nae, mandibles and associated palps, first and sec- 

 ond maxillae, and first, second, and third maxilli- 

 peds are present and apparently normal on both 

 heads, though the antennal flagella are broken 

 and the right third maxilliped has apparently been 

 lost from the upper head. Similarity in the ceph- 

 alothoraxes is limited to features pointed out 

 above. 



The lower cephalothorax has normal appendages 

 and internal organs, or traces of them, except for 

 some broken and missing articles on the pereopods. 

 The heart, hepatopancreas, and gonads apparently 

 disintegrated during the interval of time between 

 capture and fixation, hence lost all traces of their 

 conformation in life. Fluids from the disrupted cir- 

 culatory system were fixed as irregular clots. The 

 mouth, esophagus, stomach, and a fragment of the 

 gut are present, though the latter is connected 

 neither to the pyloric stomach nor to the sector of 

 intestine that courses through the abdomen to the 

 anus. However, one can visualize that the path of 

 the intestine in the lower cephalothorax was func- 

 tionally normal before it was disrupted by break- 

 down of the other internal organs that surrounded 

 it in life. 



The upper cephalothorax lacks a mouth, the ster- 

 nal plate between the mouthparts is not perforated, 

 and there is no esophagus, stomach, or fragment of 

 intestine. It seems therefore that the upper cepha- 

 lothorax, though equipped with normal head append- 

 ages, could not function in feeding. Moreover, the 

 rear part of the upper cephalothorax fitted over the 

 rear part of the lower one like a firmly pulled down 

 cap, with its branchiostegites deeply overlapping 

 those of the lower one. In this arrangement the 

 posterior part of the lower cephalothorax filled 

 the space that would normally have been occupied 

 by pereopods, external reproductive structures, 

 thoracic endophragmal system and body wall, 

 gills, and internal organs of the upper cepha- 

 lothorax. As a result there was little or no room for 

 development of these structures in the upper 

 cephalothorax, although there may have been a 

 heart. The membrane that lined the branchiostegites 

 and body wall of the upper cephalothorax seems to 

 have extended backward from the region of the 

 cervical groove to merge with its counterpart in the 

 posterior region of the lower cephalothorax, and 

 with the normal integumental lining of the abdomen 

 in order to have maintained confluence in the blood 

 sinuses. 



The abdomen, though crushed at the level of the 

 fourth and fifth segments, bears normal pleopods, 

 uropods, and telson. The anterior end of the ab- 



dominal muscle mass is preserved in a shape that 

 fits the posterior end of both cephalothoraxes, but 

 the main connection extended into the functional 

 lower one in which complete organ systems were 

 located. 



There is a large literature treating malformations 

 of decapod crustaceans, primarily lobsters, fresh- 

 water crayfishes, and crabs, but there is little pub- 

 lished information of this sort on shrimps (Bateson 

 1894; Johnson 1968; Johnson and Chapman 1969; 

 Pauley 1974), aside from the subject of disease which 

 is not at issue here (Couch 1978). The most ex- 

 haustive account is that of Bateson who, along with 

 many others before and after, discussed duplication 

 of parts, intersexes, and malformations that occur 

 during molting, Perez Farfante (1980), for example, 

 noted anomalous intersexes in the Indo-West Pacific 

 needle shrimp, Penaeopsis rectacuta (Bate). The 

 majority of these accounts treat malformed limbs 

 or their parts (for a well-illustrated example see 

 Shuster et al. 1963). Fewer studies are concerned 

 with teratology. 



Monsters with fused double cephalothoraxes, 

 though rare, have long been known among larvae 

 of the lobsters Homarus americanus H. Milne 

 Edwards and H. gammartis (Linnaeus) (Herrick 

 1896, 1911). Ryder (1886) noted four forms of con- 

 joined twins in larval American lobsters: lateral 

 fusion of cephalothoraxes that demonstrated 

 absence of eyes, possession of a single median eye 

 or paired eyes representing the right eye of the right 

 larva and left eye of the left larva, while the ab- 

 domens of each type were separate and divergent 

 at a wide angle, and cephalothoraxes of two embryos 

 fused together along their dorsal surfaces, with full 

 complement of eyes, appendages, and separate ab- 

 domens, but with internal organ systems fused. 

 Ryder attributed all of these twinnings to fusion 

 coincident with the process of gastrulation and 

 gradual formation of the embryos. Herrick (1896, 

 1911) discussed and figured some of these cases also 

 but thought that fusion came later in development 

 than gastrulation. 



I have found no account of conjoined twinning in 

 shrimps, and no report of twinning that parallels the 

 case presented here. What is amazing is that an 

 animal so bizarre could molt at all, let alone progress 

 through a series of molts to attain mature size. 

 Whether the deformity resulted from embryonic 

 malformation or from subsequent injury cannot now 

 be determined, although angle of divergence and 

 median sagittal alignment of the cephalothoraxes 

 suggests that the malformation resulted from aber- 

 rant molting. 



596 



