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

Thalassina kelanang , new species

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

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 ). 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 ), 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 ). 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 ), 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 ).

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 ). Abdominal sternite of second to fifth somites with distinct bicuspid sternal ridge between opposite pleopods; each cusp bearing 3–6 teeth ( Fig. 7B ).

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 ). 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 ). 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 ). 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 ). 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 ).

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 ). 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 ). 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 ). 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 ), (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 ). 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 ), whereas T. anomala has two petaloid depressions in the form of an inverted V ( Fig. 6B ). 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 ). 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 ). 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 ) 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 ). In T. squamifera , inner marginal setae but no terminal setae are present on the petasmal tip ( Fig. 8C ). 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 ). 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 .

Figures

Fig. 1. Thalassina kelanang, new species, holotype-male, TL = 150 mm, CL = 54.1 mm (ZMUM).

Fig. 2. Dorsal view of carapace. A, Thalassina kelanang (holotype, 150.0, 54.1 mm); B, T. anomala-Male (151.4, 51.1 mm). Scale bar = 10 mm.

Fig. 3. Dorsal view of anterior region of cephalothorax. A, T. kelanang (holotype, 150.0, 54.1 mm); B, T. anomala-Male (151.4, 51.1 mm); C, T. squamifera- Male (132.5, 47.8 mm); D, T. gracilis-Male (69.8, 25.8 mm). Scale bar = 5 mm.

Fig. 4. Dorsal view of right antennal peduncle showing movable scaphocerite. A, T. kelanang (holotype, 150.0, 54.1 mm); B, T. anomala, (absent)-Male (151.4, 51.1 mm); C, T. squamifera-Male (132.5, 47.8 mm). Scale bars: a–b = 20 mm; c = 10 mm.

Fig. 5. Right chela of pereopod 1. A–B, outer and inner aspects, T. kelanang (holotype, 150.0, 54.1 mm); C–D, outer and inner aspects, T. anomala-Male (151.4, 51.1 mm). Scale bar = 10 mm.

Fig. 6. Dorsal view of first abdominal somite. A, T. kelanang (holotype, 150.0, 54.1 mm); B, T. anomala-Male (151.4, 51.1 mm). Scale bar = 10 mm.

Fig. 7. Second abdominal somite. A–B, dorsal and ventral aspects, T. kelanang (holotype, 150.0, 54.1 mm); C–D, dorsal and ventral aspects, T. anomala- Male (151.4, 51.1 mm). Scale bar = 10 mm.

Fig. 8. Ventral view of petasma. A, T. kelanang (holotype, 150.0, 54.1 mm); B, T. anomala-Male (193, 61.4 mm); C, T. squamifera-Male (132.5, 47.8 mm); D, T. gracilis-Male (69.8, 25.8 mm). Scale bar = 5 mm.