Woltereck, 1937a: 215). B. Rostrum and cephalic appendages. C. First and second pereiopod. D. Tailfan (telson and uropods). E. Third and fifth pereiopod. Abbreviations. antp (length of antennular peduncle), cl (carapace length), rl (rostrum length), abds5 (length of fifth abdominal somite), abds6 (length of sixth abdominal somite), h tel (length/height of telson), w tel (width of telson), h ch1 (length/height of chela of first pereiopod), w ch1 (width of chela of first pereiopod), h ca1 (length/height of carpus of first pereiopod), w ca1 (width of carpus of first pereiopod), h ch2 (length/height of chela of second pereiopod), w ch2 (width of chela of second pereiopod), h ca2 (length/height of carpus of second pereiopod), w ca2 (width of carpus of second pereiopod), n spines p3 (number of spines on the dactylus of the third pereiopod), n spines p5 (number of spines on the dactylus of the fifth pereiopod).

Fig. 63. Bayesian Inference phylogram (mtDNA, 16S and COI) of Caridina from the ancient lakes of Sulawesi (for other taxa compare von Rintelen et al., in review). Numbers on branches are, from top, Bayesian posterior probabilities, ML and MP bootstrap values. The scale bar indicates the number of substitutions per site. For each sequenced specimen museum accession numbers are provided. Locality abbreviations (compare Fig. 1): Lam (Lampesue River catchment), LT (Lake Lontoa), MHL (Lake Mahalona), MS (Lake Masapi), MT (Lake Matano), MTca (Lake Matano catchment), Pat (Patingko River), Pon (Ponsoa River), TW (Lake Towuti), TWca (Lake Towuti catchment), PS (Lake Poso), PSca (Lake Poso catchment), SSul (South Sulawesi), SESul (Southeast Sulawesi).

Fig. 64. Bayesian Inference phylogram (mtDNA, 16S and COI) showing taxa within the two Malili clades (for other taxa compare von Rintelen et al., 2009). For each sequenced specimen museum accession numbers are provided. Locality abbreviations (compare Fig. 1): Lam (Lampesue River catchment), LT (Lake Lontoa), MHL (Lake Mahalona), MS (Lake Masapi), MT (Lake Matano), MTca (Lake Matano catchment), Pat (Patingko River), Pon (Ponsoa River), TW (Lake Towuti), TWca (Lake Towuti catchment), SSul (South Sulawesi).