Thalassina kelanang, H & C, 2009

H, Moh H. & C, Chong V., 2009, A New Species Of Thalassina (Crustacea: Decapoda: Thalassinidae) From Malaysia, Raffles Bulletin of Zoology 57 (2), pp. 465-473: 466-473

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Thalassina kelanang

new species

Thalassina kelanang   , new species

( Figs. 1 View Fig , 2A View Fig , 3A View Fig , 4A View Fig , 5A, 5B View Fig , 6A View Fig , 7A, 7B View Fig , 8A View Fig )

Material examined. – Holotype – male (150.0, 54.1 mm) ( ZMUM), from mound in mangrove forest, Kelanang Beach, Kuala Langat, Selangor, Malaysia, coll. H.H. Moh, Apr.2007.  

Paratypes – 1 female (141, 50.3 mm) ( ZMUM), Kelanang Beach , Kuala Langat, Selangor, Malaysia, coll. H.H.Moh, Oct. 2006   ; 1 male, (140, 52.0 mm), 4 females (120, 44.6 mm), (162, 58.9 mm), (167, 60.8 mm), (150, 55.4 mm), ( ZMUM), Kelanang Beach , Kuala Langat, Selangor, Malaysia, coll. H.H.Moh, Nov. 2006   ; 1 male, (114, 42.9 mm), 2 females (163, 58.4 mm), (140, 51.5 mm), ( ZMUM), Kelanang Beach , Kuala Langat, Selangor, Malaysia, coll. H.H.Moh, Mac.   2007; 2 males (143, 51.9 mm), (133, 48.8 mm), 2 females (120, 43.7 mm), (119, 45.4 mm), ( ZMUM), Kelanang Beach , Kuala Langat, Selangor, Malaysia, coll. H.H.Moh, Apr. 2007   ; 1 female (161, 59.1 mm), ( ZMUM), Carey Island , Kuala Langat, Selangor, Malaysia, coll. H.H.Moh, Oct. 2006   ; 1 male (183, 63.6 mm), ( ZMUM), Carey Island , Kuala Langat, Selangor, Malaysia, coll. H.H.Moh, Nov. 2006   .

Description of holotype. – Carapace elongate oval in dorsal aspect; sculptured by circular depressions or punctae, the largest pair (gastric pits) associated with post-cervical groove; upper lateral sides heavily covered with short anteriorly-directed spines; short posteriorly-directed spine on dorsal median margin not reaching first abdominal tergite ( Fig. 2A View Fig ). Rostrum flat, narrowly triangular and waisted

Comparative material examined. – Thalassina anomala   13 males and 5 females (TL; 114.6–241.1 mm) ( ZMUM), Carey Island , Selangor, Malaysia, coll. H.H.Moh, Jun.– Sep.2006   .

T. squamifera   1 male (1325, 47.8 mm) ( NSMAG, Cr.004775), Micket Creek , Darwin, N.T., Australia, coll. D. near base ( Fig. 3A View Fig ), with lateral margins that continue posteriorly as short divergent ridges (adrostral carina) extending half length of gastro-orbital carina; median sulcus or groove deep, extending beyond adrostral carina; 3–11 blunt marginal spinules or tubercles on adrostral carina. Supra-orbital , antennal and branchiostegal spines strong and sharp; orbital and sub-orbital spines short; 4–8 sharp spines at curved anterior end of branchiocardiac groove. Oblique groove with 10–14 spines on dorsal margin, anterior-most spine largest, thinly setose. Anterior margin of antennal region armed with series of short spines. Numerous tubercles on anterior margin of branchiostegite   .

Antenna with highly reduced antennal scale or scaphocerite on the outer side, scaphocerite large, setose on inner margin ( Fig. 4A View Fig ). Antennal flagellum when stretched backward reached first or second abdominal somite, length more than five times length of antennular flagellum.

Pereopods 1 (chelipeds) asymmetrical and subchelate, left chela larger than right (but see Paratypes below). Meri large, flattened laterally on dorsal surface, but broad or triangular on ventral surface; right merus with 17 dorsal spines, left with 18 dorsal spines, anterior-most 4 spines large and decurved, inner and outer ventral margins serrulate with numerous subequal denticles on ventral surface. Carpi relatively small, inner dorsal margin with a row of 7–8 strong spines, outer ventral margin armed with a row of spines, anterior-most being most prominent. Propodi granulated on entire surface, granules on the posterior half of inner ventral surface comparatively larger than those on anterior half, dorsal surface with two ridges: inner ridge armed with row of 10 strong spines ( Fig. 5A, 5B View Fig ), outer ridge on proximal three-quarters distance, armed with row of small tubercles, outer surface with long fine setae occurring in tufts along rows, ventral surface with two serrated ridges. Dactyli twice as long as fixed finger, narrow and laterally flattened, right dorsal margin armed with row of 13–15 spines and numerous long fine setae, ventral surface with two serrated ridges and two rows of fine setae, a few punctae present along dorsal surface.

Pereopod 2 subchelate, smaller than pereopod 1; basiischium laterally flattened with ventral margin armed with 6–9 strong spines and a row of setae; merus laterally flattened, dorsal margin with row of 4–6 strong decurved spines, ventral surface densely setose; carpus setose on dorsal and ventral margins, dorsal margin with 2–3 strong, decurved spines; propodal length slightly longer than width, dorsal margin of fixed finger armed with a longitudinal row of blunt teeth; dactylus with two rows of setae on dorsal margin, outer surface with medial longitudinal row of setae, ventral margin serrated with row of blunt teeth, posteroventral margin setose.

Pereopod 3 narrow and flattened laterally; coxa armed with 4–6 spines on inner surface; ischium armed with 4–6 spines on ventral margin; merus with row of 6–10 decurved spines on dorsal margin, ventral margin serrated with two rows of 10–12 spines; carpus armed with 4–5 strong spines on dorsal margin, ventral margin spineless; propodus small and laterally compressed, with setae on dorsal and ventral surfaces; dactylus slender as long as propodus, ventral margin with row of setae, dorsal margin with seven short spines and row of setae.

Pereopod 4 similar but slightly smaller than pereopod 3; dactylus slender, longer than propodus.

Pereopod 5 smaller than pereopod 4, not compressed; coxae with gonopores facing each other on either side of midventral line; outer margin armed with a row of spines.

Male abdomen elongate and narrow; somite width as wide as length; first abdominal somite smallest and narrowest; third and fourth somites largest. Dorsal tergite of first abdominal somite raised as a distinct rectangular piece, with inverted Y groove ( Fig. 6A View Fig ).

Base of pleuron of second and third abdominal somites, each with two longitudinal, serrated ribs or carinae occupying anterior three-quarters distance to posterior end of segment ( Fig. 7A View Fig ). Abdominal sternite of second to fifth somites with distinct bicuspid sternal ridge between opposite pleopods; each cusp bearing 3–6 teeth ( Fig. 7B View Fig ).

Mature male pleopod 1 uniramus, with opposing endopods modified and united to form petasma or intromittent organ; distal end of petasma narrowly oval to pointed, setal row on outer and inner margins reaching or almost reaching tip; inner distal setae modified to form fine interlocking hooks on disc-like, subterminal keel of petasma; outer proximal end of petasma armed with 3–4 strong spines ( Fig. 8A View Fig ). Pleopods 2–5 biramous; pleopods 3–5 of equal size, but shorter than pleopod 2. Uropods styliform.

Telson broadly triangular, about as long as previous somite.

Variation. – Although our holotype male has a larger right cheliped than the left, the left cheliped can be larger than the right for both male and female, but in some of our specimens the difference was not obvious. Our specimens had 14 of the former type and 11 of the latter type. Merus of right cheliped with 12–17 dorsal spines, left 15–18, anterior 3–5 spines large and decurved. In female, gonopores on inner ventral surface of coxa of pereopod 3; pleopod 1 uniramus; pleopods 2–5 larger and biramous, bearing long setae which are particularly well-developed for carrying eggs during breeding season.

Etymology. – The species is named after its type locality, Kelanang, in the district of Kuala Langat of the state of Selangor, Malaysia. The name is used as a noun.

Colour. – Carapace orange to brown on dorsal aspect, becoming grey ventrolaterally. Abdomen red to orange on dorsal aspect, pleura grey. Dorsal aspect of pereopods brownish orange, ventral aspect grey.

Biological notes. – Thalassina kelanang   construct sandy mud mounds of generally less than 0.5 m in height. At

Kelanang Beach, while the animal inhabits the fringing Rhizophora   forest, there were more mounds on open sandy mud substrate without vegetation. In contrast, T. anomala   were found in muddy substrate particularly in Carey Island, although few T. kelanang   were found on the island. Thus, the two species appear to occupy their own microhabitats in the same general area. Male T. kelanang   , unlike T. anomala   , are very aggressive inflicting painful pinches on handlers; males often ended up with broken legs if placed together in an aquarium.

Remarks. – Thalassina kelanang   shows similarities with the sympatric species, T. anomala   in terms of size, coloration and general morphology. However, their morphological differences warrant the separation of the two species. In all our 65 T. anomala   specimens, the posterior median spine of the carapace, often decurved, always overhangs the articulation with the first abdominal tergite ( Fig. 2B View Fig ). In contrast, the median spine of T. kelanang   is short, blunt and never overhangs the first abdominal tergite. However, this character is similar to that of Thalassina squamifera De Man. The   oblique groove of the carapace of T. anomala   is covered with a thick row of setae, whereas in T. kelanang   and T. squamifera   it is sparsely covered by setae. The rostrum of Thalassina kelanang   has an acute tip, proximal waist and a deep median sulcus (groove) that extends up to the posterior pair of dorsal punctae behind the posterior end of the adrostrals; the latter reaches only the anterior half of the gastro-orbital carina (see Fig. 3A View Fig ). In contrast, both T. anomala   and T. squamifera   have a triangular rostrum with a shallow median sulcus that does not reach beyond the adrostrals; the latter extends to three-quarters or full length of the gastro-orbital carina ( Fig. 3B, 3C View Fig ). In addition, both species have rather smooth or at the most three tubercles on their adrostral and gastro-orbital carinae, posterior to the orbital margin. These features of the rostrum appear to be important in separating the different species of Thalassina   . In fact, the examined T. gracilis   specimens show a distinctive depressed and more acute rostrum unlike that of T. kelanang   and others ( Fig. 3D View Fig ).

De Man (1928) pointed out the differences between T. anomala   and T. squamifera   (as a variety of T. anomala   ), in that only the latter has a scaphocerite on the antennal peduncle as well as a tuberculate ridge on the abdominal sternites (see below). Sankolli (1970) reported that T. anomala   specimens in India, except for one female, generally did not have the scaphocerite. From a total of 65 specimens of T. anomala   examined in this study, 29 of them have much reduced scaphocerites, while 36 specimens do not have scaphocerites ( Fig. 4B View Fig ). In contrast, all specimens of T. kelanang   have distinctly large, triangular scaphocerites with a row of long setae on their inner margin (see Fig. 4A View Fig ). The five specimens of T. squamifera   also have scaphocerites but only one specimen has a row of marginal setae on the right scaphocerite ( Fig. 4C View Fig ). Thalassina kelanang   has a long antennal flagellum that when stretched backwards reached more than half the length of the first abdominal somite; the flagellum of T. anomala   is much shorter, reaching less than three quarters of the carapace length. While the examined males of T. squamifera   all had broken antennae, both females bore antennal flagella that reached the posterior margins of the carapace.

The merus of the cheliped in T. kelanang   has a row of 3–5 strong spines on its dorsal margin, whereas in T. anomala   there are only two strong spines. There are also two or three strong spines in T. squamifera   . Three other distinguishing features of T. kelanang   are (i) the fixed finger of its chela is half the length of the movable finger, whereas in T. anomala   the fixed finger is a quarter to a third the length of the movable finger ( Fig. 5C, D View Fig ), (ii) 8–12 strong dorsal spines on the inner dorsal ridge of the palm, whereas T. anomala   has 14–20 blunt spines or tubercles, and (iii) lateral dorsal ridge of outer surface of palm extends to three-quarters distance but not to distal end, whereas in T. anomala   , the ridge extends right up to the distal end ( Fig. 5C View Fig ). The same characters for T. squamifera   are respectively fixed finger half the length of movable finger, 9–11 inner dorsal spines and a lateral dorsal ridge that extends between half to three quarters of distance to distal end.

Several distinctive differences between the three species are also observed in the abdomen and its appendages. Thalassina kelanang   and T. squamifera   have an inverted Y-groove on the dorsal tergite of the first abdominal somite (see Fig. 6A View Fig ), whereas T. anomala   has two petaloid depressions in the form of an inverted V ( Fig. 6B View Fig ). In T. kelanang   and T. squamifera   , the longitudinal ‘three-quarters long’ carina runs across the base of the pleuron of the second and third abdominal somites only, whereas in T. anomala   the carina runs the entire somite length and is present on the second to sixth abdominal somites ( Fig. 7C View Fig ). A sternal ridge (second to fifth somites) bearing two cusps each with 3–6 teeth/ tubercles is present in T. kelanang   as well as in T. squamifera   , whereas in T. anomala   , only one median tubercle is present ( Fig. 7D View Fig ). This is the other feature distinguishing the two varieties of mud lobster (sensu de Man, 1928).

Male holotype and paratypes of T. kelanang   (see Fig. 8A View Fig ) have a petasma or intromittent organ that is quite different from that of T. anomala   in that both outer and inner marginal setal rows of T. kelanang   are reaching its distal tip, whereas the latter’s petasmal tip is broadly rounded without setae ( Fig. 8B View Fig ). In T. squamifera   , inner marginal setae but no terminal setae are present on the petasmal tip ( Fig. 8C View Fig ). Another important difference between the petasma of the three species is the presence of 3–4 proximal spines in T. kelanang   but which are absent in both T. anomala   and T. squamifera   . All our nine male specimens of T. kelanang   have these proximal spines. The petasma of T. squamifera   is stout compared to that of its congeners. We also examined the petasma of T. gracilis   and this is distinctly different from the rest and also without proximal spines ( Fig. 8D View Fig ). Therefore, despite the close similarities between T. kelanang   and T. squamifera   ( Table 1), based on mainly differences of their petasma and the rostrum, we conclude that they are two different species.

The new species of T. kelanang   is more similar to T. squamifera   than to T. anomala   in general morphology, but can be distinguished from T. squamifera   based on the morphology of the petasma and rostrum. Thus, the characteristics of both rostrum and petasma are very useful in distinguishing the species of Thalassina   .


Zoological Museum, University of Amoy