Streptocephalus dichotomus Baird, 1860

Velu, Chinavenmeni S & Munuswamy, Natesan, 2005, Updated diagnoses for the Indian species of Streptocephalus (Crustacea: Branchiopoda: Anostraca), Zootaxa 1049, pp. 33-48 : 35-37

Streptocephalus dichotomus Baird, 1860

Material examined. Madras (13°04N, 80°17E), Poondi (13°02N, 80°10E), Chengleput (12°42N, 80°01E), Sripermbudur (13°01N, 80°17E), Krishnagiri (12°32N, 78°16E), Bhavanisagar (11°50N, 79°01E), Hogenakkal (12°44N, 74°41E), Dharmapuri (12°08N, 78°13E), Tirunelvalli (08°44N, 77°44E), Madurai (09°58N, 78°10E), Trichy (10°50N, 78°46E), Guntur (16°18N, 80°29E), Nellore (14°27N, 80°02E). The accession numbers are DZ/NM/FS/102 to 114, respectively. This species has been reported from various parts of the Indian sub­continent.

Measurements. Total length (from front of head to tip of telson between cercopods, n=20) of the specimens collected from various places are as follows: Madras (17–27.5 mm), Poondi (28.1–30.7 mm), Madurai (16.6–17.6 mm), Chengleput (29.6–36.4 mm), Sripermbudur (20.1–26.4 mm), Krishnagiri (31.2–41.6 mm), Bhavanisagar (30.7–35.6 mm), Hogenakkal (27.4–30.6 mm), Dharmapuri (28.5–34.6 mm), Tirunelvalli (21.9–27.4 mm), Trichy (20.8–22.3 mm), Guntur (25.3–31.8 mm), Nellore (18.6–20.4 mm).

Description: Male—First antennae are longer than compound eye plus peduncle ( Fig. 1 A). Second antennae proximal segment sub­cylindrical, distal segment slender, directed posteriomedially. Antennal appendage long, peduncle stout, “S” curved, longer than second antennal proximal segment, with four anteriolateral subcrenulate papillae proximal to the first curve. Peduncle bears a lateral row of slender spines at the distal curve. Cheliform “hand” elongate; “thumb” shorter than peduncle, bearing an arcuate spur, and an anterior “shoulder” opposite the spur. “Finger” is as long as peduncle, bifid, with posterior ramus smooth and arcing anteriorly, anterior ramus spinose on anterior margin, bending apically in the distal third. Anterior ramus of finger with spines arranged as a series of long spines with shorter spines interspersed in between. Longitudinal row of spines from the distal end of the anterior ramus of the finger turns to the medial surface of the ramus and at the end on the posterior surface it split into two (bifid structure) ( Fig. 1 A, B, C). Thoracic and abdominal segments are smooth. Genital segment formed by the fusion of last two thoracic segments, which bears a pair of long penes extending to second abdominal segment ( Fig. 1 E). Bases of proximal portion of penes each with a lateral linguiform projection, proximal non­retractile part of penes bears an anteriorly curved medial projection with spines on the anterior surface ( Fig. 1 E). Eversible portion of penis is with two longitudinal rows of flat, acute spines in entire length ( Fig. 1 F). Cercopods are lanceolate, setiferous to tip with fine setae and separately attached to postero­lateral margin ( Fig. 1 K).

Female. Second antennae are simple, flat, bluntly rounded at the tip ( Fig. 2 D). Brood pouch extends to the fifth abdominal segment ( Fig. 1 G, H); an orange streak has been observed on the ventral side.

Cyst. The cyst surface is covered in a series of pentagonal and diamond shaped polygons. The ridges are raised and centered fields are depressed. The surface is covered by small pores ( Fig. 1 I, J).

Remarks. Streptocephalus dichotomus Baird, 1860 can be distinguished from all other species by having a bifid finger at the posterior end of the anterior ramus in the second antennae of male; the thumb is shorter than the finger. Also unique is that the cyst surface is covered with pentagonal and diamond shaped polygons.

Figures

FIGURE 1. Streptocephalus dichotomus BAIRD. A. Male, lateral view of head. B. Male antennae, lateral view. C. Medial view of second antennae. D. Female, ventral view of head. E. Ventral view of male genital region, arrow showing the spines on the protruberances. F. Protracted penis G. Female abdomen, lateral view of brood­pouch. H. Higher magnification of the terminal end of ovisac. I. Cysts. J. Details of cyst surface with ridge, depression and pores. K. Male, Telson.

FIGURE 2. Streptocephalus simplex BOND. A. Male, lateral view of head. B. Fleshy process on the second antennae. C. Male antennae, lateral view. D. Medial view of male antenane. E. Ventral view of male genital region, arrow showing the spines on the protuberances. F. Distal part of protracted penis showing spines on their surface. G. Female, ventral view of head. H. Single antennae (upper view). I. Lateral view of female abdomen and brood­pouch. J. Cyst. K. Details of cyst showing ridges, depression and pores.